acoustic design of schools - ian sharland · 2012. 7. 23. · 7.8 acoustic design of building...

Bui lding Bul let in 93

ACOUSTIC DESIGNOF SCHOOLS

A DESIGN GUIDE

BUILDING BULLETIN 93

Acoustic Design ofSchools

Architects and Building Branch

London : The Stationery Office

DfES Project TeamRichard Daniels Building Services Engineer, School Buildings & Design UnitAlex Freemantle Architect, Formerly of School Buildings & Design UnitMukund Patel Head of School Buildings & Design Unit

AcknowledgementsDfES would like to thank the following:

Editors:Bridget Shield, London South Bank UniversityCarl Hopkins, BRE Acoustics, Building Research Establishment Ltd (BRE)

Principal authors:Carl Hopkins & Robin Hall, BRE Acoustics, Building Research Establishment Ltd (BRE)Adrian James, Adrian James Acoustics, NorwichRaf Orlowski & Sam Wise, Arup AcousticsDavid Canning, City University

Other authors and advisors:Stephen Chiles University of BathDavid Dennis London Borough of NewhamNigel Cogger The English Cogger PartnershipJohn Miller & Theodoros Niaounakis Bickerdike Allen and PartnersLes Fothergill Building Regulations Division, Office of the

Deputy Prime MinisterGuy Shackle Barron and Smith ArchitectsJulie Dockrell Institute of Education, University of LondonMindy Hadi Building Research Establishment Ltd (BRE)Matthew Ling Formerly of Building Research Establishment Ltd (BRE)Russell Brett British Association of Teachers of the DeafRichard Vaughan National Deaf Children's SocietyRoz Comins Voice Care Network UKThomas Wulfrank Arup AcousticsDavid Coley & Andrew Mitchell Centre for Energy and the Environment, Exeter University. Derek Poole Formerly of University of Wales, College of CardiffJohn Lloyd & Tom Cecil Faber MaunsellPeter Brailey Hawksmoor Engineering Ltd.Andrew Parkin RW Gregory LLPTerry Payne Monodraught LtdWayne Aston PassiventTim Spencer Rockwool Rockfon LtdDavid Whittingham Formerly of Ecophon Ltd

Photographer: Philip Locker, Photo Graphic Design, Bolton

Design & Mac file: Malcolm Ward, Malcolm Studio, Croydon.

ISBN 0 11 271105 7

Introduction 1

Scope of Building Bulletin 93Overview of contents of Building Bulletin 93

Section 1: Specification of acoustic performance 7

1.1 Performance standards 81.1.1 Indoor ambient noise levels in unoccupied spaces1.1.2 Airborne sound insulation between spaces1.1.3 Airborne sound insulation between circulation spaces and

other spaces used by students1.1.4 Impact sound insulation of floors1.1.5 Reverberation in teaching and study spaces1.1.6 Sound absorption in corridors, entrance halls and stairwells1.1.7 Speech intelligibility in open-plan spaces

1.2 Demonstrating compliance to the Building Control Body 161.2.1 Alternative performance standards

1.3 Demonstrating compliance to the client 171.3.1 Timetabling of acoustic testing1.3.2 Remedial treatments1.3.3 Indoor ambient noise levels in unoccupied spaces1.3.4 Airborne sound insulation between spaces1.3.5 Airborne sound insulation between circulation spaces and

other spaces used by students1.3.6 Impact sound insulation1.3.7 Reverberation in teaching and study spaces1.3.8 Sound absorption in corridors, entrance halls and stairwells1.3.9 Speech intelligibility in open-plan spacesReferences

Section 2: Noise control 21

2.1 Choosing a site 212.2 Recommendations for external noise levels outside school buildings 212.3 Noise survey 222.4 Road and rail noise 232.5 Aircraft noise 232.6 Vibration 232.7 Noise barriers 242.8 Noise from schools to surrounding areas 242.9 Planning and layout 242.10 Limiting indoor ambient noise levels 252.11 Impact noise 252.12 Corridors, entrance halls and stairwells 252.13 Masking noise 262.14 Low frequency noise and hearing impaired pupils 26

References

Contents

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Page

Section 3: Insulation from external noise 27

3.1 Roofs 273.1.1 Rain noise

3.2 External walls 283.3 Ventilation 28

3.3.1 Ventilators3.4 External windows 303.5 External doors 31

Sound insulation of the building envelope 323.6 Subjective characteristics of noise 323.7 Variation of noise incident on different facades 323.8 Calculations 323.9 Test Method 32

3.9.1 Conditions for similar constructions3.9.2 Conditions for similar sources

Sound insulation between rooms 333.10 Specification of the airborne sound insulation between rooms using Rw 33

3.10.1 Flanking details3.10.2 Examples of problematic flanking details3.10.3 Junction between ceilings and internal walls3.10.4 Flanking transmission through windows

3.11 Specification of the impact sound insulation between rooms using Ln,w 363.12 Internal walls and partitions 37

3.12.1 General principles3.12.2 Sound insulation of common constructions3.12.3 Flanking transmission3.12.4 High performance constructions – flanking transmission3.12.5 Corridor walls and doors

3.13 Internal doors, glazing, windows and folding partitions 413.13.1 Doors3.13.2 Lobbies3.13.3 Folding walls and operable partitions3.13.4 Roller shutters

3.14 Floors and ceilings 453.14.1 Impact sound insulation3.14.2 Voids above suspended ceilings3.14.3 Upgrading existing wooden floors using suspended plasterboard ceilings3.14.4 Upgrading existing wooden floors using platform and ribbed floors3.14.5 Concrete floors

3.15 Design and detailing of building elements 50References

Section 4: The design of rooms for speech 53

4.1 Approach to acoustic design 534.2 Internal ambient noise levels and speech clarity 534.3 Reverberation times 544.4 Amount of acoustic absorption required 544.5 Distribution of absorbent materials 544.6 Room geometry 544.7 Classrooms 55

Contents

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3 Page

4.8 Assembly halls, auditoria and lecture theatres 554.8.1 Room geometry4.8.2 Sound reinforcement

4.9 Open-plan teaching and learning areas 584.10 Practical spaces 59

4.10.1 Design and Technology spaces4.10.2 Art rooms4.10.3 Floor finishes in practical spaces

4.11 Drama rooms 604.12 Multi-purpose halls 614.13 Other large spaces 624.14 Dining areas 62

References

Section 5: The design of rooms for music 63

5.1 Aspects of acoustic design 635.2 Ambient noise 635.3 Sound insulation

5.3.1 Sound insulation between music rooms5.4 Room acoustics 64

5.4.1 Reverberation time, loudness and room volume5.4.2 Distribution of acoustic absorption5.4.3 Room geometry5.4.4 Diffusion

5.5 Types of room 675.5.1 Music classrooms5.5.2 Music classroom/recital room5.5.3 Practice rooms/group rooms5.5.4 Ensemble rooms5.5.5 Control rooms for recording5.5.6 Recording studios5.5.7 Audio equipment

5.6 Acoustic design of large halls for music performance 735.6.1 Shape and size5.6.2 Surface finishes

5.7 Design of large auditoria for music and speech 75References

Section 6: Acoustic design and equipment for pupils with specialhearing requirements 77

6.1 Children with listening difficulties 776.2 Children with hearing impairments and the acoustic environment 776.3 Hearing impairment and hearing aids 786.4 The speech signal and hearing aids 786.5 Listening demands within the classroom 796.6 Strategies developed to assist children with hearing and listening difficulties 796.7 Individual technology 80

6.7.1 Radio aids6.7.2 Auditory trainers and hard-wired systems

6.8 Whole class technology 826.8.1 Whole classroom soundfield systems6.8.2 System overview

Contents

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Page

6.8.3 Personal soundfield systems 6.8.4 Infra red technology6.8.5 Induction loop systems6.8.6 Audio-visual equipment6.8.7 Other assistive devices

6.9 Special teaching accommodation 876.10 Beyond the classroom 89

References

Section 7: Case studies 91

7.1 Remedial work to a multi-purpose hall in a county primary school 93 7.2 An investigation into the acoustic conditions in three open-plan primary schools 977.3 Remedial work to an open-plan teaching area in a primary school 1077.4 Conversion of a design and technology space to music accommodation 1137.5 A purpose built music suite 1177.6 A junior school with resource provision for deaf children 1237.7 An all-age special school for hearing impaired children 129 7.8 Acoustic design of building envelope and classrooms at a new secondary school 1397.9 Acoustically attenuated passive stack ventilation of an extension to an inner city

secondary school 1437.10 An investigation into acoustic conditions in open-plan learning spaces in

a secondary school 147

Appendices 159

Introduction to appendices 1591 Basic concepts and units 1612 Basic principles of room acoustics 1653 Basic principles of sound insulation 1674 Classroom sound insulation – sample calculations 1715 Sound insulation of the building envelope 1756 Calculation of room reverberation times 1777 Calculation of sound absorption required in corridors,

entrance halls and stairwells 1818 Equipment specifications for sound field systems in schools 1859 Noise at Work Regulations relating to teachers 19110 Example submission to Building Control Body 193

Bibliography 203

List of organisations 207

Contents

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Page

1

The constructional standards for acousticsfor new school buildings, as given inSection 1 of this document, are requiredto be achieved under the BuildingRegulations. This represents a significanttightening of the regulation of acousticdesign in schools, to reflect a generalrecognition, supported by research, thatteaching and learning are acousticallydemanding activities. In particular, thereis a consensus that low ambient noiselevels are required, particularly in view ofthe requirements of the SpecialEducational Needs and Disability Act20011 for integration of children withspecial needs in mainstream schools.

Unfortunately, a large number ofclassrooms in the UK currently sufferfrom poor acoustics. The most seriousacoustic problems are due to noisetransfer between rooms and/or excessivereverberation in rooms. There are manyreasons for the poor acoustics, for example:• The acoustics of the stock of oldVictorian schools are often unsuitable formodern teaching methods. • Modern constructions do not alwaysprovide adequate sound insulation andmay need special treatment. • Open plan, or semi-open plan layouts,designed to accommodate a number ofdifferent activities, are areas wherebackground noise and sound intrusionoften cause problems. • The acoustics of multi-purpose rooms,such as halls, have to be suitable for avariety of activities, for example music(which requires a long reverberationtime) and speech (which requires shorterreverberation times).

• Many activities, such as music anddesign technology lessons, can be noisyand will cause problems if there isinadequate sound insulation betweenareas for these activities and thoserequiring quieter conditions.

Poor acoustic conditions in theclassroom increase the strain on teachers’voices as most teachers find it difficult tocope with high noise levels. This oftenleads to voice problems due to prolongeduse of the voice and the need to shout tokeep control. Recent surveys in the UKand elsewhere show that teachers form adisproportionate percentage of voice clinicpatients.

Historically, there have been a numberof factors preventing good acoustic designand this Building Bulletin addresses theseissues.• Before 2003, Part E of the BuildingRegulations did not apply to schools. Itnow includes schools within its scope. • Although the constructional standardsfor schools previously quoted BuildingBulletin 87[2] as the standard foracoustics in schools, many designers wereunaware of the requirements of BB87 andthe standards were rarely enforced. Thesestandards have been updated to reflectcurrent research and the relevantrequirements of the DisabilityDiscrimination Act, and are included inthe compliance section, Section 1, of thisbulletin.• The pressure on finances has meant inthe past that acoustics came low on thelist of design priorities. The acousticdesign will now have a higher priority as itwill be subject to building control

Introduction

1. Now incorporated asSection IV of the DisabilityDiscrimination Act[1]

Building Bulletin 93 aims to:• provide a regulatory framework for the acoustic design of schools in support

of the Building Regulations • give supporting advice and recommendations for planning and design of

schools• provide a comprehensive guide for architects, acousticians, building control

officers, building services engineers, clients, and others involved in the design of new school buildings.

2

approval procedures.• There has been little guidance availablein the past on how to achieve the rightbalance of acoustics in the complex anddynamic environment of a school.Architects and designers have had adifficult time finding information to makedesign easy and, in particular, to helpthem choose the correct target values ofappropriate parameters.

Overall, Building Bulletin 93recommends a structured approach toacoustic design at each stage of theplanning and design process, as shown inthe table below.

Introduction

A structured approach to acoustic design at each stage of the planning and design process

Feasibility/Sketch Design � Selection of the site� Noise survey to establish external noise levels� Orientation of buildings� Massing and form of the buildings� Consideration of need for external noise barriers using the buildings, fences and screens and

landscape features� Preliminary calculation of sound insulation provided by building envelope including the effect of

ventilation openings

Detailed Design � Determine appropriate noise levels and reverberation times for the various activities and room types

� Consider the special educational needs of the pupils � Consider the design of music, drama and other specialist spaces separately from that of

normal classrooms as the design criteria are very different.� Provide the necessary façade sound insulation whilst providing adequate ventilation,

particularly in the case of spaces such as classrooms and science laboratories which require high ventilation rates

� Architectural/acoustic zoning: plan the disposition of 'quiet' and 'noisy' spaces, separating them wherever possible by distance, external areas or neutral 'buffer' spaces such as storerooms or corridors

� Consider sound insulation separately from other aspects of room acoustics using walls, floors and partitions to provide adequate sound insulation

� Design the acoustics of the rooms by considering their volume and shape, and the acoustic properties of their surfaces

� Specify the acoustic performance of doors, windows and ventilation openings � Specify any amplification systems

Building Control Approval � Submit plans, including specific details of the acoustic design, for approval by Building Control Body

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SCOPE of Building Bulletin 93

Section 1 of Building Bulletin 93supersedes Section A of Building Bulletin87[2] as the constructional standard foracoustics for new school buildings.

In addition, Part E of the BuildingRegulations includes schools within itsscope and Approved Document E[3]

gives the following guidance: “In theSecretary of State’s view the normal way ofsatisfying Requirement E4 will be to meetthe values for sound insulation,reverberation time and internal ambientnoise which are given in Section 1 ofBuilding Bulletin 93 ‘The Acoustic Designof Schools’, produced by DfES.”

The requirements of Section 1 cameinto force on 1st July 2003, at the sametime as those contained in the newApproved Document Part E[3], insupport of the Building Regulations.

Requirement E4 from Part E ofSchedule 1 to The Building Regulations2000 (as amended) states that:

“Each room or other space in a schoolbuilding shall be designed and constructedin such a way that it has the acousticconditions and the insulation againstdisturbance by noise appropriate to itsintended use.”

The Education (School Premises)Regulations 1999, SI 1999 No.2 whichapplies to both new and existing schoolbuildings, contains a similar statement: “Each room or other space in a schoolbuilding shall have the acoustic conditionsand the insulation against disturbance bynoise appropriate to its normal use.”

Compliance with the acousticperformance standards specified inSection 1 will satisfy both regulations fornew schools.

Although Building Regulations do notapply to all alteration and refurbishmentwork, it is desirable that such work shouldconsider acoustics and incorporateupgrading of the acoustics as appropriate.(In the case of existing buildings, theBuilding Regulations apply only to‘material alterations’ as defined inRegulations 3 and 4.) Although it wouldbe uneconomic to upgrade all existingschool buildings to the same standards as

new school buildings, where there is aneed for upgrading the acousticperformance of an existing building orwhen refurbishment is happening forother reasons, then the designer shouldaim to meet the acoustic performancegiven in Section 1 of BB93 to satisfy theSchool Premises Regulations and theDisability Discrimination Act.

The exemption of Local EducationAuthority (LEA) maintained schools fromthe Building Regulations has ended. Newschool buildings, including extensions toexisting school buildings and new schoolsformed by change of use of otherbuildings, are now included in theBuilding Regulations and may be subjectto detailed design checks and on-siteinspections by Building Control Bodies.

The Building Regulations and hencethe requirements of BB93 only apply inEngland and Wales. They apply to bothLEA maintained schools and independentschools.

Temporary buildings are exempt fromthe Building Regulations. Temporarybuildings are defined in Schedule 2 to theBuilding Regulations as those which arenot intended to remain in place for longerthan 28 days. What are commonly calledtemporary buildings in schools are classedas prefabricated buildings and arenormally subject to the same BuildingRegulations requirements as other typesof building. Additional guidance is givenin Clause 0.6 of Approved DocumentE[3]. A building that is created bydismantling, transporting and re-erectingthe sub-assemblies on the same premises,or is constructed from sub-assembliesobtained from other premises or fromstock manufactured before 1st July 2003,would normally be considered to meet therequirements for schools if it satisfies therelevant provisions relating to acousticstandards set out in the 1997 edition ofBuilding Bulletin 87[2].

The extension of Part E of Schedule 1to the Building Regulations 2000 (asamended by SI 2002/2871) to schoolsapplies to teaching and learning spaces.Therefore the performance standards in

Introduction

4

Introduction

the tables in Section 1 are required forcompliance with Part E for all teachingand learning spaces. Part E of theBuilding Regulations is not intended tocover the acoustic conditions inadministration and ancillary spaces not usedfor teaching and learning except in as far asthey affect conditions in neighbouringteaching and learning spaces. Thereforeconsideration needs to be given toadjoining areas, such as corridors, whichmight have doors, ventilators, or glazingseparating them from a teaching orlearning space. The performance standardsgiven in the tables for administration andancillary spaces are for guidance only.

Rooms used for nursery andadult/community education within schoolcomplexes are also covered by Part E. PartE does not apply to nursery schools whichare not part of a school, sixth form collegeswhich have not been established as schools,and Universities or Colleges of Furtherand Higher Education2. However, manyof the acoustic specifications are desirableand can be used as a guide to the designof these buildings. The standards areparticularly appropriate for nurseryschools as figures are quoted for nurseryspaces within primary schools.

The Disability Discrimination Act

1995[1], as amended by the SpecialEducational Needs and Disability Act2001, places a duty on all schools andLEAs to plan to increase over time theaccessibility of schools for disabled pupilsand to implement their plans. Schools andLEAs are required to provide:• increased access for disabled pupils tothe school curriculum. This coversteaching and learning and the widercurriculum of the school such as after-school clubs, leisure and culturalactivities.• improved access to the physicalenvironment of schools, includingphysical aids to assist education. Thisincludes acoustic improvements and aidsfor hearing impaired pupils.

When alterations affect the acoustics ofa space then improvement of the acousticsto promote better access for children withspecial needs, including hearingimpairments, should be considered. Approved Document M: 1999 – Accessand facilities for disabled people, insupport of the Building Regulations[4]

includes requirements for access forchildren with special needs. See also BS8300: 2001 Design of buildings and theirapproaches to meet the needs of disabledpeople[5].

2. Part E of the Building Regulations quotes the definition of school given in Section 4 of the1996 Education Act. In the case of sixth form colleges Section 4 of the 1996 Act should be readin conjunction with Section 2 of the same Act, in particular subsections (2), (2A) and (4) whichdeal with the definition of secondary education.

If a sixth form college is established as a school under the 1998 School Standards andFramework Act then it will be classed as a school under Section 4 of the 1996 Education Act andPart E of the Building Regulations on acoustics will apply. Only one sixth form college has beenestablished in this way up until now.

Therefore, most sixth form colleges are institutions in the Further Education sector and notschools, and Part E of the Building Regulations will not apply.

In the case of a new sixth form college it will be necessary to contact the LEA to enquire if thesixth form college has been established as a school or as an Institute of Further Education.

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Introduction

Section 1: Specification of AcousticPerformance consists of three parts.

Section 1.1 gives the performancestandards for new school buildings tocomply with the Building Regulations. These provide a good minimum standardfor school design. However, on occasionhigher standards will be necessary.

Section 1.2 sets out the preferredmeans of demonstrating compliance tothe Building Control Body.

Section 1.3 gives the testsrecommended to be conducted as part ofthe building contract.

Section 2: Noise Control describes howto conduct a site survey and to plan theschool to control noise. It also includesrecommendations on maximum externalnoise levels applying to playing fields,recreational areas and areas used forformal and informal outdoor teaching.External levels are not covered byBuilding Regulations but are taken intoconsideration in planning decisions bylocal authorities[6].

Section 3: Sound Insulation gives detailedguidance on constructions to meet theperformance standards for soundinsulation specified in Section 1.1.

Section 4: The Design of Rooms forSpeech and Section 5: The Design ofRooms for Music give guidance onvarious aspects of acoustic design relevantto schools.

Section 6: Acoustic Design andEquipment for Pupils with SpecialHearing Requirements discusses designappropriate for pupils with hearingimpairments and special hearingrequirements. It discusses the necessaryacoustic performance of spaces anddescribes the range of aids available tohelp these pupils.

Section 7 contains 10 case studiesillustrating some of the most importantaspects of acoustic design of schools.

Appendix 1 defines the basic concepts andtechnical terms used in the Bulletin.

Appendices 2 and 3 describe the basicprinciples of room acoustics and soundinsulation.

Appendices 4 to 7 give examples ofcalculations of sound insulation,reverberation time and absorption.

Appendix 8 gives equipment specificationsfor sound field systems to guide thosewho need to specify this type of equipment.

Appendix 9 gives an overview of theNoise at Work Regulations as they relateto teachers.

Appendix 10 gives an example of asubmission for approval by a BuildingControl Body.

The DfES acoustics websitewww.teachernet.gov.uk/acoustics containsfurther reference material which expandson the source material for acousticiansand designers. For example, it links to aspreadsheet which can be used to calculatethe sound insulation of the buildingenvelope and the reverberation time ofinternal rooms. The website will beregularly updated with new information,discussion papers and case studies. Thewebsite also contains complete downloadsof BB93.

Overview of contents of Building Bulletin 93

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References[1] Disability Discrimination Act (1995) Part IVwww.hmso.gov.uk[2] Building Bulletin 87, Guidelines forEnvironmental Design in Schools (Revision of Design Note 17), The Stationery Office, 1997. ISBN 011 271013 1. (Now superseded by2003 version of BB87, which excludesacoustics, and is available onwww.teachernet.gov.uk/energy)[3] Approved Document E – Resistance to thepassage of sound. Stationery Office, 2003. ISBN 0 11 753 642 3. www.odpm.gov.uk[4] Approved Document M:1999 Access andfacilities for disabled people, in support of theBuilding Regulations, Stationery Office, 1999 ISBN 0 11 753469. To be replaced shortly byApproved Document M, Access to and use ofbuildings. www.odpm.gov.uk [5] BS 8300: 2001 Design of buildings andtheir approaches to meet the needs of disabledpeople, Code of Practice. [6] PPG 24, Planning Policy Guidance: Planningand Noise, Department of the Environment, TheStationery Office, September 1994. To bereplaced by revised Planning Policy documents.

Introduction

The normal way of satisfyingRequirement E4 of The BuildingRegulations is to demonstrate that all theperformance standards in Section 1.1, asappropriate, have been met.

Section 1.2 sets out the preferredmeans for demonstrating compliance ofthe design to the Building Control Body.

Section 1.3 describes acoustic tests thatcan be used to demonstrate compliancewith the performance standards in Section1.1. It is strongly recommended that theclient require acoustic testing to becarried out as part of the buildingcontract, because testing of the completed

construction is the best practical means ofensuring that it achieves the design intent.

In all but the simplest of projects it isadvisable to appoint a suitably qualifiedacoustic consultant1 at an early stage ofthe project, before the outline design hasbeen decided. This will prevent simplemistakes which can be costly to design outat a later stage. An acoustic consultant willnormally be needed to check the designdetails and on-site construction, and tocarry out acoustic tests to confirm thatthe building achieves the requiredacoustic performance.

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Contents1.1 Performance standards 9

1.1.1 Indoor ambient noise levels in unoccupied spaces 91.1.2 Airborne sound insulation between spaces 121.1.3 Airborne sound insulation between circulation spaces and

other spaces used by students 121.1.4 Impact sound insulation of floors 131.1.5 Reverberation in teaching and study spaces 141.1.6 Sound absorption in corridors, entrance halls and stairwells 151.1.7 Speech intelligibility in open-plan spaces 16

1.2 Demonstrating compliance to the Building Control Body 171.2.1 Alternative performance standards 17

1.3 Demonstrating compliance to the client 181.3.1 Timetabling of acoustic testing 181.3.2 Remedial treatments 181.3.3 Indoor ambient noise levels in unoccupied spaces 181.3.4 Airborne sound insulation between spaces 181.3.5 Airborne sound insulation between circulation spaces and

other spaces used by students 181.3.6 Impact sound insulation 181.3.7 Reverberation in teaching and study spaces 181.3.8 Sound absorption in corridors, entrance halls and stairwells 191.3.9 Speech intelligibility in open-plan spaces 19References 19

Specification of acoustic performance 1Section 1 of Building Bulletin 93 sets the performance standards for theacoustics of new buildings, and describes the normal means of demonstrating

compliance with The Building Regulations.

1 The primary professionalbody for acoustics in theUK is the Institute ofAcoustics. An experiencedprofessional acousticianwho is competent to beresponsible for theacoustic design of schoolbuildings would normally bea corporate member of theInstitute of Acoustics.

SE

CT

ION

1.1 Performance standardsThe overall objective of the performancestandards in Section 1.1 is to provideacoustic conditions in schools that (a)facilitate clear communication of speechbetween teacher and student, andbetween students, and (b) do notinterfere with study activities.

Performance standards on thefollowing topics are specified in thissection to achieve this objective:• indoor ambient noise levels • airborne sound insulation betweenspaces • airborne sound insulation betweencorridors or stairwells and other spaces• impact sound insulation of floors• reverberation in teaching and studyspaces• sound absorption in corridors, entrancehalls and stairwells• speech intelligibility in open-planspaces.

All spaces should meet theperformance standards defined in Tables1.1, 1.2, 1.3, 1.4 and 1.5 for indoorambient noise level, airborne and impactsound insulation, and reverberation time.Open-plan spaces should additionallymeet the performance standard for speechintelligibility in Table 1.6.

The notes accompanying Tables 1.1,1.2, 1.3 and 1.5 contain additionalguidance that should be considered whendesigning the spaces to meet theperformance standards in these tables.Although good practice, this guidancewill not be enforced under the BuildingRegulations.

1.1.1. Indoor ambient noise levels inunoccupied spacesThe objective is to provide suitableindoor ambient noise levels (a) for clearcommunication of speech betweenteacher and student, and betweenstudents and (b) for study activities.

The indoor ambient noise levelincludes noise contributions from:• external sources outside the schoolpremises (including, but not limited to,noise from road, rail and air traffic,industrial and commercial premises) • building services (eg ventilation system,

plant, etc). If a room is naturallyventilated, the ventilators or windowsshould be assumed to be open as requiredto provide adequate ventilation. If a roomis mechanically ventilated, the plantshould be assumed to be running at itsmaximum operating duty.

The indoor ambient noise levelexcludes noise contributions from: • teaching activities within the schoolpremises, including noise from staff,students and equipment within thebuilding or in the playground. Noisetransmitted from adjacent spaces isaddressed by the airborne and impactsound insulation requirements.• equipment used in the space (egmachine tools, CNC machines, dust andfume extract equipment, compressors,computers, overhead projectors, fumecupboards). However, these noise sourcesshould be considered in the designprocess. • rain noise. However, it is essential that

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NOTES ON TABLE 1.11 Research indicates that teaching can bedisrupted by individual noisy events such asaircraft flyovers, even where the noise level isbelow the limits in Table 1.1. For roomsidentified in Table 1.1 having limits of 35 dB orless the noise level should not regularly exceed55 dB LA1,30min.2 Acoustic considerations of open-plan areasare complex and are discussed in Section1.1.7 and Section 4. 3 Studios require specialised acousticenvironments and the noise limits for these willvary with the size, intended use and type ofroom. In some cases noise limits below 30 dB LAeq may be required, and separatelimits for different types of noise may beappropriate; specialist advice should be sought.4 Halls are often multi-functional spaces(especially in primary schools) used foractivities such as dining, PE, drama, music,assembly, and performing plays and concerts.In such multi-functional spaces the designershould design to the lowest indoor ambientnoise level for which the space is likely to beused. For large halls used for formal drama andmusic performance lower noise levels thanthose in Table 1.1 are preferable, and levels of25 dB LAeq,30min may be appropriate. In thesecases specialist advice should be sought.

Specification of acoustic performance1

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Table 1.1: Performance standardsfor indoor ambient noise levels - upperlimits for the indoor ambient noiselevel, LAeq,30min

Type of room

Nursery school playroomsNursery school quiet roomsPrimary school: classrooms, class bases, generalteaching areas, small group roomsSecondary school: classrooms, general teaching areas,seminar rooms, tutorial rooms, language laboratoriesOpen-plan2

Teaching areasResource areasMusicMusic classroomSmall practice/group roomEnsemble room Performance/recital roomRecording studio3

Control room for recordingLecture rooms Small (fewer than 50 people)Large (more than 50 people)Classrooms designed specifically for use by hearingimpaired students (including speech therapy rooms)Study room (individual study, withdrawal, remedialwork, teacher preparation)Libraries Quiet study areasResource areasScience laboratoriesDrama studiosDesign and Technology• Resistant materials, CADCAM areas• Electronics/control, textiles, food,

graphics, design/resource areasArt roomsAssembly halls4, multi-purpose halls4 (drama, PE,audio/visual presentations, assembly, occasional music) Audio-visual, video conference roomsAtria, circulation spaces used by studentsIndoor sports hallDance studioGymnasiumSwimming poolInterviewing/counselling rooms, medical rooms Dining roomsAncillary spaces Kitchens*

Offices*, staff rooms*Corridors*, stairwells*Coats and changing areas*Toilets*

Room classification for the purpose ofairborne sound insulation in Table 1.2

Activity noise(Source room)HighLow

Average

Average

AverageAverage

Very highVery highVery highVery highVery highHigh

AverageAverage

Average

Low

LowAverageAverageHigh

High

AverageAverage

HighAverageAverageHighHighHighHighLow HighHighAverageAverage - HighHighAverage

Noise tolerance(Receiving room)LowLow

Low

Low

MediumMedium

LowLowVery lowVery lowVery lowLow

LowVery low

Very low

Low

LowMediumMediumVery low

High

MediumMedium

LowLowMediumMediumMediumMediumHighLow HighHighMediumHighHighHigh

Upper limit for theindoor ambientnoise levelLAeq,30min (dB)

351

351

351

351

401

401

351

351

301

301

301

351

351

301

301

351

351

4040301

40

4040

351

351

4540404050351

455040454550

1Specification of acoustic performance

* Part E of Schedule 1 to the Building Regulations 2000 (as amended by SI 2002/2871) applies to teaching and learning spaces and is not intended to coveradministration and ancillary spaces (see under Scope in the Introduction). For theseareas the performance standards are for guidance only.

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this noise is considered in the design oflightweight roofs and roof lights as it cansignificantly increase the indoor ambientnoise level (see the design guidance inSection 3.1.1). It is intended that aperformance standard for rain noise willbe introduced in a future edition ofBB93. To satisfy this edition of BB93 itshould be demonstrated to the BuildingControl Body that the roof has beendesigned to minimise rain noise (seeSection 1.2).

Table 1.1 contains the required upperlimits for the indoor ambient noise levelsfor each type of unoccupied space. Thenoise levels in Table 1.1 are specified interms of LAeq,30min. This is an averagenoise level over 30 minutes, as explainedin Appendix 1. The specified levels referto the highest equivalent continuous A-weighted sound pressure level,

LAeq,30min, likely to occur during normalteaching hours. The levels due to externalsources will depend on weatherconditions (eg wind direction) and localactivities. High noise levels due toexceptional events may be disregarded.

The indoor ambient noise levels inTable 1.1 apply to finished butunoccupied and unfurnished spaces.

Tonal and intermittent noises aregenerally more disruptive than othertypes of noise at the same level. Noisefrom plant, machinery and equipment innoise–sensitive rooms should therefore beconstant in nature and should not containany significant tonal or intermittentcharacteristics. Noise from buildingservices which is discontinuous, tonal, orimpulsive (ie noise which can bedistracting) should be reduced to a level atleast 5 dB below the specified maximum.

Minimum DnT (Tmf,max),w (dB) Activity noise in source room (see Table 1.1)

Low Average High Very high

High 30 35 45 55

Medium 35 40 50 55

Low 40 45 55 55

Very low 45 50 55 60

Noi

se t

oler

ance

in

rec

eivi

ng r

oom

(see

Tab

le 1

.1)

Table 1.2: Performancestandards for airbornesound insulation betweenspaces - minimum weightedBB93 standardized leveldifference, DnT (Tmf,max),w

NOTES ON TABLE 1.21 Each value in the table is the minimum required to comply with the Building Regulations. A valueof 55 dB DnT (Tmf,max),w between two music practice rooms will not mean that the music will beinaudible between the rooms; in many cases, particularly if brass or percussion instruments areplayed, a higher value is desirable. 2 Where values greater than 55 dB DnT (Tmf,max),w are required it is advisable to separate the roomsusing acoustically less sensitive areas such as corridors and storerooms. Where this is not possible,high performance constructions are likely to be required and specialist advice should be sought.3 It is recommended that music rooms should not be placed adjacent to design and technologyspaces or art rooms.4 These values of DnT (Tmf,max),w include the effect of glazing, doors and other weaknesses inthe partition. In general, normal (non-acoustic) doors provide much less sound insulation than thesurrounding walls and reduce the overall DnT (Tmf,max),w of the wall considerably, particularly forvalues above 35 dB DnT (Tmf,max),w. Therefore, doors should not generally be installed inpartitions between rooms requiring values above 35 dB DnT (Tmf,max),w unless acoustic doors,door lobbies, or double doors with an airspace are used. This is not normally a problem as roomsare usually accessed via corridors or circulation spaces so that there are at least two doorsbetween noise-sensitive rooms. For more guidance see Section 3.


11

In rooms with very low noise tolerance,including music rooms, studios androoms used for formal music and dramaperformance, any audible intermittentnoise source of this type is likely to causeproblems and specialist advice should besought.

1.1.2. Airborne sound insulationbetween spaces The objective is to attenuate airbornesound transmitted between spacesthrough walls and floors.

Table 1.2 contains the requiredminimum airborne sound insulationvalues between rooms. These values aredefined by the activity noise in the sourceroom and the noise tolerance in thereceiving room. The activity noise andnoise tolerance for each type of room aregiven in Table 1.1. The airborne soundinsulation is quoted in terms of theweighted BB93 standardized leveldifference, DnT (Tmf,max),w, between tworooms.

The BB93 standardized leveldifference, DnT (Tmf,max), is the leveldifference, in decibels, corresponding to aBB93 reference value of the reverberationtime in the receiving room:

DnT(Tmf,max) = D+10 lg dB

whereD is the level difference (dB)

T is the reverberation time in thereceiving room (s)Tmf,max is the reference reverberationtime equal to the upper limit of thereverberation time, Tmf, given in Table1.5 for the type of receiving room. Thisreference reverberation time shall be usedfor all frequency bands.

The BB93 standardized leveldifference, DnT (Tmf,max),w, is measuredin accordance with BS EN ISO 140-4:1998[1] in octave or one-third octavebands, the results are weighted andexpressed as a single-number quantity,DnT (Tmf,max),w, in accordance with BSEN ISO 717-1:1997[2].

The prediction and measurement ofDnT (Tmf,max),w between two roomsmust be carried out in both directions asits value depends upon the volume of thereceiving room, see the example below.

1.1.3 Airborne sound insulationbetween circulation spaces and otherspaces used by studentsThe objective is to attenuate airbornesound transmitted between circulationspaces (eg corridors, stairwells) and otherspaces used by students.

Table 1.3 contains the requiredminimum airborne sound insulation forthe separating wall construction, anydoorset in the wall and any ventilators inthe wall. The airborne sound insulationfor walls and doorsets is quoted in terms

Example to determine the performance standards for airborne sound insulation between a music classroom and asecondary school general teaching area.

From the music classroom (source room) to the general teaching area (receiving room): Table 1.1 shows that music classrooms have ‘very high’ activity levels and that general teaching areas have ‘low’tolerance. Table 1.2 shows that at least 55 dB DnT (0.8s),w is required.

From the general teaching area (source room) to the music classroom (receiving room): Table 1.1 shows that general teaching areas have ‘average’ activity levels and that music classrooms have ‘low’ tolerance.Table 1.2 shows that at least 45 dB DnT (1.0s),w is required.

In this example the requirement to control noise from the music classroom to the general teaching area is more stringent.

The construction should be designed to achieve at least 55 dB DnT (0.8s),w from the music classroom (source room) tothe general teaching area (receiving room), and at least 45 dB DnT (1.0s),w from the general teaching area (source room)to the music classroom (receiving room).


TTmf,max

of the weighted sound reduction index,Rw, which is measured in the laboratory.The airborne sound insulation forventilators is quoted in terms of theweighted element-normalized leveldifference, Dn,e,w. The performancestandard for ventilators is quoted in termsof Dn,e,w –10lgN where N is the numberof ventilators with airborne soundinsulation Dn,e,w.

The weighted sound reduction index ismeasured in accordance with BS EN ISO140-3:1995[3] and rated in accordancewith BS EN ISO 717-1:1997[2].

The weighted element-normalized leveldifference is measured in accordance withBS EN 20140-10:1992[4] and rated inaccordance with BS EN ISO 717-1:1997[2].

Table 1.3 excludes:• service corridors adjacent to spaces thatare not used by students• lobby corridors leading only to spacesused by students that have a hightolerance to noise as defined in Table 1.1.

The performance standard is set using

12

Type of space used by students Minimum Rw (dB) MinimumDn,e,w –10lgN

Wall including Doorset1 (dB)any glazing

All spaces except music rooms 40 30 39

Music rooms2 45 35 453

Table 1.3: Performancestandards for airbornesound insulation betweencirculation spaces andother spaces used bystudents - minimum soundreduction index, Rw andminimum Dn,e,w –10lgN(laboratory measurements}

a laboratory measurement because of thedifficulty in accurately measuring theairborne sound insulation between roomsand corridors, or rooms and stairwells inthe field. Therefore it is crucial that theairborne sound insulation of the walland/or doorset is not compromised byflanking sound transmission, eg soundtransmission across the junction betweenthe ceiling and the corridor wall (seeguidance in Section 3.10.3).

1.1.4. Impact sound insulation offloorsThe objective is to attenuate impactsound (eg footsteps) transmitted intospaces via the floor.

Table 1.4 contains the recommendedmaximum weighted BB93 standardizedimpact sound pressure level, L′nT (Tmf,max),w, for receiving rooms ofdifferent types and uses.

The BB93 standardized impact soundpressure level, L′nT (Tmf,max), is theimpact sound pressure level in decibelscorresponding to a BB93 reference valueof the reverberation time in the receivingroom:

L′nT(Tmf,max) = Li – 10 lg dB

whereL i is the impact sound pressure level (dB)T is the reverberation time in thereceiving room (s)Tmf,max is the reference reverberationtime equal to the upper limit of thereverberation time, Tmf , given in Table1.5 for the type of receiving room. Thisreference reverberation time shall be usedfor all frequency bands.

The BB93 standardized impact soundpressure level, L′nT (Tmf,max), is measured

NOTES ON TABLE 1.31 The Rw ratings are for the doorset alone.Manufacturers sometimes provide doorsetsound insulation data as a combined rating forthe wall and doorset where the Rw refers to theperformance of an ≈10 m2 high-performancewall containing the doorset. This is notappropriate as it gives higher figures than theRw of the doorset itself. However, withknowledge of the wall and doorset areas theRw of the doorset can be calculated from thesetest results. 2 Special design advice is recommended.3 Wherever possible, ventilators should not beinstalled between music rooms and circulationspaces.


TTmf,max

13

Type of room(receiving room)

Nursery school playroomsNursery school quiet roomsPrimary school: classrooms, class bases, general teaching areas, small group roomsSecondary school: classrooms, general teachingareas, seminar rooms, tutorial rooms, language laboratoriesOpen-planTeaching areasResource areasMusicMusic classroomSmall practice/group roomEnsemble room Performance/recital roomRecording studioControl room for recordingLecture roomsSmall (fewer than 50 people)Large (more than 50 people)Classrooms designed specifically for use by hearingimpaired students (including speech therapy rooms)Study room (individual study,withdrawal, remedial work,teacher preparation)Libraries Science laboratoriesDrama studiosDesign and Technology• Resistant materials, CADCAM areas• Electronics/control, textiles, food,

graphics, design/resource areasArt roomsAssembly halls, multi-purpose halls (drama, PE, audio/visual presentations, assembly,occasional music) Audio-visual, video conference roomsAtria, circulation spaces used by studentsIndoor sports hallGymnasiumDance studioSwimming poolInterviewing/counselling rooms, medical rooms Dining roomsAncillary spaces Kitchens*

Offices*, staff rooms*Corridors*, stairwells*Coats and changing areas*Toilets*

Maximum weightedBB93 standardizedimpact soundpressure level L′nT (Tmf,max),w (dB)

6560

60

60

6060

555555555555

6055

55

60606555

65

6060

6060656565606560656565656565

Table 1.4: Performance standards for impact sound insulation of floors -maximum weighted BB93 standardized impact sound pressure level L′nT (Tmf,max),w

in accordance with BS EN ISO 140-7:1998[5] in octave or one-third octavebands, the results are weighted andexpressed as a single-number quantity,L′nT (Tmf,max),w, in accordance with BS EN ISO 717-2:1997[6].

Impact sound insulation should bedesigned and measured for floors withouta soft covering (eg carpet, foam backedvinyl) except in the case of concretestructural floor bases where the softcovering is an integral part of the floor.

1.1.5. Reverberation in teaching andstudy spaces The objective is to provide suitablereverberation times for (a) clearcommunication of speech betweenteacher and student, and betweenstudents, in teaching and study spaces and(b) music teaching and performance.

Table 1.5 contains the required mid-frequency reverberation times for roomswhich are finished but unoccupied andunfurnished. The reverberation time isquoted in terms of the mid-frequencyreverberation time, Tmf , the arithmeticaverage of the reverberation times in the500 Hz, 1 kHz and 2 kHz octave bands.

Sound absorption from pinboards andnoticeboards can change when they arecovered up or painted. Absorptioncoefficients for pinboards and noticeboardsused in design calculations should be forfully covered or painted boards, asappropriate. If these data are not availablethen the absorption coefficient for theboard area used in the design calculationshould be the absorption coefficient ofthe wall to which the board is attached.

* Part E of Schedule 1 to the BuildingRegulations 2000 (as amended by SI 2002/2871) applies to teaching andlearning spaces and is not intended to coveradministration and ancillary spaces (see underScope in the Introduction). For these areas theperformance standards are for guidance only.


14

1.1.6. Sound absorption in corridors,entrance halls and stairwellsThe objective is to absorb sound incorridors, entrance halls and stairwells sothat it does not interfere with teachingand study activities in adjacent rooms.

The requirement is to provideadditional sound absorption in corridors,entrance halls and stairwells. The amountof additional absorption should becalculated according to ApprovedDocument E[7], Section 7. This describestwo calculation methods, A and B, forcontrolling reverberation in the commoninternal parts of domestic buildings. Oneof these methods should be used todetermine the amount of absorptionrequired in corridors, entrance halls andstairwells in schools. (See samplecalculations using calculation methods Aand B in Appendix 7.)

Sound absorption from pinboards andnoticeboards can change when they arecovered up or painted. Absorptioncoefficients for pinboards andnoticeboards used in design calculationsshould be for fully covered or paintedboards, as appropriate. If these data arenot available then the absorption

Type of roomNursery school playroomsNursery school quiet roomsPrimary school: classrooms, class bases, generalteaching areas, small group roomsSecondary school: classrooms, general teachingareas, seminar rooms, tutorial rooms, language laboratoriesOpen-planTeaching areasResource areasMusicMusic classroomSmall practice/group roomEnsemble room Performance/recital room3

Recording studioControl room for recordingLecture rooms3

Small (fewer than 50 people)Large (more than 50 people)Classrooms designed specifically for use by hearingimpaired students (including speech therapy rooms)Study room (individual study,withdrawal, remedial work, teacher preparation)Libraries Science laboratoriesDrama studiosDesign and Technology• Resistant materials, CADCAM areas• Electronics/control, textiles, food,

graphics, design/resource areasArt roomsAssembly halls, multi-purpose halls (drama, PE,audio/visual presentations, assembly, occasional music)2,3

Audio-visual, video conference roomsAtria, circulation spaces used by studentsIndoor sports hallGymnasiumDance studioSwimming poolInterviewing/counselling rooms, medical rooms Dining roomsAncillary spacesKitchens*Offices*, staff rooms*Corridors, stairwellsCoats and changing areas*Toilets*

Tmf1 (seconds)

<0.6<0.6

<0.6

<0.8

<0.8<1.0

<1.0<0.80.6 - 1.21.0 - 1.50.6 - 1.2<0.5

<0.8<1.0

<0.4

<0.8<1.0<0.8<1.0

<0.8

<0.8<0.8

0.8 - 1.2<0.8<1.5<1.5<1.5<1.2<2.0<0.8<1.0

<1.5<1.0See Section 1.1.6<1.5<1.5

Table 1.5: Performancestandards for reverberationin teaching and studyspaces – mid-frequencyreverberation time, Tmf, infinished but unoccupiedand unfurnished rooms

NOTES ON TABLE 1.5 1 Common materials often absorb most soundat high frequencies. Therefore reverberationtimes will tend to be longer at low frequenciesthan at high frequencies. In rooms usedprimarily for speech, the reverberation times inthe 125 Hz and 250 Hz octave bands maygradually increase with decreasing frequency tovalues not more than 30% above Tmf. 2 For very large halls and auditoria, and forhalls designed primarily for unamplified musicrather than speech, designing solely in termsof reverberation time may not be appropriateand specialist advice should be sought. In largerooms used primarily for music, it may beappropriate for the reverberation times in the125 Hz and 250 Hz octave bands to graduallyincrease with decreasing frequency to valuesup to 50% above Tmf. For more guidance seeSection 5.3 Assembly halls, multi-purpose halls, lecturerooms and music performance/recital roomsmay be considered as unfurnished when theycontain permanent fixed seating. Whereretractable (bleacher) seating is fitted, theperformance standards apply to the space withthe seating retracted.


* Part E of Schedule 1 to the BuildingRegulations 2000 (as amended by SI2002/2871) applies to teaching and learningspaces and is not intended to coveradministration and ancillary spaces (see underScope in the Introduction). For these areas theperformance standards are for guidance only.

15

coefficient for the board area used in thedesign calculation should be theabsorption coefficient of the wall to whichthe board is attached.

1.1.7 Speech intelligibility in open-plan spaces The objective is to provide clearcommunication of speech between teacherand student, and between students, inopen-plan teaching and study spaces.

For enclosed teaching and study spacesit is possible to achieve good speechintelligibility through specification of theindoor ambient noise level, soundinsulation and reverberation time. Open-plan spaces require extra specification asthey are significantly more complexacoustic spaces. The main issue is that thenoise from different groups of peoplefunctioning independently in the spacesignificantly increases the backgroundnoise level, thus decreasing speechintelligibility.

Open-plan spaces are generallydesigned for high flexibility in terms ofthe layout of teaching and study spaces.In addition, the layout is rarely finalisedbefore the school is operational. Thisincreases the complexity of assessingspeech intelligibility in the open-planspace. Therefore, at an early stage in thedesign, the designer should establish theexpected open-plan layout and activityplan with the client. The open-plan layout should include:• the positions at which the teacher willgive oral presentations to groups ofstudents• the seating plan for the students andteachers in each learning base• the learning base areas.The activity plan should include:• the number of teachers giving oralpresentations to groups of students at anyone time• the number of students engaged indiscussion at any one time• the number of people walking throughthe open-plan space (eg along corridorsand walkways) during teaching and studyperiods• any machinery (eg engraving machines,CNC machines, dust and fume extract

equipment, computers, printers, AVA)operating in the open-plan space.

The expected open-plan layout andactivity plan should be agreed as the basison which compliance with BB93 can bedemonstrated to the Building ControlBody.

The activity plan should be used toestablish the overall noise level due to thecombination of the indoor ambient noiselevel, all activities in the open-plan space(including teaching and study), andtransmitted noise from adjacent spaces. Acomputer prediction model should beused to calculate the Speech TransmissionIndex (STI)[8] in the open-plan space,using the overall noise level as thebackground noise level. Other methods ofestimating STI may also be applicable.

The performance standard for speechintelligibility in open-plan spaces isdescribed in terms of the SpeechTransmission Index in Table 1.6. Thecalculated value of STI should be between0.60 and 1.00, which gives an STI ratingof either ‘good’ or ‘excellent’. Thisperformance standard applies to speechtransmitted from teacher to student,student to teacher and student to student.

The performance standard in Table 1.6is intended to ensure that open-planspaces in schools are only built whensuited to the activity plan and layout.With some activity plans, room layoutsand open-plan designs it will not bepossible to achieve this performancestandard. At this point in the designprocess the decision to introduce anopen-plan space into the school should bethoroughly re-assessed. If, after re-assessment, there is still a need for theopen-plan space, then the inclusion ofoperable walls between learning basesshould be considered. These operablewalls will form classrooms and be subjectto the airborne sound insulationrequirements in Table 1.2. It is notappropriate to simply adjust the activity

Room type

Open-plan teaching and study spaces

Speech Transmission Index (STI)

>0.60

Table 1.6: Performancestandard for speechintelligibility in open-planspaces – SpeechTransmission Index (STI)


16

plan until the performance standard forspeech intelligibility is met.

Computer prediction software capableof simulating an impulse response shouldbe used to create a three-dimensionalgeometric model of the space, comprisingsurfaces with scattering coefficients andindividually assigned absorptioncoefficients for each frequency band. Themodel should allow for the location andorientation of single and multiple sourceswith user-defined sound power levels anddirectivity. (See guidance on computerprediction models on the DfES acousticswebsite www.teachernet.gov.uk/acoustics.)

Assumptions to be made in theassessment of speech intelligibility are:• for students, when seated, the headheight (for listening or speaking) is 0.8 mfor nursery schools, 1.0 m for primaryschools and 1.2 m for secondary schools• for students, when standing, the headheight (for listening or speaking) is 1.0 mfor nursery schools, 1.2 m for primaryschools and 1.65 m for secondary schools• for teachers, when seated, the headheight (for listening or speaking) is 1.2 m• for teachers, when standing, the headheight (for listening or speaking) is 1.65 m• the background noise level is the overallnoise level due to all activities (includingteaching and study) in the open-plan space.

1.2 Demonstrating compliance tothe Building Control BodyThe preferred means of demonstratingcompliance to the Building Control Bodyis to submit a set of plans, constructiondetails, material specifications, andcalculations, as appropriate for each areaof the school which is covered byRequirement E4 of the BuildingRegulations.The plans should identify:• the highest estimate for the indoorambient noise level, LAeq,30min, in eachspace and the appropriate upper limitfrom Table 1.1• the estimated weighted BB93standardized level difference, DnT (Tmf,max),w, between spaces and theappropriate minimum value from Table 1.2• the proposed values of Rw for partitionwalls and for doors, Dn,e,w –10lgN for

ventilators between circulation spaces andother spaces used by students, and theappropriate minimum values from Table 1.3• the estimated weighted BB93standardized impact sound pressure level,L′nT (Tmf,max),w, of floors above spacesand the appropriate maximum valuesfrom Table 1.4 • the estimated value of mid frequencyreverberation time Tmf in each space andthe appropriate range of values fromTable 1.5 • the proposed absorption treatments incorridors, entrance halls and stairwells• for open plan spaces, the estimatedrange of STI values for speechcommunication from teacher to student,student to teacher and student to student.

The supporting information shouldinclude:• construction details and materialspecifications for the external buildingenvelope • construction details and materialspecifications for all wall and floorconstructions, including all flankingdetails• calculations of the sound insulationDnT (Tmf,max),w and L′nT (Tmf,max),w• calculations of reverberation times inteaching and study spaces• calculations of the absorption area tobe applied in corridors, entrance halls andstairwells• measurements and/or calculationsdemonstrating how rain noise has beencontrolled• sound insulation test reports(laboratory and/or field) • sound absorption test reports(laboratory)• activity plan and layout for open-planspaces.

An example of a submission to aBuilding Control Body, with explanatorynotes, is contained in Appendix 10.

1.2.1 Alternative performancestandardsIn some circumstances alternativeperformance standards may beappropriate for specific areas withinindividual schools for particular


educational, environmental or health andsafety reasons. In these cases, thefollowing information should be providedto the Building Control Body:• a written report by a specialist acousticconsultant, clearly identifying (a) all areasof non-compliance with BB93performance standards (b) the proposedalternative performance standards and (c)the technical basis upon which thesealternative performance standards havebeen chosen• written confirmation from theeducational provider (eg school or LocalEducation Authority) of areas of non-compliance, together with the justificationfor the need and suitability of thealternative performance standards in eachspace.

1.3 Demonstrating compliance tothe clientTo ensure that the performance standardsare met, it is recommended that the clientshould include a requirement for acoustictesting in the building contract.

The design calculations submitted tothe Building Control Body demonstrateonly that the construction has thepotential to meet the performancestandards in Section 1.1. In practice, theperformance of the construction isstrongly influenced by workmanship onsite. If the design calculations anddetailing are correct, the most likelycauses of failure to meet the performancestandards will be poor workmanship,product substitution and design changeson site. Therefore, acoustic testing isrecommended.

The DfES acoustics website(www.teachernet.gov.uk/acoustics) will beused to encourage manufacturers andothers to disseminate acoustic test resultsalongside construction details forconstructions that consistently satisfy theperformance standards.

1.3.1 Timetabling of acoustic testingTimetabling of acoustic testing isimportant because any test that results ina failure to satisfy the performancestandards will require remedial work torectify the failure and potential design

changes to other parts of the building.For this reason it is desirable, wherepossible, to complete a sample set ofrooms in the school for advance testing.

1.3.2 Remedial treatmentsWhere the cause of failure is attributed tothe construction, other rooms that havenot been tested may also fail to meet theperformance standards. Therefore,remedial treatment may be needed inrooms other than those in which the testswere conducted. The efficacy of anyremedial treatment should be assessedthrough additional testing.

1.3.3 Indoor ambient noise levels inunoccupied spaces To demonstrate compliance with thevalues in Table 1.1, measurements ofindoor ambient noise levels should betaken in at least one in four roomsintended for teaching and/or studypurposes, and should include rooms onthe noisiest façade. These rooms shouldbe finished and unoccupied but may beeither furnished or unfurnished.Measurements should be made whenexternal noise levels are representative ofconditions during normal schooloperation.

During measurements, the followingshould apply:• Building services (eg ventilation system,plant) should be in use during themeasurement period.• For mechanically ventilated rooms, theplant should be running at its maximumdesign duty.• For naturally ventilated rooms, theventilators or windows should be open asrequired to provide adequate ventilation.• There should be no more than oneperson present in the room. (The valuesin Table 1.1 allow for one person to bepresent in the room during the test)• There should be dry weatherconditions outside.

Measurements of LAeq,T should bemade at least 1 m from any surface of theroom and at 1.2 m above floor level in atleast three positions that are normallyoccupied during teaching or studyperiods. A sound level meter complying

17


with BS EN 60804:2001 (IEC60804:2001)[9] should be used. Furtherinformation on noise measurementtechniques is available in the Associationof Noise Consultants Guidelines on NoiseMeasurement in Buildings[10].

Where there is negligible change innoise level over a teaching period,measurements of LAeq,T over a timeperiod much shorter than 30 minutes (egLAeq,5min) can give a good indication ofwhether the performance standard interms of LAeq,30min is likely to be met.However, if there are significant variationsin noise level, for example due tointermittent noise events such as aircraftor railways, measurements should betaken over a typical 30 minute period inthe school day.

1.3.4 Airborne sound insulationbetween spaces To demonstrate compliance with thevalues in Table 1.2, measurements ofairborne sound insulation should be takenbetween vertically and horizontallyadjacent rooms where the receiving roomis intended for teaching and/or studypurposes. At least one in four roomsintended for teaching and study purposesshould be tested. Measurements shouldbe taken in the direction with the morestringent airborne sound insulationrequirement.

During measurements, the ventilatorsor windows should be open as required toprovide adequate ventilation in both thesource room and the receiving room.

Measurements should be made inaccordance with BS EN ISO 140-4:1998[1] and the additional guidance inApproved Document E[7] Annex B,paragraphs B2.3 – B2.8. Performanceshould be rated in accordance with BSEN ISO 717-1:1997[2].

1.3.5 Airborne sound insulationbetween circulation spaces and otherspaces used by studentsIt is not intended that field measurementsshould be taken between circulationspaces and other spaces used by students.Laboratory data for the wall, doorsets (ifany) and ventilators (if any) should be

presented as evidence of compliance withthe values in Table 1.3.

1.3.6 Impact sound insulation To demonstrate compliance with thevalues in Table 1.4, measurements ofimpact sound insulation should be takenbetween vertically adjacent rooms, wherethe receiving room is intended forteaching and study purposes. At least onein four teaching/study rooms below aseparating floor should be tested.

Measurements should be made inaccordance with BS EN ISO 140-7:1998[5]. Performance should be ratedin accordance with BS EN ISO 717-2:1997[6].

Impact sound insulation should bemeasured on floors without a softcovering (eg carpet, foam backed vinyl),except in the case of concrete structuralfloor bases where the soft covering is anintegral part of the floor.

1.3.7 Reverberation in teaching andstudy spacesTo demonstrate compliance with thevalues in Table 1.5, measurements ofreverberation time should be taken in atleast one in four rooms intended forteaching and study purposes.

One person may be present in theroom during the measurement.

Depending upon the completionsequence for spaces within the school, itmay be possible to reduce themeasurement effort by utilisingmeasurements of reverberation time thatare required as part of airborne or impactsound insulation measurements. For thisreason, two measurement methods,described below, are proposed for themeasurement of reverberation time. Forthe purpose of demonstrating compliance,either method can be used to assesswhether the performance standards havebeen met. If one method demonstratescompliance with the performancestandard and the other demonstratesfailure, then the performance standardshould be considered to have been met.Measurement method 1: Measurementsshould be made in accordance with eitherlow coverage or normal coverage

18


measurements described in BS EN ISO3382:2000[11]. Measurement method 2: Reverberationtime measurements should be made inaccordance with BS EN ISO 140-4:1998[1] (airborne sound insulation) orBS EN ISO 140-7:1998[5] (impact soundinsulation) in octave bands.

1.3.8 Sound absorption in corridors,entrance halls and stairwellsIt is not intended that field measurementsof reverberation time should be taken incorridors, entrance halls and stairwells.

1.3.9 Speech intelligibility in open-plan spacesTo demonstrate compliance with thevalues in Table 1.6, measurements of theSpeech Transmission Index (STI) shouldbe taken in at least one in ten studentpositions in the open-plan spaces.

Measurements should be made inaccordance with BS EN 60268-16:1998[8].

Measurements should be made usingthe following heights for listening orspeaking:• to represent seated students, a headheight of 0.8 m for nursery schools, 1.0 mfor primary schools and 1.2 m forsecondary schools• to represent standing students, a headheight of 1.0 m for nursery schools, 1.2 mfor primary schools and 1.65 m forsecondary schools• to represent seated teachers, a headheight of 1.2 m• to represent standing teachers, a headheight of 1.65 m.

Simulation of the estimated occupancynoise should be carried out in the STImeasurement. This noise level will havebeen established at the design stage (seeSection 1.1.7) and is defined as the noiselevel due to the combination of theindoor ambient noise level, all activities inthe open-plan space (including teachingand study), and transmitted noise fromadjacent spaces.

References[1] BS EN ISO 140-4:1998 Acoustics –Measurement of sound insulation in buildingsand of building elements. Part 4. Fieldmeasurements of airborne sound insulationbetween rooms.[2] BS EN ISO 717-1:1997 Acoustics – Ratingof sound insulation in buildings and of buildingelements. Part 1. Airborne sound insulation.[3] BS EN ISO 140-3:1995 Acoustics –Measurement of sound insulation in buildingsand of building elements. Part 3. Laboratorymeasurement of airborne sound insulation ofbuilding elements.[4] BS EN 20140-10:1992 Acoustics –Measurement of sound insulation in buildingsand of building elements. Part 10. Laboratorymeasurement of airborne sound insulation ofsmall building elements.[5] BS EN ISO 140-7:1998 Acoustics –Measurement of sound insulation in buildingsand of building elements. Part 7. Fieldmeasurements of impact sound insulation offloors.[6] BS EN ISO 717-2:1997 Acoustics – Ratingof sound insulation in buildings and of buildingelements. Part 2. Impact sound insulation.[7] Approved Document E – Resistance to thepassage of sound. Stationery Office 2003. ISBN 0 11 753 642 3.www.odpm.gov.uk[8] BS EN 60268-16:1998 Sound systemequipment – Part 16: Objective rating ofspeech intelligibility by speech transmissionindex.[9] BS EN 60804:2001 (IEC 60804:2001)Integrating-averaging sound level meters.[10] Guidelines on Noise Measurement inBuildings, Part 1: Noise from Building Servicesand Part 2: Noise from External Sources.Association of Noise Consultants.[11] BS EN ISO 3382:2000 Acoustics –Measurement of the reverberation time ofrooms with reference to other acousticalparameters.

19


21

2.1 Choosing a siteThe acoustic design of a school starts withthe selection of the site, a noise survey ofthe site and planning the layout of theschool buildings.

Economic sites for new schools witheasy access to transport often suffer fromtraffic noise and pollution. In the past,schools have sometimes been built onsites which would not normally have beenconsidered suitable for housing. This hasbeen in part because schools have notalways been recognised as requiringparticularly high environmental standards,and in part because there has been lessformal control or regulation of noiselevels in schools than for housing.

Where school sites are adjacent to busyroads they will require the use ofintelligent design, zoning, noise screeningand, if necessary, sound insulatingbuilding envelopes together withmechanical ventilation or acousticallydesigned passive ventilation.

Many of the acoustic problems inexisting schools derive directly from theschool’s location in a noisy area. Forexisting schools, noise from road traffic isa common problem, but in some areasnoise from railways and aircraft isintrusive[1]. Noise from industrial andleisure sources is a less frequent problemand can normally be dealt with at sourceby the Local Authority using their powersunder the Environmental Pollution Act.

2.2 Recommendations for externalnoise levels outside school buildingsAlthough Requirement E4 does not applyto external noise, the followingrecommendations are considered goodpractice for providing good acoustic

conditions outside school buildings.For new schools, 60 dB LAeq,30min

should be regarded as an upper limit forexternal noise at the boundary of externalpremises used for formal and informaloutdoor teaching, and recreational areas.

Under some circumstances it is possibleto meet the specified indoor ambientnoise levels on sites where external noiselevels are as high as 70 dB LAeq,30min butthis will require considerable buildingenvelope sound insulation, screening orbarriers.

Noise levels in unoccupiedplaygrounds, playing fields and otheroutdoor areas should not exceed 55 dBLAeq,30min and there should be at leastone area suitable for outdoor teachingactivities where noise levels are below 50 dB LAeq,30min. If this is not possibledue to a lack of suitably quiet sites,acoustic screening should be used toreduce noise levels in these areas as muchas practicable, and an assessment ofpredicted noise levels and of options forreducing these should be carried out.

Playgrounds, outdoor recreation areasand playing fields are generally consideredto be of relatively low sensitivity to noise,and indeed playing fields may be used asbuffer zones to separate school buildingsfrom busy roads where necessary.However, where used for teaching, forexample sports lessons, outdoor ambientnoise levels have a significant impact oncommunication in an environment whichis already acoustically less favourable thanmost classrooms. Ideally, noise levels onunoccupied playing fields used forteaching sport should not exceed 50 dBLAeq,30min. If this is not possible at alllocations, there should be at least one area

Noise control 2Section 2 gives recommendations and guidance concerning noise control,starting with the choice of a site and the control of external noise. Local

government planning policy will be influenced by the recommendations onmaximum external noise levels in playing fields and other external areas usedby the school. Section 2 also includes discussion of the means of controlling

indoor ambient noise.

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at which noise levels are below 50 dBLAeq,30min so that some outdoorteaching is possible.

Acoustic screening from fences, wallsor buildings may be used to protectplaygrounds from noise. At positions nearthe screen, traffic noise can be reduced byup to 10 dB(A).

All external noise levels in this sectionapply to measurements made atapproximately head height and at least 3 mfrom any reflecting surface other than theground.

2.3 Noise surveyFigure 2.1 shows typical external andinternal sources of noise which can affectnoise levels inside a school.

In order to satisfy the limits for theindoor ambient noise levels in Table 1.1,it is necessary to know the external noiselevel so that the building envelope can bedesigned with the appropriate soundinsulation.

The external noise level should beestablished by carrying out a noisemeasurement survey. (Note that a briefsurvey is advisable even if the site appearsto be quiet, in case there are noisy eventsat certain times of the day.) Themeasurements should be taken duringFigure 2.1: Typical

sources of noise

PLANTROOM NOISEAND VIBRATION

NOISYCORRIDORS

NOISE VIA OPEN WINDOWS

WEATHER& RAIN NOISE

BREAK-OUT/BREAK-INOF DUCTBORNE

NOISE

DUCTBORNE NOISE

PLUMBING NOISE

DUCTBORNE NOISE FAN

TRAFFIC NOISEAND VIBRATION

PLAYGROUNDNOISE

NOISE THROUGHDOORS & WALLS

AIRCRAFT NOISE

typical school hours and include noisyevents (eg road traffic at peak hours,worst case runway usage in the case ofairports, etc). The measurements mustalso take account of the weatherconditions. For long-distance propagationof noise, the measured level is affected bywind gradients, temperature gradients andturbulence. With wind, the noise level isgenerally increased downwind or reducedupwind. (Note that temperatureinversions can radically change noisepropagation, but tend to occur only atnight-time, outside school hours.)

A noise measurement survey mustinclude octave or one-third octavefrequency band levels. This is because theattenuation of sound, for example by asound insulating wall or noise barrier,depends upon the frequency of sound. Ingeneral materials and barriers are lesseffective at controlling low frequencynoise than mid and high frequency noise.Although overall noise levels andperformance standards can be quoted asoverall A-weighted levels, calculationsmust be carried out in octave or one-thirdoctave bands (see Appendix 1) and theresults converted into overall A-weightedlevels.

In addition to the noise measurement

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Barrier

Soundsource Receiver

Ground

ab

c

Path difference = a + b – c

Figure 2.2: Attenuationby a noise barrier as afunction of path difference

2000 Hz

1000 Hz500 Hz

250 Hz

125 Hz

30

25

20

15

10

5

0 0.5 1.0 1.5 2.0

Path difference, m

Atte

nuat

ion,

dB

survey, consideration should be given topredicting the potential increases in noiselevels due to future developments (egincreases in traffic flows, new transportschemes, changes in flight paths). Thelocal highway authority should be able toadvise on whether significant changes inroad traffic noise are expected in thefuture. This is likely to be relevant fordevelopments near new or recentlyimproved roads. Where road traffic noiselevels are likely to increase, it is reasonableto base the sound insulation requirementson the best estimate of noise levels in 15years time. Similar information is likely tobe available from railway operators, andairports. The prediction[2,3] of futureexternal noise levels should be carried outby an acoustic consultant.

If the noise measurement survey showsthat the ambient external noise levels onthe site are below 45 dB LAeq,30min, andprediction work shows that they willremain below 45 dB LAeq,30min in thefuture, no special measures are likely to benecessary to protect the buildings orplaying fields from external noise.

2.4 Road and rail noiseSources of road and rail noise requireindividual assessment because of theircharacteristics.

Road traffic noise is a function of trafficflow, percentage of heavy goods vehicles,traffic speed gradient (rate of acceleration),road surface and propagation path of thenoise.

Rail noise is a function of train type, number, speed, rail type and propagationpath of the noise.

In general it is advisable to locate aschool at least 100 m away from busyroads and railways, but in towns and citiesthis is often not possible. However, theuse of distance alone is a relativelyineffective way to reduce noise. Simplerules of thumb are that the noise levelfrom a busy road increases by 3 dB(A) fora doubling of the traffic flow anddecreases by 3 dB(A) for a doubling ofdistance from the road (over hardground).

2.5 Aircraft noiseWhere a school is to be located in an areaaffected by aircraft noise, special measuresare necessary and an acoustic consultantshould be appointed.

2.6 VibrationRailways, plant and heavy vehicles close toa school can lead to vibration within theschool buildings. This vibration can re-radiate as audible noise, even when thevibration itself is not perceptible asshaking in the building. The propagationof vibration depends on groundconditions but in general when planning anew school building it is advisable for thenoise survey to include vibrationmeasurements when there is a railwaywithin 30 m of a building, or a road withsignificant HGV traffic within 20 m. Inthese cases airborne noise is also likely tobe a problem.

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2.7 Noise barriersNoise barriers are much more effectivethan distance in reducing noise from roador rail traffic. In its simplest form a noisebarrier can be a continuous close-boardedwooden fence, with a mass of not lessthan 12 kg/m2. There is relatively littlepoint in increasing the weight of thebarrier beyond this because a significantproportion of the noise passes over thetop (or round the ends) of the barrier.

The attenuation of a barrier is afunction of the path difference, that is theextra distance that the sound has to travelto pass over the top of the barrier, seeFigure 2.2. Barriers are less effective atreducing low frequency noise than midand high frequency noise. Hence, tocalculate the effectiveness of a noisebarrier it is necessary to know the sourcenoise levels in octave or one-third octavebands (see Appendix 1).

Hedges or single trees (or rows oftrees) do not in themselves make effectivenoise barriers. A common and effectivesolution is a wooden fence to act as anoise barrier, located within a band oftrees to create an acceptable visual effect.

Barriers can also be formed by otherbuildings or by landscaping using earthbunds, see Figure 2.3. The pathdifference, and hence the attenuation, will

be affected by whether the road or railwayis in a cutting or on an embankment.

2.8 Noise from schools tosurrounding areasNoise from schools to the surroundingarea can also be a problem, andconsideration should be given to nearbyresidential and other noise-sensitivedevelopments which could be disturbedby noise from playgrounds, playing fields,music rooms and halls used for eventssuch as after school concerts and discos.The local planning authority will normallyconsider this in assessing any planningapplication for new schools or extensionsto existing premises.

The effect of playground noise onchildren inside parts of the school nearthe playground should also be consideredas part of the design.

2.9 Planning and layoutAmong the most common problemsfound in schools is noise transfer betweenrooms. To a large extent this can bedesigned out without resort to very highperformance sound insulating walls orfloors, but by good planning and zoningof the building at the earliest stages ofdesign. At this stage it is possible toidentify noise-sensitive areas and to

POORNo acoustical shieldingfrom landscaping

BETTERShielding from embankment would beimproved by a fence within the trees

BESTEarth bund acts as acoustic barrier, plantingacts as visual barrier

Figure 2.3: Traffic noisebarriers

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Otherclassroom

Store Store

Store

Store

StoreGroupRoom

GroupRoom

GroupRoom

GroupRoom

GroupRoom

GroupRoom

Musicclassroom

Musicclassroom

StaffBase

GroupRoom

Instrumentstore

EnsembleRoom

Recording/ControlRoom

To otherdepartments

Corridorcreatesacoustic

separation

Easyaccess tosupportspaces

Storesprovide

acousticbuffer

Acoustic separationfor ensemble room and

group rooms

Store

Store

GroupRoom

Fig 2.4: Planning acoustic‘buffer zones’

separate these from noisy areas usingbuffer zones such as storerooms,corridors or less sensitive rooms, or bylocating buildings a suitable distanceapart. See Figure 2.4 for an example ofroom layout in a music department usingbuffer zones.

When considering external noise suchas that from roads, it is sensible to locatenoise-sensitive rooms, such as classrooms,away from the source.

Tables 1.1 and 1.2 give the requiredmaximum indoor ambient noise levels andthe minimum sound insulation levelsbetween rooms. The performancestandards in these tables should be usedin the early planning stages of a project todetermine (a) the layout of the school (b) the constructions needed to providesound insulation and (c) the compatibilityof school activities in adjacent rooms.

2.10 Limiting indoor ambient noiselevelsThe total indoor ambient noise level isdetermined by combining the noise levelsfrom all the known sources. The indoorambient noise level due to externalsources such as traffic must be added tothe noise from mechanical ventilation,heating systems, lighting and otherbuilding services. Unless care is taken,these individual sources can be loudenough to cause disturbance, particularlyin spaces where low indoor ambient noiselevels are required.

It should be noted that noise levels indB or dB(A) cannot be simply addedtogether. For example, two noise levels of40 dB(A) when combined will produce alevel of 43 dB(A). The addition of noiselevels is explained in Appendix 1.

2.11 Impact noise Impact noise within a space from footfallson balconies, stairs and circulation routes,or from movement of furniture or otherclass activities, can be a significantdistraction to teaching and learning.

Carpets and other soft yet resilientfloor finishes such as resilient backed vinylor rubber type flooring materials can beuseful in limiting this impact noise withina space. However, carpets may be difficult

to clean and are sometimes not usedbecause of their effect on indoor airquality and resultant health implications.

Resilient feet can also be fitted tofurniture to reduce impact noise within aspace.

2.12 Corridors, entrance halls andstairwellsNoise in corridors, entrance halls andstairwells can cause disturbance toneighbouring classrooms and otherteaching spaces. It is therefore importantthat reverberation in corridors, entrancehalls and stairwells is kept as low as

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possible in order to minimise noise levelsin these areas. The requirement is toprovide sound absorption in accordancewith Section 1.1.6. To satisfy thisrequirement, corridors outside classroomstypically need acoustically absorbentceilings and/or wall finishes. Carpets andother soft floor finishes can also help toreduce reverberation and the noise fromfootfalls. However, as discussed in Section2.11, the use of carpets may not beappropriate in all schools.

2.13 Masking noiseThe audibility and intrusiveness of noisefrom other areas (break-in noise) is afunction of both the level of the break-innoise and the noise level in the roomunder consideration (the receiving room).If the ambient noise level in the receivingroom is unnecessarily low, break-in noisewill be more audible. Hence where roomsare mechanically ventilated, the noisefrom the ventilation system can be usedto mask the noise from activities inneighbouring rooms. In these casesventilation noise should not be more than5 dB below the maximum ambient noiselevels listed in Table 1.1. For this type ofmasking to work it is important to ensurethat the ventilation noise follows a specificmasking noise curve and has no tonal orintermittent characteristics. Specialistacoustic advice is required before usingbuilding services noise for masking.

Other possible sources of maskingnoise are fan convectors, electric lightingcircuits, and constant levels of road trafficnoise, for example from distant arterialroads. However it should be noted thatthe noise from some sources (eg fans andother mechanical equipment) may causeannoyance to individuals, particularlyhearing impaired people, in somecircumstances. Also, some buildingservices systems may only operate atcertain times of the year.

2.14 Low frequency noise andhearing impaired pupilsMany hearing impaired pupils make useof low frequencies below 500 Hz toobtain information from speech.Therefore, for hearing impaired pupils tobe included in classes with pupils havingnormal hearing, special care should betaken to minimise low frequency indoorambient noise levels. Given the prevalenceof infections leading to temporary hearingloss, it is advisable to minimise lowfrequency indoor ambient noise levels inall classrooms, especially those used byyounger pupils.

The indoor ambient noise levels inTable 1.1 are given in terms ofLAeq,30min which is an A-weighted noiselevel. This is a convenient and widely-used parameter but is not a goodindicator of low frequency noise. Toassess indoor noise there are other ratingsystems in use which address lowfrequency noise but these are beyond thescope of this document. In cases wherelow frequency noise is likely to be aproblem, specialist advice from anacoustics consultant should be sought.Such cases include schools exposed tohigh levels of external noise (in excess of60 dB LAeq,30min, see Section 2.2),where sound insulation may reduce highfrequency noise while leavingcomparatively high levels of lowfrequency noise.

More information is given in CIBSEGuide B5 Noise and Vibration Controlfor HVAC.[4]

References [1] B Shield, J Dockrell, R Jeffery and I Tachmatzidis. The effects of noise on theattainments and cognitive performance ofprimary school children. Department of Health,2002.[2] Calculation of road traffic noise (CRTN),Department of Transport, The StationeryOffice, 1988.[3] Calculation of railway noise (CRN),(Supplement 1), Department of Transport, The Stationery Office, 1995.[4] CIBSE Guide B5, Noise and vibrationcontrol for HVAC, CIBSE, 2002ISBN 1 903287 2 51.

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General principles of sound insulation and typical constructions are discussed inthis section. Space does not allow all details for each type of construction to be

shown. Many such details are illustrated and discussed in greater detail inApproved Document E[1]. Further guidance and illustrations are also available in

Sound Control for Homes[2] and in manufacturers’ literature for proprietarymaterials and systems.

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3.1 RoofsThe sound insulation of a pitched roofdepends upon the mass of the ceiling andthe roof layers and the presence of asound absorbing material in the roofspace. Mineral wool, used as thermalinsulation in the ceiling void, will alsoprovide some acoustic absorption, whichwill have a small effect on the overallsound insulation of a roof. A denserspecification of mineral wool, ascommonly used for acoustic insulation,would have a greater effect on the overallsound insulation of the roof.

Where it is necessary to ventilate theroof space, it is advisable to make anynecessary improvements to the soundinsulation by increasing the mass of theceiling layer, which should be airtight.Recessed light fittings can make thisdifficult and sometimes it is better toplace the sound insulating material belowthe roof covering and to extend partitionwalls up to the roof layer (providingadequate ventilation can be maintained).

3.1.1 Rain noiseThe impact noise from rain on the roofcan significantly increase the indoor noiselevel; in some cases the noise level inside aschool due to rain can be as high as 70 dB(A).

Although rain noise is excluded fromthe definition of indoor ambient noise in

Section 1.1, it is a potentially importantnoise source which must be considered atan early point in the roof design tominimise disturbance inside the school.

Excessive noise from rain on the roofcan occur in spaces (eg sports halls,assembly halls) where the roof is madefrom profiled metal cladding and there isno sealed roof space below the roof toattenuate the noise before it radiates intothe space below. With profiled metalcladding, the two main treatments thatshould be used in combination to providesufficient resistance to impact sound fromrain on the roof are: • damping of the profiled metal cladding(eg using commercial damping materials) • independent ceilings (eg two sheets of10 kg/m2 board material such asplasterboard, each supported on its ownframe and isolated from the profiled metalcladding, with absorptive material such asmineral fibre included in the cavity.)

Profiled metal cladding used without adamping material and without anindependent ceiling is unlikely to providesufficient resistance to impact sound fromrain on the roof. A suitable system thatcould be used in schools is shown inFigure 3.1. The performance of such asystem was measured by McLoughlin etal[3].

Prediction models are available topredict the noise radiated from a singlesheet of material; however, a single sheetwill not provide sufficient attenuation ofimpact noise from rain. Suitablelightweight roof constructions that doprovide sufficient attenuation will consistof many layers. For these multi-layer roofconstructions, laboratory measured datafor the entire roof construction is needed.At the time of writing, a new laboratory

Figure 3.1: Profiled metalclad roof incorporatingacoustic damping

Damped aluminium tiles

Plasticised steel top sheet

50 – 100 mm mineral fibreTwo sheets of Fermacell board

Steel liner panel50 – 100 mm mineral fibre

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measurement standard for impact soundfrom rain on the roof, ISO 140-18[4], isunder development. In the future this willallow comparison of the insulationprovided by different roof, window andglazing elements and calculation of thesound pressure level in the space belowthe roof.

When designing against noise from rainon the roof, consideration should also begiven to any glazing (eg roof lights) inthe roof. Due to the variety of differentroof constructions, advice should besought from an acoustic consultant whocan calculate the sound pressure level inthe space due to typical rainfall on thespecific roof.

3.2 External WallsFor masonry walls, such as a 225 mmsolid brick wall, a brick/block cavity wallor a brick-clad timber frame wall, thesound insulation performance willnormally be such that the windows,ventilators and, in some cases, the roofwill dictate the overall sound insulation ofthe building envelope.

Timber frame walls with lightweightcladding and other lightweight systems ofconstruction normally provide a lowerstandard of sound insulation at lowfrequencies, where road traffic and aircraftoften produce high levels of noise. Thiscan result in low airborne soundinsulation against these noise sourcesunless the cladding system has sufficientlow frequency sound insulation. Theairborne sound insulation can be assessedfrom laboratory measurements carried outaccording to BS EN ISO 140-3:1995[5].

3.3 VentilationThe method of ventilation as well as thetype and location of ventilation openingswill affect the overall sound insulation ofthe building envelope. When externalnoise levels are higher than 60 dBLAeq,30min, simple natural ventilationsolutions may not be appropriate as theventilation openings also let in noise.However, it is possible to use acousticallyattenuated natural ventilation rather thanfull mechanical ventilation when externalnoise levels are high but do not exceed

70 dB LAeq,30min. The School Premises Regulations[6]

require that: “All occupied areas in a school building

shall have controllable ventilation at aminimum rate of 3 litres of fresh air persecond for each of the maximum number ofpersons the area will accommodate.

All teaching accommodation, medicalexamination or treatment rooms, sickrooms, sleeping and living accommodationshall also be capable of being ventilated at aminimum rate of 8 litres of fresh air persecond for each of the usual number ofpeople in those areas when such areas areoccupied.”

In densely occupied spaces such asclassrooms, 8 litres per second per personis the minimum amount of fresh air thatshould be provided by a natural ormechanical ventilation system undernormal working conditions, in order tomaintain good indoor air quality.

In order to satisfy the limits for theindoor ambient noise levels in Table 1.1,it is necessary to consider the soundattenuation of the ventilation openings sothat the building envelope can bedesigned with the appropriate overallsound insulation. In calculations of overallsound insulation the attenuation assumedfor the ventilation system should be fornormal operating conditions.

The main choices for the naturalventilation of typical classrooms areshown in Figure 3.2. Case Studies 7.8and 7.9 describe the recent application oftwo of these design solutions in newsecondary school buildings.

Additional ventilation such as openablewindows or vents may be required toprevent summertime overheating.

3.3.1 VentilatorsPassive ventilators normally penetrate thewalls, but in some cases they penetrate thewindow frames (eg trickle ventilators) orthe windows themselves. Often windowsare not used as intended as they causeuncomfortable draughts. For this reason,increased use is being made of purposedesigned ventilation systems with orwithout acoustic attenuation.

Many proprietary products are

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Figure 3.2: Possibletypes of natural ventilation

Secondary glazing withstaggered openingsAcoustically treated high capacity air inlet

Secondary glazing with staggered openings

Absorbent duct liningAcoustic louvres on outsideplus secondary glazing with staggered openings andacoustically treated high capacity air inlet

CLASSROOMCORRIDOR 2.7 m

2.7 m

2.7 m

2.7 m

CROSS-VENTILATION

SINGLE-SIDED VENTILATION

STACK VENTILATION

WIND TOWER/TOP DOWNVENTILATION

Absorbent duct liningAcoustic louvres on outsideSecondary glazing with staggered openingsAttenuator plenum boxElectronic noise

POSSIBLE SOUNDINSULATION MEASURES

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designed for the domestic sector and insome cases they do not have large enoughopenings for classrooms and other largerooms found in schools. The acousticperformance of any ventilator can beassessed with laboratory sound insulationtest data measured according to BS EN20140-10:1992[7]. Because of thecomplexity of the assessment of theacoustic performance of a ventilator,advice may be needed from a specialistacoustic consultant. To maintain adequateventilation, it is essential that the effectivearea of the ventilator is considered as itmay be smaller than the free area (see prEN 13141-1[8]).

It is important, particularly in the caseof sound-attenuated products, that a goodseal is achieved between the penetrationthrough the wall or window and theventilator unit. Where through-the-wallproducts are used, the aperture should becut accurately and the gap around theperimeter of the penetrating duct shouldbe packed with sound insulating materialprior to application of a continuous,flexible, airtight seal on both sides.

In some schools bespoke ventilatordesigns, such as that shown in Figure 3.3,are needed. For more examples ofventilator solutions see Case Studies 7.8and 7.9.

3.4 External WindowsThe airborne sound insulation ofwindows can be assessed from laboratorymeasurements of the sound reductionindex according to BS EN ISO 140-3:1995[5]. When choosing suitablewindows using measured data, care mustbe taken to differentiate betweenmeasured data for glazing and measureddata for windows. The reason is that theoverall sound insulation performance of awindow is affected by the window frameand the sealing as well as the glazing.

To achieve the required soundinsulation with thin glass it is oftennecessary to use two panes separated byan air (or other gas) filled cavity. Intheory, the wider the gap between thepanes, the greater the sound insulation.In practice, the width of the cavity indouble glazing makes relatively little

difference for cavity widths between 6 mmand 16 mm. Wider cavity widths performsignificantly better.

In existing buildings, secondary glazingmay be installed as an alternative toreplacing existing single glazing withdouble glazing. The effectiveness ofsecondary glazing will be determined bythe thickness of the glass and the width ofthe air gap between the panes. Anotheralternative may be to fit a completely newdouble-glazed window on the inside ofthe existing window opening, leaving theoriginal window intact. The use of soundabsorbing reveal linings improves theperformance of double-glazed windows,but the improvement is mainly in themiddle to high frequency region, where ithas little effect on road traffic and aircraftnoise spectra.

To achieve their optimumperformance, it is essential that theglazing in windows makes an airtight sealwith its surround, and that opening lightshave effective seals around the perimeterof each frame. Neoprene compressionseals will provide a more airtight seal thanbrush seals. The framing of the windowshould also be assembled to achieve anairtight construction.

It is equally important that an airtightseal is achieved between the perimeter ofthe window frame and the opening intowhich it is to be fixed. The openingshould be accurately made to receive thewindow, and the perimeter packed withsound insulating material prior toapplication of a continuous seal on bothsides.

For partially open single-glazedwindows or double-glazed windows withopposite opening panes, the laboratorymeasured airborne sound insulation isapproximately 10-15 dB Rw . Thisincreases to 20-25 dB Rw in the openposition for a secondary glazing systemwith partially open ventilation openings,with the openings staggered on plan orelevation, and with absorbent lining ofthe window reveals (see Figure 3.3). Insitu, the degree of attenuation providedby an open window also depends on thespectrum of the noise and the geometryof the situation.

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The spreadsheet of sound reductionindices on the DfES acoustic websitegives values of Rw for various types ofwindow, glazing thickness, and air gap.Indications are also given of the soundreduction indices of open windows.

3.5 External DoorsFor external doors the airborne soundinsulation is determined by the door set,which is the combination of door andframe. The quality of the seal achievedaround the perimeter of the door iscrucial in achieving the potentialperformance of the door itself. Effectiveseals should be provided at the threshold,jambs and head of the door frame. Aswith windows, neoprene compressionseals are more effective than brush seals,but their effectiveness will be stronglyinfluenced by workmanship on site. Brush

seals can however be effective and tend tobe more hard wearing than compressionseals.

It is also important that an airtight sealis achieved between the perimeter of thedoor frame and the opening into which itis to be fixed. The opening should beaccurately made to receive the door frameand any gaps around the perimeter packedwith insulating material prior toapplication of a continuous, airtight sealon both sides.

A high level of airborne soundinsulation is difficult to provide using asingle door; however, it can be achievedby using a lobby with two sets of doors,as often provided for energy efficiency, ora specialist acoustic doorset.

Softwood framing toextend reveals

Sound absorbing reveallinings to head and sides

Second casement openablefor cleaning only

Bottom hung casement,openable for ventilation,fitted with secure adjustable stay

Supporting framing below cill

Existing inward opening light,movement to be restricted

Existing brickwork wall

200 mm nominal

300 mm nominal

Figure 3.3: Secondaryglazing producing astaggered air flow path

Retrofit secondary glazing producinga staggered air flow path. Designedto limit aircraft noise intrusion toscience laboratories at a secondaryschool near an airport.

A sound reduction of approximately 20-25 dB Rw was achieved using thisdesign.

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SOUND INSULATION OF THEBUILDING ENVELOPE

There are two methods by which it ispossible to calculate the indoor ambientnoise levels due to external noise.

The first method is to calculate theindoor ambient noise level according tothe principles of BS EN 12354-3:2000[9].An Excel spreadsheet to calculate thesound insulation of building envelopes,based on BS EN 12354-3:2000 isavailable via the DfES acoustics website.The principles of this calculationspreadsheet are given in Appendix 5.

The second method is to calculate theindoor ambient noise level using themeasured façade sound insulation datafrom an identical construction at anothersite.

3.6 Subjective characteristics ofnoiseThe indoor ambient noise levels in Table1.1 provide a reasonable basis forassessment, but some noises have tonal orintermittent characteristics which makethem particularly noticeable or disturbing,even below the specified levels. This ismost common with industrial noise. At aminority of sites, achieving the levels inTable 1.1 will not prevent disturbancefrom external industrial sources, andadditional noise mitigation may berequired. In these cases advice from anacoustic consultant should be sought.

The potentially beneficial maskingeffect of some types of continuousbroadband external noise (such as roadtraffic noise) must also be borne in mind,see Section 2.12. This noise may partiallymask other sounds, such as fromneighbouring classrooms, which may bemore disturbing than the external noise.There are acoustic benefits, as well as costbenefits, in ensuring that the level ofinsulation provided is not over-specifiedbut is commensurate with the externalnoise.

3.7 Variation of noise incident ondifferent facadesIt may be convenient to determine theexternal noise level at the most exposedwindow (or part of the roof) of a

building, and to assume this exposure forother elements too. This may be suitableat the early design stage for large schools.However, where external noise levels varysignificantly, this approach can lead toover-specification and unnecessary cost.

3.8 CalculationsA calculation of the internal noise levelaccording to BS EN 12354-3:2000 canbe used to estimate whether, for the levelsof external noise at any particular site, aproposed construction will achieve thelevels in Table 1.1. By estimating theinternal levels for various differentconstructions, designers can determinethe most suitable construction in anygiven situation. BS EN 12354-3:2000allows the effects of both direct andflanking transmission to be calculated, butin many cases it is appropriate to consideronly direct transmission.

3.9 Test methodField testing of an existing buildingenvelope should be conducted accordingto BS EN ISO 140-5:1998[10], withreference to the clarifications given in thissection.

BS EN ISO 140-5:1998 sets outvarious test methods. The three ‘global’tests using the prevailing external noisesource(s) (road traffic, railway traffic, airtraffic) are preferable. At most sites roadtraffic is likely to be the dominant sourceof noise, and the correspondingstandardised level difference is denotedDtr,2m,nT . Where aircraft noise is themajor concern measurements should bemade accordingly, and the standardisedlevel difference denoted Dat,2m,nT .Similarly the standardised level differenceusing railway noise as the source isdenoted Drt,2m,nT .

The global loudspeaker test method(which generates Dls,2m,nT values) maybe used only if the prevailing externalnoise sources are insufficient to generatean adequate internal level.

It is reasonable, under certainconditions as specified below, to use thetest results to indicate the likelyperformance of building envelopes of asimilar construction, exposed to similar

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sources. If the conditions are not metthen it is not reasonable to infer theperformance from existing soundinsulation test results and the calculationprocedure should be used.

3.9.1 Conditions for similarconstructionsThe following features of any untestedconstruction should be similar to those ofthe tested construction:• type and number of ventilators • glazing specification, frame

construction and area of windows• type and number of doors• external wall construction and area• roof construction and area.

3.9.2 Conditions for similar sourcesOnly test results in terms of Dtr,2m,nT ,Dat,2m,nT , Drt,2m,nT and Dls,2m,nTvalues are applicable, and these shouldnot be used interchangeably. Thefollowing features concerning theprevailing sources of noise should besimilar to those of the previously testedconstruction:• relative contributions of road traffic,

railway and aircraft noise• orientation of the building relative to

the main noise source(s)• ground height of the building relative

to the main noise source(s).

SOUND INSULATION BETWEENROOMS

This section describes constructionscapable of achieving the different levels ofsound insulation specified in Tables 1.2and 1.4.

Appendix 3 describes how soundinsulation between adjacent rooms ismeasured and calculated.

In addition to the transmission ofdirect sound through the wall or floor,additional sound is transmitted into thereceiving room via indirect, or 'flanking'paths, see Figure 3.4.

3.10 Specification of the airbornesound insulation between rooms using RwTable 1.2 describes the minimumweighted sound level difference between

Figure 3.4: Soundtransmission pathsbetween adjacent rooms:direct sound paths throughthe wall and floor andflanking paths through thesurrounding ceiling, walland floor junctions

airborne sound

impact sound

rooms in terms of DnT (Tmf,max),w.However, manufacturers provideinformation for individual buildingelements based on laboratory airbornesound insulation data measured accordingto BS EN ISO 140-3:1995[5], in terms ofthe sound reduction index, Rw. Figure3.5 shows the values of Rw for sometypical building elements.

This section provides some basicguidance for the designer on how to uselaboratory Rw values to choose a suitableseparating wall or floor for the initialdesign. However, specialist advice shouldalways be sought from an acousticconsultant early on in the design stage toassess whether the combination of theseparating and flanking walls is likely toachieve the performance standard in Table1.2. An acoustic consultant can useadvanced methods of calculation topredict the sound insulation (eg StatisticalEnergy Analysis or BS EN 12354-1:2000[11]). The correct specification offlanking walls and floors is of highimportance because incorrect specificationof flanking details can lead to reductions inthe expected performance of up to 30 dB.

Sound insulation3

34

The following procedure can be usedto choose an appropriate type ofseparating wall or floor before seekingspecialist advice on appropriate flankingdetails.

1. From Table 1.2 determine therequired minimum weighted BB93standardized sound level differencebetween rooms, DnT(Tmf,max),w .

2. Estimate the required weighted soundreduction index for the separating wall orfloor, as follows:

a. Use the following formula to providean initial estimate of the measured sound reduction index (Rw,est) thatshould be achieved by the separating wallor floor in the laboratory.

Rw,est =

DnT(Tmf,max),w +10 lg ( ) +8 dB

where DnT(Tmf,max),w is the minimumweighted BB93 standardized leveldifference between rooms from Table 1.2S is the surface area of the separating

element (m2)Tmf,max is the maximum value of thereverberation time Tmf for the receivingroom from Table 1.5 (s)V is the volume of the receiving room(m3).

b. Estimate the likely reduction, X dB, inthe airborne sound insulation that wouldoccur in the field, to account for lessfavourable mounting conditions andworkmanship than in the laboratory test.X can be estimated to be 5 dB assumingthat flanking walls and floors are specifiedwith the correct junction details.However, if flanking walls and floors arenot carefully designed then poor detailingcan cause the airborne sound insulation tobe reduced by up to 30 dB. To allow thedesigner to choose a suitable separatingwall for the initial design it isrecommended that X of 5 dB is assumedand an acoustic consultant is used tocheck the choice of separating elementand ensure that the correct flankingdetails are specified.

c. Calculate the final estimate for the

STmf,maxV

Figure 3.5: Typical soundreduction indices forconstruction elements

60

55

50

45

40

35

30

25

20

15

10

5

01 10 20 50 100 200 400

Mass per unit area, kg/m2

Sou

nd re

duct

ion

inde

x, d

B

6 mmglass200 mmspace

6 mmglass10 mmspace

12 mmglass

25 mmwall board

6 mmglass

3 mmglass

Hollow corepanel door

Solid coretimber door

12 mmplasterboardwith50 x 100 studs

100 mm breezeunplastered

100 mm breezeplasteredone side 115 mm

brickworkplastered

115 mmconcrete slabwith 50 mmscreed

100 mm slabwith resilienthangers

100 mm slabwith rigidhangers

225 mmbrickworkplastered

150 mmstaggered studwith 12 mmplasterboard

100 mm breezeplasteredboth sides

3Sound insulation

35

weighted sound reduction index Rw thatshould be used to select the separatingwall or floor from laboratory test data:

Rw = Rw,est + X dB

3.10.1 Flanking detailsA simplified diagram indicating the mainflanking transmission paths is shown inFigure 3.6. General guidance on flankingdetails for both masonry and framedconstructions can be found in ApprovedDocument E[1]. Specific guidance onflanking details for products can alsosometimes be found from manufacturers'data sheets, or by contactingmanufacturers’ technical advisers.

3.10.2 Examples of problematicflanking detailsIn some buildings it is considereddesirable to lay a floating screed (eg asand-cement screed laid upon a resilientmaterial) across an entire concrete floorand build lightweight partitions off thescreed to form the rooms, see Figure3.7(a). This allows the flexibility tochange the room spaces. However, acontinuous floating screed can transmit asignificant quantity of structure-borneflanking sound from one room toanother.

For example, if a lightweight partitionwith 54 dB Rw was built off a continuousfloating screed the actual sound insulationcould be as low as 40 dBDnT(Tmf,max),w. In fact, even if a moreexpensive partition with a higherperformance of 64 dB Rw was built, theactual sound insulation would still be 40 dB DnT(Tmf,max),w, because themajority of sound is being transmitted viathe screed, which is the dominant flankingpath. This demonstrates the importanceof detailing the junction between thescreed and the lightweight partition. Toreduce the flanking transmission, thefloating screed should stop at thelightweight partition, see Figure 3.7(b).

Another flanking detail that can causeproblems is where a lightweight profiledmetal roof deck runs across the top of aseparating partition wall. With profilessuch as trapezoidal sections, it is verydifficult for builders to ensure that they

do not leave air paths between the top ofthe partition wall and the roof.

3.10.3 Junctions between ceilings andinternal wallsCeilings should be designed in relation tointernal walls to achieve the requiredcombined performance in respect ofsound insulation, fire compartmentationand support.

In the case of suspended ceiling systemsthe preferred construction is one in which

Through the junctionwith the external walls

Through the junctionwith the internal walls

Through the junctionwith the ceiling andfloor slab above

Through the junctionwith the floor slab below

Figure 3.6: The mainflanking transmission paths

Figure 3.7: Flankingtransmission via floatingscreed (a) Incorrect detail(b) Correct detail

(a) (b)

partitions or walls pass through thesuspended ceiling membrane, do notrequire support from the ceiling system,and combine with the structural soffitabove to provide fire resistingcompartmentation and sound insulation.

The alternative construction in whichpartitions or walls terminate at, or justabove the soffit of a suspended ceiling, isnot recommended as it demands a ceilingperformance in respect of fire resistanceand sound insulation which is difficult toachieve and maintain in practice in schoolbuildings. This is because the number offittings required at ceiling level isincompatible with testing of fire resistanceto BS 476[12], which is based on a testspecimen area of ceilings without fittings.Furthermore, the scale and frequency ofaccess to engineering services in theceiling void through the membrane (inrespect of fire) and through insulationbacking the membrane (in respect ofsound) is incompatible with maintenanceof these aspects of performance.

3.10.4 Flanking transmission throughwindowsFlanking transmission can occur betweenadjacent rooms via open windows in theexternal walls. Side opening casementwindows near the separating wall shouldhave their hinges on the separating wallside to minimise airborne soundtransmitted from one room to another.Where possible, windows in external wallsshould be located away from the junctionbetween the external walls and theseparating wall or floor. In particular,windows in the external walls of noisesensitive rooms and in the external wallsof rooms adjacent to them should be asfar as possible from the separating wall orfloor.

3.11 Specification of the impactsound insulation between rooms using Ln,wTable 1.4 describes the minimum impactsound insulation between rooms in termsof L′nT(Tmf,max),w. However,manufacturers usually provide informationfor floors based on laboratory impactsound insulation data measured according

to BS EN ISO 140-6:1998[13], in termsof Ln,w.

This section provides some basicguidance for the designer on how to uselaboratory Ln,w values to design a suitableseparating floor. However, specialistadvice should always be sought from anacoustic consultant early on in the designprocess to assess whether the combinationof the separating floor and flanking wallsis likely to achieve the performancestandard in Table 1.4. An acousticconsultant can use advanced methods ofcalculation to predict the sound insulation(eg Statistical Energy Analysis or BS EN12354-2:2000[14]).

The following procedure can be usedto choose an appropriate type ofseparating floor before seeking specialistadvice on flanking details from anacoustic consultant.

1. Determine the maximum weightedBB93 standardized impact sound pressurelevel, L′nT(Tmf,max),w from Table 1.4.

2. Estimate the required weightednormalized impact sound pressure levelfor the separating floor, as follows:

a. Use the following formula to providean initial estimate of the weightednormalized impact sound pressure level(Ln,w,est) that should be achieved by theseparating floor in the laboratory:

Ln,w,est =

L′nT(Tmf,max),w + 10 lg –18 dB

where L′nT(Tmf,max),w is the maximumweighted BB93 standardized impactsound pressure level from Table 1.4 V is the volume of the receiving room(m3)Tmf,max is the maximum value of thereverberation time Tmf for the receivingroom from Table 1.5 (s).

b. Estimate the likely increase, X dB, inthe impact sound pressure level thatwould occur in the field to account forless favourable mounting conditions andgood workmanship than in the laboratorytest.

X can be 5 dB assuming that flankingwalls are specified with the correct

36

Sound insulation3

VTmf,max

junction details. However, if flankingwalls are not carefully designed the impactsound pressure level can increase by up to10 dB. To allow the designer to choose asuitable separating floor for the initialdesign it is suggested that X of 5 dB isassumed and an acoustic consultant isused to check the choice of separatingfloor and ensure that the correct flankingdetails are specified.

c. Calculate the final estimate for theweighted normalised impact soundpressure level Ln,w that should be used toselect the separating wall or floor fromlaboratory test data.

Ln,w = Ln,w,est – X dB

3.12 Internal walls and partitions

3.12.1 General principlesFigure 3.5 shows typical values of thesound reduction index (Rw) for differentwall constructions. For comparison theperformance of other constructionsincluding doors, glazing and floors isincluded.

The solid line shows the theoreticalvalue based purely on the mass law. Forsingle leaf elements (eg walls, singleglazing, doors, etc) the mass law statesthat doubling the mass of the elementwill give an increase of 5 to 6 dB in Rw .When constructions provide less soundinsulation than predicted by the mass lawit is usually because they are not airtight.

In general, lightweight double-leafconstructions such as double glazing,cavity masonry or double-leafplasterboard partitions provide bettersound insulation than the mass law wouldindicate. At medium and highfrequencies, double-leaf constructionsbenefit from the separation of the twoleaves, with performance increasing withthe width of the air gap between theleaves and the physical separation of theleaves. (Note that for double-leafplasterboard constructions, timberstudwork is rarely used to achieve highstandards of sound insulation becauselightweight metal studs provide bettermechanical isolation between the leaves.)

37

3Sound insulation

Figure 3.8: Chart toestimate Rw for acomposite wall consistingof two elements withdifferent transmissionlosses

15.0

14.0

13.0

12.0

11.0

10.0

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.0

0.02 6 10 14 18 22 26 30

Corr

ectio

n, d

B

Transmission loss difference, dB

5%

10%

20%

30%

40%

50%

60%

Area

The percentage of the total area of the wall occupiedby the element with the lower transmission loss, eg adoor, and the difference between the higher Rw andthe lower Rw, are used to calculate the correction indB which is added to the lower Rw to give the Rw ofthe whole wall.

For example: Assume a classroom to corridor wallhas an Rw of 45 dB and a door in the wall has an Rwof 30 dB. If the area of the door is 0.85 m x 2.1 m =1.785 m2 and the area of the wall is 7 m x 2.7 m =18.9 m2, then the percentage of the wall occupied bythe door is 1.785/18.9 x 100 = 9.4%

The difference in Rw = 15 dB.

Therefore reading from the chart gives a correction ofabout 9 dB to be added to the lower Rw, giving acomposite Rw of 39 dB.

If a higher performance door of say 35 dB had beenused, the composite Rw would be 35 + 7 = 42 dB.

At low frequencies the performance ofplasterboard partitions is limited by themass and stiffness of the partition.Masonry walls can provide better lowfrequency sound insulation simplybecause of their mass. This is not obviousfrom the Rw figures, as the Rw ratingsystem lends more importance toinsulation at medium and highfrequencies rather than low frequencies.This is not normally a problem in generalclassroom applications where soundinsulation is mainly required at speechfrequencies. However, it can be importantin music rooms and in other cases wherelow frequency sound insulation isimportant.

A combination of masonry and dry-lining can be very effective in providingreasonable low frequency performancewith good sound insulation at higherfrequencies. This combination is oftenuseful when increasing the soundinsulation of existing masonry walls.

While partition walls may be providedas a means of achieving sound reduction,it should be remembered that soundinsulation is no better than that providedby the weakest element.

Figure 3.8 can be used to assess theoverall effect of a composite constructionsuch as a partition with a window, door,hole or gap in it. The sound insulation ofthe composite structure is obtained byrelating the areas and sound insulationvalues of the component parts using thegraph.

Partitions should be well sealed, assmall gaps, holes, etc. significantly reducesound insulation. (Note that this appliesto porous materials, eg porous blockwork,which can transmit a significant amountof sound energy through the pores.)

3.12.2 Sound insulation of commonconstructions Figure 3.9 shows the approximateweighted sound reduction index Rw formasonry and plasterboard constructions.

Using the procedures given in Section3.10, it is possible to determine whichconstructions are capable of meeting therequirements between different types ofrooms.

The values in Figure 3.9 are necessarilyapproximate and will depend on theprecise constructions and materials used.Many blockwork and plasterboardmanufacturers provide data for specificconstructions.

More sound reduction indices, bothsingle value and octave band data, andfurther references to specificmanufacturers’ data are in the soundreduction indices spreadsheet included onthe DfES acoustics website.

3.12.3 Flanking transmission In general, a weighted sound leveldifference of up to 50 dB DnT(Tmf,max),wcan be achieved between adjacent roomsby a single partition wall using one of theconstructions described above, providedthat there are no doors, windows or otherweaknesses in that partition wall, and thatflanking walls/floors with their junctiondetails are carefully designed. Flankingtransmission is critical in determining theactual performance and specialist adviceshould be sought from an acousticconsultant.

3.12.4 High performanceconstructions – flanking transmissionHigh-performance plasterboard partitionsor masonry walls with independent liningscan provide airborne sound insulation ashigh as 70 dB Rw in the laboratory.However, to achieve high performance inpractice (ie above 50 dB DnT(Tmf,max),w),flanking walls/floors with their junctiondetails must be carefully designed.Airborne sound insulation as high as 65 dBDnT(Tmf,max),w can be achieved on siteusing high performance plasterboardpartitions, or masonry walls withindependent linings with lightweightisolated floors and independent ceilings tocontrol flanking transmission. This willrequire specialist advice from an acousticconsultant.

For rooms which would otherwiseneed high-performance partitions it maybe possible to use circulation spaces,stores and other less noise-sensitive roomsto act as buffer zones between roomssuch that partitions with lower levels ofsound insulation can be used. Case Study

38

Sound insulation3

39

3Sound insulation

Performance Rw (dB) Walls - typical forms of construction

35–40 1x12.5 mm plasterboard each side of a metal stud (total width 75 mm)

100 mm block (low density 52 kg/m2) plastered/rendered 12 mm one side

40–45 1x12.5 mm plasterboard each side of a 48 mm metal stud with glass fibre/mineral wool in cavity (total width 75 mm)

100 mm block (medium density 140 kg/m2) plastered/rendered 12 mm one side

45–50 2x12.5 mm plasterboard each side of a 70 mm metal stud (total width 122 mm)

115 mm brickwork plastered/rendered 12 mm both sides

100 mm block (medium density 140 kg/m2) plastered/rendered 12 mm both sides

50–55 2x12.5 mm plasterboard each side of a 150 mm metal stud with glass fibre/mineral wool in cavity (total width 198 mm)

225 mm brickwork plastered/rendered 12 mm both sides

215 mm block (high density 430 kg/m2) plastered/rendered 12 mm both sides

55–60 2x12.5 mm plasterboard each side of a staggered 60 mm metal stud with glass fibre/mineral wool in cavity (total width 178 mm)

100 mm block (high density 200 kg/m2) with 12 mm plaster on one side and 1x12.5 mm plasterboard on metal frame with a50 mm cavity filled with glass fibre/mineral wool on other side

Figure 3.9: Walls -airborne sound insulationfor some typical wallconstructions

40

Sound insulation3

Performance Rw (dB) Glazing - typical forms of construction

25 4 mm single float (sealed)


4/12/4: 4 mm glass/12 mm air gap/4 mm glass

30 6/12/6: 6 mm glass/12 mm air gap/6 mm glass

10 mm single float (sealed)



35 10 mm laminated single float (sealed)



12 mm laminated single float (sealed)

40 10/12/6 lam: 10 mm glass/12 mm air gap/6 mm laminated glass

19 mm laminated single float (sealed)



12 lam/12/10: 12 mm laminated glass/12 mm air gap/10 mm glass

45 6 lam/200/10: 6 mm laminated glass/200 mm air gap/10 mm + absorptive reveals

17 lam/12/10: 17 mm laminated glass/12 mm air gap/10 mm glass

Figure 3.10: Glazing - airborne sound insulation for some typical glazing constructions

7.5 (see also Figure 2.4) describes apurpose built music suite which usesbuffer zones effectively. In some cases,such as the refurbishment of musicfacilities in existing buildings, roomlayout may not allow this, and in thesecases high levels of sound insulationbetween adjacent rooms will be required.

3.12.5 Corridor walls and doorsThe Rw values in Table 1.3 should beused to specify wall (including any glazing)and door constructions between corridorsor stairwells and other spaces. To ensurethat the door achieves its potential interms of its airborne sound insulation, itmust have good perimeter sealing,including the threshold where practical.

Note that a lightweight fire door willusually give lower sound insulation than aheavier, sealed acoustic door.

Greatly improved sound insulation willbe obtained by having a lobby doorarrangement between corridors orstairwells and other spaces. However, thisis not often practicable between classroomsand corridors. Some noise transmissionfrom corridors into classrooms isinevitable, but this may not be importantif all lesson changes occur simultaneously.

For some types of room, such as musicrooms, studios and halls for music anddrama performance, lobby doors shouldgenerally be used.

3.13 Internal doors, glazing, windowsand folding partitions Internal doors, glazing and windows arenormally the weakest part of anyseparating wall. Figures 3.10 and 3.11show the performance of a number ofdifferent types of window and door. Ingeneral, rooms which require at least 35dB DnT(Tmf,max),w should not havedoors or single glazing in the separatingwall or partition.

3.13.1 DoorsThe choice of appropriate doors withgood door seals is critical to maintainingeffective sound reduction, and controllingthe transfer of sound between spaces.

Internal doors are often of lightweighthollow core construction, providing only

around 15 dB Rw which is about 30 dBless than for a typical masonry wall (seeFigure 3.5). The sound insulation of anexisting door can be improved byincreasing its mass (eg by adding twolayers of 9 mm plywood or steel facings)as long as the frame and hinges cansupport the additional weight. However,it is often simpler to fit a new door.

The mass of a door is not the onlyvariable that ensures good soundinsulation. Good sealing around the frameis crucial. Air gaps should be minimisedby providing continuous grounds to theframe which are fully sealed to themasonry opening. There should be agenerous frame rebate and a proper edgeseal all around the door leaf. Acousticseals can eliminate gaps between the doorand the door frame to ensure that thedoor achieves its potential in terms of itsairborne sound insulation.

As a rule of thumb, even a goodquality acoustically sealed door in a 55 dBRw wall between two classrooms willreduce the Rw of the wall so that theDnT(Tmf,max),w is only 30-35 dB. Twosuch doors, separated by a door lobby, arenecessary to maintain the soundinsulation of the wall. Figure 3.12 showsthe effect of different doors on the overallsound insulation of different types of wall.In a conventional layout with access toclassrooms from a corridor, the corridoracts as a lobby between the two classroomdoors.

3.13.2 LobbiesThe greater the distance between thelobby doors, the better the soundinsulation, particularly at low frequencies.Maximum benefit from a lobby isassociated with offset door openings asshown in Figure 3.13(a) and acousticallyabsorbent wall and/or ceiling finishes.

A lobby is useful between aperformance space and a busy entrancehall. Where limitations of space preclude alobby, a double door in a single wall willbe more effective than a single door; thisconfiguration is illustrated in Figure3.13(b).

Inter-connecting doors between twomusic spaces should be avoided and a

41

3Sound insulation

Sound insulation3

42

Acoustic performance Typical construction

30 dB Rw This acoustic performance can be achieved by a well fitted solid core doorset where the door is sealed effectively around its perimeter in a substantial frame with an effective stop. A 30 minute fire doorset (FD30) can be suitable.

Timber FD30 doors often have particle cores or laminated softwood cores with a mass per unit area ≈ 27 kg/m2 and a thickness of ≈ 44 mm.

Frames for FD30 doors often have a 90 mm x 40 mmsection with a stop of at least 15 mm.

Compression or wipe seals should be used around the door’s perimeter along with a threshold seal beneath. A drop-down or wipe type threshold seal is suitable.

Doors incorporating 900 mm x 175 mm vision panels comprising 7 mm fire resistant glass can meet this acoustic performance.

35 dB Rw This acoustic performance can be achieved by specialist doorsets although it can also be achieved by a well fitted FD60 fire doorset where the door is sealed effectively around its perimeter in a substantial frame with an effective stop.

Timber FD60 doors often have particle core or laminated softwood cores with a mass per unit area ≈ 29 kg/m2 and a thickness of ≈ 54 mm. Using a core material with greater density than particle or laminated softwood can result in a door thickness of ≈ 44 mm.

Frames for FD60 doors can have a 90 mm x 40 mm section with stops of at least 15 mm.

Compression or wipe seals should be used around the door’s perimeter along with a threshold seal beneath. A drop-down or wipe type threshold seal is suitable.

Doors incorporating 900 mm x 175 mm vision panels comprising 7 mm fire resistant glass can meet this performance.

Figure 3.11: Doors -airborne sound insulationfor some typical doorconstructions

44 mm

54 mm

44 mm thick timber door, half hour fire rated

54 mm thick timber door, one hour fire rated

NOTES ON FIGURE 3.11 1 Care should be taken to ensure that the force required to open doors used in schools is notexcessive for children. To minimise opening forces, doors should be fitted correctly and goodquality hinges and latches used. Door closers should be selected with care.2 The opening force at the handles of doors used by children aged 5–12 should not exceed 45 N.3 Manufacturers should be asked to provide test data to enable the specification of doorsets.4 Gaps between door frames and the walls in which they are fixed should be ≤ 10 mm.5 Gaps between door frames and the walls in which they are fixed should be filled to the full depthof the wall with ram-packed mineral wool and sealed on both sides of the wall with a non-hardening sealant.6 Seals on doors should be regularly inspected and replaced when worn.

3Sound insulation

43

lobby used to provide the necessaryairborne sound insulation.

3.13.3 Folding walls and operablepartitions Folding walls and operable partitions aresometimes used to provide flexibility inteaching spaces or to divide open planareas. A standard folding partition withno acoustic seals or detailing may providea value as low as 25 dB Rw . However,folding partitions are available that canprovide up to 55 dB Rw . The soundinsulation depends on effective acousticsealing and deteriorates if seals or tracksare worn or damaged.

It is important that the specification offolding partitions takes into account theirweight, ease of opening and maintenance.Regular inspection and servicing willextend the life of a partition and ensurethat it achieves the required soundinsulation.

Folding partitions are useful in manyapplications but they should only be usedwhen necessary and not as a response to anon-specific desire for flexibility in layoutof teaching areas.

3.13.4 Roller shuttersRoller shutters are sometimes used toseparate kitchens from multi-purposespaces used for dining. Because rollershutters typically only provide soundinsulation of around 20 dB Rw it iscommon for noise from the kitchen todisturb the teaching activities. One

(a)

(b)

Figure 3.13: Use oflobbies and double doors(a) Lobbied doorway(b) Double door

Figure 3.12: Reductionof sound insulation of awall incorporating differenttypes of door

20

50

40

30

30 40 50

Double doors, ie one door either sideof a lobby (the diagonal straight line illustrates how the insulation value ofthe original partition can only bemaintained at 100% by incorporating aset of double doors with a lobby)

Heavy door with edge seal

Light door with edge seal

Any door (gaps round edges)

Sound insulation of wallwithout door (dB)

Sound insulation of wall with door (dB)

'very good'

'good'

'poor'

eg 100 mm: stud work with plasterboardand skin both sides (no insulation)

eg 300 kg/m 150 mm 'high' densityblockwork, plastered at least one side

eg 225 mm common brick plasteredboth sides

2

Sound insulation3

44

Figure 3.14: Existing timber floors - airborne and impact sound insulation for some typical floor/ceiling constructions

1

2

3

4

5

6

7

Basic timber floor consisting of 15 mm floorboardson 150-200 mm wooden joists, plaster orplasterboard ceiling fixed to joists

As 1, ceiling consisting of one layer of 15 mmplasterboard and one layer of 12.5 mm denseplasterboard fixed to proprietary resilient bars onunderside of joists

As 1, ceiling retained, with suspended ceilingconsisting of 2 layers of 15 mm wallboard or 2layers of 12.5 mm dense plasterboard, suspendedon a proprietary metal ceiling system to give 240 mm cavity containing 80-100 mm mineralwool (>10 kg/m3)

As 1, ceiling removed, with suspended ceilingconsisting of 2 layers of 15 mm wallboard or 2layers of 12.5 mm dense plasterboard, suspendedon a proprietary metal ceiling system to give 275 mm cavity containing 80-100 mm mineralwool (>10 kg/m3)

As 1, ceiling removed, with suspended ceilingconsisting of 2 layers of 15 mm wallboard or 2layers of 12.5 mm dense plasterboard, suspendedspecial resilient hangers to give 275 mm cavitycontaining 80-100 mm mineral wool (>10 kg/m3)

As 1 with proprietary lightweight floating floor usingresilient pads or strips (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board supported on 45 mm softwood battens laid on 25 mm thickopen-cell foam pads). 80-100 mm mineral wool(>10 kg/m3) laid on top of existing floorboards

As 1, floorboards removed and replaced with 15 mm tongue-and-groove floorboards on a 15 mmplywood, chipboard or fibre-bond board supportedon 12 mm softwood battens laid on 25 mm thickopen-cell foam pads bonded to the joists, 80-100 mm mineral wool (>10 kg/m3) laid on topof existing ceiling

35–40 80–85 180–230

50–55 65–70 220–270

55–60 60–65 450–500

55–60 60–65 450–500

60–65 55–60 450–500

50–55 60–65 270–320

55–60 55–60 240– 290

Option Construction - timber floors Rw Ln,w Depth(dB) (dB) (mm)

3Sound insulation

45

buildings. Both airborne noise and impactnoise can be problematic with woodenfloors, and both problems need to beconsidered when dealing with verticallyadjacent spaces. Adding carpets or othersoft coverings to wooden floors reducesimpact noise but has very little effect onairborne noise transmission.

Impact noise can also be a problemwith concrete floors (although airbornenoise may not be a problem); this cansometimes be solved by adding a carpet.

Where the use of carpet is proposed

solution is to provide doors in front ofthe shutters to improve the soundinsulation.

3.14 Floors and ceilingsBoth airborne and impact noise can betransmitted between vertically adjacentrooms through the separating floor andits associated flanking constructions.

Vertical noise transmission betweenclassrooms can be a problem in oldermulti-storey buildings with woodenfloors, such as traditional Victorian school

8

9

10

11

As 7 but mineral wool replaced by 100 mmpugging (80 kg/m2) on lining laid on top of ceiling

As 8 but with 75 mm pugging laid on top of boardfixed to sides of joists

As 1 with proprietary lightweight floating floorusing a continuous layer (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 6-12 mm thickcontinuous open-cell foam mat)

As 10, ceiling removed and replaced withsuspended ceiling consisting of 2 layers of 15 mmwallboard or 2 layers of 12.5 mm denseplasterboard, suspended on a proprietary metalceiling system to give 275 mm cavity containing80-100 mm mineral wool (>10 kg/m3)

55–60 50–55 240– 290

50–55 55–60 240– 290

50–55 55–60 220– 270

60–65 50–55 360– 410

NOTES ON FIGURE 3.141 Where resilient floor materials are used, the material must be selected to provide the necessarysound insulation under the full range of loadings likely to be encountered in that room and mustnot become over-compressed, break down or suffer from long-term ‘creep’ under the higher loadslikely to be encountered. Where large ranges of loading are encountered, or where there are highpoint loads such as pianos, heavy furniture or operable partitions, the pad stiffness may have tobe varied across the floor to take account of these.2 All figures are approximate guidelines and will vary between different products andconstructions. Manufacturers' data should be obtained for all proprietary systems andconstructions. These must be installed in accordance with good practice and manufacturers'recommendations and all gaps sealed.

Figure 3.14 Continued

Option Construction - timber floors Rw Ln,w Depth(dB) (dB) (mm)

Sound insulation3

46

Figure 3.15: Lightweightconcrete floors - airborneand impact soundinsulation of some typicalconstructions

1

2

3

4

5

6

7

Lightweight floor consisting of concrete planks(solid or hollow) or beam and blocks, with 30-50mm screed, overall weight approximately 100 kg/m2, no ceiling or floor covering

As 1 with soft floor covering >5 mm thick

As 1 with suspended ceiling consisting of 2 layersof 15 mm wallboard or 2 layers of 12.5 mmdense plasterboard, suspended on a proprietarymetal ceiling system to give 240 mm cavitycontaining 80-100 mm lightweight mineral wool(>10 kg/m3)


As 1 with proprietary lightweight floating floorusing resilient pads or strips (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 25 mm thickopen-cell foam pads)


As 1 with heavyweight proprietary suspendedsound insulating ceiling tile system

35–40 90–95 100–150

35–40 75–85 105–155

60–65 55–60 370–420

60–65 50–55 375–425

50–60 50–60 155–205

50–55 55–60 150–200

45–55 60–70 250– 500

Option Construction - lightweight concrete floors Rw Ln,w Depth(dB) (dB) (mm)

issues of cleaning, maintenance andeffects on air quality may need to beconsidered.

3.14.1 Impact sound insulationImpact noise on floors may arise from:• foot traffic, particularly in corridors atbreak times/lesson changeover• percussion rooms

• areas for dance or movement• loading/unloading areas (eg in kitchens and workshops) • machinery.

Where possible, impact noise should bereduced at source through use of softfloor coverings or floating floors. Carpetsare not an option in practical spaces butother soft floor coverings, such as acoustic

3Sound insulation

47

Figure 3.16: Heavyweightconcrete floors - airborneand impact sound insulationof some typicalconstructions

1

2

3

4

5

Solid concrete floor consisting of reinforcedconcrete with or without shuttering, concretebeams with infill blocks and screed, hollow orsolid concrete planks with screed, of thicknessand density to give a total mass of at least 365kg/m2, with soft floor covering >5 mm thick

As 1 with proprietary lightweight floating floorusing resilient pads or strips (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 25 mm thickopen-cell foam pads)


As 1 with suspended ceiling consisting of 2 layersof 15 mm wallboard or 2 layers of 12.5 mmdense plasterboard, suspended on a proprietarymetal ceiling system to give 240 mm cavitycontaining 80-100 mm mineral wool (>10 kg/m3)


50–55 60–65 150–200

55–60 50–55 200–250

55–60 50–60 175–230

60–70 55–60 420–470

60–70 50–55 425–475

NOTES ON FIGURES 3.15 AND 3.161 Where soft floor covering is referred to this should be a resilient material or a material with aresilient base, with an overall uncompressed thickness of at least 4.5 mm ; or any floor coveringwith a weighted reduction in impact sound pressure level of not less than 17 dB when measuredin accordance with BS EN ISO 140-8:1998[15] and calculated in accordance with BS EN ISO 717-2:1997[16]. 2 Where resilient floor materials are used, the material must be selected to provide thenecessary sound insulation under the full range of loadings likely to be encountered in that roomand must not become over-compressed, break down or suffer from long-term ‘creep’ under thehigher loads likely to be encountered. Where large ranges of loading are encountered, or wherethere are high point loads such as pianos, heavy furniture or operable partitions, the pad stiffnessmay have to be varied across the floor to take account of these.3 All figures are approximate guidelines and will vary between different products andconstructions. Manufacturers' data should be obtained for all proprietary systems andconstructions. These must be installed in accordance with good practice and manufacturers'recommendations and all gaps sealed.

Option Construction - heavyweight concrete floors Rw Ln,w Depth(dB) (dB) (mm)

Sound insulation3

48

vinyl floor or vinyl flooring laid on anacoustic mat, may be suitable.

Planning and room layout can be usedto avoid impact noise sources on floorsabove noise-sensitive rooms. Soft floorcoverings and floating floor constructionsand independent ceilings are the mosteffective means of isolation, and resilientfloor finishes are also appropriate forsome sources.

Typical airborne and impact noiseperformance are listed for a number ofconstructions in Figures 3.14, 3.15 and3.16. Note that, unlike airborne soundinsulation, impact sound insulation ismeasured in terms of an absolute soundlevel, so that a lower figure indicates abetter standard of insulation.

3.14.2 Voids above suspendedceilingsWhere partitions run up to the undersideof lightweight suspended ceilings, theairborne sound insulation will be limitedby flanking transmission across the ceilingvoid, which will often prevent theminimum values for airborne soundinsulation in Table 1.2 being achieved.Therefore, partitions should either becontinued through the ceiling up to thesoffit, or a plenum barrier should be used.

3.14.3 Upgrading existing woodenfloors using suspended plasterboardceilingsFigure 3.14 shows the airborne andimpact noise performance of a standardwooden floor with various forms ofsuspended plasterboard ceiling.

Option 2 is possibly the most widelyused system of increasing both impactand airborne sound insulation, with orwithout the original plaster ceiling. Insmall rooms good results can be achievedusing timber studs fixed only to the walls,but large timber sections are needed tospan wider rooms.

In wider span rooms it is generally moreconvenient to suspend the plasterboardfrom the floor joists above, fixing throughthe existing ceiling if this is retained,using a proprietary suspension and gridsystem (option 4). The grid can be hungfrom simple metal strips or, for higher

performance, special flexible ceiling hangers.The major manufacturers of dry-lining

systems all provide their own systems forthese options, and provide soundinsulation data and specifications for avariety of configurations. The performancefor both airborne and impact soundimproves with the depth of the ceilingvoid, with the mass of the ceiling andwith the deflection of the ceiling hangersunder the mass of the ceiling. Adding alayer of lightweight acoustically absorbentglass wool or mineral wool in the ceilingvoid increases the sound insulation,typically by 2-3 dB, but there is no pointin adding more than specified.

Performance on site is stronglydependent on good workmanship toavoid air gaps, so careful attention shouldbe given to ensuring that joints are close-butted, taped and filled and that all gapsare properly sealed. At the perimeter asmall gap should be left between theplasterboard and the walls, and thisshould be sealed using non-setting masticto allow a small amount of movementwithout cracking.

Penetrations through the ceiling needto be properly detailed to maintain anairtight seal while allowing movement,and services should not be allowed toprovide a rigid link between the ceilingand the floor above. This can be aparticular problem with sprinkler pipes. Aproblem with these constructions is thatrecessed light fittings, grilles and diffuserssignificantly reduce the sound insulation soany services should be surface-mounted.

A plasterboard finish is acousticallyreflective whereas in some rooms anacoustically absorbent ceiling is required,to meet the specifications for roomacoustics and reverberation times. Onesolution to this, if there is sufficientheight, is to suspend a separatelightweight sound absorbing ceiling underthe sound insulating plasterboard ceiling.This can be a standard lightweightcomposite or perforated metal tile system.These lightweight, acoustically absorbent,ceilings add very little to the soundinsulation but do provide acousticabsorption. Lights and services can berecessed in the absorbent ceiling.

3Sound insulation

49

The term ‘acoustic ceiling’ generallyrefers to lightweight acousticallyabsorbent ceiling tile systems, designed toprovide acoustic absorption. Note thatthese systems do not always increase thesound insulation as well.

There are, however, some systemswhich use relatively heavy ceiling tileswhich are designed to fit into ceiling gridsto provide a reasonably airtight fit. Thesemay consist of dense plasterboard ormineral fibre products, or perforatedmetal tiles with metal or plasterboardbacking plates. If properly installed andmaintained these can provide a usefulincrease in sound insulation as well asacoustic absorption. Manufacturers ofthese systems can provide both airborneand impact sound insulation figures, aswell as acoustic absorption coefficients. Ifno measured sound insulation data areprovided, it is better to err on the side ofcaution and assume that the tile will notprovide a significant increase in soundinsulation.

The sound insulation performancefigures quoted in Figure 3.14 all assumethat the floorboards are in goodcondition and reasonably airtight, withthin carpet laid on top. If retaining theoriginal floorboards it is good practice tofill in any gaps with glued wooden strips,caulking or mastic, or to lay hardboard ontop, to provide an airtight seal. If notretaining the original boards, 18 mmtongue-and-grooved chipboard can beused to achieve the same effect, with alljoints and gaps properly sealed, especiallyat the perimeters.

3.14.4 Upgrading existing woodenfloors using platform and ribbed floorsThe systems discussed in Section 3.14.3all maintain the original wooden floormounted directly on joists. This has theadvantage of maintaining the originalfloor level at the expense of loss of ceilingheight below. An alternative approach isto provide a floating floor system eitheron top of the existing floorboards (aplatform floor) or to remove the existingfloorboards and build a new floor onresilient material placed on top of thefloor joists (a ribbed floor). In both cases

the increase in both airborne and soundinsulation relies on the mechanicalisolation of the floor from the joists usingresilient material.

Figure 3.14 shows a number of typicallightweight floating floor constructionsand indicative sound insulation figures.There are many proprietary systems usinga wide range of isolating materials andmanufacturers should supply test data inaccordance with ISO 140 measurements.

The isolating layer will typically consistof rubber, neoprene, open-cell or closed-cell foams, mineral fibre or compositematerials. The isolating layer can be in theform of individual pads, strips or acontinuous layer of material.

The sound insulation increases with thedeflection of the resilient layer (up to thelimit of elasticity for the material), withthe mass of the floating layer and with thedepth of the cavity. Adding a layer oflightweight acoustically absorbent glasswool or mineral wool in the ceiling voidincreases the sound insulation, typically by2-3 dB, but there is no point in addingmore than specified. In each case thedeflection of the material under thepermanent ‘dead’ load of the floatinglayer and the varying ‘live’ loads ofoccupants and furniture must beconsidered. If the material is too resilientand the floating layer is insufficientlyheavy or rigid, the floor will deflect underthe varying loads as people move aboutthe room. For this reason it isadvantageous for the floating layer to beas heavy and as stiff as practicable, insome cases using ply or fibre-bond board(for mass) laid on top of the resilientlayer, with tongue-and-grooved chipboardon top of this.

If there are likely to be very heavy localloads in the room (eg pianos) it may benecessary to increase the stiffness of theresilient material, or, in the case of pads,to space the pads more closely together tosupport these loads.

Junctions with walls and at doors needto be designed to maintain an effectivelyairtight seal while allowing movement ofthe floating layer. Manufacturers generallyprovide their own proprietary solutionsfor this, with or without skirtings.

50

Sound insulation3

Lightweight floating floors are quitespecialist constructions, and achieving thecorrect deflection under varying live loadswithout overloading the resilient materialcan be difficult. Most materials sufferfrom long term loss of elasticity or ‘creep’under permanent loads and this should betaken into account in the design andselection of materials. The systemmanufacturer should normally be providedwith all of the relevant information andrequired to specify a system to meet all ofthe acoustic and structural requirementsover the expected lifetime of the floor. Indifficult cases the advice of an acousticsconsultant and/or structural engineershould be sought.

3.14.5 Concrete floorsIn general, concrete floors provide muchgreater low frequency airborne soundinsulation than wooden floors by virtue oftheir greater mass. There are, however,considerable variations in performancebetween dense poured concrete floors andcomparatively lightweight precast concreteplank floors. Impact sound transmissioncan be a problem even in heavy concretefloors because of the lack of damping inconcrete, and a soft or resilient floorcovering is generally required. This maysimply be carpet on suitable underlay.

Figures 3.15 and 3.16 show airborne

sound insulation and impact soundtransmission data for a number of typicalconcrete floor constructions, with andwithout suspended ceilings and floatingfloors.

3.15 Design and detailing ofbuilding elementsImportant points to remember whendesigning constructions to achieveadequate sound insulation are: • Weak elements (eg doors and glazing,service penetrations, etc) will reduce theeffectiveness of the walls in which they arelocated.• Impact sound will travel with littlereduction through a continuous membersuch as a steel beam or servicing pipe.• Partitions between sensitive spacesshould normally continue beyond theceiling up to the structural soffit or rooflayer, to prevent noise passing over thetop of the partition above the ceiling orthrough a loft space.• Openings in walls caused by essentialservices passing through should beacoustically sealed. Pipework passingbetween noise sensitive spaces should beappropriately boxed-in (see ApprovedDocument E[1]).

Figure 3.17 shows how possibletransmission paths through the structureof a building can be prevented.

allconnectionsfor plant andmachineryshould be flexible

walls must be ofadequate weightand all gaps sealed

airborne sound transmited through ceiling,light fittings, and lightweight partitions and gaps

can be dealt with by sealing gaps and increasing mass

sound can be transmitted along the structure

all gaps forducts and pipes

in walls and floorshould be well sealed

airborne sound transmittedthrough ductwork

ceiling below plant may needto be isolated from floorabove and from ductwork assuspended ceiling can bea good amplifier forstructure-borne noisecreated by badly isolatedplant

plantroomshould haveflexiblemountings,adequatefloor massand elasticity,or floatingfloor

partitions should extendup to the soffitFigure 3.17: Possible

sound transmission pathsand their prevention

51

3Sound insulation

References[1] Approved Document E - Resistance to thepassage of sound. The Stationery Office,2003, ISBN 01 753 642 3www.safety.odpm.gov.uk[2] Sound Control for Homes (BRE report 238,CIRIA report 127), 1993. Available from CRCLtd. 1993, BRE ISBN 0 85125 559 0, CIRIAISBN 0 86017 362 3, CIRIA ISBN 0305 408 X.[3] J McLoughlin, D J Saunders and R D Ford.Noise generated by simulated rainfall onprofiled steel roof structures. Applied Acoustics42 239-255, 1994[4] ISO 140-18 Acoustics - Measurement ofsound insulation in buildings and of buildingelements - Part 18: Laboratory measurementof sound generated by rainfall on buildingelements (in preparation).[5] BS EN ISO 140-3: 1995 Measurement ofsound insulation in buildings and of building elements. Part 3. Laboratory measurement ofairborne sound insulation of building elements. [6] The Education (School Premises)Regulations 1999. (Statutory Instrument 1999No 2, Education, England & Wales). TheStationery Offiice, 1999. ISBN 0 11 080331 0www.hmso.gov.uk[7] BS EN 20140-10: 1992 Acoustics -Measurement of sound insulation in buildingsand of building elements. Part 10. Laboratorymeasurement of airborne sound insulation ofsmall building elements. [8] BS 98/704582 DC. Ventilation for buildings.Performance testing of components/productsfor residential ventilation. Part 1. Externally andinternally mounted air transfer devices. Draftfor public comment (prEN 13141-1 CurrentEuronorm under approval).

[9] BS EN 12354-3:2000 Building Acoustics -Estimation of acoustic performance in buildingsfrom the performance of elements. Part 3.Airborne sound insulation against outdoorsound.[10] BS EN ISO 140-5: 1998 Measurement ofsound insulation in buildings and of building elements. Part 5. Field measurements ofairborne sound insulation of façade elementsand facades. [11] BS EN 12354–1: 2000 BuildingAcoustics. Estimation of acoustic performancein building from the performance of elements.Part 1. Airborne sound insulation betweenrooms.[12] BS 476 Fire tests on building materialsand structures.[13] BS EN ISO 140-6: 1998, Acoustics -Measurement of sound insulation in buildingsand of building elements. Part 6. Laboratorymeasurement of impact sound insulation offloors. [14] BS EN 12354-2: 2000 Building Acoustics.Estimation of acoustic performance in buildingfrom the performance of elements. Part 2.Impact sound insulation between rooms.[15] BS EN ISO 140-8: 1998 Acoustics.Measurements of sound insulation in buildingsand of building elements. Part 8. Laboratorymeasurements of the reduction of transmittedimpact noise by floor coverings on aheavyweight standard floor.[16] BS EN ISO 717-2: 1997 Acoustics - Ratingof sound insulation in buildings and of buildingelements. Part 2. Impact sound insulation.

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4.1 Approach to acoustic designThe vast majority of rooms in schools aredesigned for speech. A structuredapproach to the acoustic design of theserooms would consider the followingsubjects in the order given:1 Indoor ambient noise levels

(Table 1.1)2 Room size - floor area, shape and

volume and hence, required reverberation time (Table 1.5)

3 Amount of acoustic absorption required for reverberation time

4 Type, location, and distribution of that acoustic absorption

5 Special considerations for non-standard rooms (eg reflectors and diffusers)

6 Use of electronic sound reinforcementsystems.

4.2 Internal ambient noise levelsand speech clarityThe internal ambient noise level is veryimportant in teaching spaces as theteacher’s voice needs to be clearly heardabove the background noise. The soundpower output of conversational speech istypically 10 microwatts which results in asound pressure level of about 60 dB at 1 min front of the speaker. This output powercan be raised to around 100 microwattswhen the speaker talks as loudly aspossible without straining the voice,which increases the sound pressure level at1m to about 70 dB. By shouting, theoutput power can be further raised toaround 1000 microwatts with aconsequent further increase in soundpressure level to about 80 dB. Insubjective terms, this means that a speakercan approximately double the loudness ofthe voice by speaking very loudly, andthen double it again by shouting, seeFigure 4.1.

It is also desirable to preserve thecharacter, or nuances and intonations, ofspeech. This is particularly relevant tolanguage teaching and to the performanceof drama. The frequencies of sound inspeech range from bass to treble, that isfrom below 125 Hz to above 8 kHz.Vowels have a sustained, tonal soundwhich contains characteristics of thespeaker’s voice. Men’s voices have thelowest characteristic pitch (120 Hz),women an intermediate pitch (225 Hz),and children the highest pitch (265 Hz).Vowels contain most of the sound energyin speech but recognition of theconsonants, whose energy is generallyconcentrated towards the higherfrequency end of the speech spectrum, isthe key factor for high intelligibility.

The intelligibility of speech dependsupon its audibility as well as its clarity.Audibility is affected by the loudness ofthe speech relative to the background

Normal voice

Raised voice

Shouting

60 dB at 1 m

80 dB at 1 m

70 dB at 1 m

Figure 4.1: Soundpressure levels of speechat 1 m

The design of rooms for speech 4

SE

CT

ION

The design of rooms for speech is a critical aspect of the acoustic design of aschool. Rooms must be designed to facilitate clear communication of speech

between teachers and students, and between students.

54

noise level. An increase in the backgroundnoise will cause greater masking of speechand hence will decrease intelligibility. It ispossible to speak louder but this effect islimited and can also lead to voice strain.The indoor ambient noise levels fordifferent rooms specified in Table 1.1have been chosen to ensure that anadequate signal to noise ratio can beachieved without undue strain on theteacher’s voice, and to minimise theeffects of distraction from other sources.

4.3 Reverberation timesA classroom with a long reverberationtime of several seconds will cause syllablesto be prolonged so that they overlap andhence degrade speech intelligibility. Longreverberation times occur in large roomswith hard wall and ceiling surfaces.Adding acoustic absorption and reducingthe ceiling height will reduce thereverberation time and will improvespeech intelligibility. Table 1.5 specifiesthe reverberation times required forvarious teaching spaces ranging fromteaching classrooms to assembly halls.

Appendix 2 describes the theory andterminology of reverberation time,acoustic absorption and enclosed volume.The methodology for calculation ofreverberation time in rooms other thancorridors, entrance halls and stairwells isdescribed in Appendix 6, together withsome worked examples. There is a link toa façade sound insulation and reverberationtime computer spreadsheet for schools,from the DfES acoustics website.

Long reverberation times also increasereverberant noise levels within a room,which further decrease speechintelligibility. To compensate for this, inreverberant rooms people tend to increasetheir voice levels to make themselvesheard over the reverberant noise, whichfurther exacerbates the situation. This is acommon feature of many school diningrooms and sports halls.

4.4 Amount of acoustic absorptionrequiredThe method described in Appendix 6allows the amount and type of acousticabsorption to be calculated.

In general, in rooms for musicperformance, the reverberation timecalculations will show that relatively littleabsorption is required in addition to thatprovided by the audience.

In classrooms and other rooms forspeech, however, larger amounts of fixedacoustic absorption are often required,particularly where rooms have highceilings as often occurs in older buildings.

When calculating reverberation timesto comply with the specified values inTable 1.5 in rooms for speech, theabsorption due to furnishings such aschairs, school desks and benches, may beignored. Accurate absorption data forsuch items can be difficult to identify andif the furnishings have any effect it islikely to result in shorter, rather thanlonger, reverberation times.

4.5 Distribution of absorbentmaterialsThe location of acoustic absorption withina room is important. The traditionalcalculation of reverberation time assumesthat the absorbent surfaces in a room arereasonably evenly distributed. If this is notso, the reverberation time equation is notvalid and undesirable local variations inthe acoustics can occur, particularly inlarge rooms or halls. Large areas ofacoustically reflective material can alsolead to echoes, focusing and standingwaves.

4.6 Room geometryTo achieve adequate loudness for alllisteners in a room, it is necessary that thedirect sound from speaker to listener has aclear unobstructed path. The loudness ofthe direct sound can be enhanced bystrong, short delay reflections from roomsurfaces. These short delay reflectionsshould arrive at the listener within onetwentieth of a second (50 milliseconds) ofthe direct sound, which is approximatelythe time required for the ear to integratesuch reflections with the direct sound.Strong reflections after 50 millisecondstend to be detrimental to speechintelligibility, and ultimately, if the delay islong enough, they will be perceived asdistinct echoes.

The design of rooms for speech4

55

4.7 ClassroomsFor classrooms and other rooms forspeech, there are two approaches tolocating the acoustic absorption:

1. To make the ceiling predominantlyabsorbent. In most cases a standardacoustically absorbent suspended ceilingwill provide all of the necessaryabsorption. In the case of rooms withexposed concrete soffits (providingthermal mass to limit overheating insummertime) acoustically absorbentsuspended baffles may be used. The idealcase is often to have the central part ofthe ceiling reflective with absorption atthe edges, see Figure 4.2(a)

2. To leave the ceiling acousticallyreflective (plaster, plasterboard, concrete,etc) and to add acoustic absorption to thewalls. In these cases it is advisable tolocate most of the absorption at high leveland some on the back wall facing theteacher to prevent "slap echo" off theback wall. This is particularly important ifthe rear wall is concave or the distancefrom the speaker to the rear wall isgreater than 8.5 m. see Figure 4.2(b).

In large rooms, reflections from therear wall can be disturbing for a speaker ifthey arrive later than 50 milliseconds afterthe speech has been voiced. This canoccur if the speaker to rear wall distance isgreater than 8.5 m. To avoid this problem,the rear wall should be made acousticallyabsorbent, or acoustically diffusing.

There are instances where provision ofsound field amplification can improvespeech intelligibility, see Section 6.

4.8 Assembly halls, auditoria andlecture theatresMost school halls are used primarily forspeech functions such as assemblies,meetings and drama, and use for music isless frequent. The most common problemin school halls is excessive reverberationresulting in high noise levels and poorspeech intelligibility.

4.8.1 Room geometryThe direct sound from speaker to listenermust be as strong as possible at allpositions. Because this sound weakensrapidly with distance according to theinverse square law (the intensity isreduced by a factor of four and the soundlevel falls by 6 dB when the speaker toreceiver distance is doubled), the averagedistance between speaker and listenershould be kept as small as possible.Furthermore, there should be noobstructions along the direct sound path.

140°

speaker

audience

Figure 4.3: Ideal seatingplan

4The design of rooms for speech

b

d da

c

(b) Surface finishes in classroom or lecture theatre:a. Rear wall - sound absorbing or diffusingb. Ceiling - sound reflective (eg plasterboard)c. Floor - sound absorbing (eg carpet)d. Walls - sound reflectivee. Top of walls - sound absorbing or diffusing

d da

c

b

(a) Surface finishes in classroom or lecture theatre:a. Rear wall - sound absorbing or diffusingb. Ceiling - sound reflective (eg plasterboard)c. Floor - sound absorbing (eg carpet)d. Walls - sound reflectivee. Ceiling - sound absorbing

e e

Figure 4.2: Surfacefinishes in classroom orlecture theatre

For large rooms such as school halls,additional factors need to be consideredin relation to the direct sound. First, theseating plan should be arranged to fallwithin an angle of about 140° subtendedat the position of the speaker, see Figure4.3. This is because speech is directional,and the power of the higher frequencieson which intelligibility largely dependsfalls off fairly rapidly outside this angle.Secondly, sound is weakened as it passesover seated people at grazing incidence.Therefore, if possible, listeners should beseated on a rake where a clearance ofaround 100 mm is provided between thesightline from one row and the sightlinefrom the next, see Figures 4.4(a) and4.4(b). It is known that if people can not

see the speaker well, they will not hearwell either. It is frequently necessary inschools to have a flat floor in a schoolhall. In these cases, speakers should beraised on a platform which is sufficientlyhigh to ensure that minimum clearance isobtained at the rear rows of the hall, seeFigure 4.4(c).

The direct sound from speaker tolistener can be enhanced by strong earlyreflections that arrive within 50milliseconds, see Figure 4.4(d). Theseearly reflections increase the loudness ofthe direct sound and therefore increasespeech intelligibility. They are particularlyuseful at the furthest seats where theloudness of the direct sound has beenreduced by distance. To provide

56

b ca

(a) Adequate loudness is essential, direct sound musthave a clear unobstructed path.

(b) Loudness of direct sound towards rear isincreased with raked seating.

(c) Loudness of direct sound can be increased byputting the speaker on a platform.

(d) Reflected sound enhances direct sound if timedelay is less than 50 milliseconds.

(e) For useful sound reflections, additional pathtravelled by reflected sound must be less than 17 m:b+c – a<17 m.

(f) Rear wall can cause a disturbing echo for speakersif over 8.5 m away. Rear wall should be absorbingor diffusing.

4

Figure 4.4: Effects ofroom geometry on speech.

The design of rooms for speech

57

(c) Curved rear wall can cause focusing

(a) Barrel vault can cause focusingand flutter echoes

(b) Shallow hipped roof can causefocusing and flutter echoes

section

section

plan

Figure 4.5: Room shapeswhich can cause focusingand echoes

4reflections within 50 milliseconds of thedirect sound, hard surfaces must belocated within a certain distance of thespeaker and listener. In most rooms, thecentre part of the ceiling is the mostimportant reflecting surface and shouldbe of hard, sound-reflecting material.Other useful surfaces providing earlyreflections are side walls near the speaker,overhead reflecting panels and angledceiling panels.

The additional path travelled by thereflected sound should be no greater than17 m more than the direct sound pathbetween speaker and the seating areawhere the reflection arrives, see Figure4.4(e).

Any reflection that arrives at a listener,or back at the speaker, more than 50milliseconds after the direct sound is likelyto be disturbing, see Figure 4.4(f). Theseare most probable in school halls wherelate reflections can occur from the rearwall or a control room window at therear. Rear walls can be rendered soundabsorbing or sound diffusing to avoidthis. In the case of control roomwindows, these can be tilted to direct thereflection away from speakers andlisteners.

Focusing of sound by domes or barrelvaults illustrated in Figure 4.5(a), can be aserious fault which can cause strong latereflections or echoes. If the dome orbarrel vault is above a flat, hard floor as ina school hall, flutter echoes can occurwhich can be disturbing for speaker andlistener alike. This effect can also occurwith shallow pitched reflective roofsabove a flat floor, see Figure 4.5(b) andthe assembly hall in Case Study 7.1. Thesame effect can also occur on plan wherea room has a curved or segmented rearwall opposite a flat front wall, see Figure4.5(c).

4.8.2 Sound reinforcementWith an acoustically well designed roomit is possible for strong speakers to achievegood speech intelligibility for largeaudiences. Quieter and untrainedspeakers, however, will not be able to dothis and a speech reinforcement system islikely to be required for some functions.

The key aim of such a system is toincrease the loudness of the direct sound,particularly for more distant listeners,whilst keeping the sound as natural aspossible.

The distribution of loudspeakers andtheir directional characteristics is a keyissue in achieving high speechintelligibility. For large teaching roomsand lecture theatres, loudspeakers can bedistributed in the ceiling or on the wallsat high level. In school halls, columnloudspeakers can be located on sidewalls,or in a central cluster as shown in Figure 4.6.

The design of sound reinforcementsystems is a specialist field and specialistadvice should be sought.


4.9 Open-plan teaching andlearning areas In open-plan areas it is essential toprovide good speech intelligibility and tosecure freedom from aural distraction bymore distant sound sources and bybackground noise. Section 1 containsperformance standards for speechintelligibility in open-plan spaces. Somedegree of acoustic privacy is also desirable.This can be difficult to achieve in practiceand there have been many instances ofdistraction and disturbance between classgroups in open plan areas. Case Studies7.2, 7.3 and 7.10 describe surveys of theacoustics of open-plan teaching areas inprimary and secondary schools.

In open-plan areas, a carpeted floor isrecommended together with a soundabsorbing ceiling. In addition, soundabsorbing screens should be interposedbetween class groups. Screens should beat least 1.7 m high and ideally shouldreach to within 0.5 m of the ceiling, seeFigure 4.7.

A major improvement in the acousticprivacy between spaces in open-plan areascan be realised by installing full heightmoveable walls which, if fitted with seals,can provide a moderate degree of soundinsulation between the divided spaces. Ingeneral however it is found that suchscreens are rarely used because of the time

and effort required to open and closethem. While in theory it is possible toachieve adequate sound insulationbetween classrooms using high-performance moveable walls, there areissues of cost, weight, complexity ofinstallation and maintenance to consider.Specialist advice from an independentconsultant should always be sought ifusing such partitions to comply with thesound insulation requirements set out inSection 1 of this document.

Research has shown that in many largeopen-plan ‘flexible’ areas certain activitiesare severely restricted or have to bedropped because of noise interference.Indeed, it must be recognised that thereare but a small number of activities thatcan share a degree of acoustic linkage andeven then the timetable has to bedesigned to allow this.

Those plans which provide a generousrange of spaces in a variety of sizes can beseen to give far more opportunities inteaching than those with large openspaces and moveable screens, because inthe former it is possible to achieve goodsound insulation standards betweenspaces.

When designing open-plan areas it isimportant to provide plenty of acousticallyabsorbent surfaces and to use screens toblock direct sound paths.

58

amplifier

central cluster

microphone

Figure 4.6: Anarrangement ofloudspeakers in a schoolhall

4 The design of rooms for speech

59

Figure 4.7: Positioningof indoor screens

Screens should be as high as possibleand the ceiling must be absorbent

SECTIONIf a screen is not high enough, direct sound paths or paths with onlysmall angular changes are possible. If the angle is small, more lowand mid frequency sound will diffract over the top of the screen.If the ceiling is not absorbent, sound can be reflected over the screen.

Surrounding surfaces must be absorbent

PLANScreens near windows have littleeffect because of flanking reflectionsoff the windows.

44.10 Practical spaces Spaces for teaching practical subjects haveparticular requirements which needcareful design in order to comply with theacoustic requirements for teaching andlearning. This section addresses the needsof Design and Technology spaces and Artrooms. Music rooms are consideredseparately in Section 5. Although Scienceinvolves a significant amount of practicalactivity, the general approach describedfor classrooms (Section 4.7) can beapplied to spaces for the teaching ofScience. For further information onDesign and Technology spaces seeBuilding Bulletin 81[1] and the DfESacoustics website.

4.10.1 Design and Technology spacesDesign and Technology departments insecondary schools contain timetabledspaces for a variety of practical activities,eg graphics, resistant materials (wood,metal and plastics), electronics/control,food and textiles. They also include non-timetabled learning spaces, typicallyshared design/ ICT resource areas.

The equipment and the activities inthese spaces can vary widely dependingon the type and size of department.Activity noise and noise toleranceclassifications for different spaces aregiven in Table 1.1. It is important toestablish what activities will take place inany one space and what equipment willbe used before calculating required levelsof sound insulation to minimise thebackground noise in nearby spaces.

Resistant materials areas containingwood or metal working machinery canproduce high noise levels. Machinesextracting dust particles, CADCAM andother noisy equipment will increase theactivity noise level of a space. It isimportant to consider the effects of suchequipment on teaching activities bothwithin the space containing theequipment and in adjoining rooms.Where possible, it is advisable to locatenoisy equipment in spaces away fromrooms housing quieter activities.CADCAM equipment is sometimeshoused in a separate room or withinpurpose designed enclosures which can

reduce the noise level. The effect of noise from machines

within the space is not required to beincluded in the indoor ambient noise levelcalculations submitted for approval byBuilding Control Bodies, except in thecase of open plan arrangements. Oftenmachines can be switched off whenquieter learning activities such as grouppresentations are taking place, but thismay not always be possible. The locationand use of noisy equipment needs to bediscussed and agreed with the user.

Partially glazed partitions havecommonly been used between design andtechnology spaces, particularly between


timetabled and non-timetabled spaces.This is both for ease of supervision and toemphasise the link between related designactivities. However, these considerationsmust be balanced against the acousticrequirements. Large areas of glazing willboth increase the reverberation timewithin a space and reduce the soundinsulation of a partition. Both of thesefactors will have a detrimental effect uponthe speech intelligibility within the spaceand other nearby spaces.

Similarly, if interconnecting doors areused between neighbouring rooms thedoorsets must be chosen to provideadequate sound insulation.

Central resource areas are often locatedadjoining the circulation spaces of designand technology departments. A commonarrangement uses the central resourcearea predominantly for individual andsmall group work but such areas are notgenerally suitable for whole class teaching.Usually, there are areas of glazing anddoors between the central resource areaand adjacent practical spaces. The centralarea should be suitable for mostdesign/resource activities as long as thecirculation is restricted to the departmentand does not include access to other partsof the school.

Where spaces are open plan or dividedby moveable or extensively glazedpartitions, it may be appropriate to adoptalternative acoustic performance standardsin accordance with Section 1.2.1. Thiswill need to be based on an activity planfor the area which has been agreed withthe user.

The speech intelligibility in open planspaces will need to be assessed usingcomputer prediction models, as describedin Section 1.1.7. This may apply to ashared design/ICT resource area wheregroup presentation could take place at thesame time as other activities.

4.10.2 Art roomsArt classes in secondary schools involveindependent and group activities whichare in general quieter than those in otherpractical areas. Noise levels in secondaryschool art spaces are likely to be similar tothose in a general classroom. However,

art departments tend to have a moreinformal environment reflecting thenature of the activity, and are often ofopen-plan design. There may be moreglazing in partitions in art departmentsthan in other parts of the school, toemphasise the importance of the visualenvironment.

4.10 3 Floor finishes in practicalspacesCarpets are not appropriate for mostpractical areas and so cannot be used as away of increasing sound absorption orreducing the impact sound transmissionthrough floors in science, art and designand technology spaces. They may howeverbe suitable in some design/resource areas.

Acoustic vinyl flooring or a vinyl floorlaid on top of an acoustic mat may besuitable for practical spaces whereimproved impact sound insulation isrequired. Resistance to indentation willneed to be considered and a change offlooring may be necessary underneathfixed heavy machinery such as floormounted machine tools.

4.11 Drama roomsThere are three types of drama room incommon use:1 Rooms for small scale drama teaching

and practical work2 Drama studios – for rehearsal, teaching

and small-scale performance3 Theatres and flexible spaces primarily

for performance.Rooms for small scale drama teaching

and practical work are usually little morethan classrooms, which may be fitted withcurtains both for blackout and to reducereverberation time. They may also beprovided with a basic set of lights anddimmable main lighting.

Drama studios tend to be larger spacesdedicated to drama, with specialequipment such as moveable staging,seating rostra, lighting and sound systems.They do not normally have fixed stages orplatforms and the acoustics will tend tochange with the layout, seating andaudience. They may be fitted with heavycurtains on some or all walls, to allowsome control of reverberation time, for

60

4 The design of rooms for speech

61

Proscenium opening with afore stage projecting in frontof it

Proscenium opening at thefront of the stage, making aframe between audience andactors

Three-sided arrangement

In the round arrangement

Figure 4.8: Typicalperformance spaces fordrama

4blackout, and to allow some flexibility inthe room’s appearance. In this case thewall finishes will generally be hard(masonry or plasterboard). Studiosgenerally have wooden floors andacoustically absorbent ceilings, althoughlarge amounts of permanent lighting andrigging also provide useful diffusion.

Theatres and spaces primarily forperformance vary considerably in formand size from the conventional assemblyhall to adaptable theatres. They can betraditional theatres with fixed prosceniumand stage, open stages, thrust stages or inthe round, see Figure 4.8. Adaptabletheatres can be converted from onearrangement to another depending on thetype of performance.

Each type has different acousticcharacteristics. The basic acousticrequirements for auditoria are discussedin Section 4.8, however spaces designedspecifically for public performance arespecialised rooms and the advice both ofan acoustician and a theatre consultantshould normally be sought.

For successful drama it is necessary forthe audience to see and hear considerablybetter than in most school halls, becauseof the close relationship between actorsand their audience. In principle, toachieve close communication betweenactor and the audience it is necessary torestrict the size of the auditorium so thatthe maximum distance from any memberof the audience to the stage does notexceed 20 m. In small theatres this is notgenerally a problem, but for largeraudiences it may require the use ofbalconies and galleries, giving rise to thetraditional fan-shaped theatre (which is,however, very bad acoustically for music).Deep balconies are to be avoided as thespace under these can be acoustically‘dead’ and considerable care is required toensure that reflections from the ceilingsand walls compensate for the lack ofdirect sound in such areas.

It is common for theatres in schools tobe used not only for drama, but also forlectures, films, meetings and music, whichall have different acoustic requirements.The acoustics of multi-purpose halls arediscussed in the following section.

4.12 Multi-purpose halls In large schools the multi-purpose space,intended to act as assembly hall, theatre,concert hall and gymnasium, is passingout of favour as it is difficult for a singlehall to fulfil all of these functions well.None the less, in some cases a singleflexible hall is required for a variety ofuses and this gives rise to specific acousticproblems.

The different uses of multi-purposehalls often have conflicting acousticrequirements, making it difficult toprovide a space with optimum acousticsfor all uses. The main conflict is thatbetween speech and unamplified music.


62

4

Table 4.1 shows the general acousticrequirements for speech and music. (Seealso Section 5.7.)

Where regular performances of musicare expected, reverberation time issometimes changed using moveable areasof absorption (typically curtains) withoutchanging the volume of the space.Although this can successfully change thereverberation time at medium and highfrequencies, it often has little effect at lowfrequencies, resulting in an acoustic whichis less than ideal for either speech ormusic.

(Note that the ‘dry’ acoustic requiredfor speech is also generally suitable foramplified music.)

Further information regarding thedesign of multi-purpose auditoria is givenin Section 5.

4.13 Other large spacesSports halls, gymnasia and especiallyswimming pools have long reverberationtimes through the nature of theirconstruction and surfaces necessary totheir function. This results in high noiselevels and poor speech intelligibility.

A variety of relatively rigid, robust andhygienic, acoustically absorbent materialsare available and can be used. In general,these materials are installed on ceilingsand at high level on walls or as hangingbaffles. If there are large areas ofacoustically hard parallel surfaces, flutter


echoes can occur, significantly increasingthe reverberation time and reducingspeech intelligibility. A reasonabledistribution of acoustic absorption ordiffusion (such as provided by wallbarsagainst gymnasium walls) will eliminatethis effect.

4.14 Dining areas Dining areas suffer from excessive activitynoise. The high activity noise interfereswith conversation leading to increasingnoise levels. Therefore, sound absorptionis required in these areas to reduce thereverberant noise level. The most practicalplace to position sound absorption is onthe ceiling and the walls. Shapes insection or on plan that produce focusing,such as barrel vaulted roofs and circularwalls, should be avoided unless treatedwith sound absorbent material.

References[1] Building Bulletin 81, Design and TechnologyAccommodation in Secondary schools, to bepublished January 2004 (replacing 1986edition).

Speech

"Dry" acoustic

Short reverberation time

Good clarity, loudness and intelligibility ofspeech

Sound must appear to come from stage withsome contribution from room reflections butno perceptible reverberation

Small volume

Music

"Live" or "warm" acoustic

Long reverberation time

Even decay of sound

Good "envelopment" - audience should feelsurrounded by the sound, and musiciansshould be able to hear themselves and eachother easily

Large volume

Table 4.1: Generalacoustic requirements forspeech and music

63

5.1 Aspects of acoustic designBuilding Bulletin 86 MusicAccommodation in Secondary Schools[1]

gives detailed design advice on the rangeof types of music spaces found in schools.The performance standards of the mostcommon music room types are listed inthe tables in Section 1.

Some non-specialist classrooms may beused for teaching music theory to largegroups, with only occasional live orrecorded music. In these rooms themajority of activity depends on goodspeech intelligibility rather than anenhanced acoustic for music and in thesecases classrooms with the same acousticcriteria as normal classrooms may be used.

A brief, outlining the client's acousticrequirements, should be obtained beforestarting the design of any specialist musicfacility. The main problems are noisetransfer between spaces, unsuitablereverberation times, flutter echoes,standing waves, and high noise levels.

5.2 Ambient noise The requirements for indoor ambientnoise levels in music rooms are set out inTable 1.1. To control noise frommechanical ventilation, it is important toselect quiet fans or air handling unitswhich are connected to appropriatelysized silencers (attenuators). Typicalprimary attenuator lengths will be in therange 2.4 - 3.0 m. Air velocities in theduct system should be kept low andshould not generally exceed 5 m/s inmain ducts, 4.5 m/s in branch ducts and2.5 m/s at runouts. Terminal units(grilles etc) should be selected for lownoise output.

Noise from hot water radiator systemsshould be minimised by good design.Equipment, particularly the valves andpumps, should be designed and selectedfor quiet operation, with vibrationisolation where appropriate.

In noise-sensitive spaces, such as musicperformance spaces and recording spaces,hot water pipes should not come intorigid contact with the buildingconstruction. Resilient pipe brackets andflexible penetration details should beadopted to prevent clicking noisesresulting from expansion and contraction.

Lighting can cause disturbing buzzingand occasionally sharp cracks fromexpansion or contraction of metal fittings.In music rooms, 50 Hz fluorescent lightsshould not be used because they areinherently prone to buzzing and mainshum which is audible to some people.These effects do not occur with highfrequency (HF) fittings, which should ingeneral be specified on energy efficiencyand cost saving grounds. HF fittings areacceptable for most general music spaces.Where the quietest conditions arerequired, lighting should be restricted totungsten or similar lamps. In certainspaces such as a recording/control room,the sound caused by transformers usedwith low voltage spotlights can bedistracting.

5.3 Sound insulationStandards for sound insulation betweendifferent types of room are set out inTable 1.2. To avoid excessive noisetransfer between music rooms Table 1.2specifies a minimum of 55 dBDnT(Tmf,max),w between most music

The design of rooms for music

Music rooms require special attention in the acoustic design of a school. It is important to establish the user’s expectations of the acoustic performanceof the spaces. Musical activities range from playing, listening and composing ingroup rooms to orchestral performances in school halls, and a music room can

be anything from a small practice room to a large room for rehearsing andperforming music.

5

SE

CT

ION

64

rooms. These are minimum requirementsand will not always prevent interferencebetween adjacent rooms. It is beneficialto increase these figures, especially whenthe indoor ambient noise level issignificantly below the level in Table 1.1.This can occur in naturally ventilatedrooms on quiet sites where the indoorambient noise level is too low to provideuseful masking of distracting noise fromadjacent rooms.

The level of sound and possibledisturbance between music spaces willvary depending on the instruments beingplayed. Clearly, as the loudness of theinstruments varies from group to group,so the room-to-room sound insulationrequirement will also vary. An importantquestion is that of cost versus flexibility.High flexibility is desirable so that anyinstrument can occupy any room. Howeverit is expensive to provide sound insulationto satisfy the most stringent requirementat all locations throughout the building.Alternatively, designating groups of rooms to groups of instruments severelylimits flexibility but concentratesinvestment in sound insulation where it ismost required.

Rooms for percussion and brass willgenerate high noise levels and great careis needed in choosing their location.Rooms for percussion should, if possible,be located at ground level to minimisethe transmission of impact vibration intothe building structure. Otherwise floatingfloor constructions may be required.

Figures 2.4 and 7.5.1 illustrate theprinciples of good planning, usingcorridors and storage areas as ‘bufferzones’ between music rooms wherepossible. This allows the sound insulationrequirements to be met without resortingto very high performance constructions.However, in some cases such asrefurbishments of existing buildings theprovision of special sound insulatingconstructions, as discussed in Section 3, isthe only option.

Background noise must be controlledin circulation areas. However, limitedbreak-out of musical sounds intocirculation routes is acceptable since itallows teachers to monitor, from a

distance, unsupervised small groupmusical activities.

5.3.1 Sound insulation betweenmusic roomsThe sound insulation required betweenthe different types of music room can bedetermined from Tables 1.1 and 1.2.

Other criteria such as those of Miller[2],which take account of both soundinsulation and indoor ambient noise level,are sometimes used in the specification ofsound insulation between music rooms;however, the normal way of satisfyingRequirement E4 of The BuildingRegulations is to meet the performancestandards in Table 1.2 for airborne soundinsulation between rooms.

Case Study 7.5 gives an example of theacoustic design of a purpose built musicsuite in a secondary school.

5.4 Room acoustics

5.4.1 Reverberation time, loudnessand room volumeIn general, rooms for the performance ofnon-amplified music require longerreverberation times than rooms forspeech. Figure 5.1 shows optimum midfrequency reverberation times for speechand music as a function of room volume.

The volume of a room has a directeffect on the reverberation time (RT) andearly decay time; in general, the larger thevolume, the longer the RT. Thereverberation times should be in theranges given in Table 1.5 and should beconstant over the mid to high frequencyrange. An increase of up to 50% ispermissible, and indeed is preferred, atlow frequencies as indicated in Figure 5.2.

To achieve this it is generally necessaryfor the volume of music rooms to begreater than for normal classrooms andthis generally requires higher ceilings.These also help with the distribution ofroom modes as described in the sectionon room geometry below.

If the volume of a room is too small,even with the correct reverberation timethe sound will be very loud. This is acommon problem in small practice roomswith insufficient acoustic absorption, and

The design of rooms for music5

65

can give rise to sound levels which could,in the long term, lead to hearing damage.Many professional orchestral musicianshave noise-induced hearing loss due toextended exposure to high noise levelsboth from their own instruments and, toa lesser extent, from other instrumentsnearby. Under the Noise at WorkRegulations 1989 (see Appendix 9) thereis a general requirement to minimisenoise exposure of employees in the schoolcontext, who for this purpose include full-time, part-time and freelance peripateticmusic teachers. It is therefore importantto ensure that practice, rehearsal andteaching rooms are neither excessivelyreverberant nor excessively small for agiven occupancy.

Setting the floor area and ceilingheight is normally the first step indesigning a music room. The floor area isusually determined by the number ofoccupants and guidelines are given inBuilding Bulletin 86[1], as are methods ofcurriculum analysis to determine theneeds of a secondary school musicdepartment. A typical suite of musicrooms in a secondary school mightconsist of:

Ceiling heights and consequentlyvolumes for halls and recital rooms aregenerally equivalent to two storeys,around 6 m. For group rooms andpractice rooms, a full storey height (atleast 3 m) is normally required.

5.4.2 Distribution of acousticabsorptionThe acoustically absorbent materialrequired to achieve the correct RTshould be distributed reasonably evenlyabout the room. Where absorptionoccurs only on the floor and ceiling – forexample in a simple solution employingacoustic ceiling tiles and carpeted floor –users may experience an over-emphasis onsound reflections in a horizontal plane.This often leads to ‘flutter echoes’between walls, which result in the actual

RT being considerably longer than thecalculated RT. A better solution,especially in large rooms, is to distributesome of the absorptive material about thewalls.

Although the RT requirements in Table1.5 are for unoccupied rooms, it isimportant to remember that theoccupants will present a significantamount of absorption which will be in thelower half of the room. To give areasonably even distribution of absorptivematerial therefore, acoustic absorption is

Large performance/teaching room 85 m2

Second teaching room 65 m2

Ensemble room 20 m2

Practice/group rooms 8 m2

Control room for recording 10 m2

2.0

1.5

1.0

0.5

020 30 50 100 500 1000 2000

Reve

rber

atio

n tim

e, s

Room volume, m3

music

speech

250 500 1000 2000 4000125

160150140130120110100

Frequency, Hz

Percentageof valueat 500 Hz

Figure 5.1: Optimum mid-frequency reverberationtimes for speech andmusic, for unoccupiedspaces

Figure 5.2:Recommended percentageincrease in reverberationtimes at lower frequenciesfor rooms specifically formusic

5The design of rooms for music

66

often located at high level on the walls.Because of the absorption of the

audience, there can be large variations inRT depending on the presence or absenceof an audience. To reduce this effect,acoustically absorbent seats withupholstered backs can be used and inlarge halls the acoustic absorption of theseats has to be determined and specifiedquite carefully. An acceptable alternativein smaller halls can be the use ofretractable curtains to reduce the RTduring rehearsals when no audience ispresent.

In auditoria and music rooms, surfacesaround and above the stage orperforming area are normally reflective toprovide feedback to the performers.

Floors on stage should be reflectivealthough carpet in an auditorium may bepermissible.

5.4.3 Room geometryIt is important to consider both roomshape and proportion. In large roomssuch as halls and recital rooms, thegeometry of the room surfaces willdetermine the sequence of soundreflections arriving at the listener from agiven sound source. Early reflections, thatis those arriving within approximately 80milliseconds of the direct sound, will beintegrated by the listener’s hearing systemand will generally enhance the originalsound for music (50 milliseconds is thecorresponding figure for speech, seeSection 4).

Prominent reflections with a longerdelay (late reflections) may be perceivedas disturbing echoes. This is oftenencountered where the rear wall in a hallhas a large flat area of glass or masonry.Strong individual reflections can also lead

to ‘image shifting’ where early reflectionscan be so strong that the ear perceives thesound as coming from the reflectingsurface and not the sound source.

This problem can be exacerbated if latereflections are particularly strong. Thiscan occur when sound is focused fromlarge concave surfaces such as curved rearwalls, barrel vaults, domes, etc.Furthermore, focusing results in anuneven distribution of sound throughoutthe room. Consequently, large concavesurfaces are not generally recommendedin music spaces.

In small rooms, such as group roomsand music practice rooms, geometryaffects the distribution of standing wavesor room modes throughout the soundspectrum, particularly at low frequencies.Where the distance between two parallelwalls coincides with or is a multiple of aparticular wavelength of sound, astanding wave can be set up and thebalance of sound will be affected, seeFigure 5.3. Certain notes will beamplified more than the rest leading to anunbalanced tonal sound, sometimes calledcolouration. Bathrooms with tiled wallsare a good example of rooms withprominent room modes and, althoughthey can enhance certain notes of asinger’s voice, they will not produce abalanced sound and will tend to soundboomy. The effect is exaggerated ifdistances are the same in more than onedimension. Thus rooms which are square,hexagonal or octagonal in plan should beavoided. The same effect occurs if theroom width is the same as the roomheight, or is a simple multiple of it.

Ideally, the distribution and strength ofroom modes should be reasonablyuniform. Perhaps the best way to control

1.00.8

0.60.4

0.20

1.00.8

0.60.4

0.2

1.00.8

0.60.4

0.20

0

0

1.00.80.60.40.2

1.00.80.60.40.2

0 0

Figure 5.3: Standingwaves in different modes0 – No sound pressure1.0 – Maximum soundpressure


67

these low frequency modes is to selectroom dimensions that are not in simpleratios. It should not be possible to expressany of the room dimensional ratios aswhole numbers, for example, a proposedspace 7 m wide, 10.5 m long and 3.5 mhigh (2:3:1) would not be considered anadvisable shape from an acoustic point ofview. Mathematically, an ideal ratio is1.25 : 1 : 1.6; this is sometimes referredto as the ‘golden ratio’ but many otherratios work equally well.

Both flutter echoes and room modescan also be controlled by using non-parallel facing walls, but this is oftenimpractical for architectural reasons; theuse of absorption or diffusion is equallyeffective.

5.4.4 DiffusionIn addition to the correct RT, the roomshould be free from echoes, flutterechoes, and standing waves and the soundshould be uniformly distributedthroughout the room, both in theperformance and listening areas. Toachieve this without introducing toomuch absorption, it may be necessary tointroduce diffusing hard surfaces todiffuse, or scatter, the sound. These arenormally angled or convex curvedsurfaces but bookshelves, balcony frontsor other shapes can also provide diffusion,see Figure 5.4. Acoustic diffusion is acomplex subject, and if calculation ofdiffusion is likely to be required aspecialist should be consulted.

5.5 Types of room

5.5.1 Music classroomsFigure 5.5 shows a 65 m2 music classroomfor a range of class-based activitiesinvolving a number of differentinstruments. The room proportion avoidsan exact square. The height is assumed tobe between 2.7 m and 3.5 m, creating areasonable volume for the activities (seeSection 5.4.3). The main points to noteabout the acoustic treatment of the spaceare described below.

To minimise the possibility of flutterechoes or standing waves occurringbetween opposing parallel walls, surfaces

are modelled to promote sound diffusion.On the side wall this takes the form ofshelving to store percussion instruments,etc. On the back wall, framed pinboards(with non-absorptive covering) are set atan angle, breaking up an otherwise plainsurface.

Full length heavy drapes along the backwall can be drawn across to vary theacoustics of the space.

The observation window into theadjacent control room is detailed toensure a high level of sound insulationbetween the two spaces (see Figure 5.6and the discussion of control roomsbelow).

The door into the room is of solid coreconstruction with a small vision panel.The door and frame details, Figures 5.7

Figure 5.4: Surfaceswhich provide specular anddiffuse reflections

PLANE SURFACE - specular reflection

SIMPLE ANGLED PANELS - diffuse reflection

CURVED PANELS - diffuse reflection

50 mm to 500 mm (larger depth extendsdiffusion to lower frequencies)


68

and 5.8, are designed to maximise thesound insulation properties of the wall asa whole.

The floor is fitted with a thin pilecarpet providing an absorbent surfacewhile the ceiling has a hard reflectivesurface. The type of carpet can have asignificant effect on the overall RT in aroom. It is worthwhile checking theprecise absorption coefficient of anysurface finish. (A spreadsheet of indicativeabsorption coefficients for commonmaterials is on the DfES acousticswebsite.)

5.5.2 Music classroom/recital roomFigure 5.9 shows a larger, 85 m2,classroom. The proportions of the roomare in a ratio of fractional numbers (2.6 :3.8 : 1) with the height between 2.7 mand 3.5 m as for the 65 m2 musicclassroom. The acoustic treatment issimilar to that for the 65 m2 room but asthis space is larger, and bigger groups arelikely to rehearse and perform here,drapes are provided on two adjacentwalls.

Figure 5.5: Acoustictreatment to musicclassroom


window to control roomdetailed to provide goodlevel of sound insulation

solid core door with smallvision panel

door frame detailimportant

shelving provides surfacemodelling to help diffusesound

full length drapes used tovary acoustic response

framed pinboards set atan angle provide surfacemodelling to promotesound diffusion

room not anexact square

thin pilecarpet on

floor

69

Head & jamb with singleor double seals

Generous rebateto frame, withheavy duty hinges

Continuous grounds andfill to frame and opening

Threshold seal (may beretractable type)

Handlebut nokeyhole

1.00

m

2.00

m

Viewingpanel

914 mm widestructural opening

Solid core timber doorassembly Elevation showing how theperformance of a door assemblydepends on a number of featuresof the construction, not just on themass of the door leaf

Figure 5.7: Desirablefeatures of an acousticdoor installation

150 mm (min) dense blockwork

Solid concrete lintel

Mineral wool or equivalentTwin 75x44 mm hardwood frames

Maximum possible spacing between panes of glassPerforated metal lining

13x44 mm architrave

12 mm and 6 mm glass in neoprenechannels to hardwood beads

Softwood opening lining150x38 mm

Figure 5.6: Sectionthrough control roomwindow


70

5.5.3 Practice rooms / grouproomsFigure 5.10 shows a typical 8 m2 grouproom which will accommodate bothinstrumental lessons and compositiongroups and which can be used forindividual practice. Points to note are asfollows.• One wall is at an angle of 7° to avoid flutter echoes (a particular issue insmall rooms) and prominent standingwaves. Window and door reveals provide

useful diffusion to other walls.• A full length drape can be pulled across the window to increase surface absorption and reduce loudness. • The window is fairly small andpositioned in the centre of the wall tocontrol the amount of external noisereaching the space and avoid soundtravelling between adjacent group rooms.• Floor and ceiling finishes are as for the larger rooms.

VERTICAL SECTION

PLAN

Figure 5.8: Vertical andhorizontal sections througha door installation. Takenfrom BBC EngineeringGuide to Acoustic Practice,2nd Edition 1990. Thesedrawings are reproducedhere with the kindpermission and co-operation of the BBC


71

Figure 5.9: Acoustictreatment to musicclassroom/recital room

Figure 5.10: Acoustictreatment to 8 m2 grouproom


solid core door withsmall vision panel

door frame detailimportant

store providessound insulationbetweenclassrooms

window to control roomdetailed to provide goodlevel of sound insulation

shelving providessurface modellingto help diffusesound

framed pinboards set at an angleprovide surface modelling to promotesound diffusion

full length drapeson two sides used

to vary acousticresponse

thick pile carpeton the floor

dimensional rationot whole numbers

wall at an angle to avoidflutter echoes and standingwaves

drapes can be used to varyacoustic response

small window tominimise disturbance

from external noise

thin pile carpet onthe floor

72

5.5.4 Ensemble roomsFigure 5.11 shows a plan of a 25 m2

ensemble room. In terms of shape, thesame rules apply as for larger musicspaces. Ceilings should be high, of theorder of 3 m or more. Surface finishesmay comprise carpet on the floor, asuspended plasterboard ceiling to providethe necessary bass absorption, and amixture of hard and soft wall finishes toprovide the required RT. An acousticdrape along one wall can provide a degreeof acoustic variability.

5.5.5 Control rooms for recordingControl rooms for recording haveassumed a much greater significance dueto the need to prepare tapes ofcompositions for GCSE assessment.Figure 5.12 shows an 11 m2 controlroom for recording. A teacher or pupilcan record a music performance takingplace in an adjacent space after which therecording may be heard on headphonesor loudspeakers. The RT specified inTable 1.5 is < 0.5 s.

Notable aspects of the acoustictreatment are as follows:• Sound absorbing panels on the walls behind the monitor loudspeakers are used to control strong early soundreflections which could distortloudspeaker sound.• Shelving units on the window wall provide surface diffusion.• Drapes are fitted on all threeobservation windows. If a curtain is pulled across one window, problems of flutter echoes and prominent resonances associated with two facing hard parallel surfaces are reduced. Ideally, the effect can be avoided by installing glazing in one of each pair of windows at 5° off parallel. Drapes also provide additional privacy.• The external window is small to minimise disturbance from external noise.A venetian blind can be used to controlsunlight, or a blackout blind may beprovided if required. • The floor is carpeted.• Figure 5.6 shows a detail of a typical

Figure 5.11: Acoustictreatment to 25 m2

ensemble room

Full length drape to vary acoustic response


ENSEMBLE ROOM25 m2

73

control room window. Two panes of heavy plate glass (of different thicknessesto avoid the same resonances) areseparated by an air gap of about 100-200 mm. Such a large gap may notalways be possible but 50 mm should beconsidered a minimum. Each pane ofglass is mounted into a separate frame toavoid a direct sound path. The glass ismounted in a neoprene gasket to isolate itfrom the wooden frame. Acousticallyabsorbent material, such as mineral woolor melamine foam, is incorporated intothe reveal to absorb any energy thatenters the air gap.

5.5.6 Recording studiosA recording studio as such rarely exists ina school. The control room for recordingmay have an observation window onto anordinary ensemble room orprofessional/recital room. A professionaltype recording studio would require alower indoor ambient noise level thanthat given in Table 1.1, and specialistadvice should be sought.

5.5.7 Audio equipmentThe design and selection of recordingequipment and audio systems is a fast-evolving subject and guidance on specifictechnologies would be rapidly out ofdate. Although members of staff within aschool will have their own preferences forspecific items of equipment, these may be

based on experience of only a few systemsand alternatives should at least beconsidered. Advice from an independentdesigner or consultant familiar with thefull range of available equipment shouldbe sought.

5.6 Acoustic design of large hallsfor music performanceLarge halls designed primarily for musicare rare in schools, where the main use ofany large hall is likely to be for assembliesand other speech-related uses. Assemblyhalls, theatres and multi-purpose halls arediscussed in Section 4. If a purpose-builtconcert hall is required a specialistacoustics designer should always beconsulted early in the project, but thissection sets out some general principleswhich can be considered at the conceptstage.

5.6.1 Shape and sizeKey acoustic requirements are sufficientvolume to provide adequate reverberationand a shape that will provide a uniformsound field with strong reflections off theside walls. A rule of thumb is that thevolume of a concert hall should be at least8 m3 per member of audience, which istypically twice that for a theatre orcinema. In most cases this will lead to arectangular floor plan with a relativelyhigh ceiling. Other shapes, such as theelongated hexagon or asymmetrical

Figure 5.12: Acoustictreatment torecording/control room


half length drapes canbe pulled acrosswindow to increaseabsorbency

sound absorbing panelsbehind speakers

small window tominimise

disturbance fromexternal noise

solid core door withsmall vision panel door frame detail

important

floor carpeted

all observation windows detailedfor good acoustic insulation

74

shapes, can work well but require veryadvanced acoustic design. Fan-shapedhalls generally do not provide the lateralreflections beneficial to listening to music.

Balconies and side-wall boxes orgalleries may be used although they tendto reduce the volume of the hall for agiven audience size. Any overhangs mustbe kept small to allow reasonable soundto seats under the balcony. Figure 5.13indicates the recommended proportionsof an overhang so that good acousticconditions are maintained beneath theoverhang. Balcony, gallery and box frontscan be used to break up large areas of flatwall and provide essential diffusion,especially on parallel side walls whereflutter echoes may otherwise occur.

Ceilings can be flat with some surfacemodelling, or can be more complexshapes to direct sound towards theaudience. A steeply pitched ceiling(around 45° assuming the ridge runsalong the length of the auditorium) canalso be good. Shallow pitches can cause‘flutter’ echoes between a flat floor andthe ceiling, see Case Study 7.1.

Shapes with concave surfaces, such asdomes and barrel vaults, cause focusing ofsound which can result in problematicacoustics and these are best avoided.Where concave surfaces are unavoidableand cause a focus near the audience theyshould be treated with absorbent ordiffusing finishes.

If seating is on a rake, this should notbe too steep as musicians find it difficultperforming into a highly absorbentaudience block - in effect, they receivevery little feedback. Generally, rakes

which provide adequate sightlines willgive satisfactory acoustic conditions. Thisrake will generally be less than in atheatre or cinema.

The size and shape of the concertplatform is of great importance. A full 90-piece symphony orchestra requires a stageat least 12 x 10 m, with allowance forchoir risers behind. The front of theplatform will not generally be as high as atheatre stage and may be only 400 mmabove stalls floor level, but orchestralplayers will require risers or rostra so thatplayers at the rear of the platform can seethe conductor. Surfaces around the stageshould be acoustically reflective andshould be designed to provide somereflected sound back to the players, sothat they can hear themselves and eachother, as well as directing some soundtowards the audience. This designrequires computer or physical scalemodelling by a specialist acoustician.

5.6.2 Surface FinishesUnlike in theatres and assembly halls, thesurface finishes in a concert hall with thecorrect volume will generally beacoustically reflective, for exampleplastered or fair-faced brick or blockwork.Large areas of flat lightweight panelling,such as wood or plasterboard, tend to beabsorbent at low frequencies, whichresults in inadequate reverberation atthese frequencies. The result tends to be alack of ‘warmth’ or ‘bass response’ and isa common problem in many halls. Woodpanelling, if used, must be very heavy orstiff. Curved wooden panels are oftenused as acoustic reflectors because theircurvature gives added stiffness, reducestheir inherent panel absorption andprovides acoustic diffusion.

In most performance venues theseating and the audience provide themajority of the absorption and, therefore,constitute a controlling factor in theroom acoustic conditions. The selectionof seats and, particularly, the relativeabsorption of occupied and unoccupiedseats is of great importance. In general, itis helpful if the room acoustics arerelatively unaffected by the number ofoccupants. This, however, tends to mean

H

D

Figure 5.13:Recommended balconyoverhang proportionswhere the depth D shouldnot exeed the height H.


75

that seating must be very absorptive andprobably not a preferred type for schooluse. A seat which is moderatelyupholstered on the seat and back is likelyto be a good compromise. Where tip-upseats are provided they should beupholstered underneath as well as on theseat; otherwise acoustic conditions will bevery different during rehearsal andperformance. Most auditorium seatingmanufacturers supply acoustic test data.Where there is no fixed seating, largeareas of acoustic drapes or other operableacoustic absorption can be used to reducereverberation in rehearsal conditions whenthe seats are removed.

5.7 Design of large auditoria formusic and speechTable 5.1 lists the general acousticcharacteristics that are required for amulti-purpose auditorium.

There are four commonly consideredapproaches to designing these spaces:

1. To design a concert hall with a largevolume (≈10 m3 per seat), and to reducethe volume of the auditorium whenneeded for speech. This approach isrecommended when the overwhelmingrequirement is for a good musicalacoustic, with a relatively small proportion

of theatre or other speech use. Unless thevolume can be reduced substantially, thisapproach requires large amounts ofabsorbent material to be deployed, whichin turn can reduce loudness to the extentat which a speech reinforcement system isneeded. Nearly all auditoria adopting thisapproach depend on high-quality speechreinforcement systems, which are difficultto design in a reverberant hall.

2. To design a small volume (not morethan 6 m3 per seat) with acoustics suitablefor a theatre, with additional reverberantvolumes accessed by openable flaps ormoveable ceilings. As the volume needs tobe increased by up to 80%, withreasonably even distribution of absorption,this is often impracticable. In the few caseswhere this approach has been tried, theresults have been poor because it isdifficult to provide openings large enoughto be transparent to the long wavelengthsof low frequency sound.

3. To design to a compromise volume andRT, often with curtains or other moveableacoustic material to provide some variationin RT. The result tends to be anauditorium which is acceptable for a rangeof uses, but not particularly good for anyof them - especially music. Very large areas

Low ambient noise levels

Even distribution of sound

Lack of acoustic defects

Loudness or acoustic efficiency

Good direct sound

Good early reflections

Feedback to performers

Low noise levels from plant, ventilation, lighting and stage machinery arerequired. Noise from outside the auditorium should ideally be imperceptible.

The acoustic should not change significantly from one seat to another.

There should be no echoes or focusing effects.

The sound level reaching the listener should be as high as possible withoutcompromising other requirements.

The sightlines to the source should not be impeded and distances should beas short as possible.

Reflecting surfaces around and close to the stage, and reflections off theside walls and off the ceiling are required.

Some sound from the stage should be reflected back to the source. Thisgives confidence to the performers and helps with musical ensemble.

Table 5.1: Acousticcharacteristics for a multi-purpose auditorium


of curtain are required to have anysignificant effect in a large hall, and thesewill have relatively little effect at lowfrequencies, resulting in a room that iseither ‘boomy’ for speech or ‘dead’ formusic.

4. To design a small volume (≈6 m3 perseat) with acoustics suitable for a theatre,with an electro-acoustic enhancementsystem to introduce more reflected sound.These systems were originally designed toenhance the acoustics of naturally poorauditoria, but their success has recentlyled to their being built in to newauditoria where a wide range of acousticconditions is required. The best systemsprovide good acoustics over a wider rangeof uses than would otherwise be possible,without the audience (or musicians) beingaware that the sound that they hear is notdue to the ‘real’ acoustic of theauditorium. These systems are seen asacoustically very advanced and are notcommonly used in schools, but present aviable option where a large hall is to beused for both speech and music on aregular basis. These systems requireloudspeakers in the auditorium side wallsand ceilings, and should not be confusedwith the sound reinforcement system forspeech (in this case a central cluster ofloudspeakers over the forestage),although some electro-acousticenhancement systems can also be used forspeech reinforcement.

References[1] Building Bulletin 86, Music Accommodationin Secondary Schools. DfEE, 1977. ISBN 0 11 271002 6. [2] J Miller, Design standards for the soundinsulation of music practice rooms. AcousticsBulletin 18(6), Institute of Acoustics, 1993.

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Acoustic design and equipment for pupils withspecial hearing requirements

77

6.1 Children with listeningdifficultiesA recent survey by the British Associationof Teachers of the Deaf (BATOD)[1]

showed that about 75% of deaf childrenwere being educated within mainstreamschools. With the continuing trendtowards inclusive education there is noreason to suppose that this proportionshould do anything but increase.

In addition to the children withpermanent hearing impairments there arelarge numbers of children withinmainstream schools who have listeningdifficulties placing them in need offavourable acoustic conditions. Theseinclude children:• with speech and language difficulties • whose first language is not English • with visual impairments • with fluctuating conductive deafness • with attention deficit hyperactivity disorders (ADHD) • with central auditory processing difficulties.

Effort given to addressing the acousticneeds of the hearing impaired populationalso favours other groups whose needs forgood acoustic conditions are not dealt withelsewhere in this document. Put together,the number of children falling into one ormore of these categories couldconceivably be a significant proportionwithin every mainstream classroom.

6.2 Children with hearingimpairments and the acousticenvironmentThe majority of children with hearingimpairments use speech and hearing astheir main form of communication. TheBATOD survey[1] indicated that 67% ofchildren with hearing impairments wereusing an auditory-oral approach and a

further 26% used an approach whichcombined sign with auditory-oralcomponents. For these groups a pooracoustic environment can be a significantbarrier to inclusion.

A hearing loss is typically describedwith reference to the audiogram. This is agraphical representation of an individual’sthreshold of hearing for a number of puretones (typically measured at 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz and 8 kHz) and presented to each ear usingheadphones. At face value, it suggests thatthe hearing impairment can be consideredas a simple auditory filter and as suchshould predict a child’s understanding ofspeech using traditional acoustic models.Although reliable, it says little about anindividual’s hearing for speech or the keyskill of listening to speech withbackground noise. The audiogram is not agood predictor of educational outcome[2]

and only a poor predictor of maximumspeech recognition score[3]. Consequently,great care should be taken whenconsidering the audiogram of a child as apredictor of the difficulties the childmight have in a school environment.

At present there is little empirical datathat specifically addresses the acousticcriteria required for the hearing impairedschool population (see for example thereview of the literature by Picard andBradley[4]). What is currently available,however, suggests that the individualhearing needs of the hearing impairedchild are likely to be more demandingthan those of children with normalhearing. It would be helpful for theprofessional specifying classroom acousticsfor a particular child to have availablemeasures of the child’s aided hearing andconsequent acoustic requirements interms of, for example, acceptable levels of

When considering classroom acoustics, children with a permanent hearingimpairment have traditionally been treated as a special group, separate fromthe mainstream school population. This is a situation that is not supported bythe surveys of the school population carried out by the British Association of

Teachers of the Deaf.

6

SE

CT

ION

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6.3 Hearing impairment andhearing aidsModern hearing aids are designed to makespeech audible to the listener without beinguncomfortably loud[7]. They deal largelywith the issue of audibility and are less ableto address the issues of distortion thattypically accompany a sensorineural hearingimpairment.

One of the major challenges in thedesign of hearing aids is dealing with noise.Recent developments include the use ofalgorithms that attempt to enhance speechwhilst reducing background noise, andbetter implementation of directionalmicrophones. However, noise will continueto remain a significant obstacle to effectivelistening. Noise not only masks theamplified speech signal but also leaves achild tired from the effort required to listen.It is therefore essential that attention begiven to creating a quiet classroom.

Sound insulation must be of a highstandard, with the lowest background noiselevels possible to ensure that a good signalto noise level is achieved. Typically a signalto noise level of +20 dB is considereddesirable[5]. Short reverberation times arealso critical in ensuring that sound does notbuild up when the class are working ingroups. Care must also be taken to ensurethat the level of low frequency noise is keptto a minimum. For many people withimpaired hearing, low frequency noise canhave a devastating impact on speechrecognition, masking many importantspeech sounds in a manner that cannot beappreciated by those with normal hearing.

6.4 The speech signal and hearing aidsSpeech, as a signal, is a critical factor inclassroom listening and an importantspeech source is the teacher. Evidence hasshown that teachers’ voices are not alwayssufficiently powerful to deliver thenecessary levels of speech required toensure the best listening opportunities[8].A growing body of evidence suggests thatteachers are at above average risk fromvoice damage[9]. Few teachers have voicetraining and the vocal demands ofteaching are probably underestimated.

Hearing aids are usually set up toamplify a ‘typical’ speech signal based onvarious measures of the long-term averagespeech spectrum recorded either at theear of the speaker or at a distance of 1 mdirectly in front of the average speaker, asif in conversation. If the actual speechsignal is weaker than average, perhaps

Acoustic Parameter

Unoccupied noise level

Reverberation time(unoccupied)

Signal to noise level

British Association ofTeachers of the Deaf[5]

35 dB(A)

0.4 s across frequency range125 Hz to 4 kHz

+20 dB across frequencyrange 125 Hz to 750 Hz+15 dB across frequencyrange 750 Hz to 4 kHz

American Speech LanguageHearing Association[6]

30 – 35 dB(A)

0.4 s

≥ +15 dB

Acoustic design and equipment for pupils with special hearing requirements

Table 6.1:Recommendations ofBATOD and ASHA for theacoustics of classrooms

noise, desirable reverberation times andrequired signal to noise levels. However,such hearing measures are not routinelyobtained.

Because it is not possible at present toprovide definitive acoustic requirementsfor hearing impaired individuals, it isappropriate for acousticians and architectsto be aware of the requirements publishedby specialist professional organisations.These include the British Association ofTeachers of the Deaf[5] and the AmericanSpeech Language Hearing Association[6]

(see Table 6.1). Account has been takenof these recommendations in the settingof performance criteria in Section 1.

6

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because of distance, or is masked bybabble or steady state background noisesuch as that from a classroom computerfan, then the hearing impaired listenerwill have increased difficulty. Listening tospeech will become particularly effortfuland challenging[10].

Children are not only required to listento the teacher but also to other children.Children typically have less powerfulspeaking voices[8] and listening to theirpeers is frequently identified by childrenwith hearing impairments as beingdifficult. One study suggests that 38% ofa child’s time in the classroom might bespent working in groups and 31% of theremaining time spent in mat work[11],both situations where listening to otherchildren is important. There are nowholly satisfactory solutions to this.Technology and careful class managementhave a role to play but considerableattention needs to be paid to establishinglow reverberation times and maintaininglow ambient noise levels in order toreduce the auditory difficulties.

To minimise the challenges to hearing,use is often made of small acousticallytreated rooms attached to mainstreamclassrooms in the primary school. Theserooms are typically large enough for agroup of four to eight children to workin. To allow supervision by the classteacher they will have a large window toallow a clear view into the classroom. Theroom will need to have a sufficient degreeof sound insulation from the classroom toallow the children to talk to each otherwithout being disturbed or disturbing therest of the class. The favourable acousticconditions and short distances betweenchildren and teacher, if present, ensurethat communication is as easy as possible.

6.5 Listening demands within theclassroomMuch of educational activity withinclassrooms revolves around speech. Someexperts claim that 80% of all classroomactivities require listening and speaking. Itis important that within any room theacoustic characteristics allow for effectivespoken language communication. TheUK version of the Listening Inventories

for Education[12] identifies the followinglistening demands within the classroom:• listening to the teacher when s/he isfacing away from the listener• listening when the class is engaged in activities• listening to the teacher while s/he is moving around the classroom• listening when other children are answering questions• listening when other adults are talking within the same room• listening to peers when working in groups• listening in situations with competing background noise from multimedia equipment.

A teacher should manage teaching insuch a way as to ameliorate the challengesfaced by a student with hearingdifficulties. However, the better theacoustic conditions, the less challengingwill be the situations described above.

6.6 Strategies developed to assistchildren with hearing and listeningdifficultiesEffective classroom management by theteacher is critical in ensuring that thechildren can have access to all that isspoken and there are many guidelinesavailable for teachers (see for examplepublications by the Royal NationalInstitute for the Deaf[13], the NationalDeaf Children’s Society[14] andDfES[15]). Classroom management alone,however, cannot ensure that speechcommunication is sufficiently audible andintelligible if the classroom acoustics arenot adequate, or if a child has a hearing orlistening difficulty.

In order to ensure that children areable to hear the teacher and, to a lesserextent, their peers, a number oftechnological solutions have beendeveloped, see Table 6.2. These solutionsthat work in tandem with the child’s ownhearing aids (if used) can be classified aseither individual technology or whole classtechnology. In both these cases it isimportant to understand the underlyingprinciples when specifying classroomacoustics.

6Acoustic design and equipment for pupils with special hearing requirements

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6.7 Individual technologyThere are two main types of aid that canbe used to assist children’s hearing on anindividual basis: radio aids that can becoupled to a child’s hearing aids, andauditory trainers that are used withheadphones.

6.7.1 Radio Aids Radio aids (also known as radio hearingaids or personal FM systems) are widelyused by children with hearing impairmentsin schools. They help overcome causes ofdifficulty in a classroom situation by:• providing a good signal to noise ratio

• reducing the impact of unhelpful reverberation• effectively maintaining a constantdistance between the speaker and thelistener.

All radio aids have two maincomponents: a transmitter and a receiver.The person who is speaking (usually theteacher) wears the transmitter. Amicrophone picks up their voice. Typicallythe microphone is omnidirectional and isattached to the lapel of the speaker,however there are head wornmicrophones available that help ensure aconsistent transmitted signal to the child.

6 Acoustic design and equipment for pupils with special hearing requirements

Technology

Personal radio aids

Classroom soundfieldsystems

Personal soundfieldamplification

Auditory trainers and hard-wired systems

Induction loop systems

Advantages

Reduce the effect of the distance betweenspeaker and listenerPortable and convenientParticularly useful in situations where there isa poor signal to noise ratio at the position ofthe listener

Reduce the effect of the distance betweenthe speaker and listenerInclusive technologyBenefit to the teacher and the classCan ensure good signal to noise levels aremaintained throughout the classroom

PortableAddresses the issue of speaker to listenerdistanceCan ensure favourable signal to noise levelsfor a particular listener or small group oflisteners

Provide excellent signal to noise levelsProvide a high level of sound insulationCan be arranged to allow group work

Discreet and cheapMost hearing aids have a telecoil facility

Disadvantages

Do not address the needs of group workdirectlyCan require a high level of sophistication togain maximum benefitBenefits can be lost if the child’s personalhearing aid microphones are used in noisyenvironments

Do not address the needs of group workdirectlyPoor classroom acoustics (eg highreverberation times or poor sound separationbetween neighbouring teaching areas) canlimit the benefit of this technology

Can be cumbersome to transport andmanageDoes not address the needs of group workdirectly

Users are restricted in movement when usingthe deviceCan be heavy and uncomfortable to useNot an inclusive technology

Unpredictable acoustic response for thehearing aid userSpill over of signal into other roomsDo not deal with the needs of group workSusceptible to electromagnetic interferenceUser normally isolated from environmentalsounds

Table 6.2: Advantagesand disadvantages ofdifferent technologies foraiding hearing and listeningin the classroom

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The sounds are transmitted by an FMradio signal to the receiver, which is wornby the child. The receiver converts thesignal to a sound that the child can hear.

Radio aids are usually used inconjunction with the child's hearing aids.Most children use ‘direct input’ (alsoknown as ‘direct connection’ or ‘audioinput’) to the hearing aids using a lead.Direct input is a facility available on manybehind-the-ear (post-aural) hearing aidsand a smaller number of in-the-earhearing aids.

Alternatively, the child can use aninductive neck loop - a small wire loopthat can be worn over or under clothes.The loop is connected to a radio aidreceiver usually worn around the waist orattached to a belt.

Direct input is generally recommendedas preferable to the use of a neck loop forchildren in school. This is because thelevel of sound that a child hears using aneck loop can be variable and there is arisk of electromagnetic interference fromnearby electrical equipment.

Radio aids are also beneficial forchildren who have cochlear implants.The radio aid receiver is connected to thechild's implant processor using adedicated lead.

Traditionally, radio aid receivers havebeen worn in a chest harness or on a belt.Recent developments include miniatureradio aid receivers that connect directly toa hearing aid and are worn entirelybehind-the-ear. Behind-the-ear hearingaids that include built-in radio aidreceivers are also being manufactured.

Most radio aids can be set up so thatthe child will not only hear the voice ofthe speaker using the transmitter, but alsoenvironmental sounds such as their ownvoice and the voices of other childrennear to them. Radio aids can do this in anumber of different ways and it is oftennecessary to strike a balance betweenallowing the child to hear the voices he orshe needs to listen to and the impact ofhearing unwanted background noise.

For the best listening condition thehearing aid user will normally be requiredto mute his or her microphone on thehearing aid and listen exclusively to the

transmitted voice of the speaker. This isgood for formal teaching situations butrequires considerable skill on the part ofthe teacher to include the hearingimpaired child in classroom discussion.This solution is less helpful for childrenengaged in group activity, where the childwill need to work with a small group ofpeers.

Most radio aids are able to operate on arange of carrier frequencies. For example,each school class might have its ownfrequency so that there is no interferencewith a neighbouring class. In the UK,radio aid channels lie in the range173.350 MHz to 177.150 MHz. Thosechannels in the range 173.350 MHz to173.640 MHz are dedicated exclusively touse by radio aids. A licence is required touse radio aids operating on frequenciesbetween 175.100 MHz and 177.150MHz.

The sounds heard by a child using aradio aid will depend on the quality andcorrect use of their own hearing aids. Thelevel of amplification is determined by thesettings of the hearing aids, not the radioaid. Accepted procedures exist for settingup a radio aid to work with hearing aids(a process sometimes known as‘balancing’).

A general principle is that if a child usesa hearing aid, then the child is also likelyto find a radio aid helpful in manyclassroom situations.

Radio aids have often been seen as thesolution to poor acoustics in theclassroom. However, it must be notedthat they only partially solve the problem;the solution must lie in addressing theissue from three directions:• the class teacher and classroom management style• technology that assists listening • careful attention to classroom acoustics.

Current information about radio aids isavailable from a number of sourcesincluding the National Deaf Children’sSociety[16].

6.7.2 Auditory trainers and hard-wired systems An auditory trainer is a powerful amplifierused with high-quality headphones. As a


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large, stand-alone piece of equipment, anauditory trainer can be designed withoutthe restrictions of size that exist withtypical behind-the-ear hearing aids, and agood quality high level sound output withextended low and high frequency rangecan be achieved.

Within the mainstream educationalenvironment, auditory trainers are mostlikely to be used for short periods ofindividual work and speech therapysessions. However, it is also possible tolink several auditory trainers together forgroup work. In some schools for deafchildren this equipment is permanentlyinstalled within a classroom. The teacher’svoice is picked up by a microphone andthe output is available at every desk. Eachchild wears headphones that are configuredto meet their individual amplificationrequirements. The children may also wearmicrophones to enable everyone in theclass to participate in discussions.

6.8 Whole class technology The use of a personal system is sometimesessential for a hearing aid user to be ableto succeed in a particular environment.

There is, however, a trend to use theinclusive technology termed ‘sound fieldamplification’ to ensure that the signallevel of the speech is delivered to all partsof the classroom at an appropriate levelabove the background noise. Thistechnology is of benefit for all withlistening difficulties in the classroom, notjust the hearing aid user, and has particularbenefits for classroom management andthe voice of the class teacher.

It is important to note that whole classtechnology is not a substitute forremedying poor classroom acoustics.However, it can be particularly valuable inmaintaining good signal to noise levelsand improving classroom management.Soundfield amplification systems are alsoused in conjunction with personal radioaids. In situations where a deaf child ispart of a mainstream class, advice shouldbe sought from members of a relevantprofessional group (educationalaudiologist, clinical audiologist or teacherof the deaf) as to the most appropriatetechnology.

6.8.1 Whole classroom soundfieldsystems Soundfield systems provide distributedsound throughout a classroom. They usea wireless link between the microphoneand amplifier which will operate on VHF,UHF radio or infra red frequencies.Soundfield systems have been shown tobe beneficial for hearing children andchildren with a mild or temporary hearingloss. They will not by themselves usuallyprovide sufficient improvement in signal-to-noise ratio for a child with a significanthearing loss, when a personal radio aid isalso usually necessary.

A soundfield system is perhaps morewidely known as a sound reinforcementsystem; the term ‘soundfield’ systemoriginated from the field of Audiologyand continues to be associated withclassroom sound reinforcement systems.The technology has matured since it wasfirst introduced into classrooms in the late1970s in the USA, and has evolved totake into account new technologies andteaching management styles. Its benefitshave been variously described as:

Figure 6.1: A simpleschematic drawing of asoundfield system in atypical classroom

Teacher radio microphonesystem

Optionalstudent (shared) system

Headwornmicrophone

Radiomicrophonetransmitter Handheld radio microphone

Optionalpersonal FM receiver(s)

Antenna 1 Antenna 2 Optional secondreceiver

Personal FMtransmitter

MIXER/AMPLIFIEROptional

Musicor

AV playerLoudspeakersconnectedas required

Radio microphonereceiver

Radio microphonereceiver

Notes:1. Main system shown in blue.2. Optional handheld transmitter can share receiver with teacher transmitter. Transmitters must be switched on and off as required.3. Alternative second receiver allows simultaneous use of teacherand student transmitters.4. Personal FM transmitter(s) for use by pupils with serious hearingimpairment can be connected to output of system.5. CD, cassette and/or video player can optionally play throughthe system.


• academic improvements for all class members• more on task behaviour• greater attentiveness• improved understanding of instructions• less repetition required from the teacher• improved measures of speech recognition• reduced voice strain and vocal fatigue for the teacher.

6.8.2 System overviewFigure 6.1 shows a simplified blockdiagram of a typical soundfield system.Each element shown can be a separateunit, or some of these can be combinedinto an integrated unit. The current trendis for manufacturers to create moreintegrated products, designed especiallyfor classroom soundfield use. Typicalarrangements of loudspeakers are shownin Figure 6.2.

Table 6.3 describes the various

components of a soundfield system. Apossible detailed specification is includedin Appendix 9.

Where a soundfield system has notbeen designed specifically for theclassroom it should be used for a trialperiod before being selected from therange available. The manufacturers andresellers should all provide installationinformation including commissioning ofinstallations, operating instructions andongoing support. Large rooms or roomsthat are unusually shaped will usuallyneed specialist advice. Teachers mustreceive adequate training in using thesystems.

6.8.3 Personal soundfield systems A child who cannot physically wear aconventional hearing aid, who has aunilateral hearing loss, or has CentralAuditory Processing Disorder or

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1

2

3

4

Figure 6.2: A plan of aclassroom showing fouralternative speaker layouts.The speakers are drawnhorn-shaped to show thedirectionality of the speakeroutput, although manymodern speakers are flat

1 Speakers mounted one quarter of wall length fromcorners, mounted flush with wall, at 2 m height, directedto point on floor at angle of about 60°.2 Speakers mounted at centre of room, 600 mm apart insquare orientation, directed to the room corners.3 Speakers mounted flush with ceiling, facing directly atfloor, in centres of 4 quadrants of the ceiling.4 Speakers mounted in room corners, directed to centreof room.

The four speaker layouts were investigated using acomputer model to predict the interference effects due tophase changes of the speaker outputs.

Layout 1 causes some peaks in the room, but is likely towork reasonably well.

Layout 2 produces large interference effects and istherefore not recommended.

Layout 3 produces the most even coverage at allfrequencies and the least loudspeaker interaction. It istherefore recommended for all rooms where a suspendedceiling exists. Loudspeakers should be selected to providea wide and even coverage that is constant with frequency.

Layout 4 provides relatively even coverage of the roomwith interference effects which, although complex, appearrelatively benign. Location of loudspeakers in room cornerstends to produce a rise in the bass response of systems,which will usually require equalisation using system controlsto produce optimum speech clarity and naturalness.

Layouts 1 and 4 using wall mounted loudspeakers arerecommended where ceiling mounted units are notpractical. For layout 1 speakers should be mounted atleast 1 m from the side wall. Location of wall mountedspeakers at least 2 m above the floor, and at least 600mm below the ceiling is recommended. Brackets shouldkeep the loudspeakers very close to the wall to minimiseself-interference effects.

Attention Deficit Disorder, might use aportable soundfield system. Personalsoundfield systems comprise a radiotransmitter and microphone worn by theteacher and a small, portable unit for thechild. The portable unit includes an FMreceiver, amplifier and loudspeaker and isdesigned to be carried around school bythe child and placed on the desk next to

them. The sound of the teacher's voice isamplified and played through theloudspeaker.

6.8.4 Infra red technologyInfra red technology has been availablefor many years with little market presence.However, this technology has recentlyundergone considerable development and

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Component

Loudspeaker Wall mounted, ceilingmounted and flat panelspeakers are used inschools.

Microphone andtransmitterUsing Infra red, UHF orVHF carrier frequenciesand high qualityheadworn or lapelmicrophones. Radiosystem information isavailable atwww.radio.gov.uk

ReceiverMatched to theTransmitter

Amplifier

Requirements

The purpose should be to provide high qualitydistributed sound reinforcement throughout thewhole classroom and over the whole speechfrequency range. Selection of appropriatespeakers should therefore address thisrequirement.

This should be a high quality system whichretains both the frequency and dynamicproperties of speech. It is important thatteaching styles can be accommodated so achoice of microphones should be available. It is important that the transmitter can operatewithout interference from other systems orfrom public services.

Will provide a complementary system to thetransmitter, avoiding interference or frequencydropout.

The amplifier should be correctly matched tothe loudspeaker system. It should offer a wideflat frequency response which can be adjustedif necessary. It should allow for additionalinputs from multimedia within the classroom,such as the TV, computer and radio andoutputs to radio systems.

Comments

Often the location of loudspeakers isdetermined by the necessity to fit in with thecurrent use of the classroom, when notinstalled as part of the original building work.

In order to retain good dynamic range acompander system is typically required (seeFigure 6.3). A head worn microphone canimprove the consistency of the transmittedsignal and help to prevent feedback that ispresent in systems that do not have feedbackcontrol technology. However teachers oftenlike a choice of microphone and will useheadworn, lapel or wrap around microphonesdepending on activity and personalpreference. Battery life of at least one schoolday is essential for a transmitter if it is to beacceptable for school use.

A compander technology and diversity systemis particularly suitable for classroom use,ensuring good dynamic range and avoidingfrequency dropout respectively. Some teaching situations require twin channelinputs, so that a pass around radiomicrophone can be used.Where infra red systems are being usedseparate additional receivers might benecessary to avoid ‘blind spots’.

Some schools might require an additionaloutput facility for use by deaf children withpersonal FM systems.The amplifier is usually combined with thereceiver unit.

Table 6.3: Componentsof a soundfield system


85


Technology

Infra redFrequency range2.3–2.5 MHz

Radio VHF narrowband173.35–177.15 MHz

Radio UHF wideband790–865 MHz

Advantages

Physically limited to enclosed room Allows equipment to be shared between roomsWideband transmissionCan be used with personal hearing aids using a neckloop (an induction loop worn round the neck)

Reserved frequency bands for use in schoolsMany frequency bands availableEquipment compatible across manufacturers

Can allow a higher quality signal than narrow bandequipmentMany frequency bands available, although a site licencemight be required

Disadvantages

Occasionally needs extra IR receivers ina room

Poor signal quality when compared towideband

Not available for personal FM equipment

Table 6.4: Advantagesand disadvantages of infrared and radio technologies

CompressorMicrophonepre-amplifier FM transmitter

Radiolink FM receiver

ExpanderPower

amplifierA B

C D

Overload point of microphone & pre-amplifier

Electronic noise floor

Receiver noise floor

Signal/noiseratio @ A

Signal/noise @

Signal/noise@ DB C

Compressor action Expander action

Maximum transmittermodulation

Overload point of receiver output

SignalAmplitude

&

Radio MicrophoneTransmitter Unit

Radio MicrophoneReceiver Unit

Figure 6.3: FM RadioMicrophone System

is available to be used with many of thetechnologies identified within this section.

One of the major developments is theuse of the 2.3 MHz and 2.5 MHzfrequencies, allowing greater resistance tointerference from fluorescent lighting andsunlight.

Table 6.4 compares the advantages anddisadvantages of infra red and radiotechnologies.

6.8.5 Induction loop systems Induction loop systems take advantage ofthe telecoil facility available with mosthearing aids and cochlear implants. Atelecoil is a small receiver capable ofpicking up audio frequency,electromagnetic signals. It is usuallyactivated by setting a switch on thehearing aid to the "T" position. Aninduction loop system comprises a soundinput (usually a microphone), an amplifierand a loop of cable which is run aroundthe area in which the system is to be used.The loop generates an electromagneticfield which is picked up by the telecoil inthe hearing aid. The hearing aid user willhear the sound while they are within thelooped area.

Induction loop systems have manyapplications, from large-scale installationsin theatres and cinemas to small, domesticproducts used to listen to the television.In the UK they are now rarely used in aclassroom setting. Alternatives such asradio aids offer improved and moreconsistent sound quality and are lesssusceptible to interference. Inductionloop systems can also be difficult to use inmultiple applications, as the signal fromone area can overspill into another.

In schools, induction loop or infra redhearing aid systems should be consideredin large assembly rooms or halls. This isprimarily for visitors to the school ratherthan for deaf pupils themselves, whowould normally have their own assistivelistening equipment. They should also beconsidered in performance spaces,meeting rooms and at reception areadesks. In such situations the output froman existing PA system is often connecteddirectly to the loop amplifier.

Pay phones in schools should have

86


EXPLANATION OF TECHNICAL TERMS

Matching Loudspeakers and AmplifierAudio power amplifiers for sound reinforcement are made with two main typesof outputs described as ‘low impedance’ and ‘100 V’ or ‘high impedance’.Similarly loudspeakers come in 4 or 8 ohms (low impedance) or 70 V or 100 V(high impedance).

Low impedance amplifiers and loudspeakersIf an amplifier is rated for 2, 4, 8 or 16 ohms, then it is a low impedance type.Care must be taken to ensure that the loudspeakers add up to a total load thatis both within the amplifier's power rating (W or watts), and between itsmaximum and minimum load impedance range. Low impedance speakers,usually rated at 8 ohms for smaller types, have to be connected in a way thatcreates a total load within the range the amplifier is designed for. Highimpedance, 100 V or 70 V loudspeakers cannot be used satisfactorily. Theadvantage of low impedance systems is optimum audio performance, especiallyat low frequencies. Hi-fi loudspeakers are usually low impedance.

4-16 Ohm outputpower amplifier

R8 Ohms, 5 W

R8 Ohms, 5 W

R8 Ohms, 5 W

R8 Ohms, 5 W

Two loudspeakerswired in series= 16 Ohms, 10 W

+

+

+

+

+

–

–

–

–

–

Two loudspeakerswired in series= 16 Ohms, 10 W

Pairs @ 16 Ohmswired in parallel= 8 Ohms againand 20 W

4 Ohms to 16 Ohmsload range,20 watts @ 16 Ohms40 watts @ 4 Ohms

Calculating the load impedance

For loudspeakers wired in series – add up the individual impedances R = R + R +.......+ R

– add up the individual power P = P + P +.......+ P

For loudspeakers wired in parallel – add up reciprocals of the individual impedance

– add up the individual power P = P + P +.......+ P

In above example R + R = 8 + 8 = 16 for each series pair = R , R

Wiring the pairs in parallel gives

1 2

total 1 2 N

1Rtotal

1R1

1R2

1R N

= + +.......+

total 1 2 N

+ = ===+

1+2 3+4

1R +R 1

116

116

216

18

1R total

Therefore R = 8total

total 1 2 N

1

2

3

4

2 3 4

1R +R

R100 V, 5 W

R100 V, 5 W

R100 V, 5 W

R100 V, 5 W

All loudspeakers wired in parallel100 V, 20 W

+

+

+

+

+

–

–

–

–

–

Calculating the load impedance

Impedance is taken care of automatically by the 100 V transformer in the system.

Total power is the sum of all devices connected.

100 V outputpower amplifier

1

2

3

4

High impedance, 70 V or 100 V amplifiers and loudspeakers

87

6Design of acoustic criteria for pupils with hearing impairments andspecial hearing requirements

inductive couplers (a form of inductionloop).

Induction loop systems should beinstalled in accordance with BritishStandard BS7594. Their advantages anddisadvantages are listed in Table 6.2.

6.8.6 Audio-visual equipmentWherever possible, classroom equipmentshould be integrated with the assistivelistening devices used by deaf children.For example, the audio output from audiovisual equipment, televisions and cassetterecorders, can be connected to radio aidor soundfield transmitters. ‘Direct input’leads are available to enable the audiooutput of computers or languagelaboratory equipment to be connecteddirectly to a child’s hearing aid.

6.8.7 Other assistive devicesThere is a wide range of other devicesthat can be used by deaf children inschool, besides those that primarily assistlistening. These include subtitled andsigned video, speech recognition softwareand text telecommunication devices, egtelephones.

For further details of these devicescontact the professional or voluntaryorganisations listed at the end of thissection. Furthermore, it is recommendedto seek advice to ensure that all publicspaces meet the needs of deaf and hard ofhearing people.

6.9 Special teaching accommodationIt is not the intention within thisdocument to address the needs of specialschools for deaf children. Specialist adviceshould always be sought from aneducational audiologist or acousticianwhen designing or modifyingaccommodation for this particularpurpose.

Many hearing impaired children attendmainstream schools with resourcefacilities, sometimes called ‘units’. Thesecontain specialised rooms that exceed theacoustic specifications for regularclassrooms. Within these rooms, childrenare able to learn the language skills thatmight not be possible in a busymainstream classroom. They are also

EXPLANATION OF TECHNICAL TERMS CONTINUED

High impedance, 70 V or 100 V amplifiers and loudspeakersIf an amplifier is rated for 70 V or 100 V, then it is a high impedanceamplifier. It will also have a power rating. High impedance loudspeakers,rated at 70 V or 100 V must be used. All loudspeakers should be either 70V or 100 V. In this case the loudspeakers are simply wired in parallel andtheir individual power requirements are added up. Thus four 100 Vloudspeakers rated at 5 W would be wired in parallel and will provide a 20W load to the amplifier. External transformers can be added to lowimpedance loudspeakers to convert them for high impedance use. Theadvantage of this method is simple wiring. PA, paging and SFSloudspeakers are usually 100 V types in the UK.

Radio Microphone System

Compander system (See Figure 6.3)FM (frequency modulated) radio links provide a signal to noise ratio that isdetermined by the modulation bandwidth of the transmitter. Widerbandwidths allow fewer channels in a band of available frequencies, soregulations limit the bandwidth to two system types described as widebandFM and narrowband FM. Even wideband provides a limited signal to noiseratio of about 65 dB from real products. This is adequate if everything isperfectly adjusted so that a user's voice hits just below the maximumpermitted signal level. However real users vary their voices, different usersshare systems AND they are often not correctly adjusted anyway. Acompander system combines a compressor on the transmitter of thesystem, and an expander on the receiver. The two are matched in theiraction so that the result on the receiver output is very close to the originalinput signal. What happens is that a larger signal range of say 90 dB iscompressed by 50% to fit into 45 dB. This allows for an improved safetymargin in the transmitter so that it does not overload, and allows a wideworking range that will tolerate user variations. At the receiver the 45 dBrange is expanded back to 90 dB. This pushes the system noise down andthe signal up. The result is a signal free from distortion due to overload andwith a much reduced background noise when a soft talker is turned up atthe receiver.

Diversity receiverA FM radio microphone system emits a signal that has a fairly longwavelength. The waves can reflect from room surfaces and arrive at thereceiver antenna in a way that causes the waves to cancel. The result is a‘dropout’ which will be heard as a disappearance of the audio from thesystem. If the dropout is maintained, for example if the user is standing stillin a location that produces a cancellation, the receiver can even hunt andlocate an alternative signal to lock onto - though this is uncommon. Adiversity receiver provides two independent radio and audio paths, includingtwo spaced antennae. The spacing minimises the risk that both antennaewill receive a cancelled signal simultaneously. The unit will automatically andinstantaneously select the stronger of the two signals to the audio output.While audio dropouts may be only slightly disturbing to a person with normalhearing, the hearing impaired child, especially one reliant upon a personalFM receiver, will get nothing and could therefore frequently lose the wholemeaning or context of a piece of verbal information. Therefore, wherepossible, diversity receivers should be used.

88


British Association of Audiological Scientists

British Association of Educational Audiologists

British Association of Teachers of the Deaf

British Society of Audiology

National Deaf Children’s Society

Royal National Institute of the Deaf

Organisations

Term

Natural-oral approach

Residual hearing

Hearing aid

Cochlear implant

Central auditory processing difficulty

Radio aid

Glossary

http://www.baas.org.uk

http://www.edaud.org.uk

http://www.batod.org.uk

http://www.b-s-a.demon.co.uk

http://www.ndcs.org.uk

http://www.rnid.org.uk

Explanation

An approach to the education of children with hearing impairments thatseeks to promote the acquisition of spoken language using residualhearing.

A term used to describe the hearing abilities that remain in the case of ahearing impairment.

A battery powered device worn by an individual, either behind the ear or inthe ear. A hearing aid will be selected and programmed to provide themaximum audibility of the speech signal consistent with an individual’sresidual hearing.

A special kind of hearing aid where the inner ear is directly stimulatedelectrically via an implanted electrode.

A broad term used to describe listening difficulties, which are not due tothe outer, middle or inner ear.

An assistive listening device, designed to provide an FM radio link betweena transmitter (usually on the speaker) and the listener (coupled directly tothe hearing aids).

places where children can interact withina favourable acoustic environment.

It is not uncommon for these rooms tobe used for ‘reverse integration’, where asmall group of children from themainstream work with the hearingimpaired children. Occasionally thisprovision may be directly attached to amainstream class in the form of a ‘quietroom’ leading from the classroom. Inother situations the accommodationmight be a separate room or evenbuilding. Teachers and supportprofessionals might also use the areas fora range of activities involved in the

audiological management of the hearingimpaired child. Case Study 7.6 describes ajunior school with a hearing impairedunit, now renamed as the RPD (ResourceProvision for the Deaf). Thecharacteristics of rooms in an RPD are:• excellent sound insulation• very short reverberation times• very low ambient noise levels• flexible space for individual and small group work• good lighting• storage facilities for audiological equipment.

89

References[1] M Eatough, Deaf Children and Teachers ofthe Deaf England, BATOD magazine, 2000.[2] S Powers, S Gregory and E D Thoutenhoofd, The EducationalAchievements of Deaf Children, DfES, 1998.[3] J M Bamford, et al., Pure tone audiogramsfrom hearing-impaired children. II. Predictingspeech-hearing from the audiogram. Br JAudiol, 15(1), 3-10, 1981.[4] M Picard and J S Bradley. Revisitingspeech interference in classrooms. Audiology, 40(5), 221-44, 2001.[5] BATOD, Classroom Acoustics -Recommended standards. 2001.[6] ASHA, Position Statement and guidelinesfor acoustics in educational settings. ASHA, 37(14), 15-19, 1995.[7] S Gatehouse and K Robinson. Speechtests as a measure of auditory processing, in Speech Audiometry, Second Edition, M Martin, (Editor) Whurr: London, 1997.[8] A Markides, Speech levels and speech-to-noise ratios. Br J Audiol, 20(2), 115-20, 1986.[9] J A Mattiske, J M Oates and K M Greenwood. Vocal problems among teachers: a review of prevalence, causes,prevention, and treatment. J Voice, 12(4), 489-99, 1998.[10] T Finitzo-Hieber and T W Tillman. Roomacoustics effects on monosyllabic word discrimination ability for normal andhearing-impaired children. J Speech Hear Res, 21(3), 440-58, 1978.[11] O Wilson et al., Classroom Acoustics,Oticon Foundation in New Zealand: Wellington,2002.[12] D Canning. Listening Inventories ForEducation U.K., in LIFE UK, City University,London, 1999.[13] RNID, Guidelines for mainstream teacherswith deaf pupils in their class. Education guidelines project, RNID, 2001.[14] National Deaf Children’s Society, DeafFriendly Schools – a Guide for Teachers andGovernors, NDCS, 2001.[15] DfES, Special Education Needs Code ofPractice, DfES/581/2001.[16] B Homer, R Vaughan and K Higgins, RadioAids, NDCS, 2001.[17] National Deaf Children’s Society, QualityStandards in Education - England, NDCS, 1999.

6Design of acoustic criteria for pupils with hearing impairments andspecial hearing requirements

6.10 Beyond the classroom As far as possible children with hearingimpairments should be included in allschool activities. Improving listeningconditions through better acoustics is avery important part of this, but not theonly relevant factor. There are manyothers such as teaching style and context,staff training, deaf awareness issues, and awhole school approach to specialeducational needs.

Classrooms are not the only placeswhere hearing impaired children interact.It is often overlooked in school design,but critical learning and interaction takesplace outside the classroom, and ifhearing impaired children are to be fullyincluded, attention should be given to allareas of the school where the childrenmight be expected to interact with others.These areas include rooms where aspectsof the curriculum are delivered: libraries,assembly areas, sports halls, music rooms,ICT suites and gymnasia. In these areasthe need for good speech communicationis essential although constrained by theactivities taking place.

Inclusion in most music activitiesrequires good acoustic conditions, goodplanning and structuring of lessons, andthe appropriate use of assistive listeningdevices.

Perhaps the most difficult areas forinclusion are large spaces such as assemblyhalls and sports halls. These areas requirecareful design and forethought.

In other areas, not used for deliveringthe curriculum, children still need to beable to interact verbally. These include thecorridors, cloakrooms, medical rooms,school office, dining room, play areas andtoilets. In these communal placesimportant social interaction often takesplace and if inclusion is to be effective,these areas need to be designed with theacoustic needs of the hearing impairedchild and the child with listeningdifficulties in mind.

91

7

SE

CT

ION

Case study 7.1 – Remedial work to a multi-purpose hall in a county primary school 93

Case study 7.2 – An investigation into the acoustic conditions in three open-plan primary schools 97

Case study 7.3 – Remedial work to an open-plan teaching area in a primary school 107

Case study 7.4 – Conversion of a design and technology space to music accommodation 113

Case study 7.5 – A purpose built music suite 117

Case study 7.6 – A junior school with resource provision for deaf children 123

Case study 7.7 – An all-age special school for hearing impaired children 129

Case study 7.8 – Acoustic design of building envelope and classrooms at a new secondary school 139

Case study 7.9 – Acoustically attenuated passive stack ventilation of an extensionto an inner city secondary school 143

Case study 7.10 – An investigation into the acoustic conditions in open-plan learning spaces in a secondary school 147

Case studies

This section contains ten case studies which illustrate some of the principles ofthe acoustic design of schools described in previous sections, and give

examples of solutions to problems of poor acoustics in schools.

Page

93

The school is situated at a considerabledistance from the main road runningthrough a large village in a quietresidential area. In the early 1990s, it wasextended by adding seven new classbasesand a new multi-purpose hall. Activities inthe hall include assemblies, singing,concerts and physical education. The hallis of particular interest because it requiredremedial measures not long after complet-ion to alleviate acoustic problems thatwere being experienced by teaching staff.

The new hall is adjacent to playingfields and background noise levels aroundthe school are low. Therefore there islittle disturbance to occupants of the hallfrom external noise.

The hall is built of conventionalmasonry cavity walls comprising 100 mmfacing brick outerleaf, 50 mm cavity, and140 mm blockwork inner leaf with aplaster finish. A plan and section of thehall are shown in Figure 7.1.1.

The roof has a hipped form and isconstructed of steel trusses with 100 mmby 50 mm softwood rafters at 600 mmcentres. It is covered with slates on

battens and felt. The shallow pitchedceiling is formed from tongue and groovetimber boards (119 mm by 19 mm),overlain with 150 mm thermallyinsulating mineral wool batts. The roofvoid increases from a height of 200 mmat the eaves to 2 m at the ridge.

Large external windows with openinglights are located in the north east andsouth east walls with a row of smaller highlevel opening lights located in the externalwall to the south west, above thecirculation corridor. The circulationcorridor connects the hall to the mainbuilding at ground floor level via glazeddoors in a glazed screen. The corridoralso provides a useful acoustic bufferbetween the hall and the nearbyclassrooms and offices. External windowsand doors are all thermally double glazed.Internal doors and the glazed screen areof 6 mm glass.

Wall bars and similar apparatus aresupported off the two long walls. Thefloor is of sprung timber strip toaccommodate physical education, dancing,etc. The hall is naturally ventilated.

Section

extent of ceiling acoustic treatment

Circulation corridorCircula

tion c

orrido

r

curtains providedover glazed doorsand windows

wall bars

Glazed screens

N

Figure 7.1.1: Plan andsection of the new hallshowing extent of remedialtreatment

Case Study 7.1: Remedial work to a multi-purpose hall in a county primary school 7.1

94

The new hall suffered from:• poor speech intelligibility, particularly with small groups of 30 or less• distortion or colouration of speech • unusually high background noise noise levels, eg from the shuffling of children’s feet.

Teachers found that they couldimprove speech intelligibility slightly ifthey slowed down their normal rate ofspeech or addressed groups of pupils froma sidewall rather than near the centreline.In fact, speech from around the centrelineof the hall appeared louder than normaland sounded coloured or distorted.

An acoustical assessment showed thatspeech was most distorted when bothspeaker and listener were near thecentreline. Flutter echoes and enhancedreverberation were clearly evident anddisturbing. When speaker and listenerwere both near a side wall the conditionswere less severe although still poor.

The acoustical faults correlated wellwith the teachers’ complaints. Themajority of complaints stemmed fromexcessive reverberation, attributable to thepredominantly hard surfaces in the hall.Both floor and ceiling were hard andacoustically reflective. Excessivereverberation caused consecutive syllablesin speech to run into one another,reducing intelligibility.

This problem was compounded by theshape of the ceiling. It has a shallow pitchwith hipped ends, similar to an invertedconcave dish. Sound focused by the hardreflective ceiling onto the hard floor

below and the resulting multiplereflections were detected as a longerreverberation time (RT) near thecentreline. This effect caused sounds toappear louder than normal and colouredor distorted.

To rectify these faults, it was proposedthat the ceiling should be madeacoustically absorbent. This would reducethe RT to a level suitable for primaryschool uses and reduce the focusingeffect.

Although it provided a solution in thiscase, it is not normally advisable forceilings to be sound absorbing in roomswhere good speech intelligibility is arequirement. If the size, shape andgeometry of the space are right in the firstplace, then the ceiling should be reflectiveto sound. The reason for the success ofthe ceiling treatment in this case was theoverriding need to make a substantialreduction in RT and the fact that thefloor has a timber finish, which provides auseful reflection path in the absence of acomparable reflection from the ceiling.

The school wanted to retain the timberceiling. Therefore the timber boards weretaken down and a series of 20 mm by 200mm slots were cut into them (see Figure7.1.2) to give an open area ofapproximately 25%. A mineral fibreacoustic quilt, 25 mm thick, was laiddirectly over the slots in the ceiling void.The quilt was faced with an acousticallytransparent black scrim on the hall sidefor aesthetic reasons. The existing layer ofthermal insulation was replaced over theacoustic quilt. Figure 7.1.1 indicates thearea of the ceiling that was treated. Theacoustic treatment to the timber ceiling isconsidered to be in keeping with theappearance of the hall (see photograph,Figure 7.1.3).

In addition to the ceiling treatment,acoustically diffusing panels wererecommended for the walls to distributesound evenly around the hall and preventflutter echoes. An example of a diffusingpanel is shown in Figure 7.1.4. However,these panels were omitted due to lack offunds. As a result of this omission and thepresence of an acoustically absorbentceiling, there is a tendency for sound to

Figure 7.1.2: Detail oftimber slats used to linethe hall ceiling

30 20 20

2010

0

dimensions in millimetres

Case Study: Remedial work to a multi-purpose hall in a county primary school7.1

95

reverberate around the hall in a horizontalplane, particularly when occupancy is highand the floor is obscured. Under certainconditions, this manifests itself asdistracting flutter echoes between thehard parallel side walls. One teacherreported this effect as a disturbing‘ringing’ noise whilst rehearsing musicand dance with a small group of childrenat the south west side of the hall.

Following implementation of remedialacoustic treatment to the ceiling, theresponse from the teachers to themodified acoustics of the hall was veryfavourable and all reported a verynoticeable improvement.

Speech intelligibility was found to bemuch improved when addressing bothsmall and large groups of children, andnoise from physical activities and childrenshuffling feet during assembly has beenreduced to acceptable levels.Communication during physicaleducation and similar noisy activities iseasier, and accompanied by lower levels ofbackground noise.

The reverberation time was measuredin the same positions before and after the

remedial work. Two sets of measurementswere made; one with the source andreceiver on the centreline of the hall andthe other with the receiver positioned 2 mfrom a side wall. Measurements weremade while the space was unoccupied.Curtains were pulled back to their normalbunched positions either side of internaland external doors and windows. This

approx 1 m

Figure 7.1.4: Example ofacoustically diffusing panel

Figure 7.1.3: The hall ceilingafter acoustic treatment

Case Study: Remedial work to a multi-purpose hall in a county primary school 7.1

96

arrangement was considered to producethe most reverberant condition likely tobe encountered during every day smallgroup activities.

Before remedial work, the measuredTmf was 2.8 seconds on the centreline butfell to 2.5 seconds along the side of thehall. Figure 7.1.5 shows the measured RTcurves as a function of frequency. TheTmf after treatment is generally withinthe range for a primary school hall, whichshould be between 0.8 and 1.2 seconds.

Concerts and musical activities takeplace in less reverberant conditions thanbefore, with substantial reductions incolourations and distortions. Theseconditions have been found to besatisfactory. The introduction of acousticabsorption into the ceiling of the new hallhas been successful in providing acousticconditions which are suited to primaryschool uses.

It is clear from this study that theacoustics of a hall are of fundamentalimportance in the effective functioning ofthis key space in a primary school. Inmany halls, hard wall and floor finisheswill be necessary and the required

43.83.63.43.2

32.82.62.42.2

21.81.61.41.2

10.80.60.40.2

0125 250 500 1000 2000 4000

Range of mid-frequency reverberation time, T forprimary school hall fromTable 1.5

Octave band centre frequency, Hz

Reve

rber

atio

n tim

e, s

measured on centreline before treatment

measured 2 m from side wall before treatment

spatially averaged RTafter acoustic treatment

mf,

Figure 7.1.5: Measuredreverberation time in thenew hall before and afterimplementation of acousticmeasures

acoustic absorption will need to beaccommodated in the ceiling. Ideally,absorbent and reflective surfaces shouldbe more or less evenly distributed onboth walls and ceiling. This case study,where modification of the existing ceilingwas complicated and costly, highlights theimportance of considering the acousticrequirements at the design stage.

7.1Case Study: Remedial work to a multi-purpose hall in a county primary school

97

An investigation of the acousticconditions in three recently built openplan primary schools was carried out.Sound insulation between classrooms andreverberation times and sound levels inunoccupied classrooms were measured.

The effect of noise from adjacent areason speech intelligibility within thelearning bases was assessed. The SpeechTransmission Index (STI) was measuredin the classrooms using Maximum LengthSequence (MLS) analysis equipment asdescribed in BS EN 60268-16. In eachcase an artificial mouth, positioned wherethe teacher usually stood during lessons,was used to produce a reference signalwhich was received by a microphone atdifferent positions within the room.Speech intelligibility was rated using themeasured STI values.

7.2.1 School 1 (pupils aged 5 -11 years)The layout of the school is shown inFigure 7.2.1(a). The walls are full heightbetween the classrooms and the corridors,with teaching areas accessed via openarches from the corridors The twoteaching areas on each side of thecorridors are open plan, being separatedonly by a quiet/IT area. Measurementswere conducted in the Yellow and Greenteam areas indicated. The layout of theGreen team area with measurementpositions is shown in Figure 7.2.1(b).

Measurement resultsThe measured classroom mid frequencyreverberation times (Tmf) are shown in Table 7.2.1.

LAeq,10min (dB)

Room

Y1G1G2

Mid-frequencyreverberation time (s)

0.40.40.4

The sound level (LAeq,10min) wasmeasured in classroom Y1 when occupiedduring a typical interactive science lesson,and when unoccupied after the school dayhad finished. The sound level was alsomeasured in the unoccupied Yellow team(Team 4) practical area indicated inFigure 7.2.1. The measured sound levelsare shown in Table 7.2.2.

It should be noted that although thelevel in classroom Y1 was measured afterthe children had left the school, thecorridor adjacent to the room was stilloccasionally used by those involved in

Classroom Y1occupied

62.7

Classroom Y1unoccupied

42.4

Practical areaunoccupied

54.2

after school activities. The sound level inthe unoccupied practical area was measuredwith lessons being conducted in all theadjacent teaching rooms.

As the school was in use, 10 minuteswas the longest practical time period forthe measurements of indoor noise levels.

The speech transmission index (STI)was measured at 5 positions in theunoccupied room G3 with and withoutmasking noise being generated in roomsG1 and G2. The position of the artificialmouth and the 5 microphone positionsare shown in Figure 7.2.1. The maskingnoise had the same level as was measuredduring the science lesson in classroom Y1and was shaped to give similar levels, inthe third octave frequency bands between50 Hz and 5 kHz, as those measured.

Microphoneposition

12345

STI

0.8030.6730.7610.7390.745

Rating

ExcellentGoodExcellentGoodGood

STI

0.6540.691

Rating

GoodGood

STI

0.6390.6420.4260.5500.555

Rating

GoodGoodPoorFairFair

No masking Mask in room G1 Mask in room G2

Rooms

Y1 to Y4G1 to G2G1 to G3G2 to G3

DnT(0.8s),w (dB)

16192414

Table 7.2.1: Classroommid-frequencyreverberation times

Table 7.2.2: Soundlevels in Yellow team area

Table 7.2.3: Average STIvalues in unoccupied roomG3 with and withoutmasking sound in roomsG1 and G2

Table 7.2.4: Measuredsound insulation betweenclassrooms

Case Study 7.2: An investigation into the acoustic conditions in threeopen-plan primary schools 7.2

98

Figure 7.2.1: School 1 layout (a) Whole school (b) Green Team test area

H16

Yellow Team

Yellow Team Yellow Team

Yellow Team

Kitchen

SecondHall

FirstHall

Quiet/I.T.Area

Quiet/I.T.Area

Staff room Green Team

Green Team Green Team

Quiet/I.T.Area

Green Team

Team 2Practical Area

Foyer

Key Stage 1Library

Key Stage 2Library

Yellow Team Yellow Team

Quiet/I.T.Area

Quiet/I.T.Area


P.E. Store

RainbowRoom

Rec.

Dep. Head

Head

Office

Servery P.E.Store

Store

Studio 1

Y4 Y1

Y2Y3

G1

G2G3Red Team

homebase 1Red Team

homebase 2

Red Teamhomebase 3

Blue Team

Blue Team

Blue Team

Blue TeamBlue Team

Quiet/I.T.Area

Studio 2


Studio 3

H16

FirstHall

Staff room Green Team

Green Team

Quiet/I.T.Area


Foyer

Key Stage 1Library

c.

Servery P.E.Store

Store

G1

G2G3

1 2

3

4

m5

m

2

Artificial mouth used for speechintelligibility test

Key:

Microphone positions

Case Study: An investigation into the acoustic conditions in three open-plan primary schools 7.2

(a)

(b)

99

DiscussionThis school was selected for investigationprimarily because it had been reportedthat the school’s open-plan design workedwell. The head gave the impression thathe strongly favoured the open-plan layoutand stated that he had been closelyinvolved with the design process of thenew school. However, other members ofstaff were less enthusiastic.

A team leader in the school stated thatthe open-plan design suited the teachingpractices in the school although it hadtaken some time to get used to at first.Other teachers were forthright in theirdisapproval of the school’s design and therestrictions that it imposed.

Of the teachers whose opinions werecanvassed, the majority stated that theyfelt the open-plan design led to problemsassociated with disturbance. Timetablingwas organised so that the activities inadjacent teaching areas produced similarlevels of noise in order to avoiddisturbance to pupils involved in quietactivities.

According to the teachers consulted,usually the arrangement was acceptablebut problems could be caused if a teacherunfamiliar to the pupils was taking a classin an adjacent area. In such circumstancesthe usual strict enforcement of disciplineon the children could be subvertedleading to disturbance in adjacent areas.

The measured levels in the unoccupiedYellow team practical area and classroomY1 were greater than those specified inSection 1. In the practical area, it can beassumed that the measured level wasaffected by sound from adjacent occupiedclassrooms. For example, it was notedthat during measurements in theunoccupied practical area one of theteachers constantly reminded the childrento work quietly by uttering the command“Shh” at regular intervals. At a differenttime, a teacher in classroom Y4 raised hervoice sufficiently for her words to be

heard clearly in classroom Y1. This was aresult of her feeling the need to admonisha pupil for holding a conversation fromthe open corridor with one of her classmembers.

The behaviour of the teachers andpupils did not appear to be unusual andthe strong impression was given that theday of the investigation was a typicalschool day.

The measurements of the SpeechTransmission Index (STI) showed thatspeech intelligibility was reducedconsiderably during an interactive sciencelesson in classroom Y1. This was due tothe increased sound level (LAeq,10min)during the lesson.

The mid-frequency reverberation timein each of the classrooms was 0.4 seconds,which is acceptable for classrooms forhearing impaired pupils. Because of this,in the absence of children and teachers,the measured STI rating varied betweengood and excellent in unoccupiedclassroom G3. However, when maskingnoise was generated in room G2, the STIrating was reduced to poor and fair inpositions 3, 4 and 5. This suggests that,when the teacher is speaking to the classfrom the usual position, pupils sittingclosest to room G2 are likely toexperience more difficulty understandingthe teacher’s words than other pupils inthe classroom due to noise emanatingfrom room G2. The measurement of STIshowed that noise generated in G1 hadno significant measurable effect on speechintelligibility in room G3. This is likely tobe due to the stagger between theentrances to rooms G1 and G2 onopposite sides of the corridor.

It should be noted that STI is anobjective measurement of speechintelligibility, and cannot quantifydisturbance to pupils. Disturbance maydepend, for example, on whether pupilsperceive sound generated in adjacent areasto be interesting or threatening.

Case Study: An investigation into the acoustic conditions in threeopen-plan primary schools 7.2

The STI measurement results are shownin Table 7.2.3.

The results of sound insulationmeasurements between classrooms areshown in Table 7.2.4.

100

7.2.2 School 2 (pupils aged 3 -7 years)The school layout is shown in Figure7.2.2. Classrooms 1 to 3 are for receptionclasses and no measurements wereconducted in this area, where someremedial work had been carried out.Originally, the nursery wall onto thecorridor was only 2.4 m high with a gapabove. However, the disturbance toclassrooms 1, 2 and 3 from the high noiselevels resulting from normal nurseryactivities necessitated the closing off ofthe nursery area using full height acousticpanels above the existing nursery wall.

The walls separating the classroomsfrom the corridor area are approximately

1.2 m high. Some common resourceareas, eg the library and thescience/technology area, are located inthe corridor space. It is possible to seeover the low wall into the corridor anddirectly from one classroom to another inthe vicinity of these walls. Although theheight of the walls between classroomsincreases towards the external wall of aclassroom, at no point is there acontinuous barrier from the floor to theceiling between the classrooms. The gapabove the partition wall provides a clearsound path, see Figure 7.2.3, and couldwith forethought have been easily closedoff. However, it is doubtful if this wouldhave made a big difference to the soundtransmission given the low walls onto thecorridor.

Measurement results Measurements were conducted in rooms4 to 9.

Because the classrooms were identicalin appearance, the mid-frequencyreverberation time was measured only inunoccupied classroom 8, and was 0.5 seconds.

STI was measured in classroom 8.

workroomstaff

toilets

toilets

lobby

wc

store

staffroom

store

staff room

malefemale

lobby

library

area

dis'd

cloaksclnr.

wc

quiet

duct

toilets

utility

community

storewc

areaquiet

room

office

dis'd

wc

staff room

store toilets

storechair

store

wc

store

office

mtr

pestore

girls

boys

roommedical

caret

aker secretary

stockroom

headteacherlobby

toilets

toilets

groupteaching

recepti

oncla

sses

classroom6classroom

7

technologyscience/

classroom5

foodclassroom

3

classroom4

classroom2

classroom1

nursery

junior dining/studio

entrancefoyer

musicstudio/

hall

servery

kitchenroomplant

classroom9

classroom8

library

1

23

4

m

m

2


Key:

Microphone positions

Figure 7.2.3: Partitionwall between classrooms.Note the large gap (>300 mm) above theglazed head of the partition.

Figure 7.2.2: School 2layout

Remedial work: Absorbent screens hung above rear wall to receptionarea. Existing wall was only 2.4 m high and was open above. Noise

from reception area disturbed classes in classrooms 1 and 2.

Approximately 1.2 m high rearwalls of classrooms ontocorridor

Partitions between classroomsto about 600 mm below ceilingwith single glazing betweenpartition and ceiling


101

First, measurements were conducted atthe positions indicated in Figure 7.2.2,without any masking noise in adjacentareas. After this, white noise wasgenerated as masking sound in room 9 torepresent noise from an occupiedclassroom and STI was measured inpositions 3 and 4 in room 8. Maskinglevels of 60 dB(A) and 70 dB(A) wereused. White noise was used as maskingsound because no pupils were in theschool during the measurements.Therefore, a typical classroom soundspectrum could not be recorded and usedas the masking signal. The artificialmouth was positioned 1m in front of thewhite board on the wall between rooms 8and 9. as shown in Figure 7.2.2.

The average STI values measured areshown in Table 7.2.5.

Table 7.2.6 shows the measuredairborne sound insulation betweenclassrooms in terms of the weightedBB93 standardized level difference(DnT(0.8s),w). Table 7.2.7 shows themeasured sound levels in the classroomswith a sound source in classroom 9.

DiscussionBrief discussions were held with the headof the school and a few other teachersbefore and after measurements began.The head stated that she liked the openplan design since it meant that pupilswere accustomed to seeing her and shecould enter classrooms without causingundue disturbance.

When the school was first used,problems with high noise levels had beenexperienced in the reception class area but

these were alleviated by the addition ofacoustically absorbent panels on the wallopposite the classrooms. No other adversecomments about the acoustics in theschool were made by any of the teachersinterviewed although one teacher diddescribe an unusual situation caused bythe lack of acoustic isolation betweenclassrooms.

The same story was being read topupils in adjacent classrooms at the sametime. The teacher said that she becameaware that her colleague in the adjacentclassroom was one or two words ahead ofher in the story. She described thesituation as being “like hearing an echo”and attempted to speed up her reading inorder to synchronise the delivery to bothclasses.

The design of the school means thatacoustic isolation between classrooms andthe area outside the classrooms would beexpected to be low. The results of themeasurements taken bear this out. 13 dBDnT(0.6s),w between classrooms 7 and 8is a very low level of sound insulation.Indeed, 28 dB DnT(0.6s),w betweenclassroom 9 and classroom 4 (which are

Microphoneposition

12343344

STI

0.6560.6160.6400.5880.4590.2630.5410.430

Rating

GoodGoodGoodFairFairBadFairPoor

Rooms

7 and 89 and 4

DnT(0.8s),w (dB)

1328

Classroom 4 5 6 7 8 9

LAeq,2min (dB) 68.2 69.5 72.8 75.8 81.4 96.1

Table 7.2.5: Average STIvalues in classroom 8 withand without different levelsof masking noise inclassroom 9


Table 7.2.7: Sound levelsin classrooms 4, 5, 6, 7, 8and 9 with sound source inclassroom 9


Maskinglevel (dB(A))

60706070

102

not adjacent, see Figure 7.2.2) issignificantly lower than the 45 dBbetween adjacent classrooms required inTable 1.2 of Section 1.

Comparison of STI values in aclassroom with and without maskingnoise generated in an adjacent classroomdemonstrates that there is a significantreduction in speech intelligibility due tothe masking noise

The data in Table 7.2.5 show that theSTI values and, consequently, speechintelligibility were reduced in the twopositions used for the measurementswhen masking noise was generated in theadjacent classroom and when the level ofthe noise was increased. Position 4 was

better screened from classroom 9 thanposition 3 where there was an almostuninterrupted path between the tworooms owing to the lower dividingpartition at this point. The measurementsshow that speech intelligibility in position3 is reduced by masking noise generatedin room 9. The masking noise had lesseffect on STI in position 4 than inposition 3. However, position 4 had thelowest STI value of the four measurementpositions. This is largely due to theartificial mouth being directed into theclassroom perpendicularly from the wall.Directing the artificial mouth towardsposition 4 would have increased the STIvalue at this position. Thus, unless the

8

7

6

3

2

1

5 4

9

10

Curtains to screenclassroom openings

Recently addedextensions

m

m

Curtainsto this extensionremovedduring test


Key:m

Figure 7.2.4: School 3layout showing recentlyadded extensions


103

teacher is looking directly at a child at thisposition, the speed intelligibility will onlybe ‘fair’.

Since the mid-frequency reverberationtime measured in two of the classroomswas 0.5 seconds problems with speechintelligibility can be attributed to highambient noise levels in the classrooms.Because the sound insulation between therooms is so low, it is likely that noisegenerated in adjacent areas will contributeto the overall sound levels in the rooms.

7.2.3 School 3 (pupils aged 4 -8 years)This is a recently built school which hasbeen extended. The extensionsaccommodating rooms 1 to 8 are shownin Figure 7.2.4. Measurements wereconducted in the original school buildingwith children present and in theextensions both with and without thechildren present.

Measurement resultsTable 7.2.8 shows mid frequencyreverberation times measured in theclassrooms. Tables 7.2.9 and 7.2.10 showmeasured sound levels in occupied andunoccupied classrooms respectively.

The results from the measurements inSchools 1 and 2 demonstrate that STIvalues are reduced by noise from adjacentareas and that those positions closest tothe noise are likely to be most affected.Therefore, STI was measured in only oneposition in two classrooms. In room 3,STI was measured with the curtainsbetween rooms 3 and 4 open and closed.All measurements were conducted withthe artificial mouth positioned where theteacher would usually stand, see Figure7.2.4, and the receiving microphone waspositioned 3 m in front of the artificialmouth. The results are shown in Table7.2.11.

DiscussionThe head in this school was strongly infavour of the open plan design of theschool for the following reasons:• she felt that the staff worked better as a team• she felt that the children worked

better as a group• she felt that open-plan design allowed more flexibility• she felt that organising pupils in common teaching areas was “more natural”, especially for those joining the reception class.However, prior to this investigation, thehead had contacted her local educationauthority due to problems encountered inthe extensions to the school containingrooms 1 to 4 and 5 to 8. Here, difficultieshad been encountered which resulted in‘acoustic curtains’ being fitted to separatethe classrooms from the communal areas4 and 5. When the measurements weremade, the curtains were temporarilyremoved from rooms 6 to 8.

The measurement results given in Table7.2.8 show that the reverberation time inthe original building is shorter than in thetwo extensions. They also show that thereverberation times in the rooms withcurtains (rooms 3 and 4) are lower thanthose in rooms without curtains (rooms 5

Room LAeq,3min (dB)

5 35.44 32.83 31.8

Room Mid-frequency reverberation time (s)

9 0.46 0.75 0.93 0.64 0.6

Room

5643109

Lesson type

Project workLiteracyProject workNumeracyProject workRoom empty

LAeq,3min (dB)

74.969.769.369.866.256.2

Table 7.2.8: Classroommid-frequencyreverberation times

Table 7.2.9: Sound levelsin occupied classrooms

Table 7.2.10: Soundlevels in unoccupiedclassrooms


104

Room STI Rating

9 0.570 Fair3 (curtains open) 0.689 Good3 (curtains closed) 0.693 Good

Rooms Curtains DnT(0.6s),w (dB)

3 to 4 open 10 dB3 to 4 closed 15 dB3 to 2 open 21 dB3 to 2 closed 28 dB

Table 7.2.11: AverageSTI values in unoccupiedclassrooms. Note: adjacentrooms were occupiedduring the measurementsin Room 9.


and 6), which exceed the values specifiedin Table1.5. These results suggest thatthe acoustic problems experienced by staffin the extensions to the original buildingcan largely be attributed to the lack ofsound absorption and the consequentrelatively long reverberation times inthese areas compared with the originalschool building. The original buildinghad acoustically absorbent ceilingswhereas the extension did not.

The results from the measurement ofSTI show that in unoccupied classroom 3speech intelligibility was good with thecurtains both closed and open. In room9, the speech intelligibility rating was fair.Since the reverberation time in room 9 is0.5 seconds, this lower rating can beattributed to noise generated by childrenin the adjacent areas at the time of themeasurements.

The results shown in Table 7.2.12show that the curtains reduce the soundtransmission between classrooms, inaddition to reducing reverberation times,although none of the sound insulationvalues measured meets the specification of45 dB in Table 1.2 of Section 1.

Table 7.2.9 shows the sound levelsrecorded in different rooms whilst lessonswere taking place. Pupils were engaged inproject work in room 4 while in rooms 3and 6, more formal literacy and numeracylessons were being conducted.

Project work meant that the childrenwere working in small groups and noiselevels generated by their interaction

during these activities were higher thanwould be expected in a formal lesson. Forexample, in the numeracy lesson in room3, the teacher sat in one corner of theclassroom with the children seated closeto her. In this lesson the teacher spokeand the children responded when it wasappropriate.

The level in room 5 was approximately5 dB higher than the level measuredduring the literacy lesson in room 6. Thispart of the extension did not havecurtains fitted between the rooms at thetime of this investigation. In the otherextension, where curtains were fitted, thelevels measured in room 4 (project work)and room 3 (numeracy lesson) werevirtually the same. The curtains betweenrooms 3 and 4 were drawn so that only agap of around 300 mm remainedbetween the curtain and the wallseparating room 3 from 4.

A teacher in the school volunteeredcomments on teaching conditions inrooms 1 to 4. She said that she found itdifficult to hear some softly spoken pupilsdue to the high noise levels in theclassroom and that parents would informher if and when their child had difficultyhearing what was being said in lessons.

The teacher was of the opinion thatroom 2 was worse to teach in than rooms1 and 3 because of the low soundinsulation of the walls separating therooms and the consequent noisetransmission from rooms 1 and 3.Unprompted she described the difficultiesexperienced when reading the same storyto her class as the teacher in the adjacentroom but being a sentence or two behindor in front of her colleague next door.

The teacher felt that the curtains hadimproved conditions in the classrooms.Cupboards had also been placed in theopenings between rooms 1, 2, 3 and 4 inan attempt to improve sound insulationbetween the different teaching areas. Inher opinion, the cupboards had beenuseful for this purpose.

7.2.4 SummaryIn all the schools visited, the headteachers appeared to approve of the openplan design in their school. Some teachers


105

shared their head’s enthusiasm for thedesign but others felt that problemscaused by the transmission of soundbetween rooms were significant.

The measurement of STI in the schoolsdemonstrated that speech intelligibility isreduced by noise generated in adjacentrooms. In all the open-plan schools, highambient noise level was the mostsignificant cause of low speechintelligibility.

From the few opinions canvassed in theschools it would appear that there arebenefits to adopting an open-plan design.These appear to be that the design isfavourable for team working, that itengenders a feeling of inclusion in theschool and that it allows for a visuallyattractive environment. However, placingcupboards in spaces between rooms inorder to increase isolation between themmay detract from the original open-plandesign.

From the results of this survey, it isdifficult to justify the use of open-plan

schools in terms of their acousticenvironment. None of the schools metthe requirements for sound insulationbetween classrooms contained in BuildingBulletin 93. Although reverberation inclassrooms was well controlled (apartfrom in the extension in School 3),ambient sound levels during teachingperiods were too high for the measuredSTI values to indicate good speechintelligibility. As a consequence of thelevels in the classrooms, both teachers andpupils would need to speak more loudlyin order to be clearly understood.

In many open plan teaching spaces it isdifficult to achieve clear communicationof speech between teacher and students.

For this reason, careful considerationshould be given as to whether to includeopen-plan teaching spaces in a school. Ifopen-plan areas are required thenrigorous acoustic design is necessary tosatisfy the performance standards inSection 1.


107

The primary school in Case Study 7.1extended its facilities in the early 1990sby adding seven new classbases and amulti-purpose hall to the existing school.The new classbases were arranged in twoopen-plan areas, of three and fourclassbases respectively.

The teaching area with four classbases,numbered 4 to 7 in Figure 7.3.1, is aninteresting example of the limitations ofan open-plan environment. Acousticproblems were experienced by theteaching staff which subsequently led tothe implementation of remedial measures.Visits were made to the school before andafter the remedial work.

The new extension to the school is ofconventional masonry cavity walls,comprising 100 mm facing brickouterleaf, 50 mm cavity and 140 mmblockwork inner leaf with a plaster finish.

The roof over the teaching area ismade up of a combination of pitchedsections with a tiled exterior and flat roofconstructions with a felt finish. Each pairof adjacent classbases has a roof lightlocated in a flat roof section. Windows arethermally double glazed and openable.

Internal walls are generally constructedof either 100 mm or 140 mmlightweight blockwork. Surface finishesare generally hard and reflective exceptfor the floor which is covered in a shortpile carpet. The walls are plastered andhave an emulsion paint finish. The ceilingin the open-plan teaching areas isconstructed of 12.5 mm plasterboardwith a painted skim finish.

The general features to note about thelayout of the open-plan teaching areas are:• All four teaching spaces areincorporated in an open-plan arrangement.• The physical separation between classbases 4 and 5, and between classbases6 and 7 is minimal which impliesnegligible acoustic separation. A smallimprovement in acoustic separation maybe gained by strategic positioning of tallitems of furniture, eg bookcases, betweenadjacent classbases.• The physical separation betweenclassbases 5 and 6 is only partial and isformed by the projection of the grouproom on one side and book shelving on

the other.• The teaching spaces are separatedfrom potentially noise producing andnoise sensitive spaces, eg other classroomsand the main hall, by a corridor. Thisarrangement is advantageous for reducingnoise disturbance to or from other partsof the school.• Toilets and services provided in the corner of each pair of bases are bufferedfrom the teaching spaces by lobbieddoors.

Teaching staff perceived the open-planteaching area to be difficult to work inbecause of poor acoustics. They had two

Base 7

Base 6

Base 5

Base 4

Group Room

Services

Services

Figure 7.3.1: Plan ofopen-plan teaching spacesbefore modifications

Case Study 7.3: Remedial work to an open-plan teaching areain a primary school 7.3

108

main complaints. Firstly, when teaching ina classbase, they could clearly hearteaching activities in other classbases, eventhe most distant ones, and they found thisvery disturbing and disruptive. Someteachers perceived this as a ‘funnelling’ ofsound from one end of the open-planteaching area to the other. Conditionswere worst during normal table activitieswhen a comparatively active and excitedclass returned to an adjacent classbasefrom a PE lesson.

Secondly, noise levels within a classbaseduring teaching activities were excessivelyhigh and adversely affected concentrationand working ability.

Remedial measures were designed toimprove the acoustic separation betweenclassbases in order to reduce difficultiesarising from mutual disturbance, and toreduce the build-up of noise levels duringclassroom activities to promote animproved teaching environment.

The acoustic separation betweenclassbases was increased by installing a fullheight double-leaf glazed partitionbetween the group room and bookshelvesas shown in Figure 7.3.2. The glazing is 6 mm thick and doors have perimeter andthreshold acoustic seals. This constructionextends the size of the group room andforms an effective acoustic barrierbetween the two pairs of bases 4 and 5,and 6 and 7.

To provide further acoustic separationbetween the individual bases 4 and 5, and6 and 7, several tall bookcases werepositioned along the dividing linebetween these classbases. The acousticalseparation provided by this type of partialbarrier is, of course, considerably lesseffective than that provided by a fullheight partition.

Noise controlNoise levels during class were highbecause surfaces were hard andacoustically reflective with the exceptionof the carpeted floor. Acoustic absorptionwas added to reduce these noise levels.The ceiling was the most suitable area fortreatment and acoustic tiles were appliedover the whole of the ceiling in the open-plan teaching area. The precise absorption

ExtendedGroup Room

Tall book shelves

Tall book shelves

Glazed partitionsand doors

with acoustic seals

Base 5

Base 4

Base 7

Base 6

Figure 7.3.2: Arrangmentof open-plan teachingspaces followingmodifications (a) floor plan(b) new glazed partitionextending the group room

Case Study: Remedial work to an open-plan teaching areain a primary school7.3

(a)

(b)

109

coefficient of the ceiling tiles is notknown, but an absorption coefficient of0.9 over the speech frequency range isnormally needed to maximise the benefitof an acoustic ceiling. As well as controllingnoise within the classbase, the ceilingtreatment helps to reduce the propagationof sound from one classbase to another.

The teachers reported an immediateimprovement in aural conditions with theinstallation of the partitions. They foundthat they were now only disturbed by theclassbase immediately adjacent to them.By strategic location of items of tallfurniture they were able to slightly reducethis remaining source of disturbance.

The acoustic ceiling, installed a fewmonths later, was perceived by teachers toproduce a small but significant reductionin the noise levels during class activities.

Acoustic measurementsThe noise levels during class and thereverberation times of the spaces weremeasured. Measurements were also madeto evaluate how well sound propagatesfrom one classbase to another. Themajority of measurements were madeafter the remedial treatment had beenimplemented although noise levels duringclass were also measured before treatment.

Activity noiseThe noise levels were measured in thefour classbases, before and after theremedial treatment, during typical tableactivities. Approximately 25 pupils werepresent with 1 or 2 teachers in eachclassbase. The octave band frequencyspectrum for all measurements wasconsistent in shape and a typical soundlevel spectrum for classroom table activitybefore treatment is given in Table 7.3.1.

For typical table activities, thebackground noise levels prior to theacoustic modifications ranged from 67dB(A) to 71 dB(A). Following the

installation of the acoustic ceiling andpartitions, noise levels ranged from 64dB(A) to 69 dB(A), a reduction of 2 to 3dB(A) which appears to be a small butsignificant subjective decrease.

Reverberation timeThe reverberation time was measured inclassbases 4 and 5. After remedialtreatment, the unoccupied mid-frequencyvalue was 0.4 seconds with a rise to 0.7 seconds at 125 Hz. The mid-frequencyreverberation time, which will undoubtedlyhave dropped with the installation of theacoustically absorbent ceiling, is nowgenerally below 0.6 seconds, as requiredfor primary school classrooms in Table 1.5.

Sound insulationThe sound insulation was measuredbetween classbases 5 and 6. A value forDnT(0.6s),w of 48 dB was obtained whichmeets the requirements between standardclassrooms specified in Section 1.

Sound propagationBefore the partitioning of the room,simple tests showed that speech couldeasily be understood between extremeends of the open-plan area even whenthere was no line of sight. Whilst thepartitioning provided by extending thegroup room gives good sound separationbetween two pairs of teaching bases, theacoustic ceiling and physical obstructions,such as tall bookshelves, are the onlymeans of achieving a degree of acousticseparation between the other adjacentbases.

To measure the sound propagationwith distance across an adjacent pair ofclassbases, a broadband sound source wasused to simulate the radiation of soundfrom a nominal teaching position andsound level measurements were madeacross the classbase and into the adjacentclassbase. Figure 7.3.3 illustrates the three

Case Study: Remedial work to an open-plan teaching areain a primary school 7.3

Octave band centre frequency (Hz)63 125 250 500 1 k 2 k 4 k 8 k

Sound pressure level (dB) 56 60 65 69 68 62 57 54

Table 7.3.1: Typicalmeasured activity noiselevels in an open-planclassbase before remedialtreatment

110

propagation paths that were investigated:• from base 4 to base 5 with line of sight• from base 4 to base 5 via an indirect path• from base 5 to base 6 via the partitioning formed by extending the group room.

The results for the three paths areshown in Figures 7.3.4 (a) and (b).

By comparing the two figures, it isevident that the reduction in sound levelwith distance between bases 4 and 5 isvery modest compared with the largereduction between bases 5 and 6 (ieacross the partition). This is clearlyreflected by the subjective impressions ofteachers who are disturbed by noise froman adjacent classbase on the same side ofthe partition but are not disturbed byclassbases beyond the partition.

The erection of a physical barrier acrossthe middle of the open-plan teaching areawas clearly effective in improvingconditions. It is important to note theconstructional simplicity of this barrierand its acoustical effectiveness in reducingsound transmission. This was achieved byusing two partitions with a large air cavityin between (the extended group room). Asingle partition would have needed to besubstantially heavier with more elaborateacoustical detailing.

The new partition did not solve all theproblems of sound transmission sinceclassbases 4 and 5, and classbases 6 and 7were still open to each other and somemutual disturbance is still occurring. Thishas been reduced by partial barriers butcan not be effectively eliminated withouta complete barrier.

The acoustic ceiling treatment isbeneficial in reducing noise levels but didnot result in a dramatic effect since theclassbases were already carpeted andfurnished.

ConclusionsThe effect of mutual disturbance in open-plan teaching areas is clearly illustrated inthis case study and relatively simpleremedial measures have been shown towork moderately well.

Before embarking on the design of anopen-plan teaching area, seriousconsideration should be given as towhether the advantages of the open-planarrangement outweigh the seriousinherent acoustic disadvantages.

Case Study: Remedial work to an open-plan teaching areain a primary school7.3

R3

R1

S3

S1

S2

R2

ExtendedGroup Room

Base 7

Base 6

Base 5

Base 4

KEY

Source positions

Receiver positions

S3S1 S2

R3R1 R2

Figure 7.3.3: Soundpropagation pathsinvestigated

111

100

80

60

40

20

0 2 4 6 8 10 12

Distance from teaching position, m

Soun

d pr

essu

re le

vel,d

B

buffer zonebetweenspaces

Base 5 Base 6

Significant reduction across theglazed partitions either sideof the buffer zone(or group room)

100

80

60

40

20

0 2 4 6 8 10 12Distance from teaching position, m

Soun

d pr

essu

re le

vel,d

B

buffer zonebetweenspaces

Base 4 Base 5

Minimal reduction across theopen buffer zone

Slightly greater reductionbetween classbases for an obstructed speaker-listener path

Figure 7.3.4: Soundpropagation from oneclassbase to another

(b) with full height doublepartition

(a) without full heightpartition

Case Study: Remedial work to an open-plan teaching areain a primary school 7.3

113

Existing school buildings may have spacesthat are less than ideal and compromiseshave to be made during remodelling. Adesign and technology (D&T) workshopwas converted into music accommodationfor an 11–16 comprehensive school with600 pupils on its roll. Figure 7.4.1 showsplans of the original workshop and theconversion.

The floor area of the conversion is 96 m2, including an adjacent 13 m2 spacewith independent access.

The original workshop was built in1954 using a prefabricated, reinforcedconcrete system of modular design havingconcrete roof panels and double skinwalls; there is a wood block floor. Thesouth-east and north-west facades of thebuilding were fully glazed from a sillheight of about 1.0 m. The ceiling heightin the main space was 3.3 m. The size ofthe main space was suitable for a musicroom but there were some disadvantageswith the accommodation:• Existing floor and ceiling surfaces

were hard, resulting in an unacceptablylong reverberation time of 2 seconds.Standing waves and flutter echoes werelikely due to parallel walls and hardsurfaces.• The north-west wall abutted the

Figure 7.4.1:(a) Plan of the originalworkshop (b) Plan showingconversion to musicaccommodation

(a) (b)

Case Study 7.4: Conversion of a design and technology spaceto music accommodation 7.4

114

school playing field. The extent of glazingwas excessive and considered undesirablefrom a security point of view on a sidewith potential for intrusion.• The school playground, a potentialsource of noise, is adjacent to the south-east wall.• A second design and technologyworkshop is adjacent to the space(although an entrance lobby and storeprovide a buffer between the teachingspaces).• The building is free-standing andcirculation is external which results in anexcessive number of entrances.• The reverberation time of the spacewas too long for a music room.

The adaptation Structural alterations were kept to aminimum in order to constrain costs andmaximise available funds for acoustictreatments and finishes. Within the

existing area, it was possible to provide amusic room of 65 m2, three group roomsand a store, see Figure 7.4.1(b).Performances to an audience or largescale rehearsals take place in the schoolhall. The largest group room (orensemble room) is converted from theexisting store and can be accessedseparately, if necessary, to avoid disturbingclasses. The dimensions of this space arenot ideal as proportions are long andnarrow but compromise has beenaccepted and the wall treatment isdesigned to optimise room responses. Anentrance lobby houses coats and bags andprovides additional sound insulationbetween the main space and the adjacentD&T room.

The sound insulation of the musicroom was a priority. The key aspects ofthe acoustic treatment are shown inFigure 7.4.2, and described below.

Construction In order to improve security, glazing to the north-west wall was removed andthe opening was infilled up to two thirdsof its height with rendered blockwork. Medium density block (1500kg/m3) was used to give appropriatesound insulation. The top third of eachpanel was thermally and acousticallydouble glazed with bottom-hungopenable fanlights.

Angled panels of medium densityparticle board were fixed to studdingon the inside face of the north-westwall of the main space. These help toprevent standing waves between parallelside walls and can provide much neededdisplay space. The panels are withoutfabric covering since this wouldcompromise the high frequency response.Panels are omitted where there are shelvesas these have an equivalent acoustic effect.Angled panels are also used in the grouprooms.

Secondary acoustic glazing was addedto the windows to the south-east(playground) side, as two sliding panels.This allows access for maintenance and toopen casements or fanlights. Solarreflective film was added to the outside ofthe existing fenestration to reduce solar

Angled panelsand shelvingprovide surfacemodelling tohelp diffusesound

Carpetto floorincreasesabsorptivity

Full lengthdrapes

Full lengthdrapes can

be usedto vary

acousticabsorbency

Acousticdouble glazing

to increasesound insulationfrom playground

Wall at an angleto avoid flutter echoes andstanding waves

Full lengthdrapes

Observationwindows detailedfor good soundinsulation

Lobby increasessound

insulationbetween music

and D & T

Angled panels and shelvingprovide surface modelling

Figure 7.4.2: Planshowing acoustictreatments

Case Study: Conversion of a design and technology spaceto music accommodation7.4

115

gain. In a new building, an alternativesolution may be to incorporate a fixedsunshade or ‘brise soleil’ at the eaves soffit.

Internal doors into the musicclassroom, the adjacent D&T space andthe ensemble room were upgraded toheavy solid core doors with double sealsall round including threshold seals. Doorsto the two group rooms have visionpanels for supervision with 10 mm glass.Acoustically double-glazed observationwindows are formed in the partition wallsto the ensemble room and one of thegroup rooms.

Fixtures and finishes The existing plasterboard ceiling finishwas retained; the existing wood blockfloor to the main space was also retainedand carpeted for acoustic reasons. Theensemble room floor has a basic underlayand corded carpet, so that the finish isnot too acoustically absorptive.

Wall finishes in the main space aresupplemented by heavy drapes of at least

0.5 kg/m2 at 200% gather, providingacoustic variability and control. Thecurtain track is ceiling mounted alongthree sides of the room providingmaximum flexibility allowing curtains tobe positioned to suit the configuration ofthe musical activity. This is useful in aschool where one classroom serves anumber of functions.

Curtains are also provided in group rooms. In the ensemble room, they arepositioned at the south-east end of thespace, screening the doorway or bunchedin the corner as required.

On completion, acoustic measurementswere taken in the music classroom,ensemble room and a group room (allwhen unoccupied). Resulting mid-frequency reverberation times are depictedin Figure 7.4.3. This graph shows thatmeasured values are in accordance withTable 1.5 of Section 1, and demonstratesthe potential of providing acousticvariability using drapes.

In the 65 m2 classroom it can be seen

Figure 7.4.3: Graphshowing effects of drapeson reverberation times inclassroom, ensemble roomand group room

10 20 30 40 500

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Mid-frequency valuein unconverted space

prior to adaptation

Mid

-freq

uenc

y re

verb

erat

ion

time,

s

Percentage of wall covered by drapes

KeyClassroomEnsemble roomGroup room

Position ofdrapes

CLASSROOMbunchedrear wallrear and side

ENSEMBLE ROOMbunchedone wall

GROUP ROOMbunchedone wall

Percentageof wall area covered

10%27%53%

5%14%

5%28%

Case Study: Conversion of a design and technology spaceto music accommodation 7.4

that curtains can be very effective inreducing mid-frequency reverberationtime. Because of the number of variablescombining to affect the reverberationtime in a room including volume, theweight and location of curtains, surfacefinishes and furniture, the results shownhere are indicative only. The graph showsthat the ensemble room at 13 m2 has ameasured RT of 0.7 to 0.8 seconds,within the range given in Table 1.5 of 0.6 to 1.2 seconds for an ensemble room.

The background noise level in theunoccupied music classroom measuredwhilst adjacent classes were in session was 29 dB LAeq, 1hr. This suggests that theindoor ambient noise level is less than therequired level of 35 dB LAeq, 30min givenin Table 1.1 of Section 1.

116

Case Study: Conversion of a design and technology spaceto music accommodation7.4

117

The music department at a school with650 pupils between the ages of 11 and 18was replaced. The new self-containedsuite comprises a large music room, threemusic practice rooms, an ensemble roomand ancillary accommodation.

The school is located in a quiet ruraldistrict with low ambient outdoor noiselevels. The music block is several metresaway from other buildings, which ensuresthat noise egress to other parts of theschool is minimised.

The building is constructed of masonrywith an external leaf of brickwork, aninsulated cavity and internal leaf and wallsof blockwork, some of which areplastered. The density of the blockwork isnot known but ideally it should be thehighest available, ie 2000 kg/m3. Thetiled roof has an internal sheathing ofplywood which benefits sound insulation.

A full height blockwork crosswall, upto the roof soffit, separates the largemusic room from the rest of the building.The music practice rooms also have fullheight walls.

Windows are double-glazed and can beopened. Doors are generally hollow corewith basic seals giving around 20 dB Rwfor the doorsets.

The music suite is a good example ofhow to control noise transmissionbetween rooms, and thus reducedisturbance, by careful planning of theroom layout, see Figure 7.5.1. The keyfeatures are:• The large music room is separated

from other music rooms by a corridor and storage areas.

• The ensemble room with its associated recording/control room is also separated from other rooms by a corridor.

Music classroomThe geometry of the large music room isgood, with a rectangular plan shape and afairly steeply pitched ceiling, see Figure7.5.2. The light fittings and recessed rooflights provide some useful modelling tobreak up and diffuse the sound.

Two large encased purlins, projectingdown from the plane of the ceiling causea minor localised problem. Small sound

colourations occur when musicians play inthe area underneath the main roof beams.It is possible that these are caused bystrong reflections from the junctionbetween the roof beam and ceiling asshown in Figure 7.5.2. Additionallocalised measurements would benecessary to investigate this effect. Asolution in this particular case would beto treat one side of the beam withabsorbent material, as indicated.

As a general principle, it is useful toincorporate elements into a ceiling toprovide diffusion and hence uniformity in

tt

0 1 2 3 4 5m

Figure 7.5.1: Plan ofmusic department(furnished)

coats

rooflights

Case Study 7.5: A purpose built music suite 7.5

MUSICROOM

Entrance

recording/controlroom

practice room 4/ensemble room

practice room3

practice room2

practice room1

disabled wc

Office

stor

e

118

the sound field. For effective diffusion,projections of 0.3 m to 0.5 m arenecessary. However, such projectionsshould be distributed over the wholeceiling area; a single large projection canlead to a prominent and potentiallydisturbing reflection, as in this case.

Surface finishes are generally hard andreflective except for the floor which iscovered with a short pile carpet. In detail,the walls are of plastered blockwork withan emulsion paint finish and the ceiling isof plasterboard with a plaster skim finish.This combination of hard and soft finishesensures that the reverberation issufficiently long for music performance

and adequate for teaching.No provision has been made for

varying the acoustics, eg by use of heavycurtains. This would be desirable but notessential.

The measured mid-frequencyreverberation time (RT), with 25 childrenand 4 adults present, was 1.0 secondswith a rise to 1.5 seconds at 125 Hz. Thefull RT curve as a function of frequency isshown in Figure 7.5.3.

This RT is within the range forensemble rooms specified in Table 1.5 ofSection 1.

Electrically operatedrooflight

10370

12752600

975

30°

Sound reflection

Sound source

Possible locations foracoustic treatment

Figure 7.5.2: Sectionthrough music room

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

063 125 250 500 1000 2000 4000


Reve

rber

atio

n tim

e, s

Figure 7.5.3: Measuredreverberation time in themusic room

Case Study: A purpose built music suite7.5

119

Practice roomsAll practice rooms include one pair ofnon-parallel walls which reduces thepossibility of sound colouration fromstanding waves.

The practice room volumes are of theorder of 20 m3 and can accommodate upto 5 pupils working on composition.Ceiling heights are 2.6 m which is lowerthan desirable but acceptable.

The measured mid-frequency RT inone of the practice rooms was 0.4 secondswith a rise to 0.9 seconds at 125 Hz. Thisis at the lower limit recommended forpractice rooms which results in a ‘dry’sound but is nevertheless satisfactory. Themoderate rise in bass frequencies isgenerally a welcome feature givingfullness of tone to certain instruments.

A combination of acoustically reflectiveand absorbent finishes has been used. Thewalls are of blockwork with a paint finish,the floor is carpeted with short pile carpetand the ceiling is treated with acoustictiles. Although the selection of materialshas resulted in acceptable reverberationtimes, the distribution of absorption isconcentrated on the ceiling and floor whichtends to emphasize sound reflections inthe horizontal plane; an undesirable effectthat has been noted by users. This problemcould be overcome by redistributing aproportion of the absorption onto thewalls, eg by installing absorbent wallpanels and replacing some absorbentceiling tiles with reflective ones.

Ensemble roomThe ensemble room is square which couldgive rise to strong standing waves andhence possible colouration. However, onewall has simple angled reflective panelsacting as diffusing elements which workeffectively to counteract this. Surfacefinishes in this room are the same as in

the practice rooms. Again the distributionof absorption is uneven although thesound field is rendered more diffuse bythe installation of the angled panels onone wall, see Figure 7.5.4. Treatment ofthese panels with hessian is not desirablesince it could reduce ‘brilliance’ of thesound as there is already sufficient highfrequency absorption in the carpet andceiling.

The measured mid-frequency RT was 0.4 seconds with a rise to 0.6 seconds at125 Hz. This is lower than the range givenin Table 1.5. A longer mid-frequency RTcould have been achieved by reducing theceiling absorption. There would then havebeen scope for having acoustic variabilityusing curtains.

Recording/control roomThe control room is also square butwithout the benefit of diffusing elements.This could give rise to standing wavesalthough these were not evident. Theshelving and equipment probably providesufficient diffusion to avoid soundcolouration. A facing wall could betreated with absorbing material to assist inpreventing this.

This room has the same surface finishesas the practice rooms and is generallysuitable for music practice and composingas well as monitoring and recordingsound from the ensemble room.(Monitoring is normally done in a verydead acoustic although a suitablecompromise has been struck here betweenpracticing and monitoring).

There is good visual communicationwith the ensemble room through anacoustic double-glazed window.

Sound insulationThe measured sound level differencebetween two practice rooms in octave

Board angledat approx. 5°

10 mm thick full height hardboard on battens

ENSEMBLE ROOM PLAN

Figure 7.5.4: Simpleacoustically diffusingelements

Case Study: A purpose built music suite 7.5

120

bands is shown in Table 7.5.1. Thisequates to a weighted BB93 standardizedlevel difference of 44 dB DnT(0.8s),w.

The sound insulation between practiceroom 2 and the adjacent corridor waslimited by the poor sound insulation ofthe doorset between them. The weightedBB93 standardized level differencebetween the ensemble room (practiceroom 4) and practice room 2 was 47 dBDnT(0.8s),w.

Indoor ambient noiseThe indoor ambient noise level wasmeasured in practice room 3 during aperiod when people were moving aroundthe building but no significant musicalactivity was taking place. The results areshown in Table 7.5.2. This equates to asingle figure value of approximately 30 dB(A). It means that there is littlemasking of intrusive noise from adjoiningspaces. Therefore, separation of sensitivespaces by storerooms and corridors isparticularly important.

Table 7.5.3 compares the subjectiveassessments of the acoustic quality of thespaces with the acoustic measurements.

DiscussionOne of the key issues relating to acousticsin music accommodation is soundtransmission between different roomswhich may cause disturbance to musicpractice and teaching.

Clearly, the layout of the buildingprovides good separation between mainrooms or groups of rooms. The measuredDnT(0.8s),w from the ensemble room topractice room 2 was 47 dB.

However, the situation is morecomplicated because disturbance to a

musician or teacher is also a function ofthe indoor ambient noise in the roomthey are playing/teaching in: the higherthe indoor ambient noise (if relativelysteady) the more masking of externalsounds occurs and hence the lower thedisturbance from external noise.

The sound insulation was significantlyreduced by transmission throughdoorsets. The installed doors are hollowcore with poor seals around the perimeterand threshold. The two sets of doubledoors in the music suite do not haveeffective seals at the meeting stiles. This isa common problem with double doorsbut can be overcome by careful detailingwith rigid fixings at the meeting stiles. Itmight have been better to use unequalpaired doors instead of double doors. Thesmall leaf can then usually be bolted shutmaking the seal much more effective thanon a normal double door. A wide singledoor is also a possibility.

Upgrading seals to proper acousticseals and replacing doors by the solid coretype would improve performance close tothat required. (Preventing doors fromsqueaking would also be beneficial inreducing disturbance.)

A second key issue is the acousticcharacteristics of each of the differenttypes of space.

The large music room has a very goodgeometry for providing a diffuse soundfield. The 1.0 seconds Tmf is sufficientlylong to provide fullness of tone but shortenough to maintain clarity which is animportant quality in music teaching. Therise in RT at bass frequencies is beneficialin terms of adding ‘warmth’ to theacoustic characteristic.

The music practice rooms also have an

Octave band centre frequency (Hz)

63 125 250 500 1 k 2 k 4 k

Level difference D (dB) 22 27 34 46 50 52 58


125 250 500 1 k 2 k

Measured sound pressure level (dB) 38 33 26 21 25

Table 7.5.1: Measured leveldifference between twopractice rooms

Table 7.5.2: Measured indoorambient noise levels inpractice room

Case Study: A purpose built music suite7.5

121

appropriate geometry in plan, namely twonon-parallel walls. However, absorption isnot evenly distributed on the roomsurfaces which prevents a sufficientlydiffuse sound field.

The ensemble room appears to bemuch favoured by teachers and musiciansalike who feel comfortable with its size. Asquare plan shape is always problematic interms of standing waves although this hasbeen mitigated by using simple andeffective diffusing panels.

The associated control room includes awell designed acoustic double-glazedviewing window and the two spacestogether form a good quality recordingsuite. The window consists of 2 x 6 mmglass panes with a 100 mm air space.

ConclusionsThe music block is exemplary in mostrespects in terms of its fitness for teachingand practicing music at secondary schoollevel. The acoustic design is generallygood but there are some minorshortcomings such as inappropriateselection of doorsets and door seals, and

poor distribution of absorption in practicerooms.

In summary, the main points to noteabout the acoustic design of the musicblock are:• location of the building at a distance

from other buildings• separation of large music room and

groups of rooms by full height walls, corridors and buffer zones

• selection of a simple rectangular plan shape for the large music room

• selection of non-parallel walls for practice rooms

• use of simple angled wall panels to provide sound diffusion in the ensemble room

• use of solid, acoustically reflective materials for walls and ceilings in the large music room to ensure sufficientlylong reverberation.

Acoustic measurements

Subjective Airborne soundimpressions of Mid-frequency insulation Indoor ambientthe acoustic character reverberation DnT(Tmf,max),w noise levelof the space time, Tmf (s) LAeq (dB)

Music room Moderately 1.0reverberant. Diffusesound field.Adequate loudness

Practice room Modest 0.4 44 29(Tutorial 2) reverberation. Non between

diffuse sound field. practiceReverberation rooms 2concentrated in and 3horizontal plane.Can hear instrumentsplaying in adjacent rooms but just tolerable.

Ensemble room Modest 47reverberation. between theAdequate loudness. ensembleDisturbance from room andpractice rooms only practiceduring quiet moments. rooms

Corridor Can clearly hearpiano from practiceroom and clarinetfrom ensemble room.

Table 7.5.3: Comparison ofsubjective and objectiveassessments

Case Study: A purpose built music suite 7.5

(dB)

123

This case study describes a junior schooland hearing impaired unit which providean inclusive environment for hearingimpaired children who are educatedthrough a natural aural approach. Thechildren attached to the unit all have a‘significant’ hearing loss and abilities thatfall within the ‘average’ range. Theguiding principle that underlies theirplacement within the school is that theyshould be allowed to make best use oftheir residual hearing. The children havefull access to the national curriculum andare members of a mainstream class.Children also have the use of a specialistteaching resource facility as describedbelow.

Characteristics of the schoolThe junior school is of average size withabout 230 children aged between 7 and11. Sixteen children are includedspecifically within the resource provisionfor deaf pupils, although this numberincludes children currently attending theinfants’ school and is liable to fluctuationdepending on the unpredictable changesin the size of the hearing impairedpopulation.

AccommodationThe school was built in the late 1950sand is set away from the road in a quietlocation. The school has been pleasantlydecorated throughout. Some attentionhas been given to reducing internal noiseby carpeting classrooms and somecorridors. Most of the ceilings have somedegree of acoustic treatment. There areno open-plan classrooms within the juniorschool. It is the intention of the school tofurther improve the acoustics of theclassrooms and a report on soundtreatment has been commissioned.

There are 8 classrooms of similar size.In addition there is a dedicated ICTspace, a drama room, music room and alarge hall. A library has been establishedin one of the larger corridors.

Attached to the main building by acovered walkway is a building formerlycalled the hearing impaired unit, but nowrenamed as the RPD (resource provisionfor the deaf). This has extensive soundtreatment and the main teaching room issituated so that it does not face theplayground.

This case study focuses on two rooms:the main teaching space in the RPD(marked as RPD on the plan) and a

MAIN ENTRANCE

First Floor

Class 1 Class 2 Class 3

Class 4 Class 5

Class 6 Class 7 Class 8

Staff

ICT

Hall

Dramaroom

RPD

PLAYGROUND AREA

Figure 7.6.1: Schoolroom layout

Case Study 7.6: A junior school with resource provision for deaf children 7.6

124

typical classroom within the school (Class4 on the plan).

Figure 7.6.2 shows the children allfacing each other during circle time. Thehearing impaired child has been placednext to the teacher to ensure that she canhear the teacher well and see all

contributions. Figure 7.6.3 shows thelayout of the room and the positions ofthe children during circle time. Theteacher is wearing a radio transmitter thattransmits her voice directly to the child’shearing aids and to a classroom soundfieldamplification system. This will ensure thatthe teacher does not have to raise hervoice and distort her speech unhelpfully.All children benefit and as a consequenceare better able to participate.

Acoustic and behavioural measuresA number of acoustic and behaviouralmeasures have been obtained in order topresent an account of the acousticenvironment of the classroom. Thesemeasures include:• listening inventories for education(LIFE UK, see Section 6.5)• sound level during school day (1 minute average dB(A))• short term sound level measurements (2 minute runs at 6 time intervals)• room acoustic measures. LIFE UK is a protocol for evaluatinglistening abilities of children. Applicationof the protocol indicates that the class areable to hear the teacher and each otherwell most of the time, see Figure 7.6.4.The hearing impaired child has a similarprofile with the exception of several

T

L

Staffroom

Corridor

Windows

TL - loudspeaker

- teacher- child- hearing impaired child

6.8 m

7.6 m3.3 m high

L

LL

Figure 7.6.3: Class 4layout

Figure 7.6.2: ‘Circletime’ in Class 4

Case Study: A junior school with resource provision for deaf children7.6

125

critical areas, primarily the child indicatesthat she needs to be able to see theteacher’s face in order to understand whatis being said. This is consistent with thebenefits offered by lip-reading in less thanideal listening conditions. This can beaddressed through the teacher modifyingher teaching style. Other areas where thehearing impaired child finds greaterdifficulty include listening to her peersanswer questions; listening when there isanother adult talking; and listening whenthere is intrusive noise, for example from

the corridor. The child indicates that sheis making satisfactory use of the personalradio system and classroom amplificationsystem to overcome many of the potentialobstacles to hearing effectively.

Figure 7.6.5 shows a chart obtainedusing a noise logging dosimeter placed atthe front of the classroom and out of thereach of the children. The chart presentsthe one minute history of the sound levelobtained between 11.30 am and 15.28 pmduring a typical school day. ‘A’ representsthe class quietly engaged in group work.

100806040200

11:3

0

11:4

4

11:5

8

12:1

2

12:2

6

12:4

0

12:5

4

13:0

8

13:2

2

13:3

6

13:5

0

14:0

4

14:1

8

14:3

2

14:4

6

15:0

0

15:1

4

15:2

8

A B C D ETime

Soun

d pr

essu

re le

vel,

dB(A

)

5

4

3

2

1

0

LIFE UK scores for Class 4

LIFE UK scores for hearing impaired child

1 - always easy to hear2 - mostly easy to hear3 - sometimes difficult to hear4 - mostly difficult to hear5 - always difficult to hear

Listening to teacher but not beingable to see her face

Listening to teacher but withnoise in corridor

Listening to the teacher whilst classare tidying up and moving around

Listening to peeranswer a question

Listening to the teacher whilst class are tidying up after an activity is finished

Listening with no noise outside classroom

Listening with noise outside classroom

Listening when overheadprojector is switched on

Listening when theteacher walks around

Listening during assembly

Listening to peerswhen working in groups

Listening to teacherwhilst another adult talks

Listening to teacherduring a test

Figure 7.6.5: Soundlevels in Class 4 during theday

Figure 7.6.4: LIFE UKscores for Class 4

Case Study: A junior school with resource provision for deaf children 7.6

126

‘B’ is the lunch break. During the periodmarked ‘C’ the class are again engaged inquiet group work; the end of period ‘C’coincides with a break. During the periodmarked ‘D’ the sound level gradually riseswhile the children take part in a carefully

controlled circle time discussion. Aclassroom soundfield system is used bythe class teacher and a personal radio FMsystem is used by the one hearingimpaired child who uses a hearing aid.Period ‘E’ represents the end of the school

70

60

50

30

40

125 200 315 500 800 1250 2000 3250 5000

Teacher speaking and instructing kids for "think and write, children quiet.Analyser positioned back left.

Teacher quiet and children working on task with quiet babble. Analyser positioned back left.

As above but with children becoming progressively louder as the task progresses.Analyser positioned back right.

Teacher speaking and the children are quiet. Halfway through recording teacherstops talking and children start to work with light babble. Analyser positioned back right.

Some teacher talk close to microphone, mostly children's light babble.Analyser positioned front left.

As above but with recording interrupted by the lunch bell. Analyser positioned in mid-front right.

Children get ready to leave. The class is noisy. Analyser positioned in the middle of the class.

Soun

d pr

essu

re le

vel,

dB

Third-octave band centre frequency, Hz

Figure 7.6.6: Frequencyspectra for variousclassroom activities


127

day and the sound level rises as childrenand adults use the room informally.

Figure 7.6.6 shows the third-octaveband frequency analysis for some of theclassroom activities.

Room acoustic measures

Ambient noise levelMeasured levels with the classroom emptywere in the range 32-36 dB LAeq, butthis was after the end of school so did notinclude noise from other areas of theschool. Noise from other areas was notperceived by the teachers as a problem.

Sound level changes due to use ofsoundfield systemMeasurements of the sound pressure leveland LAeq did not show changes thatcould be definitely attributed to the useof the system. The teacher beingmeasured had, as judged subjectively, anexceptionally powerful voice, and it isquite possible that she was able tomonitor the acoustic impact on the classand adjust her speaking level accordingly.

It is worth noting that the system isnot purely an amplification system, itexists to distribute the sound from theteacher’s voice evenly about the classroom.Simultaneous acoustic measures wouldhave been useful to indicate the extent towhich this was achieved.

Subjectively, there was an increase inclarity at mid and high frequencies. Theincrease in clarity does not imply apleasant quality of sound and it was feltthat the sound from the speakers wasrather harsh. This could be a function ofthe frequency response of the speakers orthe adjustment of the system.

Room acoustics assessment, Class 4The measured reverberation times (RTs)are shown in Figure 7.6.7. The Tmf isabove the value specified in Table 1.5. Inaddition, detailed analysis of the measuredimpulse responses showed flutter echoesbetween the parallel, reflective walls.These were not at such a level as to beannoying but they probably reducespeech clarity in the room. The room haspredominantly reflective wall surfaces and

although the ceiling and the carpetsprovide some absorption, more absorptionon the walls would reduce or eliminatethe flutter echoes as well as reducing theRTs to acceptable levels.

Room acoustics assessment, RPDroomThe measured RTs are shown in Figure7.6.8. As expected for an RPD room, theTmf is lower than the value of 0.4 secondsgiven in Table 1.5 for classrooms designedspecifically for use by hearing impairedpupils. Furthermore, the RT across thefrequency range is lower than 0.4 secondsas recommended in Table 6.1. There areno apparent flutter echoes or otherproblems and no complaints of acousticproblems in this room, which would be

Figure 7.6.7:Reverberation times inunoccupied Class 4

Figure 7.6.8:Reverberation times inunoccupied RPD room

Case Study: A junior school with resource provision for deaf children 7.6

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atio

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Reve

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128

7.1 m

7.1 m2.8 m high

Windows

Audiologicaland

radio aidspares

Sink

Figure 7.6.10: Teachingresource base room layout

Figure 7.6.9: Teachingresource base

teaching purposes outside playtime. Thelargest space faces away from theplayground. The windows are not double-glazed and there is no air conditioning,however the setting is very quiet and therooms are large.

Strengths of the schoolA review of the school shows that therehas been considerable investment inensuring that the school is one thatreduces acoustical barriers to learning forhearing and hearing impaired childrenalike. The key features are:• carpeting to reduce noise in corridors and classroom noise caused by movement • attaching rubber ends to chairs and tables to reduce movement noise • maximising lighting, and whereappropriate using blinds, so that childrenand teachers are visible but notsilhouetted against the light, therebyensuring that lip-reading is effective • using personal radio systems for the hearing impaired children to limit the effects of distance from the teacher • using a soundfield system, whichprovides benefit to the hearing impairedchild directly by increasing the strengthand naturalness of the speech signal, andindirectly by modifying classroombehaviour in a positive manner • making use of expertise in the in-service training of staff throughout the school • providing an acoustically well-specified area for supporting those special needs of hearing impaired children that cannotbe met within the mainstream classroom.

Future developments at the schoolThe school is about to undergo majorroof repairs. As part of the process theschool will take the opportunity toupgrade the acoustic treatment within theclassrooms, seeking to lower thereverberation times. This will assist inreducing noise build up during criticallearning times of group work and classdiscussion. The lower reverberation timeswill enable the soundfield system to workmore effectively, and possibly enable theschool to use ceiling mounted speakersystems for future installations.

considered to be very well designedacoustically.

Teaching resource baseThe RPD is separated from the mainschool by a short covered walkway. Thereare two rooms and the entrance lobbyoutside the rooms is large enough toprovide a space for small group work. Thelarger room shown in Figures 7.6.9 and7.6.10 is used for teaching larger groups.The whole building has extensive soundtreatment, ensuring that the environmenthas little reverberation. The building is setin the playground, but is only used for


129

This case study describes the acoustics ofan all-age special school for hearingimpaired pupils. The school is located ontwo sites. The primary aged pupils attenda primary special school for hearingimpaired children and the secondary agepupils attend a special unit within amainstream secondary school about onemile away from the primary school.

The primary school, the secondaryspecial unit and the audiology room inthe primary school are describedseparately.

The primary special school

The primary school is a school in whichonly severely hearing impaired pupils aretaught. It was founded in 1975 and catersfor up to 115 children between the agesof 3 and 11. The school consists of nineteaching classrooms and a nursery as wellas a hall, a dining room and moreinformal open areas which are used foractivities such as art and cookery. There isalso an audiology room which is discussedin more detail later.

Pupils are taught in small groups by ateacher aided by a classroom assistant.The teachers wear radio transmitters andall pupils wear radio hearing aids so thatthey can make use of their residualhearing. Sign language (accompanied byspeech) is used for teaching.

Classes were observed to gain aninsight into the use of the school andmeasurements of background noise,reverberation time and sound insulationwere carried out.

LocationThe school is located on the outskirts of acity, a considerable distance away fromthe main road, in a residential area.

Layout and constructionA part plan of the school showing theclassrooms for Year 2 and Year 3W isshown in Figure 7.7.1. Good internalspace planning has generally ensured thatnoise sensitive areas have not been placedimmediately adjacent to noise producingareas, thus avoiding the need for highperformance sound insulating

constructions. The dining room and mainhall are separated from the nearestteaching rooms by an area which is usedfor activities such as art. Where there aretwo adjacent classrooms, storage areashave been created between them to act asa buffer zone. The school is single storey,so impact noise from footfalls and chairsbeing moved above is not an issue. Thepartitions are blockwork; the doors aretimber hollowcore doors with no seals.The roof construction is not known, butthe quiet location means that ingress ofexternal noise is not problematic. Allclassrooms are naturally ventilated.

The classrooms for Year 2 and Year 3Ware adjacent but are separated by storerooms. Both rooms are entered through acommon area which is used for art andcraft work, for storing teaching aids and asan area in which the classroom assistantscan prepare teaching material. Thiscommon area is a useful acoustic buffer

Circulation

ResourcesRoom

External

CommonArt/Craft

area

Year 2

Year 3WWCs

Elec. intake

Store

Kitchen

StoreStore

Figure 7.7.1: Part plan ofprimary school showingYear 2 and Year 3Wclassrooms

Case Study 7.7: An all-age special school for hearing impaired children 7.7

130

zone separating the classrooms from thecorridor. Despite the fact that the twoclassrooms have been designed so thatnoise from one does not disturb teachingin the other, classes were being taughtwith the doors open between eachclassroom and the common area. Noisefrom one classroom was thus clearlyaudible in the classroom next door.

Surface finishesIn classrooms, surface finishes have beenused to control reverberation times. Allclassrooms have thin carpet on the floors.The pitched classroom ceilings arecovered in mineral fibre tiles; these extenddown to cover the walls at high level(from the ceiling down to the height ofthe tops of the doors). The walls have apainted plaster finish with hardboardpinboards dispersed around them.

The amount of absorption providedensures that the reverberation time issufficiently short to provide goodconditions for speech.

The measured unoccupied mid-frequency RT in the classroom for Year3W was 0.3 seconds with a rise to 0.7seconds at 125 Hz. The full spectrum isshown in Figure 7.7.2.

Sound insulationSound insulation measurements werecarried out between the Year 2 and Year3W classrooms because these representeda ‘worst case’ sound transmissionconfiguration, no two other classrooms

being located so close together.The sound insulation between the Year

2 classroom and the common art/craftarea via the Year 2 classroom door, whichwas closed, was also measured.

The BB93 standardized weightedsound level differences, DnT(0.4s),wbetween Year 2 and Year 3W classroomsand between Year 2 classroom and thecommon art/craft area were as follows:Year 2 classroom to Year 3W classroom:

DnT(0.4s),w = 53 dBYear 2 classroom to common area:

DnT(0.4s),w = 18 dB

Ambient noise levels during lessonsMeasurements of ambient noise weremade during a desk-based lesson in theYear 2 classroom. A teacher, two classroomassistants and five children were present.Maximum sound levels of 85 dB LAmaxwere measured. The equivalent continuoussound level was 65 dB LAeq. Althoughthere was some noise made by the pupilstrying to talk, the dominant noise sourcewas due to the teacher talking to theclassroom assistants. Noise from the Year3W classroom was also audible.

Measurements of ambient noise werealso made during a physical educationlesson in the main hall. The classconsisted of a teacher, two assistants andapproximately 10 children. Noise levelswere very similar to those measured inthe Year 2 class; namely a maximumsound level of 84 dB LAmax and anequivalent continuous sound level of 65 dB LAeq.

Unocupied noise levelsNoise levels were measured in the Year 2and Year 3W classrooms during a timewhen the rooms were unoccupied. Theseresults are shown in Table 7.7.1.

The measured values were 40 dB LAeqin the Year 2 classroom and 29 dB LAeqin the Year 3W classroom. The dominantnoise source in the Year 2 classroom wasfrom the fan on a computer. In Year 3Wthere was no computer on, but at highfrequencies noise from a fluorescent lightfitting was dominant.

1

0.8

0.6

0.4

0.2

063 125 250 500 1000 2000 4000


Reve

rber

atio

n tim

e, s

Figure 7.7.2: Measuredreverberation time in Year3W classroom

Case Study: An all-age special school for hearing impaired children7.7

131

DiscussionA fundamental issue in the design ofrooms for teaching hearing impairedchildren is the level of background noisewhich should be allowed. Backgroundnoise is amplified by hearing aids andreduces the signal to noise ratio ofspeech, reducing the effectiveness of thepupils’ residual hearing.

The quiet location of the primaryschool and the absence of mechanicalventilation in the building ensures thatindoor ambient noise levels in classrooms(29 dB LAeq in classrooms withoutcomputers) are low. This is lower than therecommended maximum indoor ambientnoise level for classrooms for teachingseverely hearing impaired pupils (seeTable 6.1 of Section 6).

A potential disadvantage of lowbackground noise levels is that there islittle masking of intrusive noise, so goodsound insulation is essential. The layoutof the school has been designed to tacklethis by not locating noise-sensitive roomsadjacent to noise-producing rooms.

The sound insulation between the Year2 and Year 3W classrooms of 53 dBDnT(0.4s),w meets the performancestandard in Table 1.2. This would beexceeded between other classrooms in theschool which are further apart than theYear 2 and Year 3W classrooms. Ifteaching were to be carried out with thedoors between rooms shut, there wouldbe little risk of noise from one classroomdisturbing the class in the adjacent room.

The measured sound insulation of 18 dB DnT(0.4s),w between the Year 2classroom and the common area is poorand implies that the door is a weak soundinsulating element. If a class was beingtaught in the Year 2 or Year 3Wclassroom while a separate teachingactivity was going on in the commonarea, then it is highly likely that noise

from one would disturb the other. Thiswas not perceived to be a problem by theteaching staff, as the classes were beingtaught with the doors open. Effectiveframe and perimeter seals would improvethe performance of the doors slightly, butthe door constructions would need to bechanged to incorporate solid cores inorder to significantly improve the soundinsulation.

The control of reverberation time isvital, firstly to ensure that speech isintelligible and secondly to prevent anexcessive build up of reverberant noisewhich can impair speech discrimination.The measured classroom mid-frequencyreverberation time of 0.3 seconds meetsthe performance standards in Table 1.5.

It is often recommended that classroomceilings are sound absorptive around theperimeter but reflective in the centre toaid propagation of the teacher’s speech tothe rear of the classroom. In this school,the classrooms were very small and pupilssit near the teacher because of the smallnumbers in each class, so soundpropagation to the back of a largeclassroom is not an issue. In largerclassrooms for teaching hearing impairedchildren, however, a central soundreflective ceiling zone may beadvantageous.

Key design points to note are:

• quiet site location, away from any major noise sources such as roads, railwaysand industrial premises

• separation of classrooms by buffer zones such as store rooms, corridors andlobbies

• use of carpet and sound absorptive ceiling tiles in all classrooms to control reverberation times.


63 125 250 500 1 k 2 k 4 k 8 k

Year 2 LAeq (dB) 38 33 44 37 33 29 23 20

Year 3W LAeq (dB) 39 28 22 17 17 17 25 25

Table 7.7.1: Measuredunoccupied noise levels inclassrooms

Case Study: An all-age special school for hearing impaired children 7.7

132

A special unit in a mainstreamsecondary school

The special unit for hearing impairedpupils is located in a refurbished block ofthe mainstream secondary school andconsists of six teaching classrooms, theresources area, a speech therapy room andan office for the headteacher of the unit.

When in the special school unit, pupilsare taught in small class groups. Pupils areencouraged to communicate using signlanguage, lip-reading, speech and residualhearing with the help of hearing aids. For30% of the time, hearing impaired pupilsare taught in integrated classes in themainstream school.

The special school unit forms aninteresting comparison with the primaryage part of the same school which islocated in a nearby primary school, and issome 20 years older.

The unit was visited only four monthsafter it was opened. During the visit,discussions were held with the headmasterof the hearing impaired unit to obtain hisopinions on its acoustics. Measurementsof background noise, reverberation timeand sound insulation were carried out.

LocationThe secondary unit is surrounded onthree sides by open countryside, and is farfrom any main roads. The unit is at oneend of the school, so that the potentialfor noise break-out from other classroomsis minimised. Background noise levels onthe site are low.

Layout and constructionThe special school accommodation isdivided between the ground and secondfloors, with mainstream accommodationin between on the first floor. Figure 7.7.3shows the plan of the ground floor.

Unlike the primary school, classroomsare located immediately adjacent to eachother with no non-sensitive buffer zonesin between. Partitions between adjacentclassrooms are studwork and consist ofone layer of 12.5 mm plasterboard andone layer of 19 mm plasterboard on eachside of a 48 mm stud. The partitionbetween the headmaster’s office and thespeech therapy room is built of staggered70 mm studs with two layers of 15 mmplasterboard on each side and mineralwool in the cavity. The partitions havebeen built to full height up to structuralslab level. The headmaster complained,however, that there were gaps at thepartition heads which reduced the soundinsulation of the partitions, meaning thatsound from one classroom could often beheard in the adjacent room. Examinationof the partition heads revealed that pipepenetrations of the partitions had notalways been properly sealed.

In many cases adjacent classrooms haveconnecting doors. All the doors in thespecial school are single solid core timberdoors of 40 - 50 mm thickness with wiperseals acting on a raised timber thresholdand compression frame seals. Externalwindows are double-glazed with a deepcavity (approximately 200 mm) and areopenable via a sliding casementmechanism.

The party walls between the specialistschool and the adjoining mainstreamschool accommodation are masonry.

The first floor mainstream classroomshave been carpeted to reduce impactnoise transmission to the ground floor

Classroom 5

Classroom 4

Classroom 3

Circ

ulat

ion

Tea room

Headmaster'sOffice

Speech Therapyroom

Male WC(part of mainstream

school building)

StoreWC

External

Figure 7.7.3: Groundfloor plan of secondaryschool unit for hearingimpaired pupils


133

classrooms, although the carpet has only athin pile and does not appear to haveunderlay beneath it. Floor slabs are ofconcrete. No mechanical ventilation isprovided.

Surface finishesAll the classrooms have thin pile carpetsand mineral fibre suspended ceilings. Theplasterboard walls have a sound reflectivefinish. Pinboards on the walls are timber,backed by an airspace and provide somecontrol of low frequency reverberationtimes. The speech therapy room also has athin carpet and a suspended mineral fibretile ceiling. The amount of absorptionprovided ensures that the reverberationtime is sufficiently short to provide goodconditions for speech.

Reverberation timeThe measured unoccupied mid-frequencyRT of classroom 4 was 0.4 seconds with asmall rise to 0.5 seconds at 125 Hz.

The measured unoccupied mid-frequency RT of the speech therapy roomwas 0.3 seconds with a flat spectrumdown to 125 Hz.

Sound insulationSound insulation measurements werecarried out between classrooms 4 and 5which are horizontally adjacent.

The weighted BB93 standardized leveldifference between classrooms 4 and 5was 34 dB DnT(0.4s),w .

The sound insulation between severalother areas was also measured and thefollowing weighted BB93 standardizedlevel differences obtained:• classroom 5 to mainstream classroomdirectly above: DnT(0.8s),w = 48 dB• headmaster’s office to speech therapyroom: DnT(0.4s),w = 47 dB• male toilets to speech therapy room:

DnT(0.4s),w = 52 dB

Unoccupied noise levelsNoise levels were measured in classroom 4and the speech therapy room during atime when the rooms were unoccupied,but when there were staff elsewhere in thebuilding. The noise spectra are shown inTable 7.7.2.

The corresponding indoor ambientnoise levels are 26 dB LAeq in classroom 4and 19 dB LAeq in the speech therapyroom. The dominant noise sources inclassroom 4 were a faint buzzing noisefrom the radiator and from fluorescentlight fittings. Talking in other classroomsin the unit was just audible. The mainnoise sources in the speech therapy roomwere a clock ticking and a fluorescentlight fitting buzzing. The headmaster’svoice as he talked on the telephone in hisoffice next door was clearly audiblealthough the words were not intelligible.It should be noted that at highfrequencies the reported octave bandnoise levels in the speech therapy roomwere actually due to electrical noise in thesound level meter; actual noise levels wereprobably lower.

DiscussionMeasured noise levels in a typicalclassroom and the speech therapy roomwere very low (26 dB LAeq and 19 dBLAeq respectively) and are lower than therecommended noise levels in Table 6.1.This is appropriate in rooms in whichhearing impaired pupils are taught, toensure good speech signal to noise levels.There was no unpleasant tonal content inthe frequency spectra.

Very low unoccupied ambient noiselevels mean that any extraneous noiseintrusion will be especially audible. Thesite location and high performanceexternal windows ensure that noise ingressfrom outside does not cause problems.The teaching staff have, however,


Leq (dB) 63 125 250 500 1 k 2 k 4 k 8 k

Classroom 4 34 30 29 18 22 13 12 13

Speech therapy room 28 23 15 12 12 11 11 12

Table 7.7.2: Measuredunoccupied noise levels inClassroom 4 and thespeech therapy room


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complained about the sound transmissionbetween horizontally adjacent rooms. Thesound insulation appears to be of a lowerstandard than they had expected in a newpurpose-built unit. These subjectivecomments are borne out by the results ofthe objective sound insulationmeasurements. The DnT(0.4s),w of 34 dBmeasured between classrooms 4 and 5 islower than that required for classrooms inmainstream schools. Where backgroundnoise levels are low, hearing impairedpupils cannot discriminate betweenintrusive noise and speech as easily aspupils with full hearing, and a higherstandard of sound insulation is needed. Aminimum DnT(0.4s),w value of 50 dB isrequired, see Table 1.2.

Measurements showed that the soundinsulation performance of the partitiondid not rise at high frequencies as wouldnormally be expected. This confirms theexistence of small gaps which were foundat the partition heads. Notwithstandingthis, the mid frequency level differenceacross the partition is poor (between 30dB and 35 dB). This indicates that thestudwork partition selected was not of asufficiently high performance. A partitionwith staggered studs, increasedplasterboard thicknesses and mineral woolin the cavity would provide a higherstandard of sound insulation. The overallsound insulation performance betweenadjacent classrooms is, however,ultimately limited by the communicatingdoor. Although the doors are of a veryhigh standard (this is discussed furtherbelow) they are still a weak soundinsulation element. Whilst this may not bea serious problem between classroomsand the corridor, the presence of doorsbetween classrooms is inconsistent withthe requirement for a high standard ofsound insulation. Connecting doors arenot recommended.

The sound insulation measuredbetween the headmaster’s office and thespeech therapy room was 47 dBDnT(0.4s),w . This is below theperformance standard in Table 1.2 forsound insulation between an office and aspeech therapy room. The headmasterhad complained that he was sometimes

disturbed by noise from the speechtherapy room and whilst in theunoccupied room the headmaster’s voicewas audible but not intelligible. This levelof privacy means that although theheadmaster’s conversations would remainconfidential, intrusive noise may disturbthe concentration of both the headmasterand of users of the speech therapy room.A higher standard of studwork wallconstruction between rooms may havebeen considered to be impracticable inthe special school design. An alternativesolution would have been to locate non-sensitive acoustic buffer zones, such asstorage areas, between the headmaster’soffice and other noise producing rooms.

A value of 48 dB DnT(0.4s),w wasmeasured from one of the ground floorclassrooms for hearing impaired pupils tothe mainstream classroom directly aboveit on the first floor. This is an appropriatestandard of sound insulation for themainstream classroom and no complaintshave been made by the teaching staff.

Visual inspection of the doorsetsconfirmed that they were of suitablequality and likely to meet the 30 dB Rwsound insulation specification for doorsetsin Table 1.3.

Reverberation times in the classroomsare well controlled due to the provision ofacoustic absorption on the floors andceilings. The mid-frequency RT of 0.4 seconds meets the performancestandards in Table 1.5. The wooden wallpanels help to control the RT at lowfrequencies, on which hearing impairedpeople often rely for information. Theteaching staff judged the classroomacoustics to be satisfactory.

The RT in the speech therapy room isalso well controlled due to the carpet andmineral fibre suspended ceiling. The mid-frequency value of 0.3 seconds meets theperformance standards in Table 1.5.

Conclusions The acoustic design of the special schoolunit is good, in terms of room acousticsand unoccupied noise levels, althoughthere are some deficiencies in the soundinsulation provided by the party wallconstructions.


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Key points to note are:• The site is in a quiet location, awayfrom any major noise sources such asroads, railways and industrial premises.• Communicating doors betweenadjacent classrooms limit the soundinsulation that can be achieved and areinconsistent with the need for low levelsof intrusive noise.• Partitions are full height, but poorworkmanship has resulted in small gaps atpartition heads.• Sound transmission problems betweenthe headmaster’s office and the speechtherapy room could have been avoided bybetter space planning.• Use of carpet and sound absorptiveceiling tiles in all classrooms and thespeech therapy room helps to controlmid-frequency reverberation times.• Wooden pinboards backed by anairspace help to control low frequencyreverberation times.• First floor classrooms are carpetedwhich reduces impact noise transmission.However, there was no underlay whichwould have reduced the impacttransmission further.

Audiology room

In the primary school for hearingimpaired children there is an audiologyfacility, which consists of a technician’sroom and an audiometric test room.

The tests carried out in theaudiometric test room are generallycarried out in the ambient acoustic fieldrather than using headphones. Activitiesrange from testing hearing saturationlevels and hearing aid discomfort (duringwhich high noise levels of up to 90 dB(A)are generated in the room) to testing forspeech discrimination against backgroundnoise, which requires low ambient noiselevels.

Measurements were carried out ofindoor ambient noise, sound insulationand reverberation time in the audiologysuite. In addition, a discussion was heldwith the audiologist who uses the suite toobtain his opinion of the suitability of theacoustics.

Layout and constructionThe location of the audiology suite withinthe primary school is shown in Figure7.7.4. The audiometric test room isentered directly from the corridor. Thetest room also has an external wall and awindow onto an enclosed courtyard.

The walls of the audiometric test roomare a single skin of 100 mm thickblockwork of an unknown density. Thesingle leaf doors into the technician’sroom and the corridor are a hollowcoretimber construction with no frame orthreshold seals. Noise from the corridorwas clearly audible in the test room.There is a fixed double glazed windowbetween the test room and thetechnician’s room which incorporates adeep acoustic cavity between the panes ofglass. The external window which looksonto the courtyard is single glazed and isopenable.

The roof construction is not known,but the quiet site location means thatingress of external noise is notproblematic. There is no mechanicalventilation system.

Circ

ulat

ionStoreDeputy

Head

Secretary

Head TeacherExternal

courtyardAudiometryTest Room

Circulation

Technician'sRoom

Tea Room

Staff Room

Cleaner

WC

Figure 7.7.4: Plan ofaudiology facility


136

Surface finishesThe audiometric test room is carpetedand has a mineral fibre suspended ceiling.Apart from where there are windows ordoors, the entire wall area is also linedwith mineral fibre tiles. Subjectively, theroom is very dead acoustically.

Audiologist’s opinionThe audiologist finds intrusive noise verydisturbing to his work, particularly whenhe is carrying out tests of speechdiscrimination against background noise.This means that the times when he cancarry out certain measurements aredetermined by possible activity in thecorridor. When there is no activity in thecorridor, the background noise levels inthe room are sufficiently low for his tests.

Conversely, when loud noises aregenerated in the audiometric test room(for example when hearing aid discomfortis being tested), these can clearly be heardin the corridor, although this does notcause disturbance to teaching.

The audiologist did not express anydissatisfaction with the internal roomacoustics, but noted that achieving lowambient noise levels should be a firstpriority when designing audiologyfacilities and that good room acousticswere worthless without sufficiently lowbackground noise levels or good enoughsound insulation.

Acoustic measurements

Reverberation timeThe unoccupied mid frequencyreverberation time, Tmf, in theaudiometric test room was 0.2 secondswith a small rise to 0.3 seconds at 125 Hz.The RT across the frequency spectrum isshown in Figure 7.7.5.

Sound insulationThe sound insulation measured betweenthe technician’s room and the audiometrytest room was 36 dB DnT(0.4s),w.

Unoccupied noise levelsNoise levels were measured in theaudiometry test room when the room wasunoccupied. The results are shown inTable 7.7.3.

The noise level corresponds to an A-weighted sound pressure level of 21 dB LAeq. The dominant noise sourcewas water running through the radiator.Voices in the corridor outside wereaudible. It should be noted that at highfrequencies the reported octave bandnoise levels in the audiometry test roomwere due to electrical noise in themeasurement system; actual noise levelswould have been lower.

DiscussionGuidance for the acoustic design ofaudiology facilities in hospital audiologydepartments is given in Health TechnicalMemorandum 2045 "Acoustics:Audiology"[1], but the suite in the schoolis used for educational audiology and assuch is provided by the County in whichthe school is situated rather than by theHealth Service.The guidance includesmaximum permissible ambient soundpressure levels in third octave bands andreverberation times for audiometric testrooms, depending on the audiometrictests which will be carried out in therooms. Because the use of eachaudiometric facility is specialised, the endusers of any facility should be consultedand reference made to HTM 2045[1]

before the acoustic design of a facility isundertaken.

In this test room the background noise

1

0.8

0.6

0.4

0.2

063 125 250 500 1000 2000 4000


Reve

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n tim

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Figure 7.7.5: Measuredreverberation time inaudiometry test room

[1] ‘Acoustics: Audiology’,Health TechnicalMemorandom 2045,HMSO, 1996.


137

levels are sufficiently low for theaudiologist to carry out his tests. Thebackground noise spectrum does notcontain any unpleasant tones, due to thequiet nature of the school site.

The limited sound insulation affordedby the single leaf masonry wall and thepoor quality single door mean thatintrusive noise levels in the test room arehigh when there is activity in the corridor.The high intrusive noise levels disrupt theaudiologist’s work. An appropriate soundinsulation performance for the wallbetween the test room and the corridorwould be very dependent on the specificrequirements of the audiologist and theschool, but it is likely that a double leafmasonry wall construction plastered onboth sides (each leaf at least 415 kg/m2

including plaster) would be the minimumrequired. The door from the corridor intothe test room is a weak sound insulationelement and would limit the performanceof any upgraded wall construction. Thebest solution would be to allow entry tothe test room only via the staff room andtechnician’s room. Failing this, a lobbieddoor arrangement would be required.

HTM 2045 recommends thatreverberation times at all frequenciesbetween 125 Hz and 4 kHz are between0.2 seconds and 0.25 seconds inaudiology test rooms. The measuredreverberation times are generally withinthis range, given the accuracy of the on-

site measurements. Thus the reverberationtime in the test room has been wellcontrolled by the selection of surfacefinishes. Recommendations are also madefor reverberation times in third octavebands from 31.5 Hz to 100 Hz. Due tothe small size of the test room,reverberation times could not bemeasured accurately at these lowfrequencies.

Conclusions Although background noise levels are lowand the reverberation time is wellcontrolled, the poor sound insulationmeans that the test room is unsatisfactoryfor its purpose.

Key points to note are:• The site is in a quiet location, awayfrom any major noise sources such asroads, railways and industrial premises, so background noise levels are low.• The audiometric test room is poorly located adjacent to a noisy corridor.• The 100 mm blockwork wall between the test room and the corridor isinsufficient in controlling noise intrusion.• The single door between the test roomand the corridor is a weak soundinsulation element.• The reverberation time is well controlled by the use of carpet, a mineralfibre tile suspended ceiling system andmineral fibre tiles on all the walls.

Table 7.7.3: Measurednoise levels in audiometrytest room, unoccupied


Leq (dB) 63 125 250 500 1 k 2 k 4 k 8 k

Audiometry test room 35 24 21 17 12 10 11 13


139

Figure 7.8.1 shows a site plan, based on the site survey carried out at the startof the project. The high external noiselevels are generated by low-flying aircraftand traffic on nearby busy roads. Oneoption would have been to acousticallyseal the building envelope andmechanically ventilate the building.However, this was too expensive for theavailable budget. The design team alsowished to reduce lifetime costs and optedfor a naturally ventilated building whichwould maintain the same internal noiselevels.

Being an inclusive school, the designhad to accommodate pupils and othermembers of the community with hearingproblems. The target for backgroundnoise was set at 35 dB(A). At the sametime the design had to provide fresh air ata rate of up to 8 litres per second for eachof the usual number of occupants. Thisequates to approximately 4.5 air changesper hour in both ground and first floorclassrooms.

Standard products such as attenuatedtrickle ventilators inserted into windowopenings, as are often used in housing,would not have achieved the required airflow rates. Alternative purpose designedsystems were therefore required.

Classrooms are naturally ventilated bymeans of inlet vents under the externalwindows and passive stacks located at highlevel at the rear of the rooms, adjacent tothe central corridors. The inlet louvresduct air into the classrooms via grilles justinside the perimeter convector grilles.These inlet grilles are controlled byclassroom users by easy to operateopenable flaps covering the grilles.

Both inlets and outlets are acousticallyinsulated to prevent the entry of externalnoise.

Depending on the prevailing weather,wind driven or temperature drivenventilation provides sufficient fresh air.• The more windy the weather, thegreater the pressure difference across thebuilding envelope and the greater the air

Figure 7.8.1: Site planshowing external noiselevels, LAeq

N

SCHOOL

Church

Pub

aircraft take-offand landing

traffic

traffic and light railway

55-60 dB

50 dB

55-60 dB

60-65 dB

Airport runwayto

south east

Case Study7.8: Acoustic design of building envelope and classroomsat a new secondary school 7.8

140

movement in the ducts.• The temperature difference when theinternal spaces are warmer than outside,as in winter, drives the stack effectventilation causing air to rise up thecentral ducts.• The central ducts which leave the backof the classrooms join into a combined

duct over the first floor corridor whichthen rises to the outlet at roof level. Thepassive stack effect is enhanced byproviding roof glazing over the combinedsection of duct which is painted black andencased over a drop ceiling area in thecorridor. Solar gain raises the airtemperatures in the top section ofductwork causing the air to rise. This isparticularly effective in hot weather.• An aerofoil is positioned at the ductoutlet to enhance the wind driven stackeffect. The problem of wind blown rain instorm conditions led to modification ofthe aerofoils to incorporate louvresbeneath the aerofoil sections. This willprobably have made the aerofoils on theirown considerably less effective.• The windows are openable and aredesigned to increase the maximumpossible ventilation rate so that when thewind and stack driving forces are smallthere will still be adequate ventilation,although this will obviously let in someambient noise.

The ventilation system is completelyunder the control of the occupants inindividual spaces, who can open and closeflaps over the inlets below the windows

WEST- EAST STAGGERED SECTION THROUGH CLASSROOMS IN SOUTH WING

aerofoil cover creates up draft of used air inacoustically attenuated ducts

used air outlouvres closed at night in winter

open in summer

fresh air inthrough

acousticallyattenuated

openings

air heated by radiators in winterrises and mixes with cool fresh airentering through vents

exposed thermal massheat retained in concrete floor slab

re-emitted at nightnight ventilation in summer

prevents daytime overheating

exposed thermal mass

fixed louvres added after building completion to prevent rain penetration in storm conditions will reduce aerofoil effect

sunlight entering through rooflight heats extract duct to assist air movement by stack effect

DIRECTION OF PREVAILING WIND

profiled metal deck roofacoustically filled abovepartition walls

sunlight controlled byadjustable rooflight louvre blinds

Manually operated fresh air vents.In winter - some fresh air vents closed

during daytime to reduce heat lossand all closed at night.

In summer - open at nightfor night ventilation

downstands acousticallylined

used air outby convection and wind-assistancelouvres closed at night in winteropen in summer

fresh air inthroughacousticallyattenuatedopenings

middaysummer sun

early orlate sun

Figure 7.8.2: Schematicdiagram of ventilationpaths through two storeysection of building

Linear grill

Radiator

Ventilation flap

Acoustic infill glued toaluminium casing

Fixed divider

2 layersof self-extinguishing

fire retardentnylon mesh

Insect mesh

Ground level

80 mm cavity insulation

Overhanging sill toprevent direct passage

of sound

Figure 7.8.3: Groundfloor air vents

Case Study: Acoustic design of building envelope and classroomsat a new secondary school7.8

141

and high level adjustable louvres at theback of the classrooms, controlled by ashort pole.

Ground floor vents (Figure 7.8.3) andfirst floor vents (Figure 7.8.4) are ofdifferent design. These proprietary/purpose designed external vents on thewindow walls are acoustically insulated.

The airborne sound insulation ofprototype ground floor and first floorventilators was tested in the laboratory.The resulting element-normalized leveldifferences in octave bands and theresulting Dn,e,w values are shown inTable 7.8.1. As a result of these tests, theground floor vent design was modified toimprove its performance. This includedthe addition of an overhanging sill andextended internal nibs of sound absorbingmaterial. The final design, shown inFigure 7.8.3, appears as effectiveacoustically after installation as the firstfloor vents.

The passive stacks are acoustically linedwhich prevents cross-talk betweenclassrooms which share the samedischarge ductwork. Four classrooms areventilated via one final extract duct.

Air flow tests were carried out intypical classrooms. These showed that ona typical spring day, with a moderate wind(10-15 kph), with all the vent flaps andlouvres open, air entered at between 0.8and 1.6 m/s depending on locationwithin the building, and left through thehigh level louvres at between 0.3 and 0.7m/s, again depending on location. Thiscorresponds to a fresh air rate of 5.3 airchanges per hour.

Metal deck roof The roof structure, from outside in, is asfollows: • 0.9 mm gauge stucco embossed aluminium external covering

• 120 mm (compressed to 110 mm) thermal insulation• 30 mm acoustic insulation• vapour control layer• 0.9 mm gauge polyester powder coated steel (internal support decking).

There is no void within the roof exceptbetween the profiles of the supportdecking. The profile voids are filled atpartition lines with inserts of acousticallyabsorbent material.

There is some flanking transmissionthrough the continuous profiled steel roofconstruction, which reduces the soundinsulation between rooms.

Concrete floor At first floor level, the floor finish on theprecast concrete floor is a steel meshreinforced sand/cement screed on 50 mmthick acoustic mineral wool board, whichprevents the transmission of impact soundto the ground floor rooms below.

Linear grill

Radiator

Ventilation flap

Acoustic infillFixed divider

2 layersof self-extinguishing

fire retardentnylon mesh

Insect mesh

Sound reducing andinsulating aluminium faced

composite panel

Figure 7.8.4: First floorair vents

Table 7.8.1: Element-normalized leveldifferences for prototypeground floor and first floorvents

Case Study: Acoustic design of building envelope and classroomsat a new secondary school 7.8


Dn,e (dB) 63 125 250 500 1 k 2 k 4 k 8 k Dn,e,w (dB)

Ground floor vent 28.0 21.6 22.5 25.8 40.8 57.9 54.0 53.9 33

First floor vent 24.5 19.6 22.2 28.4 42.2 50.8 53.4 53.0 34

142

Internal partitionsInternal partitioning generally uses twolayers of 12.5 mm plasterboard each sideof metal studs, with quilt in the cavity,giving a construction width of 200 mm.Laboratory test results for this form ofconstruction indicate a sound reductionindex of 52 dB Rw. Performance on siteis usually at least 5 dB less than this. Testscarried out on site show a considerablevariation in performance, from 44 dB to38 dB Dw. The walls therefore meet thestandard of 38 dB for classrooms given inBuilding Bulletin 87, that was required atthe time of the design. However some failto meet the 43 dB Dw design target forthe project, which is lower than thepresent standard given in Table 1.2.There are a number of causes of theperformance loss. On the first floor,flanking sound carried through thelightweight roof was seen to be acontributory factor, despite the use offillers in the profile voids. However, thebest performance was also recorded inone of the first floor rooms. A reduction

in insulation was found in some groundfloor rooms where partitions directly abutthe precast concrete first floor. Theconclusion was that variability inconstruction standards, rather thandetailing, was the key factor.

Generally, staff and pupils at the schooldo not consider noise between spaces tobe a problem, and are happy with theacoustics.

Classrooms are provided with acoustictreatment in specific ceiling areas to bringthe mid-frequency reverberation timesbelow 0.8 seconds. At first floor level, thisis provided at the rear of the rooms, overthe sloping soffit which encloses servicesand also helps to reflect daylight from therooflights into the back of the room. Onthe ground floor, suspended ceilings runalong both sides of classrooms to encloseservices and cut off indirect sound paths.In the centre, the first floor precastconcrete floor slab is exposed to absorbre-radiated solar radiation and to reinforcedirect speech sound paths.

Case Study: Acoustic design of building envelope and classroomsat a new secondary school7.8

143

The site plan shows that the newextension is adjacent to a heavily pollutedinner city road. The road is a very busytwo lane highway and is the main sourceof noise in the area.

Acoustic designThe acoustic design was based on thenoise limits recommended in BuildingBulletin 87(BB87) of 40 dB LAeq,1h inclassrooms and not more than 50 dBLAeq,1h in a gymnasium. These values arenow superseded by the performancestandards in Section 1 of BuildingBulletin 93.

Noise surveyNoise surveys were carried out on sitebefore and after the completion of thenew extension. The aim was to establishthe external noise levels and use thesedata to calculate the required soundinsulation for the building envelope.

The measured free-field external noiselevel was 70 dB LAeq. The major sourceof noise was road traffic on the very busymain road.

The rooms with most exposure to roadtraffic noise are:Ground Floor: Gymnasium First Floor: Language classrooms 1, 2 and 3Second Floor: Mathematics classrooms 2, 3,4 and 5 and ICT rooms 1 and 2.

Sound insulation of the buildingenvelopeThe noise levels to which various parts ofthe building envelope would be exposedwere calculated by extrapolation from thebaseline noise measurements according tothe Calculation of Road Traffic Noise.Design calculations of internal noise levelswere made on an iterative basis todetermine required acoustic specificationof the windows, the roof and the windscoop system so that background noiselevels given as guidance in BB87 wouldnot be exceeded.The building envelope comprised:• walls: part brick/block cavity, partblockwork with a terracotta tile rainscreen and mineral fibre in the cavity• windows: double glazing incorporating10 mm and 6.4 mm laminated glass• main roof: proprietary double skin steelroofing system (38 dB Rw)• mansard roof: proprietary roofingsystem, supplemented by an internalplasterboard lining with mineral fibre infill• roof lights: double glazingincorporating 4 mm glass.

Recommendations were given for theattenuation of external noise through thewind scoop system. It was recognised thatnew measures to attenuate external noisemight affect the airflow characteristics andtherefore any suggestions would need tobe confirmed by the manufacturer.

The manufacturer of the wind scoopsystem arranged for acoustic tests to beundertaken in a UKAS test laboratory. Anumber of different internal liningtreatments were tested. The results aresummarised in Table 7.9.1.

Initial calculations for the classroomsindicated that a 5 m length of lined ductwould provide sufficient attenuation toreduce the internal noise to approximately40 dB LAeq. For classrooms on thesecond floor, the wind scoop ducts werenot long enough and it was necessary toincrease the attenuation by fitting anadditional attenuator. For classrooms onthe lower floors the length of the windscoop duct was sufficient and noadditional attenuator was required. Theproposed duct details are summarised inTable 7.9.2.

B u s y r o a d

Qu i e t

s t r e e t

Si d

e s

t re

et

housing

Commercial

Commercial

Chur

ch

housing

housing

Newextension

Existing school

housing

Case Study7.9: Acoustically attenuated passive stack ventilation of anextension to an inner city secondary school 7.9

144

Post-completion measurements ofindoor ambient noise levelsFollowing completion of the building,measurements of the indoor ambientnoise levels were carried out at a numberof different locations in each room andaveraged. Simultaneous measurementswere taken of the free-field external noiselevel which was 70.6 dB LAeq,5h andwithin 1 dB of the level measured prior todevelopment. The measurement resultsare summarised in Table 7.9.3 where theyare compared with the design targets and

predicted values.The measured results in the

Gymnasium, Languages 1, Mathematics 2and Mathematics 3 were found to meetthe design limits. The failure to meet theinternal noise limit in Languages 3, ICT 1and ICT 2 can be explained by the factorsnoted in the comments column, that is,excessive noise transmission via unsealedwindow frames and the noise fromcomputer fans in the operational ICTrooms.

Internal noise measurements were also

Case Study: Acoustically attenuated passive stack ventilation of anextension to an inner city secondary school7.9

Table 7.9.1: Laboratorymeasurement data for theairborne sound insulationof the wind scoop system

Table 7.9.2: BB87background noise levelsand proposed duct details

Table 7.9.3: Comparisonbetween the BB87background noise levels,calculated and measuredindoor ambient noise levels

Test element

620 mm x 620 mm square holeVent, unlined with dampers openVent, unlined with dampers closedVent lined with acoustic tile, dampers openVent lined with acoustic tile, dampers closedVent lined with open cell foam, dampers openVent lined with open cell foam, dampers closedVent lined with open cell foam, linear ceiling grille fitted

Dn,e,w (C;Ctr) (dB)

13 (0;0)16 (0;0)26 (0;-1)26 (0;-3)35 (-1;-5)26 (0;-3)35 (-1;-4)27 (-1;-4)

Classroom

Mathematics 2, 3, 4 and 5

ICT 1 and 2

Languages 1, 2 and 3

Gymnasium

Floor

2

2

1

Ground

BB87 backgroundnoise levels LAeq,1hr (dB)

40

40

40

50

Treatment

Internal acoustic lining plus500 mm attenuator

Internal acoustic lining plus1800 mm attenuator

Internal acoustic lining

Thermal insulation only toblockwork ducts

BB87 backgroundnoise levels Calculated Measured

Room LAeq,1h (dB) LAeq,1h (dB) LAeq,1h (dB) Comments

Gym 50 45 42 Significant flanking transmission around escape door

Languages 1 40 37 38Languages 3 40 40 43 Some window frames not yet sealedMathematics 2 40 39 38Mathematics 3 40 40 38Mathematics 4 40 41 41ICT 1 40 42 44 Computer noise presentICT 2 40 33 42 Computer noise present

145

carried out with the ventilation systemopen and closed. The results did notdisplay any significant change in level norwas there any significant variation in thesound pressure level around the room.

Ventilation designThe close proximity of the road meantthat open windows could not be used forventilation because road traffic noisewould cause problems and airbornepollutants emitted by the heavy roadtraffic could be carried into the buildingthrough low level open windows.

The rooms exposed to traffic noise aretherefore ventilated using a wind scoopsystem with the exception of a manager’soffice which is provided with a noise-attenuated ventilator unit. This type ofunit was originally developed to complywith the requirements of the NoiseInsulation Regulations 1975. The uniteither comprises a variable speed poweredventilator which is designed to beinstalled in the building façade and apermanent air vent, or it may be a singleunit which combines both. There arenormally two speed settings and theRegulations set limits on noisetransmission through the units and theself noise of the fan.

The acoustic consultant suggested thatattenuated ventilators should also be fittedin Mathematics classroom 1, theMathematics office and the staff room asopening the windows in these roomswould result in noise levels exceeding theBB87 guidance of 40 dB LAeq,1hr .

Taking into account the characteristicsof the new building and site conditions,adequate ventilation has been achieved asdescribed below.

(i) Teaching areas (Classrooms, ICTRooms, Science Laboratory andGymnasium)All new teaching spaces are naturallyventilated by a wind scoop type systemthrough terminals mounted at roof level.The roof terminals are designed to beomni-directional allowing the intake offresh air regardless of the prevailing winddirection. Each terminal is divided intoequal quadrants; two are positivelypressurized by the wind to create a freshair intake, the remaining two on theleeward side are negatively pressuredallowing stale air to be exhausted.

Air is ducted from the terminals eitherdirectly into the second floor rooms ordown to the ceiling of the first floorclassrooms and gymnasium. Each terminal

Case Study: Acoustically attenuated passive stack ventilation of anextension to an inner city secondary school 7.9

extra coolingin summertime

fresh air fromprevailing westerlywind

exhausted airopposite to

prevailing wind

exhustair

freshair

acoustic liningin all ducts

stair well

classroom classroom

classroom

sports hall

w.c.'s

Fan assisted

Fugure 7.9.2: The roofterminals, viewed frominside during construction

Figure 7.9.1: Sectionthrough new extensionshows stack ventilation inoperation

has been carefully sized according to thevolume of the space to be ventilated, thenumber of people who will normallyoccupy each space and any potentialsource of additional heat, for examplesolar gain or computers. The performanceof each terminal has been modelled for avariety of wind speeds to ensure thatadequate fresh air can be provided.

Each terminal is individually controlledby dampers set in the ends of the duct tomodify the ventilation rate according tothe actual conditions in each room.During summer time the control is basedon room temperature because higherventilation rates are required to keep therooms within acceptable comfort levels.With passive stacks, temperaturedifferences within the room and thelength of the ducts will result in improvedextract. During the winter the quantity offresh air needs to be minimized, reducingheat losses via exhaust air, hence there iscontrol by an air quality sensor.

A manual override allows users to havecontrol of the system depending on theirexperience of room conditions. Allwindows are openable to allow additionalfresh air to be introduced, for example,during changeover of lessons whenindoor ambient noise levels are lesscritical.

The proposed system takes fulladvantage of the prevailing siteconditions. Fresh air is both drawn inand exhausted at the highest level. Windspeeds at 15 m above the ground will behigher than at street level due to fewerobstructions by surrounding buildings.The quality of the air also generallyimproves with increasing distance fromthe source of pollution, which in thiscase is road traffic. Heavy pollutants fromvehicle exhausts tend to remain at streetlevel particularly in conditions of highatmospheric pressure.

The ventilation strategy also allows fornight time cooling of the building.Studies have shown that air quality bymain roads improves at night due tolower traffic flows. At the end of each daystale air left in the building can be fullyreplaced and then warmed, depending onthe season, ready for the next morning.

(ii) Rooms for specialist activities(Changing rooms, toilets, shower areasand science laboratories)Natural ventilation is not suitable forcertain parts of the building. Thereforelimited mechanical intake and extract areused in areas which require a high rate ofventilation, for example in changingrooms where high levels of water vapourand body odours need to be removed.The mechanical system extracts air at lowlevel, with a simple heat recoveryapparatus used to reclaim heat, andreplacement air is filtered to removeairborne particles.

The science laboratory requires specificextract ventilation to fume cupboards.This is achieved by mechanical extractventilation systems that exhaust awayfrom the other roof terminals, with make-up air being naturally induced via a windscoop and opening window lights.

This case study demonstrates that free-field external noise levels can be reducedby approximately 30 dB inside naturallyventilated classrooms using a soundattenuated passive stack ventilationsystem.

146

Case Study: Acoustically attenuated passive stack ventilation of anextension to an inner city secondary school7.9

Motorised volumecontrol damper Eggcrate

ceiling diffuser

Acoustic lining fitted tointernal dividers,capping and trunk

Exhaust airPrevailing Wind

Anti bird mesh

Figure 7.9.3: Sectionthrough ventilation stackshows stack operation andacoustic treatment

Figure 7.9.4: Three ofthe roof teminals, duringconstruction

147

Case Study: An investigation into the acoustic conditions in open-planlearning spaces in a secondary school 7.10

An investigation was carried out into theacoustic conditions in open plan learningspaces in a secondary school, constructionof which was completed in 1991. Figure7.10.1 shows the site. The ground andfirst floor plans can be seen in Figure7.10.3.

The curriculum model divides the dayinto 3 hour subject modules. Teamteaching is fundamental to the curriculumand to facilitate this, there are severalrelatively large open plan learning bases,as shown in Figure 7.10.2, that typicallyhold around seventy students.

Some of the learning bases are used forteaching particular subjects such asMathematics or English. All the learningbases are subdivided into smaller areas sothat different lessons or activities can take

0 50m

HARDPLAYAREA

CAR PARK

CAR PARK

CAR PARK

Figure 7.10.1: Sitelayout

Corridor

Corridor

Cloakroom Toilets

AREA C

AREA B

PCs

PCsTeacher's

office

SCREENS

SCREENS

LOCKERS

LOCK

ERS

ENTRANCEENTRANCETO

BUILDING

SCREEN

Soft seatingarea

Overheadvideo

projector

Class/launch presentationspace

Whiteboard

LEARNING BASE 1 (English)

Teacher'sPC

AREA A

AREA D

Figure 7.10.2: Open planlearning base 1

148

Case Study: An investigation into the acoustic conditions in open-planlearning spaces in a secondary school7.10

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Figure 7.10.3: Schoollayout


149


place at the same time. Typically, moveablescreens or lockers are used to separate thedifferent areas within a learning base.

Acoustic measurements Measurements of sound pressure level,reverberation time, speech intelligibilityand airborne sound insulation were madein the school to assess the acousticenvironment. These measurements weremade in learning base 1 (English learningbase), the art area, the workshop andtechnology areas, and language teachingrooms (study area 1 and study area 5).

Sound pressure levels were measuredover 30 minute periods (starting on thehour or half-hour) during the school dayto determine LAeq,30min, LA90,30min,LA10,30min, LAFmax and LAFmin.Observations of classroom activity werenoted in order to attribute measuredlevels to specific activities and events.

In the open plan area of learning base1, the Speech Transmission Index (STI)

was measured according to BS EN60268-16 to assess speech intelligibility.

Airborne sound insulation wasmeasured between adjacent languageteaching classrooms. These classroomswere enclosed rooms and did not formpart of the open plan teaching space.

In addition to the acousticmeasurements, teaching staff completed aquestionnaire about the effect of theschool layout on their work.

Figure 7.10.4: Studentsin area A of learning base 1

100

90

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30

8:30

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LAFmaxLA10LAeqLA90LAFmin

Soun

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essu

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vel,

dB(A

)

At 13.40 approximately 70 Year 10 pupils occupied allareas of the learning base with roughly equal numbersin areas A, B and C, and remained there until 16.00. Atleast two of the groups were involved in activitiesrequiring speech during the whole of this period. Formost of the time, one of the three groups was involvedin an activity such as reading or private study that didnot require communication with others. Area D wasused occasionally by up to three students working withcomputers.

8.30 – 10.15 Discussionbetween teacher andaround 12 sixth formstudents in area A

10.20 – 13.00 Similaractivity as early morningwith 1 teacher and around12 students

Students return from short break at 10.20

Area unoccupiedat 13.00

Figure 7.10.5: Learningbase 1 – sound pressurelevels in area A


150


Learning base 1The open plan layout of learning base 1 isshown in Figure 7.10.2. Figure 7.10.4shows students working in area A oflearning base 1.

Sound pressure levelsFigures 7.10.5 and 7.10.6 show graphs ofthe continuous sound pressure levelsmeasured in areas A and C. Figure 7.10.7shows the difference in LAeq,30minbetween area A and area C of learningbase 1 (area A – area C).

It was intended that observations madeduring the measurements would allowanalysis of individual events that causedisturbance. This aim proved not to bepossible. For example, when a telephonerang in learning base 1 there was noobserved reaction from the students. Thetelephone in the room was used to informteachers that the students could go forlunch and appeared to be viewed asnothing unusual by the students.

Between 08.30 and 11.00 the teacherand students occupied area A. During thistime the difference between LAeq,30minin areas A and C was between 7 and 10dB (see Figure 7.10.7). Themeasurements thus demonstrate thatthere is a maximum of 10 dB attenuationof airborne sound between areas A and C.Therefore, if another class were present inarea C carrying out a quiet activity suchas private reading, the students in area Cwould be able to clearly hear the activitynoise emanating from area A. Thesemeasurements indicate that if the airbornesound insulation were measured betweenareas A and C then it would not meet theminimum performance standard forairborne sound insulation of 45 dBDnT(0.8s),w required between generalteaching areas.

Between 11.00 and 13.00 the level inarea C was sometimes higher than in areaA. The reason for this is not knownbecause area C was unoccupied, but

110

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dB(A

)

At 13.40 approximately 70 Year 10 pupils occupied allareas of the learning base with roughly equal numbersin areas A, B and C, and remained there until 16.00. Atleast two of the groups were involved in activitiesrequiring speech during the whole of this period. Formost of the time, one of the three groups was involvedin an activity such as reading or private study that didnot require communication with others. Area D wasused occasionally by up to three students working withcomputers.

8.30 – 10.15 Discussionbetween teacher andaround 12 sixth formstudents in area A

10.20 – 13.00 Similaractivity as early morningwith 1 teacher and around12 students

Figure 7.10.6: Learningbase 1 – sound pressurelevels in area C

Students return from short break at 10.20

Area unoccupiedat 13.00

151


could be due to sound generated fromthe playground outside.

When all areas in the learning basewere occupied between 14.00 and 16.00,LAeq,30min increased to levels between65 and 70 dB. To gauge the effect of thisincrease in LAeq,30min on speechintelligibility, it is instructive to considerthe required signal to noise ratio in aclassroom which is generally taken to be aminimum of 15 dB, or, ideally, 20 to 25 dBwhen hearing impaired children are beingtaught. In these noise levels, a teacher’svoice would have to be raised to a level ofat least 80 to 85 dB in order to be heardby the students. It is unlikely that ateacher would be able to shout at asufficiently high level to communicatewith hearing impaired students. Thus,based upon measured sound pressurelevels, the open-plan space is inadequatein terms of speech intelligibility.

The measurements that indicateinadequate signal to noise ratios werecorroborated by the fact that staffreported difficulties in listening tostudents in the open-plan setting. Inaddition, some students also reported thatit was difficult to hear the teachers whenthey spoke quietly.

Reverberation timeThe mid-frequency reverberation time inlearning base 1 was 0.6 seconds, whichmeets the performance standards in Table 1.5.

Speech intelligibilityFor the speech intelligibility measurements,the STI was measured in area C oflearning base 1.

STI was measured at two microphonepositions with an artificial mouth used totransmit the measurement signal. Sixmeasurements were made at eachmicrophone position. The artificial mouthwas sited by the white board in a positionthat was used by the teacher whenaddressing the class and referring toinformation on the white board. Thesignal level at a point 1 m in front of theartificial mouth was adjusted until a levelof 68 dB(A) was measured. The positionsof the artificial mouth and themicrophones are shown on Figure 7.10.8.

STI measurements were made whenthe space was empty. Masking sound froma loudspeaker was used to simulateoccupied conditions with groups ofapproximately 12 students in each classbase. In the afternoon when all the areasof learning base 1 were occupied,measured levels in the learning base werebetween 65 and 70 dB LAeq,30min (seeFigures 7.10.5 and 7.10.6). Case Study7.2 indicates that there is little point inmeasuring speech intelligibility at suchhigh masking sound levels because thespeech intelligibility is likely to be ‘Bad’,‘Poor’ or ‘Fair’ with low signal to noiseratios where the signal (speech) level issimilar to the noise level.

To assess the effect of sound

Time

12

10

8

6

4

2

0

–2

–4

–6

Diffe

renc

e in

LAe

q,30

min

(a

rea

A - a

rea

C), d

B(A)

8:30

–

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9:30

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0 –

Figure 7.10.7: Learningbase 1 – difference insound pressure levelsbetween area A and area C

152


transmission from adjacent areas onspeech intelligibility in area C,measurements were conducted with andwithout masking sound generated in thelearning base. Two masking conditionswere used: 1) masking sound in area A;2) masking sound simultaneously in areasA and B. The masking sound wasproduced from a loudspeaker using awhite noise signal shaped to the soundspectrum recorded whilst the teacheraddressed her students during a tutorialsession with the sixth form students. Thespectrum was measured at a distance ofapproximately 5 m from the teacher, thelevel at that point being 54 dBLAeq,30min. When masking sound wasgenerated in area A only, the masking

sound level was adjusted until 54 dBLAeq was measured in the same positionas that used to measure the level of theteacher speaking. When masking soundwas generated simultaneously in areas Aand B, the same shaped sound signal wasfed to the loudspeakers in each area andthe level adjusted until 57 dB LAeq wasmeasured at a position midway betweenareas A and B.

Measured STI data are shown in Tables7.10.1 and 7.10.2.

From the tables it can be seen that thespeech intelligibility was ‘Good’ atmicrophone positions M1 and M2 whenthere was no masking sound. Hence,when the other areas in the learning baseare not occupied, the speech intelligibilityis acceptable. When there was maskingsound in area A or areas A and B (ie witheither one or two of the other teachingareas simulated as being occupied),speech intelligibility was ‘Good’ atmicrophone position M1 but ‘Fair’ atmicrophone position M2. The reason forthe reduction in speech intelligibility atmicrophone position M2 is because it iscloser than position M1 to the otherteaching areas, where masking sound wasgenerated. Therefore, when other areas inthe learning base are occupied, the speechintelligibility between the teacher and

Figure 7.10.8: Learningbase 1 – artificial mouthposition (AM) andmicrophone positions M1and M2 in area C

Average

Standard deviation

Rating

No maskingsound

STI

0.702

0.041

Good

Masking sound in area A

STI

0.666

0.054

Good

Masking sound inareas A and B

STI

0.644

0.048

Good

Average

Standard deviation

Rating

No maskingsound

STI

0.655

0.037

Good

Masking sound in area A

STI

0.569

0.031

Fair

Masking sound inareas A and B

STI

0.571

0.084

Fair

Table 7.10.1: Learningbase 1 – measured STIvalues at microphoneposition M1, with andwithout masking sound

Table 7.10.2: Learningbase 1 – measured STIvalues at microphoneposition M2, with andwithout masking sound

AM M1

M25.40m

0.82m

Movable partitions

2.60m

2.20m2.20m

4.45m

153


students sitting near microphone positionM2 is not acceptable. In the afternoon,when all the areas of learning base 1 wereoccupied, measured levels in the learningbase were between 65 and 70 dBLAeq,30min (see Figures 7.10.5 and7.10.6). STI measurements were notmade with this masking sound conditionas the speech intelligibility would beexpected to be ‘Bad’, ‘Poor’ or ‘Fair’ dueto the low signal (speech) to noise ratio asin Case Study 2.

The teachers in this school adoptedstrategies to make the best use of theirsurroundings, for example, gatheringstudents more closely around them (seeFigure 7.10.15) to help overcomeproblems with speech intelligibility and toreduce disturbance to those involved inother activities within the room. Itappeared that co-operation between staffworking in the same open-plan area andcareful planning of lessons was animportant aspect in coping with thespeech intelligibility problems in theseareas. For example, a teacher in area Cnotified her colleague in area A that herclass would be engaged in quiet reading

after they had finished a more noisyactivity. This was to reduce disturbance tothe reading of a play in area A.

The school has tried to teach languagesin the open-plan learning bases, however,it had been decided that such lessons canonly be taught effectively in enclosedclassrooms. It is not known whether thiswas due to ambient levels being too highfor good speech intelligibility in open-planareas or whether it was due to disturbancefrom adjacent areas in a learning base. Itis to be expected that conditions forlanguage teaching need to be more closelycontrolled than for teaching some othersubjects. Measuring STI enables speechintelligibility in rooms to be objectivelyassessed. However it does not enabledisturbance to be quantified since thiscould depend on how distracting theactivities are in adjacent areas.

Workshop and technology areas

Sound pressure levelsFigures 7.10.9 and 7.10.10 show graphsof the continuous sound pressure levelsrecorded in the workshop and technology

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8.30 Room occupied byapproximately 25 students andstaff. Little practical activity.Students mostly working on abench close to the whiteboard.

10.30 Studentsengaged inpractical activities,eg sawing wood

13.00 Studentsengaged inpractical activity

14.05 Approximately 25students in the room.Saws and sandingmachines being used.

9.20 Studentsbreak forbreakfast

Figure 7.10.9: Workshoparea sound pressure levels

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areas. The levels in these areas aresignificantly higher than would beexpected in classrooms due to themachinery noise. During the period ofhighest noise, 76 dB LAeq,30min, thesignal to noise ratio would result ininadequate speech intelligibility for ateacher talking to a group of students.

Reverberation timesThe mid-frequency reverberation time inthe workshop was 1.2 seconds, whichdoes not meet the performance standardsin Table 1.5.

The mid-frequency reverberation timein the technology area was 0.8 seconds,which does not meet the performancestandards in Table 1.5.

A mid-frequency reverberation time of1.2 seconds in the workshop combinedwith levels greater than 70 dB LAeq,30minwill provide inadequate speechintelligibility. However, in rooms wherestudents use machine tools such as lathes,good speech intelligibility is essential forsafety.

Art area

Sound pressure levelsThe art area on the first floor is shown inFigure 7.10.3. During the measurementsit was occupied by Year 7 students andteaching staff. The room was divided bypartitions into three areas, indicated asA1, A2 and A3.

Measurements were taken in areas A1and A2, which held between 20 and 25students. Throughout the day, activitiesundertaken in the art area did not appearto change significantly. Noise sourcesincluded hairdryers which were used todry items of art work. Figures 7.10.11and 7.10.12 show graphs of the soundpressure levels recorded in areas A1 andA2 respectively. For most of the day thenoise level varies from 65 to 75 dBLAeq,30min. Thus, for a teacher talking toa group of students in the art area, thesignal to noise ratio would be inadequatefor good speech intelligibility.

8.30 Approximately 20students in the room.Engaged in group workand using computers.Teacher had to raisevoice to addressstudents from his desk.

13.00 Nomachines beingused apart fromcomputers

14.05 Approximately 25students in the room.Using computers,discussions being heldand a small routingmachine being used.

10.35 Studentsusing computers.Discussionsbetween studentsand a small routingmachine beingused.

9.20 Studentsbreak forbreakfast

Figure 7.10.10:Technology area soundpressure levels

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Reverberation timeThe mid-frequency reverberation time inthe art area was 0.9 seconds, which doesnot meet the performance standards inTable 1.5 for an art room.

Language teaching rooms (studyareas 1 and 5)These rooms were enclosed classroomsthat were originally intended to be sixthform study rooms. However, they weresubsequently designated as languageteaching rooms owing to the difficulties

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Figure 7.10.11:Art area – sound pressurelevels in area A1

Figure 7.10.12:Art area – sound pressurelevels in area A2

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experienced in teaching two differentlanguages (eg German and French)simultaneously in different areas of theopen plan space.

Sound pressure levelsFigures 7.10.13 and 7.10.14 show thesound pressure levels recorded in studyareas 1 and 5 respectively. When theclassrooms were unoccupied the measuredlevels were less than 50 dB LAeq,30min.When there was speech in the room,LAeq,30min was typically between 65 and75 dB. In general, LAeq,30min wasbetween 15 dB and 20 dB higher than

LA90,30min, indicating that the signal tonoise ratio could potentially providereasonable speech intelligibility. When thespaces were occupied and studentsand/or staff were speaking, there was agreater difference between LAeq,30minand LA90,30min in the enclosedclassrooms than in the fully occupiedopen-plan spaces. This indicates that thesignal to noise ratios are likely to behigher in the enclosed classrooms than inthe open-plan spaces.

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Figure 7.10.14:Language study area 5sound pressure levels

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each study area was 0.5 seconds, whichmeets the performance standards in Table 1.5.

Airborne sound insulationThe measured airborne sound insulationbetween study area 1 and study area 2 is40 dB DnT(0.8s),w, which does not meetthe performance standards in Table 1.2.

SummaryTeaching in an open-plan area in asecondary school requires a different typeof working from teaching in traditionalenclosed classrooms. This is due in part tothe noise levels in open-plan teachingareas. In this school, both students andteachers in the open-plan areas reportedbeing disturbed by noise, whilst inenclosed classrooms very little disturbancewas reported. Some of the techniquesobserved in primary schools in CaseStudy 9.2 were used when it wasimportant to ensure that students couldhear the teacher during noisy periods. Forexample, students were gathered moreclosely around their teacher. Also,teaching staff in the area co-operated witheach other to minimise disturbance toclasses in adjacent areas.

It is concluded that it is difficult tojustify the use of open-plan areas insecondary schools in terms of theiracoustic environment. This is a similarconclusion to that in Case Study 7.2 foropen-plan primary schools. High noiselevels in occupied open-plan areas are theprimary cause of inadequate speechintelligibility, especially for those studentsfurthest from the teacher. STImeasurements demonstrated that forthese students, the performance standardsin Table 1.6 of Section 1 were not met.

When all areas of the learning basewere occupied, measured sound pressurelevels were between 65 and 70 dBLAeq,30min. At these levels, the signal tonoise ratios are likely to be less than 10 dBand speech intelligibility will beinadequate. When the teaching areas wereoccupied and students and/or teacherswere speaking, there was a greaterdifference between LAeq,30min andLA90,30min in the enclosed classroomsthan in the open-plan spaces. Thissuggests that the signal to noise ratios aregenerally higher in enclosed classroomsthan in open-plan areas. Hence, speechintelligibility is likely to be better inenclosed classrooms than in fully occupiedopen-plan areas.

In many open-plan teaching spaces it isdifficult to achieve clear communicationof speech between teacher and student,and between students. For this reason,careful consideration should be given asto whether to include open-plan teachingspaces in a secondary school. If open-planareas are required then rigorous acousticdesign is necessary to meet the requiredperformance standards in Section 1.

Fugure 7.10.15:Students in learning base 1gathered around theteacher in area A

159

Appendix 1 – Basic concepts and units 161

Appendix 2 – Basic principles of room acoustics 165

Appendix 3 – Basic principles of sound insulation 167

Appendix 4 – Classroom sound insulation – sample calculations 171

Appendix 5 – Sound insulation of the building envelope 175

Appendix 6 – Calculation of room reverberation times 177

Appendix 7 – Calculation of sound absorption required in corridors, entrance halls and stairwells 181

Appendix 8 – Equipment specifications for sound field systems in schools 185

Appendix 9 – Noise at Work Regulations relating to teachers 191

Appendix 10 – Example submission to Building Control Body 193

Introduction to appendices

The ten appendices provide supporting information for the main sectionsof Building Bulletin 93, including explanations of acoustic terms, samplecalculations and other background information.

There are many technical terms anddescriptors used in acoustics, which cannot be covered in-depth in these shortappendices. However, to help non-acousticians, Appendices 1 to 3 includedefinitions of those acoustic terms whichare used in BB93, and describe the basic

principles of the behaviour of sound inbuildings. There are many acoustics textbooks available, some of which are listedin the bibliography These can be referredto for a more complete description of allacoustic terms and descriptors.

Page

Appendix 1: Basic concepts and units

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Nature of soundSound is usually generated by thevibrations of a surface, which give rise topressure fluctuations in air or some otherelastic medium. Sound is transmittedthrough the medium as sound waves, andmay be described in terms of soundpressure or sound power. Noise isgenerally defined as unwanted sound.

Decibels Sound levels are usually measured indecibels (dB) and relate absolute values toa reference value. The decibel scale islogarithmic and it ascribes equal values toproportional changes in sound pressure,which reflects the response of the humanear to sound. For example, an increase insound pressure from 10 to 20 Pa wouldsound the same to the human ear as anincrease from 1 to 2 Pa. Use of alogarithmic scale has the added advantagethat it compresses the very wide range of

sound pressures to which the ear maytypically be exposed to a moremanageable range of numbers.

Sound pressure levelThe sound pressure level, Lp, is a measureof the total instantaneous sound pressureat a point in space. The threshold ofhearing occurs at approximately 0 dBsound pressure level (which correspondsto a reference sound pressure of 2.10-5 Pa)and the threshold of pain is around 140dB. Some typical sound pressure levels areshown in Figure A1.1.

Sound power levelThe sound energy radiated by a sourcecan also be expressed in decibels. Thesound power is a measure of the totalsound energy radiated by a source persecond, in Watts. The sound power level,Lw, is expressed in decibels, referenced to1 pW.

Jet aircraft at5 metres

Artillery fire at1 metres

Platform of under-ground train station

Noisy office

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Averagesuburban area

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Bedroom orquiet whisper

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Figure A1.1: Typicalsound pressure levels

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Addition of sound levelsBecause the decibel scale is logarithmic,levels in decibels can not be simply addedtogether. To combine two sound levels, A dB and B dB, to give the total soundlevel, C dB, the following equation isused:

C = 10 lg (10A/10 + 10B/10) dB A1.1

When two identical sounds occursimultaneously, the resulting level is only3 dB higher than for a single source. Bycontrast, an increase of 10 dB normallyrepresents a doubling of perceivedloudness of the sound. Hence doublingthe amount of sound energy results invery much less than a doubling insubjective loudness.

To combine more than two levels, thefollowing equation is used:

L = 10 lg (10A/10 + 10B/10+ 10C/10+

10D/10+……) dB A1.2

Frequency of soundFrequency is analogous to musical pitch.It depends upon the rate of vibration of

the air molecules which transmit thesound and is measured as the number ofcycles per second or Hertz (Hz). Thehuman ear is sensitive to sound in therange 20 Hz to 20 kHz. Examples of thefrequency ranges of musical instrumentsand the human voice are shown in FigureA1.2. For acoustic engineering purposes,the frequency range is normally dividedup into discrete bands. The mostcommonly used are octave and one-thirdoctave bands.

Octave bandsFor an octave band the upper limitingfrequency of each band is twice the lowerlimiting frequency. Octave bands aredescribed by their centre frequency valuesand bands typically used for buildingacoustics purposes range from 63 Hz to4 kHz.

One-third octave bandsEach octave band can be divided intothree one-third octave bands. The one-third octave bands are described by theircentre frequency values and bandstypically used for building acousticspurposes range from 50 Hz to 5 kHz.

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A-weighted levelsThe sensitivity of the ear is frequencydependent. Sound level meters are fittedwith a weighting network whichapproximates to this response and allowssound levels to be expressed as an overallsingle figure value, in dB(A). For clarityand convenience, the ‘A’ is often includedin the acoustic descriptor, eg LAeq, ratherthan in brackets after the units. Forexample, A-weighted levels can be quotedas 55 dB LAeq.

The A-weighted level can also becalculated manually from octave band orone-third octave band data. For octaveband data, see Table A1.1, values areadded to the respective sound levels andthe resulting values for all octave bandsare combined logarithmically (usingEquation A1.2)

Measurement of time-varying soundsMost sounds are not steady and thesound pressure level fluctuates with time.Therefore, it is necessary to express theresults of a measurement over a period oftime in statistical terms. Some commonlyused descriptors are discussed below.

Equivalent continuous sound level The most widely used unit is theequivalent continuous A-weighted soundpressure level (LAeq,T). It is an energyaverage and is defined as the level of anotional sound which (over a definedperiod of time, T) would deliver the sameA-weighted sound energy as the actualfluctuating sound.

Percentile levelA percentile level is the highest levelexceeded for a certain percentage of a

measurement period. The mostcommonly used percentile levels are:LA1,T - This is the A-weighted levelexceeded for 1% of the measurementperiod. It is often used to representtypical maximum levels that occur duringthe measurement period.LA10,T - This is the A-weighted levelexceeded for 10% of the measurementperiod. It is often used to represent thesound level from road traffic.LA90,T - This is the A-weighted levelexceeded for 90% of the measurementperiod. It is often used to represent thebackground level.

Maximum and minimum sound levelsLAmax,T is the maximum sound pressurelevel measured during the measurementperiod T. LAmin,T is the minimum soundpressure level measured during themeasurement period T.

Sound level meter time constantsTo give meaningful results, sound levelmeters use sound pressure levels averagedover short intervals (within the overallmeasurement period, T). Time constantsfor this averaging, defined in internationalstandards, include ‘fast’ (125 ms) and‘slow’ (1 s).

The percentile levels described aboveare affected by the choice of timeconstant. By definition, all percentilelevels must be measured with the fast timeconstant.

LAeq,T is not affected by the soundlevel meter time constant.

LAmax,T and LAmin,T can be measuredwith either fast or slow time constants soit is important that the results state whichtime constant has been used.


Octave band centre frequency (Hz) 63 125 250 500 1 k 2 k 4 k

A-weighting correction (dB) –26.2 –16.1 -8.6 -3.2 0 1.2 1.0

Table A.1.1: A-weightingcorrections

Appendix 2: Basic principles of room acoustics

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Reflection and absorption of soundOnce emitted from a source, sound wavesin a room travel through the air until theyreach a boundary surface or otherobstacle. When a sound wave reaches asurface it will be partly reflected off thesurface back into the room and continuetravelling in a new direction, and it willbe partly absorbed by the surface with theabsorbed energy being dissipated as heat.

Absorption coefficient, αThe amount of sound energy that can beabsorbed by a surface is given by itsabsorption coefficient, α. The absorptioncoefficient can take values in the range 0to 1. A surface that absorbs no sound (iea totally reflective surface) has anabsorption coefficient of 0 and a surfacethat absorbs all sound incident upon ithas an absorption coefficient of 1. Thusthe higher the value of α, the more soundwill be absorbed. In practice, mostsurfaces have values between 0 and 1.Some typical absorption coefficients aregiven in Table A6.1 and on the DfESacoustics website.

Absorption classesThe absorption of surfaces varies withfrequency. Therefore, absorptioncoefficients are generally given for eachoctave band. A surface is categorised asbeing in a particular absorption class, A toE (according to BS EN ISO 11654:1997)depending on its absorption coefficientsacross the frequency range. To determinethe absorption class the octave bandvalues are plotted on a graph from BS ENISO 11654:1997 as shown in Figure A2.1.Note that a very reflective surface may beunclassified.

Scattering coefficient, sWhen sound is reflected from a surface itis partly reflected in a specular direction(ie the angle of incidence equals the angleof reflection) and partly scattered intoother directions. The amount of reflectedsound energy that will be scattered isgiven by the surface’s scatteringcoefficient, s. This is in the range of 0 to 1where a perfectly smooth surface givingpure specular reflection has a scatteringcoefficient of 0 and a very irregularsurface scattering all sound away from the

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specular direction has a scatteringcoefficient of 1. Scattering coefficients area relatively new measure in roomacoustics so there is little data currentlyavailable but they are important in roomacoustics computer modelling.

Reverberation time, TAfter being emitted from a source, soundwaves are repeatedly reflected from roomsurfaces and, as a result of absorption,gradually reduce in strength. Thereverberation time, T, of a space is ameasure of the rate at which the sounddecays. It is defined as the time taken forthe reverberant sound energy to decay toone millionth of its original intensity(corresponding to a 60 dB reduction inthe sound level).

The reverberation time is proportionalto the volume of the room and inverselyproportional to the quantity of absorptionpresent:

T = 0.16 V / ∑ Siαi s A2.1

where Si and αi are respectively thesurface area and absorption coefficient ofeach surface i in the room. An example ofthe application of this equation is given inAppendix 6.

Mid-frequency reverberation time, TmfThe sound absorption of surfaces usuallyvaries with frequency and therefore thereverberation time in a space also varieswith frequency. Hence, values of T arenormally given in frequency bands. InBB93 the reverberation time criteria areset in terms of the average value of thethree octave bands, 500 Hz, 1 kHz, and2 kHz, denoted as Tmf

Tmf = (T500 + T1k + T2k) / 3 s A2.2

Other acoustic measuresSound heard in a room generallycomprises an extremely complicatedcombination of many reflected andscattered sound waves. This situation ismade manageable by considering only theoverall statistics of the sound field such asthe reverberation time. Unfortunately,this does not convey all the intricate

details of the sound field that determinepeoples’ subjective responses. There aremany other measures used to representvarious aspects of subjective response toroom acoustics. For school acoustics thereis a need to have criteria for subjectivespeech intelligibility for which theobjective measure selected for BB93 is theSpeech Transmission Index.

Speech Transmission Index, STIThe intelligibility of speech in a room is acomplex function of the location of thespeaker, the location of the listener,ambient noise levels, the acousticcharacterisics of the space, and theloudness and quality of the speech itself.In addition, if a sound reinforcementsystem is used, it depends on the designand adjustment of this system. TheSpeech Transmission Index, STI, is anobjective measure defined in BS EN60268-16:1998, which accounts for allthese factors.

To measure the STI, a special soundsource is located at the position of thetalker (with the normal microphone inplace for any sound reinforcementsystem). The resulting signal is detected atthe listening position. Signal processingusing the modulation transfer functionbetween transmitted and received signalsis carried out to determine the STI.

STI is a value between 0 and 1, thehigher the value, the better the speechintelligibility. Speech intelligibility ratingscorresponding to STI values are asfollows:

STI Speech Intelligibility

0.1 to 0.3 Bad0.3 to 0.45 Poor0.45 to 0.6 Fair0.6 to 0.75 Good0.75 to 1 Excellent

Appendix 2: Basic principles of room acoustics

Appendix 3: Basic principles of sound insulation

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Airborne sound insulationSpeech, AV systems, and musicalinstruments are all sources of airbornesound in buildings. Sound in a room (thesource room) causes the surroundingsurfaces, such as walls, ceilings and floorsto vibrate. This vibration is transmittedthrough the building structure andradiated into other rooms (receivingrooms) in the building. Depending uponthe building construction, varyingamounts of energy are lost during thesound transmission process, resulting inairborne sound insulation between rooms.The greater the airborne sound insulationbetween two rooms, the lower the resultingsound level in the receiving room.

Measurement of airborne soundinsulationThe site measurement procedures forairborne sound insulation are given in BSEN ISO 140-4:1998. Normally, pinknoise or white noise is played through anamplifier and loudspeaker in the sourceroom, to provide a high sound levelacross the frequency range of interest.The sound level in the source room mustbe high enough to ensure that the levelsin the receiving room are above thebackground noise level.

The resulting sound levels in thesource and receiving rooms are measuredin one-third octave bands. As the soundlevels vary with location, they areaveraged either across a number of fixedmicrophone positions or by using acontinuously moving microphone. Theresulting time and space averaged soundlevels are denoted L1 in the source roomand L2 in the receiving room.

Level difference, DD is the difference in sound levels in dBbetween the source room and thereceiving room in one-third octave bands:

D = L1 - L2 dB A3.1

This level difference depends on:• direct sound transmission through theseparating element (ie separating wall or floor)

• flanking sound transmission (seeSection 3) through flanking elements (egflanking walls, suspended ceilings, accessfloors etc)• wall and floor dimensions• reverberation time of the receivingroom.

Standardized level difference, DnTThe reverberation time, T, measured in aroom may be significantly different fromthe value predicted at the design stagedue to a lack of detailed knowledge offinishes, furniture and fittings and theirabsorption characteristics. This means thatthe predicted sound level difference, D,which depends on T, is also subject tochange. To avoid problems, a referencereverberation time, To, can be used inpredictions of D. When the building isconstructed and D is measured, themeasured reverberation time, T, isreferenced to To. This gives thestandardized level difference, DnT.

DnT = D + 10 lg (T / To) dB A3.2

BB93 standardized level difference,DnT(Tmf,max)DnT is widely used to set sound insulationcriteria for dwellings, where To is taken as0.5 seconds. Although BB93 uses DnT inthe sound insulation criteria for schools, avalue of To = 0.5 seconds would not beappropriate for many school rooms.Hence, To is specified in BB93 as themaximum value of Tmf given in Table 1.5of Section 1. This new descriptor forairborne sound insulation in schools iswritten as DnT(Tmf,max) to highlight thealternative value of To that is used.

Sound reduction index, RThe sound reduction index, R, of anelement such as a wall, floor, door orwindow describes the sound transmittedthrough that element. It is measured in alaboratory with suppressed flankingtransmission. R varies with frequency andis expressed as a value for each one-thirdoctave band or octave band.

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Apparent sound reduction index, RÚsing field measurements of the leveldifference, D, it is possible to estimate thevalue of the sound reduction index, R, fora partition. However, because fieldmeasurements include flankingtransmission, the resulting quantity iscalled the apparent sound reductionindex, R´.

The apparent sound reduction index,R´, of wall or floor constructions inschools (and all other buildings), isusually lower than the laboratorymeasured value of R. The differencebetween the results is usually due toflanking transmission and a lowerstandard of workmanship on site.Guidance on flanking transmission isgiven in Section 3. Problems due toworkmanship can be reduced by closesupervision during the constructionprocess.

Weighted sound reduction indices andlevel differences Rw, R´w, Dw, DnT,w, DnT(Tmf,max)Most constructions provide higherairborne sound insulation against mid andhigh frequency sounds (such as speech)than low frequency sounds (such as thebass in music). This typical characteristicis defined in BS EN ISO 717-1:1997 as arating curve that can be applied to one-third octave band values of R, R´, D,DnT or DnT(Tmf,max) from 100 Hz to3.15 kHz. The rating curve is used tocalculate the following single-numberquantities: weighted sound reductionindex, Rw; weighted apparent soundreduction index, R´w; weighted leveldifference, Dw; weighted standardizedlevel difference, DnT,w; weighted BB93standardized level differenceDnT(Tmf,max).

Impact sound insulationIn the case of impact sound, the buildingconstruction is caused to vibrate as aresult of a physical impact, such asfootsteps on floors or stairs. The resultingvibration is radiated into other rooms inthe building.

Measurement of impact soundinsulationThe site measurement procedures forimpact sound insulation are given in BSEN ISO 140-7:1998. Impact soundinsulation is measured using an ISOstandard tapping machine, which consistsof a series of hammers driven by anelectric motor so as to produce acontinuous series of impacts on the floorunder consideration. The resulting soundlevel in the receiving room is measured inone-third octave bands. The receivingroom is usually the space directly belowthe floor excited by the tapping machine,although the impact sound insulation canalso be measured in other neighbouringrooms. As the sound levels will vary withlocation in the receiving room, they areaveraged either across a number of fixedmicrophone positions or by using acontinuously moving microphone.

Impact sound pressure level, Li The impact sound pressure level, Li, is thetime and space averaged sound pressurelevel in the receiving room, while the ISOstandard tapping machine excites the flooror stairs above the receiving room.

Standardized impact sound pressure level LńTThe impact sound pressure level, Li,depends on the reverberation time, T, ofthe receiving room. In the same way thatD is standardized to give DnT forairborne sound insulation to avoidchanges caused by variations of T, anequivalent descriptor is defined for impactsound as the standardized impact soundpressure level, LńT:

LńT = Li - 10 lg (T /To) dB A3.3

BB93 standardized impact soundpressure level LńT(Tmf,max)LńT is widely used for dwellings, whereTo is taken as 0.5 seconds. In a similarmanner to airborne sound insulation forschools, a value of To = 0.5 seconds is notappropriate for many school rooms so Tois specified in BB93 as the maximumvalue of Tmf given in Table 1.5 of Section1. This new descriptor for impact sound

insulation in schools is written asLńT(Tmf,max) to highlight the alternativevalue of To that is used.

Weighted standardized impact soundpressure levels LńT,w andLńT(Tmf,max),wTo reduce the impact sound pressure leveldata from values in frequency bands to asingle-number quantity, BS EN ISO 717-2:1997 contains a rating curve that canbe applied to one-third octave bandvalues of LńT or LńT(Tmf,max) from 100 Hz to 3.15 kHz. The rating curve isused to calculate the following single-number quantities: the weightedstandardized impact sound pressure level,LńT,w or the weighted BB93standardized impact sound pressure level,LńT(Tmf,max).It is important to note that impact soundinsulation is measured in terms of anabsolute sound level, so that a lowernumber indicates a better standard ofimpact sound insulation. This is theopposite of airborne sound insulation,which is based on differences in levels sothat a higher number indicates a betterstandard of airborne sound insulation.

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Appendix 4: Classroom sound insulation – sample calculations

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Figure A4.1 shows a secondary schoolclassroom adjacent to a science laboratory,plantroom and corridor. In this example,the designer has decided to build theseparating walls between these spaces withmasonry. The calculations below are usedto determine the specification of themasonry wall (eg mass per unit area,thickness, surface finishes) required tomeet the performance standards inSection 1.

There are three walls to consider: • Wall 1 - between classroom and sciencelaboratory• Wall 2 - between classroom andcorridor• Wall 3 - between classroom andplantroom.

The performance standards forairborne sound insulation are containedin Section 1. For each of the three wallsthe following apply:

• The performance standard for Wall 1 isin terms of the weighted BB93standardized level difference,DnT(Tmf,max),w, in Table 1.2. Todetermine the blockwork specification,the weighted sound reduction index ofthe wall is estimated fromDnT(Tmf,max),w.

• The performance standard for Wall 2 isin terms of the weighted sound reductionindex in Table 1.3.

• For Wall 3, between the plantroom andthe classroom, there are no explicitperformance standards in Section 1.Therefore the sound insulation betweenthe plantroom and the classroom needs toensure that the performance standards aremet for the indoor ambient noise level inthe adjacent classroom (Table 1.1). Thesound insulation is calculated using thenoise levels of the actual equipment in theplantroom.

Wall 1 From Tables 1.1, 1.2 and 1.5 in Section 1the minimum performance standards forthe airborne sound insulation are:

Classroom to Science Laboratory: 40 dB DnT(0.8s),w

Science Laboratory to Classroom: 45 dB DnT(0.8s),w

As the two room dimensions are similarand the values of Tmf,max are both 0.8 s,the specification for the masonry wall isbased on the more stringent criterion, 45 dB DnT(0.8s),w.

As an initial estimate, the proceduredescribed in Section 3.10 can be used toestimate the weighted sound reductionindex, Rw, for the separating wall. Thefirst stage is to calculate Rw,est.

Rw,est = DnT(Tmf,max),w + 10 lg (S x Tmf,max / V) + 8 dB

Rw,est = 45 + 10 lg (21 x 0.8 / 168) + 8 dB

Rw,est = 43 dB

To obtain Rw the factor X is added toRw,est to account for less favourablemounting conditions and workmanshipthan in the laboratory test. From Section3.10, X can be estimated to be 5 dB.

Rw = Rw,est + X dB

Rw = 43 + 5 dB

Rw = 48 dB

Figure A4.1: Plan ofsecondary schoolclassroom and adjacentspaces

Corridor

Plantroom Science LaboratoryClassroomVolume = 168 m3

Wall 3

Wall 2

Wall 1S = 21 m2

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Therefore, suitable specifications formasonry separating walls and appropriatesurface finishes that achieve at least 48 dBRw can be identified by the designer.

Wall 2The performance standards for theairborne sound insulation of the corridorwall and door are given in Table 1.3:

Wall between a classroom and a corridor:40 dB Rw

Door between a classroom and a corridor:30 dB Rw

In this example there are no ventilatorsor glazing in the wall. If there wereventilators then they would have to meetthe performance standard in Table 1.3.Glazing in the corridor wall does not havea separate performance standard becausethe performance standard for the wall isfor the combined sound insulation of anyglazing and the wall. An example of acorridor wall with glazing is included atthe end of this appendix.

From Section 3, Figure 3.11, a 44 mmthick timber door with half hour firerating typically achieves 30 dB Rw if it is“a well fitted solid core doorset where thedoor is sealed effectively around itsperimeter in a substantial frame with aneffective stop”.

Blockwork SpecificationThe minimum Rw values for the wallsare:

Wall 1: 48 dB RwWall 2: 40 dB Rw

Figure 3.9 can be used to draw up aninitial specification for the walls alongwith laboratory test reports from themanufacturer. For Wall 1 and Wall 2 thefollowing specifications might beproposed:

Wall 1: 100 mm medium density blocks(140 kg/m2) with a 13 mm plaster finishon both sides

Wall 2: 100 mm low density block (70 kg/m2) with a 13 mm plaster finish on both sides

The Rw specification for Wall 1 is only

an estimate of the type of separating wallperformance needed to achieve 45 dBDnT(0.8s),w and takes no account offlanking transmission which is usuallycritical in determining the performance.Therefore, at this stage the designershould seek specialist advice from anacoustic consultant to assess whether theproposed combination of separating andflanking walls is likely to achieve theperformance standards.

Wall 3Wall 3 has to provide sufficient soundinsulation to ensure that the indoorambient noise levels in the classroom donot exceed 35 dB LAeq,30min (Table 1.1).As there will be other noise sourcescontributing to the indoor ambient noiselevel, the level due to noise transmittedthrough Wall 3 will have to be significantlyless than 35 dB LAeq,30min. BB93 doesnot recommend a standard method forthis situation but one approach is todesign Wall 3 so that the noisetransmitted from the plantroom is at least10 dB below the indoor ambient noiselevel in the classroom. Using this method,the noise transmitted through Wall 3needs to be less than 25 dB LAeq,30min inthe classroom.

The noise transmitted from theplantroom to the classroom depends onthe frequency spectrum of the noise in theplantroom and the sound insulationspectrum of the separating wall. For thesecalculations, plantroom equipmentlocations and noise emission data arerequired. Precise equipment details areusually not known until the later stages ofa project, therefore generic sound leveldata are normally used in calculations andthe assumptions quoted in thespecification.

The calculations are often complex andnormally require an acoustic consultant.Guidance for these calculations can befound in the following references: CIBSE (2002). Guide B5: Noise andVibration Control for HVCA. CIBSE.ISBN 1903287251.Fry, A. ed. (1988). Noise control inbuilding services. Oxford: Pergamon.ISBN 0080340679.

Appendix 4: Classroom sound insulation – sample calculation

173

Wall 2 with glazingWalls between classrooms and corridorsmay contain glazing, therefore thisexample is a reassessment of Wall 2 withthe following areas:

Area Masonry 16.6 m2

Glazing 5.6 m2

Door 1.8 m2

Total wall 24 m2

The door is treated in the same way asin the example above with a value of 30 dB Rw.

The combined Rw criterion for themasonry wall and the glazing also remainsat 40 dB Rw.

This combined criterion would beachieved if the masonry wall and theglazing each provide at least 40 dB Rw. A masonry wall specification for this hasalready been described above and thereare three glazing configurations given inFigure 3.10, which also provide 40 dB Rw. However, these glazingconfigurations can sometimes be relativelyexpensive due to the use of thick and/orlaminated glass and/or wide cavities.

An alternative approach is to improvethe masonry wall specification to allowthe use of another glazing configuration.

From Figure 3.9 the followingmasonry wall should give at least 45 dB Rw: 100 mm medium densityblocks (140 kg/m2) with a 13mm plasterfinish on each side.

From Figure 3.8, glazing with differentRw values can be assessed to see whetherthe criterion of 40 dB Rw will be met bythe combined value for the wall andglazing. A potential solution would be touse glazing with sound insulation of 35 dB Rw. This is 10 dB lower than the45 dB Rw sound insulation of themasonry wall. For a glazing area of 25%of the wall area that excludes the door,Figure 3.8 gives a correction factor ofapproximately 5 dB. The combined Rw iscalculated from the Rw for the glazingplus the correction factor, which equals40 dB Rw. Hence this combination ofmasonry wall and glazing meets theperformance standard. Further reductionsin glazing specification could be obtainedby reducing the area of glazing or byusing a wall with a higher Rw.

Appendix 4: Classroom sound insulation – sample calculation

Appendix 5: Sound insulation of the building envelope

175

This appendix describes two methods thatcan be used to calculate the indoorambient noise level due to external noiseas described in Section 3. The firstmethod calculates the indoor ambientnoise level according to the principles ofBS EN 12354-3:2000. The secondmethod calculates the indoor ambientnoise level using the measured façadesound insulation data from an identicalconstruction at another site.

Principles of the calculation methodbased on BS EN 12354-3:2000This section describes the calculationprocedure based on BS EN 12354-3:2000.

The chosen frequency range shouldinclude all frequency bands thatdetermine the indoor ambient noise level,LAeq,30min. However, for many externalnoise levels, it is appropriate to calculatethe façade insulation using octave bandsbetween 125 Hz and 2 kHz.

Two main equations are used tocalculate the internal level in eachfrequency band.

The first equation gives the internallevel due to sound transmission throughan element of the building envelope:

L2 = L1,in – R + 10lg (S/V) + 11 + 10lg T dB A5.1

whereL2 is the internal level due to the soundtransmitted through the element (dB)L1,in is the external free-field sound levelincident on the element (dB)R is the sound reduction index of theelement (dB)S is the internal surface area of theelement (m2) V is the room volume (m3)T is the room reverberation time (s).

The second equation gives the internallevel due to sound transmission through aventilator installed in the buildingenvelope:

L2 = L1,in – Dn,e – 10lgV + 21 + 10lg T dB A5.2

whereDn,e is the element-normalised soundlevel difference of the ventilator (dB).

The overall A-weighted internal level isobtained by combining (as in EquationA1.2) the contributions from all elementsand ventilators within each frequencyband, adding the relevant A-weightingcorrection to each resultant frequencyband level, and then combining all the A-weighted frequency band levels together.

Elements: Laboratory soundinsulation dataLaboratory testing of building elementsshould be conducted in accordance withBS EN ISO 140-3:1995 to obtain therequired sound reduction index, R.

Ventilators: Laboratory soundinsulation dataLaboratory testing of ventilator unitsshould be conducted in accordance withBS EN 20140-10:1992 to obtain therequired element-normalized leveldifference, Dn,e,w.

Some ventilators may have the facilityto control the air flow rate, either bybeing fully opened or fully closed, or byhaving some form of variable control. Insuch cases calculations should be based onthe performance in the fully openposition.

The mounting position of ventilators,for example in the middle or near an edgeof a wall, or in a corner, affects theairborne sound insulation. Manufacturers’data on ventilators should giveinformation on the position of theventilator during the laboratory testaccording to BS EN 20140-10:1992. Thisshould be used to ensure that thelaboratory mounting position isrepresentative of the mounting position inthe field.

Some ventilators are available in avariety of sizes but performance data maycorrespond only to one size. In such casesan estimate can be made for the areacorrection, Ac, to be added to eachfrequency band Dn,e value. The area

176

correction Ac in dB is given by:

Ac = 10 lg ( Aref / Aactual ) dB A5.3

whereAref is the area in m2 of the ventilatorfrom the laboratory sound insulation testAactual is the area in m2 of the ventilatorto be used.

Excel spreadsheetAn Excel spreadsheet to calculate thesound insulation of building envelopesbased on BS EN 12354-3:2000 isavailable via the DfES acoustics website.This Excel spreadsheet allows users toselect from a range of typical buildingelements and ventilators and enter dataobtained from laboratory tests ofelements or ventilators.

The spreadsheet provides two options,A and B, to calculate internal levels usingoctave bands between 125 Hz and 2 kHz.

Option A allows the user to entermeasured free-field octave band data as a‘user-defined spectrum’. Option A is thepreferred option. However, if measureddata are not available then option B canbe used to give an estimate based upon anA-weighted value and an assumedspectrum shape, either C or Ctr from BSEN ISO 717-1:1997. Estimations usingoption B can be useful with someprediction methods such as CRTN forroad traffic noise and CRN for railwaynoise, which generate only A-weightedlevels. The user can enter external free-field LAeq levels and choose from thegeneric spectra described in BS EN ISO717-1:1997. The C spectrum (SpectrumNo. 1) is used to represent railway trafficat medium and high speed, and roadtraffic travelling at greater than 80 km/h.The Ctr spectrum (Spectrum No. 2) isused to represent noise from urban roadtraffic, jet aircraft at large distances,propeller driven aircraft, and railwaytraffic at low speeds.

Spectra of aircraft noise at relativelyclose distances are likely to depend greatlyon aircraft type and operation, andspecialist advice should be sought.

Principles of the calculation methodbased on field test dataThis section describes the calculation ofthe indoor ambient noise level using themeasured façade sound insulation datafrom an identical construction at anothersite.

The chosen frequency range shouldinclude all frequency bands that determinethe indoor ambient noise level,LAeq,30min. However, for many externalnoise levels, it is appropriate to calculatethe façade insulation using octave bandsbetween 125 Hz and 2 kHz.

Field tests of building envelopeinsulation according to BS EN ISO 140-5:1998 give results in frequency bandsexpressed as the standardized leveldifference, D2m,nT.

The internal level in each frequencyband may be calculated according to thefollowing equation:

L2 = L1,in – D2m,nT + 6 + 10lg T dBA5.4

whereL2 is the internal level due to the soundtransmitted through the facade (dB)L1,in is the external free-field sound levelincident on the facade (dB)D2m,nT is the standardized leveldifference (dB)T is the room reverberation time (s).

The overall A-weighted internal level isobtained by adding the relevant A-weighting to each frequency band level,and then combining all the A-weightedfrequency band levels, according toEquation A1.2.

Appendix 5: Sound insulation of the building envelope

Appendix 6: Calculation of room reverberation times

177

For empty rooms with volumes less than200 m3, simple room geometry and areasonable distribution of soundabsorption, the reverberation time, T, canbe calculated using Sabine’s formula andabsorption coefficients appropriate to theroom surfaces as shown below.

T = seconds

where V is the volume of the room in m3

and A is the absorption area in the roomin m2.

Table 1.5 gives the recommended mid-frequency reverberation times for rooms.The mid-frequency reverberation time,Tmf, is the arithmetic average of thereverberation times in the 500 Hz, 1000 Hz and 2000 Hz octave bands.

Tmf = s

For n surfaces in a space, the totalabsorption area, A, can be found usingthe following equation:A = α1S1 + α2S2 +...+ αnSn

where α1,…,αn are the absorptioncoefficients of the different surfaces in theroom and S1,…,Sn are the areas of thesurfaces having absorption coefficientsα1…αn.

Absorption coefficients can be obtainedfrom the spreadsheet on the DfESacoustics website and/or frommanufacturers’ data. Values for somecommon materials, used in the workedexample which follows, are given in Table A6.1.

Two decimal places should be used forthe absorption coefficient values forcalculations.

In empty teaching rooms with volumesless than 200 m3 and simple roomgeometry, the absorption area, A, neededto give the required reverberation time, T,can be obtained by rearranging Sabine’sformula as follows:

A = m2

For such rooms the formula can also beused to estimate the amount of additional

0.16VA

0.16VT

Note: Reverberation timecalculations using Sabine’sformula in all octave bandscan be carried out usingthe method illustrated inthe worked example thatfollows. However,neglecting air absorptionslightly underestimates theequivalent soundabsorption area in a room.

Material

Fair-faced concrete or plastered masonry

Fair-faced brick

Painted concrete block

Windows, glass façade

Doors (timber)

Glazed tile/marble

Hard floor coverings (eg linoleum,parquet) on concrete floor

Soft floor coverings (eg carpet) onconcrete floor

Suspended plaster or plasterboardceiling (with large airspace behind)

Sound absorption coefficient, α250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

0.01 0.01 0.02 0.02 0.03

0.02 0.03 0.04 0.05 0.07

0.05 0.06 0.07 0.09 0.08

0.08 0.05 0.04 0.03 0.02

0.10 0.08 0.08 0.08 0.08

0.01 0.01 0.01 0.02 0.02

0.03 0.04 0.05 0.05 0.06

0.03 0.06 0.15 0.30 0.40

0.15 0.10 0.05 0.05 0.05

Table A6.1: Absorptioncoefficient data for somecommon materials

T500 Hz + T1000 Hz + T2000 Hz3

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absorption area required to give a desiredmid frequency reverberation time. (Notethat the absorption due to any surfacethat is to be covered with additionalabsorption must be discounted.)

The procedure is illustrated in theworked example shown below.

Specialist advice may be needed forlarge (>200 m3) rooms or rooms wheremusic is to be performed

Worked example A school laboratory is required to have a mid-frequency reverberation time of less than0.8 seconds. The room is rectangular in plan, is 7 m wide, 9 m deep and has a ceilingheight of 3 m. There is one door and the glazing is located in one of the 7 m x 3 mwalls. The room volume is 7 m x 9 m x 3 m = 189 m3. The glazing has an area of 6 m2 and the door has an area of 2 m2.

Step 1 Calculate the surface area related to each material in the room (ie floor, walls,doors, ceiling and windows)

Surface Surface finish Area (m2)Floor Hard floor covering 63Door Timber 2Walls (excluding door and glazing areas) Painted concrete block 88Ceiling Suspended plaster 63Windows Glass 6

Step 2 Obtain values of absorption coefficients for the room surfaces. In this case, thevalues are taken from Table A6.1.

Absorption coefficient αSurface Area (m2) 500 Hz 1000 Hz 2000 HzFloor 63 0.04 0.05 0.05Door 2 0.08 0.08 0.08Walls 88 0.06 0.07 0.09Ceiling 63 0.10 0.05 0.05Windows 6 0.05 0.04 0.03

Step 3 Calculate the absorption area (m2) related to each surface in octave frequencybands (Absorption area = surface area × absorption coefficient)

Absorption area (m2)Surface Area (m2) 500 Hz 1000 Hz 2000 HzFloor 63 63 × 0.04 = 2.52 63 × 0.05 = 3.15 63 × 0.05 = 3.15Door 2 0.16 0.16 0.16Walls 88 5.28 6.16 7.92Ceiling 63 6.30 3.15 3.15Windows 6 0.30 0.24 0.18


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Step 4 Calculate the sum of the absorption areas (m2) obtained in Step 3

500 Hz 1000 Hz 2000 Hz Total absorption area (m2) 14.56 12.86 14.56

Step 5 Calculate the reverberation time for the room using Sabine’s formula

500 Hz 1000 Hz 2000 Hz

T = seconds 2.08 2.35 2.650.16VA

Step 6 Calculate the mid-frequency reverberation time (Tmf) from the reverberation times in the 500 Hz, 1000 Hzand 2000 Hz octave bands.

Tmf = = 2.36 seconds

This reverberation time exceeds the required value.

Step 7 Identify a sound absorbing material that is suitable for use in a school laboratory and determine the bestposition for the material.

A manufacturer produces a non-flammable sound absorbing material that can be cleaned relatively easily. Thefollowing absorption coefficient data is provided for the material.

2.08 + 2.35 + 2.653

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hzα 0.20 0.45 0.85 1.00 1.32

Because the room is used as a laboratory, it is decided that the most appropriate place for the sound absorbingmaterial is on the ceiling or high on the walls.

Step 8 Estimate the required area of the sound absorbing material and calculate the mid-frequency reverberationtime when it is in place.

As a first estimate, it is decided to cover the entire ceiling with the sound absorbing material. The total absorptionareas in the 500 Hz, 1000 Hz and 2000 Hz octave frequency bands are then calculated.

Absorption area (m2)Surface Area (m2) 500 Hz 1000 Hz 2000 HzFloor 63 2.52 3.15 3.15Door 2 0.16 0.16 0.16Walls 88 5.28 6.16 7.92Ceiling 63 63.0 x 0.45 = 28.35 63 x 0.85 = 53.55 63 x 1.00 = 63.00Windows 6 0.30 0.24 0.18Total absorption area 36.61 63.26 74.41

Reverberation time (s)T = seconds 0.83 0.48 0.41

0.16VA

Note: Because the mid-frequency reverberation time is required, calculations need only be conducted in the 500 Hz, 1000 Hz and 2000 Hz octave bands. However, should reverberation times need to be calculated for alloctave bands, the calculation method is the same as that illustrated for each octave band.


180

Step 9 Calculate the new mid-frequency reverberation time.

Tmf = = 0.57 seconds

This reverberation time meets the reverberation time requirements in Section 1.1 for the school laboratory.

0.83 + 0.48 + 0.413


Appendix 7: Calculation of sound absorption required incorridors, entrance halls and stairwells

181

Approved Document E contains guidanceon the addition of sound absorption tocommon areas in buildings containingdwellings. Where the addition of soundabsorption to common areas in schools,such as corridors, entrance halls orstairwells, is required, it is advised thatthe approach described in ApprovedDocument E be used.

Approved Document E describes twomethods, A and B, for controllingreverberation in common internal parts ofbuildings. These methods are reproducedbelow from Approved Document E.

Method A For entrance halls, corridors or hallways,cover an area equal to or greater than thefloor area, with a Class C absorber orbetter. It will normally be convenient tocover the ceiling area with the additionalabsorption.

For stairwells or a stair enclosure,calculate the combined area of the stairtreads, the upper surface of theintermediate landings, the upper surfaceof the landings (excluding ground floor)and the ceiling area on the top floor.

Either, cover at least an area equal tothis calculated area with a Class Dabsorber, or cover an area equal to at least50% of this calculated area with a Class Cabsorber or better. The absorptivematerial should be equally distributedbetween all floor levels. It will normallybe convenient to cover the underside ofintermediate landings, the underside ofthe other landings, and the ceiling areaon the top floor.

Method A can generally be satisfied bythe use of proprietary acoustic ceilings.However, the absorptive material can beapplied to any surface that faces into thespace.

Method B In comparison with Method A, Method Btakes account of the existing absorptionprovided by all surfaces. In some cases,Method B should allow greater flexibilityand require less additional absorptionthan Method A.

For an absorptive material of surfacearea S in m2, and sound absorptioncoefficient, α, the absorption area A isequal to the product of S and α. The totalabsorption area, AT, in square metres isdefined as the hypothetical area of atotally absorbing surface, which if it werethe only absorbing element in the spacewould give the same reverberation time asthe space under consideration.

For n surfaces in a space, the totalabsorption area, AT, can be found usingthe following equation.

AT = α1S1 + α2S2 +...+ αnS n

For entrance halls, provide a minimumof 0.20 m2 total absorption area per cubicmetre of the volume. The additionalabsorptive material should be distributedover one or more of the surfaces.

For corridors or hallways, provide aminimum of 0.25 m2 total absorptionarea per cubic metre of the volume. Theadditional absorptive material should bedistributed over one or more of thesurfaces.

Absorption areas should be calculatedfor each octave band between 250 Hzand 4 kHz inclusively.

Absorption coefficient data (to twodecimal places) should be determined asfollows:

For specific products, use laboratorymeasurements of absorption coefficientdata determined using BS EN20354:1993 Acoustics – Measurement ofsound absorption in a reverberation room.The measured third octave band datashould be converted to practical soundabsorption coefficient data, αp in octavebands, according to BS EN ISO11654:1997 Acoustics – Sound absorbersfor use in buildings – Rating of soundabsorption.

For generic materials, use the octaveband data in Table 7.1 of ApprovedDocument E or the more comprehensivedata on the DfES acoustics website. Thesecontain typical absorption coefficient datafor common materials used in buildingsand may be supplemented by otherpublished data.

182

Worked exampleA school has an entrance hall that hasparquet on a concrete floor (7 m x 5 m)with a ceiling height of 3.2 m. The ceilingarea is equal to that of the floor. The 5 mx 3.2 m façade is completely glazed andincorporates a glass door. Wooden doorshaving a total surface area of 2.4 m x 2.7m lead to the corridor described below.The walls are of fair-faced brick.

The corridor has equal floor andceiling areas of 20 m x 2.4 m and aceiling height of 2.7 m. The 20 m x 2.7 mexternal wall of the corridor has half its

surface area (27 m2) glazed. The corridorhas parquet on a concrete floor and itsunglazed walls are of painted concreteblocks.

Each end of the corridor consists ofwooden doors, of surface area 2.4 m x2.7 m. In addition there are two woodendoors, each of area 2 m x 1.8 m, leadingto classrooms off the corridoor.

The sound absorption coefficientsnecessary to control reverberation in thetwo spaces using Method B are calculatedas shown below.

Example calculation for an entrance hall (Method B)

Step 1 Calculate the surface area related to each absorptive material (ie for the floor, walls, doors and ceiling).

Surface Surface finish Area (m2)Floor Parquet on concrete 35.00Doors (wooden) Timber 6.48Walls (excluding door area) Fair-faced brick 54.32Façade (and door) Glazing 16.00Ceiling To be determined 35.00

Step 2 Obtain values of absorption coefficients for the floor, walls, glazing and doors. (The values below are takenfrom Table 7.1 of Approved Document E.)

Surface Area Absorption coefficient (α) in octave frequency bands(m2) 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

Floor 35.00 0.03 0.04 0.05 0.05 0.06Doors (wooden) 6.48 0.10 0.08 0.08 0.08 0.08Walls 54.32 0.02 0.03 0.04 0.05 0.07Glazing(façade & door) 16.00 0.08 0.05 0.04 0.03 0.02Ceiling 35.00 To be determined

Step 3 Calculate the absorption area (m2) related to each surface in octave frequency bands. (Absorption area = surface area x absorption coefficient)

Surface Absorption area (m2)250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

Floor 1.05 1.40 1.75 1.75 2.10Doors (wooden) 0.65 0.52 0.52 0.52 0.52Walls 1.09 1.63 2.17 2.72 3.80Glazing (façade and door) 1.28 0.80 0.64 0.48 0.32

Step 4 Calculate the sum of the absorption areas (m2) obtained in Step 3250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

Total absorption area (m2) 4.07 4.35 5.08 5.47 6.74

Step 5 Calculate the total absorption area (AT) required for the entrance hall. The volume is 112 m3 and therefore AT = 0.2 x 112.0 = 22.4 m2.

Appendix 7: Calculation of sound absorption required in corridors,entrance halls and stairwells

183

Step 6 Calculate additional absorption area (m2) to be provided by the ceiling. If values are negative in any octaveband then there is sufficient absorption from the other surfaces to meet the requirement without any additionalabsorption in this band. (Additional absorption = AT –total absorption area (from Step 4))

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 HzAdditional absorption area (m2) 18.33 18.05 17.32 16.93 15.66

Step 7 Calculate required absorption coefficient (α) to be provided by ceiling(α = Additional absorption area / area of ceiling)

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 HzRequired absorption coefficient 0.52 0.52 0.49 0.48 0.45

Step 8 Identify a ceiling product from manufacturers’ laboratory measurement data that provides absorptioncoefficients that exceed the values calculated in Step 7.

Example calculation for a corridor (Method B)

Step 1 Calculate the surface area related to each absorptive material (ie for the floor, walls, doors and ceiling).

Surface Surface finish Area (m2)Floor Parquet on concrete base 48.00Glazing 27.00Doors Timber 20.16Wall (excluding door area and glazing) Painted concrete block 73.80Ceiling To be determined 48.00

Step 2 Obtain values of absorption coefficients for the floor, walls, glazing and doors. (The values below are takenfrom Table 7.1 of Approved Document E.)

Absorption coefficient (α) in octave frequency bandsSurface Area 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 HzFloor 48.00 0.03 0.04 0.05 0.05 0.06Glazing 27.00 0.08 0.05 0.04 0.03 0.02Doors 20.16 0.10 0.08 0.08 0.08 0.08Wall (excluding door areaand glazing) 73.80 0.05 0.06 0.07 0.09 0.08Ceiling 48.00 To be determined

Step 3 Calculate the absorption area (m2) related to each surface in octave bands. (Absorption area = surface area x absorption coefficient)

Absorption area (m2)250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

Floor 1.44 1.92 2.40 2.40 2.88Glazing 2.16 1.35 1.08 0.81 0.54Doors 2.02 1.61 1.61 1.61 1.61Wall (excluding door areaand glazing) 3.69 4.43 5.17 6.64 5.90


184

Step 4 Calculate the sum of the absorption areas (m2) obtained in Step 3

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 HzTotal absorption area (m2) 9.31 9.31 10.26 11.46 10.93

Step 5 Calculate the total absorption area (AT) required for the corridor. The volume is 129.6 m3 and therefore AT = 0.25 x 129.6 = m2.

Step 6 Calculate additional absorption area (m2) to be provided by ceiling. If values are negative in any octaveband then there is sufficient absorption from the other surfaces to meet the requirement without any additionalabsorption in this band. (Additional absorption = AT – total absorption area (from Step 4))

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 HzAdditional absorption area (m2) 23.09 23.09 22.14 20.94 21.47

Step 7 Calculate required absorption coefficient (α) to be provided by ceiling(α = Additional absorption area / area of ceiling)

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 HzRequired absorption coefficient 0.48 0.48 0.46 0.44 0.45

Step 8 Identify a ceiling product from manufacturers’ laboratory measurement data that provides absorptioncoefficients that exceed the values calculated in Step 7.


Appendix 8: Equipment specifications for sound field systems in schools

185

Specification Descriptor Standard Recommended value or range CommentsSymbol

Characteristic sensitivity Lp >85 dB @ 1 W

RMS power >10 W continuous band limited pink noise 150 Hz to 8 kHz

Frequency response +/– 3 dB over range 150 Hz to 8 kHz

Coverage angle Min 90° H x 60° V Wall mounting typeMin 90° H x 90° V Ceiling mounting type

Loudspeaker type 2-way, Must be matched to 100 V preferred amplifier and system

suitably wired.

Enclosure Flame retarding for wall mounted applications.Fire rated back enclosure for all ceiling loudspeakers that penetrate a fire rated ceiling.Acoustically rated back enclosure for all ceiling loudspeakers that penetrate a ceiling separating classroom floors.

Brackets Brackets for wall mounted enclosures should provide lockable adjustment vertically and horizontally. Fixing to wall and loudspeaker to be a minimum of two secure screws or bolts each. Secondary safety bond to be provided between loudspeaker and mounting surface.

Standard loudspeakersA standard specification for loudspeakers is difficult, since there are circumstanceswhen specialised solutions are required. The specification provided below is a generalrecommendation for typical loudspeakers used in a set of four to six in a classroomwithin the normal range of sizes.

186

NXT or other distributed mode loudspeakersThese loudspeakers use new and emerging technology. An ‘exciter’ causes a panel to vibrate and the panel emitssound. The characteristics of the exciter, its location on the panel and the panel material are all important forcorrect operation. Products include ceiling tiles, wall mounting posters, projection screens and whiteboards thatserve also as loudspeakers. There are advantages in the use of these loudspeaker types, as they provide a betteraverage sound coverage in a room and provide a better average speech intelligibility under some conditions. Thereason for this is not fully understood. Fewer NXT type loudspeakers are required, and it may be found that onewall mounted whiteboard model will suffice for the smaller classroom.


Characteristic sensitivity Lp >85 dB @ 1 W

RMS power >10 W continuous band limited pink noise 150 Hz to 8 kHz

Frequency response +/– 3 dB over range 150 Hz to 8 kHz

Coverage angle Average 120° H x 120° V

Loudspeaker type 100 V preferred for ceiling type as Must be matched toseveral will be connected in parallel. amplifier and system

suitably wired.

Enclosure Most require no enclosure, but usually have to be spaced away from the wall on a mounting frame. Units for classroom use should be of Class 1 or better for spread of flame. Where used in an acoustically separating ceiling, provision must be made to maintain the sound insulation behind the loudspeakers.

Brackets Adjustment of aiming angle is not necessary. Brackets must provide a minimum of two fixing points.


187


Specification Descriptor Standard Recommended value CommentsSymbol or range

Inputs 1 mic/line Mic (-50 dBu sensitivity) • 1 mono, compatible with teacherline (-10 dBu sensitivity) radio microphone receiverswitchable • 1 stereo (mixed to mono),

to enable music playback,connection to computer

1 stereo line Stereo phono or 3.5 mm audio output. Alternatively built-injack (-10 dBu sensitivity) cassette player

• Prefer minimum of 1 additionalmono input to enable second

1 mic/line Min/line switchable as microphone for class discussionabove use when child using personal

FM system is present.

Equivalent input noise Mic input <-110 dB

Frequency response +/– 3 dB over range Mic or line input80 Hz to 15 kHz

Outputs 1 line level -10 dBu, unbalanced, For connection of personal FMphono or mini-jack or induction loop amplifier.continuous band limited Can be formed by resistivelypink noise 150 Hz to 8 kHz attenuating the speaker output.

1 speaker 100 V, 40 W For connection of 100 V typecontinuous band limited loudspeakers. Amplifiers are available pink noise 150 Hz to 8 kHz with both low impedance and 100 V

outputs. Usually only one should be used at a time. Amplifier MUST matchwith type of loudspeaker used.

Dynamic range >75 dBA from Allows for usable listening range and amplifier noise floor to scope for adjustment of controls.clipping point

Distortion THD+N < 2% from 150 Hz to 8 kHz

Equalisers Bass min +/– 6 dB variation Minimum 2 band equaliser operating@ approx 100 Hz on the mixed output signal.

Treble min +/– 6 dB variation Preferred minimum 2 band equaliser @ approx 10 kHz operating on each input.

Hum and noise >85 dB below Under normal range of control maximum output level settings.

Mixer Amplifier

188

Radio Microphone SystemA diversity receiver is preferred. See sidebar for further details.


System main parameters Wideband FM Radio Microphone These channels are providedSystem operating in the VHF high for service to the hearing band channels allocated for use in impaired without requirementpersonal FM systems. for a licence.

Must conform to IR 2030, publishedby the Radiocommunications Agencyunder the category Short RangeDevices. See www.radio.gov.uk forlatest standards.

If necessary to accommodate a large These channels require anumber of channels within a single licence, with an associatedschool or site, licensed radio annual fee.microphone units operating in the UHF band can be used.

Channel selection It is preferred that the system has This enables a spare unit toa user programmable support all units within achannel selection. school or group of schools.

Also enables channels to be easily changed in the event of interference or the desire to tune the system to match a compatible personal FM receiverbrought in by a student.

Microphone input Compatible with plug-in dynamic and electret microphones. Robust connector with locking mechanism and high quality cable retention is required. A permanently wired microphone is not acceptable.

Transmitter antenna Can be used with a 1/4 wave cableconnection antenna. Robust connector with locking

mechanism and high quality cable retention is required. A permanently wired antenna is not acceptable.

Transmitter controls Volume Transmitter should be provided with a Some cheaper transmittersand indicators or gain means to adjust the level of the signal. provide no gain adjustment.

This should be recessed or This limits use with otherscrewdriver controlled to minimise the microphones and some users.risk of accidental adjustment. This actually controls the

modulation of the radio sectionof the transmitter.

On/Off A switch should be provided to enable An on/off switch should notSwitch the transmitter to be switched off be used unless the receiver is

to preserve battery life. This should also turned off.be recessed to prevent If the TX is off, the receiver accidental operation. may pickup an alternative

source on the same channel.


189

continued Mute A switch should be provided to This allows the audio to switch enable the audio signal output be turned off to allow

from the transmitter to be muted private conversation, etc.without turning off the transmitter.

Battery A means of indicating the battery An alternative means ofswitch transmitter to be switched off to testing batteries can be

preserve battery life. This should be provided instead.recessed to prevent accidentaloperation.

Transmitter It is preferred that there is a means Transmitter level is actually level of checking the operating level of easy to measure at either end.indicator the transmitter, either on the

transmitter unit, or on the receiver.

Channel Channel selection should beselector available by means of an easy to

understand control that is protected against accidental operation.

Receiver antenna Diversity receiver with dual antennas. Diversity provides Built-in or detachable telescopic protection against signal or helical antennas. loss due to reflections in the

room. Reduces signal ‘drop-out’.

Receiver controls Volume An output volume control aids in Alternatively, given and indicators Control setting up a system. compatibility with the

amplifier, the gain may be adjusted there instead.

On/Off A front panel operable on/off switchswitch is required.

System frequency 100 Hz to 10 Hz ± 1 dB Performance of whole response transmitter to receiver system

without microphone connected.

Dynamic range ≥ 85 dB This sets the maximum signal to noise ratio available from the equipment. It is the performance of the whole transmitter to receiver system without the microphone connected.

Distortion THD+N < 0.5% from 150 Hz to 8 kHz at any signal level

Transmitter battery Life ≥ 6 hours from a rechargeable nicad Battery life should be battery under continuous measured under real operating transmission conditions conditions. Many published

figures are not trustworthy as Battery compartment should be they are actually for a standby robust, enabling battery to slide in. condition.A loose, plug-on battery connection is not acceptable.


190


Microphone type Omni-directional headworn microphone. Robust cable and connector with locking mechanism and good cable retention. Condenser microphone types must be compatible with radio microphone transmitter powering system or contain easily changed battery with long service life.

Frequency response 100 Hz to 12 kHz ± 3 dB when used Microphone response is in recommended operating position partly dependent upon

surrounding surfaces. Microphone response should be considered when used as intended, not in an anechoic measurement.

Sensitivity Microphone sensitivity should match the gain range of the transmitter enabling full transmitter modulation to be achieved when worn as recommended and used with a raised voice level.

Dynamic range > 65 dBA

Sensitivity > -46 dBV re 1 V/PaSuitable for use in close proximity to the mouth

Headworn Microphone


Appendix 9: Noise at Work Regulations relating to teachers

191

There is growing concern about thepossibility of long-term hearing damageto those teachers who generally work inthe noisier school environments, forexample PE teachers, CDT teachers andmusic teachers. The Health and SafetyExecutive has recently carried out a studyof noise exposure among these teachersdue to their potential for exposure tohigh noise levels. It is known thatorchestral musicians are at risk of noiseinduced hearing damage[1,2] andtherefore peripatetic music teachers mayexperience additional risk. It is necessaryunder the Noise at Work Regulations[3]

to ensure that teachers of ‘noisy’ subjectsare not exposed to levels of noise likely tocause, or increase, risk of hearingdamage. The noise levels to whichteachers are exposed can be reduced tosome extent by good acoustic design ofschools, for example by ensuring that thereverberation time is short so as not toincrease the noise level in a room.However, there will inevitably be someoccasions when the noise associated witha particular teaching activity approaches,or is above, the levels known to pose arisk to hearing.

The risk of noise induced hearingdamage is a function of both noise leveland the duration of exposure to the noise.The noise levels to which employees maybe exposed, and the wearing of hearingprotection, are currently subject to theNoise at Work Regulations 1989[3].However, in February 2003 the EuropeanUnion published a new directive, thePhysical Agents (Noise) Directive[4],relating to noise at work which will resultin the UK legislation being changed in2006.

The main points of the currentregulations, the European Directive andthe likely changes to UK legislation in2006 are summarised below.

Action levelsThe current regulations are expressed interms of action levels, that is levels ofnoise exposure at which certain actionsare required by employers and/or

employees (together with manufacturersof equipment).

Action levels are defined in terms ofdaily personal noise exposure LEP,d whichtakes account of both level and exposuretime. LEP,d is similar to LAeq,T (seeAppendix 1) but is always normalised toan exposure time of 8 hours. Forexample, a person exposed to acontinuous noise level of 85 dB(A) for 8 hours per day experiences a dailypersonal noise exposure of 85 dB(A)LEP,d. For each halving of the dailyexposure time, the LEP,d reduces by 3 dB(A), so that a daily exposure of 4hours to a noise level of 85 dB(A) isequivalent to 82 dB(A) LEP,d , and a dailyexposure of 2 hours to a noise level of 85 dB(A) is equivalent to 79 dB(A)LEP,d. Similarly, a doubling of exposuretime increases LEP,d by 3 dB(A).

Current RegulationsThe Regulations apply to employers,employees and self-employed people (whohave the duties of both employers andemployees). Peripatetic music teachers,for example, may fall into this last category.

Whatever the level of noise, employershave a duty under the Regulations toreduce the noise level to the lowest levelreasonably practicable.

The first action level is 85 dB(A) LEP,d.If any employee is likely to be exposed tothis level or above, employers’ dutiesunder the Regulations include thefollowing :• to ensure that a competent personmakes a noise assessment which isadequate to identify which employees areexposed to this level or above• to inform employees of the risks ofnoise and ways in which the risk may bereduced• to provide, and maintain, hearingprotection for those who request it.

Employees also have a duty at thisaction level to maintain any equipmentthat is provided by the employer toreduce the risk of hearing damage, and toreport any defects in the equipment.

192

The second action level is 90 dB(A)LEP,d. If any employee is likely to beexposed to this level or above, employers’additional duties under the Regulationsinclude the following :• to reduce noise exposure of employeesthrough noise control measures otherthan hearing protection• to mark hearing protection zones wherenoise reaches the second action level withrecognised signs• to provide hearing protection to allemployees and to ensure that it is worn.

At this action level employees mustagain maintain any equipment provided,and must also wear the hearing protectionprovided.

The regulations also specify a peakaction level of 200 Pascals (equivalent toan unweighted sound level of 140 dB).This represents an instantaneous soundlevel, caused for example by a loud bang.Where this level is exceeded, employersand employees have the same duties as atthe second action level. Exposure to thepeak action level is normally linked withthe use of cartridge operated tools, gunsor similar loud explosive noises, but canoccur during the loud playing of amusical instrument[1].

Changes to the RegulationsNew legislation will come into force inFebruary 2006 to comply with thePhysical Agents (Noise) Directive. Formusicians, who may include musicteachers, the new legislation will not beenforced until 2008.

The main changes to the legislation arethat, in effect, the action levels will belowered by 5 dB(A). In general, theactions currently required at 85 and 90 dB(A) LEP,d will be mandatory at 80 and 85 dB(A) LEP,d respectively. Inaddition an overall personal exposure levelof 87 dB(A) LEP,d is to be introduced;this is the limit of exposure at the earwhich means that the level at the ear(with or without hearing protection)must never exceed 87 dB(A) LEP,d.

Two peak exposure limit values areincluded in the directive: 112 Pa at whichthe duties required at 80 dB(A) LEP,d

apply, and 140 Pa at which the duties at85 dB(A) LEP,d are required. 200 Paremains as an overall peak exposure limit.

Another feature of the new directivewhich may be relevant to teachers is thatit will be possible to assess noise exposureon a weekly, rather than a daily basis, ifexposure varies significantly from day today.

Further informationThe above summary of some aspects ofthe Noise at Work Regulations is includedfor information, but does not purport tobe a complete statement of theRegulations. Employers and employeeswho believe that they may have dutiesunder the Regulations should obtain acopy of the Regulations and should befamiliar with the requirements. For a fullversion of the regulations see the HMSOweb site[5]. For information on theeffects of noise, the current regulations,the new Directive and its implications forthe UK see the Health and SafetyExecutive website[6]. The text of theDirective may be found on the website ofthe Official Journal of the EuopeanUnion[4]. For a discussion of theimplications for music teachers seewww.musiced.co.uk.

References[1] R Canham and B Shield. Noise surveys oforchestral musicians at the Barbican concerthall. Proc. Institute of Acoustics 21(6), 217-225, 1999.[2] A Wright Reid. A sound ear. Association ofBritish Orchestras 2001.[3] Noise at Work Regulations 1989.[4] Directive 2003/10/EC of the EuropeanParliament and of the Council of 6 February onthe minimum health and safety requirementsregarding the exposure of workers to the risksarising from physical agents (noise). OfficialJournal of the European Union L042, 15 February 2003, 38-44. [5] www.hmso.gov.uk [6] www.hse.gov.uk

Appendix 9: Noise at Work Regulations relating to teachers

193

All submissions to the Building ControlBody (BCB) should clearly identify therelevant performance standards fromSection 1, how they will be met, and theperformance that the design is expectedto achieve. Calculations, test reports etcshould preferably be included inappendices to the submission, rather thanin the main body of the submission. Theextent of acoustic information required tosatisfy the BCB may vary betweenAuthorities and individuals. This exampleprovides an indication of the minimumlevel of information that should beprovided. The right hand columncontains a commentary on thesubmission.

A set of symbols has been created foruse on plans in submissions to allow aquick visual inspection of the BB93performance standards for each acousticcriterion and the performance that thedesign is expected to achieve. Thesymbols can be downloaded from theDfES acoustics website. Hand-produceddrawings would also be acceptable.

Example submissionThe following items are provided insupport of the submission to the BuildingControl Body to demonstrate compliancewith the acoustic requirements of Part Eof the Building Regulations.

The ground floor plan of the roomsand the acoustic performance standardsare shown in Figure A10.1. On the firstfloor there are classrooms above theground floor classrooms and musicclassrooms.

A 10.1 Indoor ambient noise levels inunoccupied spacesThe performance standards in TableA10.1 for indoor ambient noise levels

Appendix 10: Example submission to Building Control Body

This example submissionfocuses on only a few ofthe rooms, although thesame level of detail wouldbe required for all relevantrooms in the school.

Table A10.1: BB93 performance standards –indoor ambient noise level

35/35 35/35

45/45

35/35

35/3535/35

0.9/1.0 0.9/1.0

0.7/0.80.7/0.8

55/55

55/55

45/45

45/45

MusicClassroom

MusicClassroom

Classroom Classroom

Assembly Hall

e

f

d

b

a

a f– See Figure A10.3

For wall constructions see Table A10.6 and Figure A10.2

45/45

55/55

55/55

55/55

100%

1.11.0 - 1.2

31/30

37/35 37/35

31/30

48/45 48/45

c

40/40 40/40

Figure A10.1: The plan ofthe rooms and the acousticperformance standards

BB93 performancestandard LAeq,30min(dB)

≤ 35

Room

Classroom

The 30 minute time period with thehighest external noise level during theschool day, 59.9 dB LAeq,30min, ishighlighted in the table.

The Leq,30min noise spectrumcorresponding to the 30 minute timeperiod with the highest external noise

level, 59.9 dB LAeq,30min, is shown inTable A10.3.

The construction of the externalenvelope of the school will be a cavitybrick/block wall with 6/12/6 glazing.The sound transmitted through thefaçade has been calculated for theclassroom to determine the indoorambient noise level. The upper limit forthe reverberation time of the classroomfrom Table 1.5, Section 1 has been usedin the calculation.

Ventilation will be provided by anacoustic ventilator and a passive stack roofventilator with acoustic attenuationtreatment. The ventilation requirementhas been calculated based on 3 litre/s perperson.

The calculations have been carried outusing the Excel spreadsheet based on BSEN 12354-3:2000 from the DfESacoustics website The results are shown inTable A10.4.

The indoor ambient noise level iscalculated to be 34.7 dB LAeq,30minwhich is just below the upper limit forclassrooms, 35 dB LAeq,30min, andtherefore satisfies the performancestandards in Table 1.1, Section 1.

Note 1 of Table 1.1, Section 1 givesguidance on indoor levels from individualexternal noisy events. The facade willoffer a similar reduction in performancefor LA1,30min as for LAeq,30min, hencethe indoor level should not regularlyexceed 55 dB LA1,30min.

For these classrooms there are no noisesources due to building services thatrequire consideration.

194


Depending upon the site,each elevation could beexposed to a different levelof noise. Therefore adifferent ventilationstrategy could be used oneach elevation. This wouldrequire separatecalculations.

Table A10.2: Noise survey data – LAeq,30minand LA1,30min (external noise)

Details of the noise surveyshould be provided in anAppendix. Sufficientinformation should beprovided to allow the BCBto confirm that themeasurement times andpositions are appropriateand representative for theproposed school.The external noisespectrum is required tocalculate the indoorambient noise level due tosound transmission throughthe façade.In this example, only asingle noise measurementhas been taken at theproposed façade positionfor the few classroomsunder consideration.Normally, noisemeasurements would betaken at the positions of allthe proposed schoolfaçades. In some casesthese measurements wouldbe adjusted to takeaccount of some facadesbeing shielded from thenoise by the proposedbuilding.

57.556.858.057.757.456.956.159.159.459.858.658.557.457.958.257.459.956.6

66.164.864.866.066.964.663.966.367.164.966.466.265.366.865.666.071.365.0

Table A10.3: Noise survey data – Leq,30min external noise spectrum

On sites where there is agreater incidence ofindividual noisy events suchas from aircraft overflightsor near a railway a moredetailed noise survey wouldnormally be expected.

have been taken from Table 1.1, Section 1.A noise survey was carried out at the

site on XX.YY.ZZZZ to establish thenoise climate. Free-field external noiselevels in terms of LAeq,30min andLA1,30min were measured at a positioncorresponding to the proposed schoolfacade closest to the dominant externalnoise source, the nearby road. Themeasured data are shown in Table A10.2.

Time

08:00 – 08:3008:30 – 09:0009:00 – 09:3009:30 – 10:0010:00 – 10:3010:30 – 11:0011:00 – 11:3011:30 – 12:0012:00 – 12:3012:30 – 13:0013:00 – 13:3013:30 – 14:0014:00 – 14:3014:30 – 15:0015:00 – 15:3015:30 – 16:0016:00 – 16:3016:30 – 17:00

LAeq,30min(dB)

LA1,30min(dB)

Leq,30min (dB) Octave band centre frequency (Hz)

Time 125 250 500 1 k 2 k

16.00 – 16.30 62.0 58.5 56.1 55.9 52.7

A 10.2 Airborne sound insulationbetween spacesThe performance standards for theairborne sound insulation between spaceshave been taken from Tables 1.1 and 1.2,Section 1.

195


The submission shouldreference the calculationprocedure (eg BS EN12354-3:2000, BS8233:1999 etc). Thesubmission should alsocontain references to thesource(s) of all soundinsulation data used in thecalculations. The followingoptions are suitable: copiesof laboratory soundinsulation test certificatesin the appendices of thesubmission, reference tolaboratory accreditationnumber and test reportnumber, reference tobooks or papers.

In this example there areno significant internal noisesources. Hence, onlyexternal noise sourceshave been considered.When there are significantinternal noise sources,Section 1.1.1 describeswhich internal sourcesshould be considered in thecalculation of the indoorambient noise level.


125 250 500 1 k 2 k

External Leq,30min (dB) 62.0 58.5 56.1 55.9 52.7

Area (m2) Façade element sound insulation R (dB)

Double glazing 6/12/6 14 20.0 19.0 29.0 38.0 34.0

Brick/block cavity wall 7 41.0 45.0 45.0 54.0 58.0

Number of Ventilator sound insulation Dn,e (dB)ventilators

Acoustic vent 1 20.1 23.4 28.7 40.3 52.6

Passive stack roof

ventilator 1 20.0 26.0 31.0 36.0 44.0

Reverberation time (s) 0.8

Room volume (m3) 168

Internal LAeq,30min (dB) 34.7

Table A10.4: Calculation of indoor ambient noise level in the classroom due to external noisetransmitted through the façade

The performance standard for airbornesound insulation between rooms has beenassessed in both directions but only thehighest DnT(Tmf,max),w values are shownin Table A10.5.

The minimum weighted sound

Table A10.5: Airborne sound insulation between spaces

Source room Receiving room BB93 performance standardDnT(Tmf,max),w (dB)

Classroom Classroom 45

Classroom Assembly hall 45

Assembly hall Classroom 55

Music classroom Music classroom 55

Assembly hall Music classroom 55

Music classroom Assembly hall 55

reduction indices (Rw) required toachieve the DnT(Tmf,max),w performancestandards for the separating walls havebeen estimated using the approachdescribed in Section 3.10.

The wall constructions to be used inthe school are shown in Figure A10.2.

Table A10.6 contains information onthe separating walls to be used betweendifferent rooms.

The proposed flanking details areshown in Figure A10.3. Each detail inFigure A10.3 corresponds to the detailidentified on Figure A10.1. Theseflanking details have been used toestimate the field airborne soundinsulation according to BS EN 12354-1:2000, to confirm that the performancestandards in terms of DnT(Tmf,max),w canbe achieved.

The floor construction to be used tosatisfy the performance standards isshown in Figure A10.4. Test report

No. XYZXYZ, laboratory accreditationNo. ZZZZ contains the airborne soundinsulation data for this floor.

196

The submission shouldreference the calculationprocedure (e.g BS EN12354-1:2000) that hasbeen used to estimate theairborne sound insulation ofthe separating element andassociated flanking elements.Details and assumptionsmade in the calculationsshould be contained in theappendices of thesubmission.

The submission shouldinclude all relevant flankingdetails and reference thecalculation tools or softwareused to estimate the soundinsulation due to thecombination of direct andflanking transmission.

The submission shouldreference the source(s) ofall sound insulation data.Copies of laboratory soundinsulation test certificatescan be included in theappendices of thesubmission, or referencecan be made to the testreport number and thelaboratory accreditationnumber.

Table A10.6: Separating walls - airborne sound insulation between spaces

*Estimated using the approach described in Section 3.10.


Source room

Classroom

Classroom

Assembly hall

Music classroom

Assembly hall

Music classroom

Receiving room

Classroom

Assembly hall

Classroom

Music classroom

Music classroom

Assembly hall

Separating wallconstruction(Refer to FigureA10.2 for details)

(3)

(2)

(3)

(4)

(3)

(3)

Minimum laboratorysound insulation forseparating wall*Rw (dB)

49

42

49

60

50

52

Separatingwall laboratoryperformance Rw (dB)

53

45

53

63

53

53

Laboratory test report

Test report No. XXXXXX,Laboratory accreditationNo. ZZZZ

Test report No. ZZZZZZ,Laboratory accreditationNo. ZZZZ


Test report No. YYYYYY,Laboratory accreditationNo. ZZZZ



197

(1) 40 dB R w

(2) 45 dB R w

(3) 53 dB R w

(4) 63 dB R w

(5) 48 dB R w

Figure A10.2: Wallconstructions


100 mm 1900 kg/m3

fair faced blockwork

100 mm 1900 kg/m3 blockworkwith 12.5 mm 10.5 kg/m2 plasterboardand 25 mm mineral wool lining

140 mm 2400 kg/m3

fair faced blockwork

208 mm staggered metal stud partitionwith 2 x 12.5 mm 10.5 kg/m2 plasterboardand 50 mm mineral wool in cavity

70 mm metal stud with 12.5 mm 10.5 kg/m2

plasterboard and 50 mm mineral wool in cavity

The submission shouldreference the source(s) ofall laboratory soundinsulation data for thewalls, doorsets andventilators. Copies oflaboratory sound insulationtest certificates can beincluded in the appendicesof the submission, orreference can be made tothe test report number andthe laboratory accreditationnumber.

A10.3 Airborne sound insulationbetween circulation spaces and otherspaces used by studentsThe performance standards in TableA10.7 for airborne sound insulationbetween circulation spaces and otherspaces used by students have been takenfrom Table 1.3, Section 1.

The walls and doorsets to be used inthe school are referenced in Table A10.8along with references to the laboratorysound insulation test certificates. Doorsetswill have a vision panel and neopreneblade seals to the jambs and head, anddrop threshold seals.

Table A10.7: BB93 performance standards - airborne sound insulation between circulationspaces and other spaces used by students

Space used bystudents

Classroom

Music classroom

Circulationspace

Corridor

Corridor

Separatingelement

WallDoorset

WallDoorset

BB93 performance standardRw (dB)

≥ 40≥ 30

≥ 45≥ 35

198


EXTERNAL FACADE

CLASSROOM CLASSROOM

Flexible cavity stop within cavity continuous for theheight of the crosswall

Mastic filled joint

Partition to passthrough wall linning

Mastic filled joint

CLASSROOM CLASSROOM

140 mm denseblockworkcrosswall tiedinto 100 mmcorridor wall

CORRIDOR

Plasterboardsoffit treatment

on timber batterns

Deflection headdetail packed with mineral wool and sealed with soft setting mastic

Concrete screed withembedded heating pipeson polystyrene insulationand polyurethaneresilient layer

Figure A10.3: Flankingdetails

a

b

c

d

e f

A10.4 Impact sound insulation offloorsThe performance standards in TableA10.9 for impact sound insulation havebeen taken from Table 1.4, Section 1.

The floor construction to be used inthe school is in Table A10.10 along withreferences to the estimation method and

199


Table A10.8: Separating elements - airborne sound insulation between circulation spaces and other spaces used by students

The submission shouldreference the source(s) ofall sound insulation data.Copies of laboratory soundinsulation test certificatescan be included in theappendices of thesubmission, or referencecan be made to the testreport number and thelaboratory accreditationnumber.

Table A10.9: BB93 performance standards - impact sound insulation

Table A10.10: Separating floor - impact sound insulation

laboratory sound insulation test certificates.The separating floor construction

shown in Figure A10.4 with a permanentcarpet (ie glued to the floor) will be usedin the classroom and the music classroomto achieve the performance standards.The first floor science laboratories willhave vinyl flooring instead of carpet.

The submission shouldinclude all relevant flankingdetails and reference thecalculation tools orsoftware used to estimatethe sound insulation due tothe combination of directand flanking transmission.

Separatingelement

Wall

Doorset

Wall

Doorset

Separating element(Refer to Figure A10.2for wall details)

(1)

Product X, Manufacturer X

(2)

Product Y,Manufacturer X

BB93 performancestandardRw (dB)

≥ 40

≥ 30

≥ 45

≥ 35

Separating elementlaboratory performanceRw (dB)

40

31

45

37

Laboratory test report

Test report No. XXXXXX, Laboratory accreditation No. XXXX

Test report No. YYYYYY, Laboratory accreditation No. XXXX

Test report No. ZZZZZZ, Laboratory accreditation No. XXXX

Test report No. YYYYYY, Laboratory accreditation No. XXXX

Ground floor room

ClassroomMusic classroomScience laboratory

First floor room

ClassroomClassroomClassroom

BB93 performance standard L’nT(Tmf,max),w (dB)

≤ 60≤ 55≤ 65

Ground floor room

Classroom

Music classroom

Science laboratory

First floorroom

Classroom

Classroom

Classroom

Floor construction

As Figure A10.4 with 5 mm permanentneedlefelt carpet

As Figure A10.4 withpermanent vinyl flooringinstead of carpet

Estimation method

Predictions using BS EN 12354-2:2000 and test report No. YYYYYY,laboratory accreditation No. XXXX

Predictions using BS EN 12354-2:2000 and test report No. YYYYYY,laboratory accreditation No. XXXX

EstimatedL’nT(Tmf,max),w (dB)

53

53

62

200


Painted blockwork

Carpet on concrete floor

Glazing

Suspended plasterboard ceiling

Absorbent ceiling - Product X Manufacturer Y

Absorbent tile for back wall - Product X Manufacturer Y

Volume (m3)

T (s)

Tmf (s)


Area (m2) 125 250 500 1 k 2 k

Absorption coefficients

60 0.10 0.05 0.06 0.07 0.09

56 0.05 0.05 0.1 0.2 0.45

14 0.1 0.07 0.05 0.03 0.02

30 0.2 0.15 0.10 0.05 0.05

26 0.45 0.50 0.55 0.30 0.15

16 0.17 0.38 0.48 0.68 0.88

168

Reverberation times

0.88 0.89 0.77 0.75 0.54

0.7

Table A10.12: Reverberation times for the classroom

Figure A10.4: Separatingfloor construction

Table A10.11: BB93 performance standards -reverberation times

A10.5 Reverberation in teaching andstudy spacesThe performance standards in TableA10.11 for the reverberation times havebeen taken from Table 1.5, Section 1.

The reverberation times for theclassrooms and the assembly hall havebeen calculated as described in Appendix6 of BB93.

Room data sheets may bea convenient way topresent information aboutthe various room finishesto the BCB as they mayalready have beengenerated for the school.These data sheets mayalso be an appropriateplace to identify the otheracoustic standardsproposed for the school.

5 mm needlefelt carpet60 mm screed incorporating heating pipeworkPolystyrene insulation5 mm Polyethylene resilient layer150 mm 2400 kg/m3 concrete25 mm mineral wool12.5 mm plasterboard or proprietary acousticceiling product

Room

Classroom

Assembly hall

BB93 performance standard Tmf (s)

<0.8

0.8 – 1.2

201


ClassroomThe absorption coefficients and thepredicted reverberation times for theclassroom are shown in Table A10.12.The predicted Tmf is 0.7 seconds whichsatisfies the performance standard of <0.8 seconds in Table 1.5, Section 1.

The predicted octave bandreverberation times also satisfy theguidance in Note 1 of Table 1.5, Section1 that the reverberation times in the 125 Hz and 250 Hz octave bandsincrease up to a value not more than 30%above Tmf.

The central section of the ceiling willbe a suspended plasterboard ceiling toprovide a reflective central section withthe absorbent ceiling around the ceilingperimeter as shown in Figure 4.2(a),Section 4.

Assembly hallThe absorption coefficients and thepredicted reverberation times for theassembly hall are shown in Table A10.13.The predicted Tmf is 1.1 seconds whichsatisfies the performance standard of 0.8 – 1.2 seconds in Table 1.5, Section 1.

The predicted octave bandreverberation times also satisfy theguidance in Note 2 of Table 1.5, Section1 that the reverberation times in the 125 Hz and 250 Hz octave bandsincrease up to a value not more than 50%above Tmf.

The central section of the ceiling willbe a suspended plasterboard ceiling toprovide a reflective central section withthe absorbent ceiling around the ceilingperimeter as shown in Figure 4.2(a),Section 4.

The submission shouldreference the source(s) ofall absorption data used inthe reverberation timecalculations. The followingoptions are suitable: copiesof laboratory soundinsulation test certificatesin the appendices of thesubmission, reference totest report number andlaboratory accreditationnumber, or reference tobooks or papers.

Fair-faced blockwork

Parquet on concrete floor

Glazing

Suspended plasterboard ceiling

Absorbent ceiling - Product X Manufacturer Y

Absorbent tile for back wall and top of side walls - Product X Manufacturer Y

Volume (m3)

T (s)

Tmf (s)


Area (m2) 125 250 500 1 k 2 k

Absorption coefficients

170 0.05 0.05 0.05 0.08 0.14

192 0.04 0.04 0.07 0.06 0.06

76 0.15 0.05 0.03 0.03 0.02

140 0.2 0.15 0.10 0.05 0.05

52 0.51 0.68 0.85 0.92 1.00

90 0.46 0.67 0.83 0.93 0.95

1152

Reverberation times

1.50 1.35 1.18 1.12 1.02

1.11

Table A10.13: Reverberation times for the assembly hall

202

A10.6 Sound absorption in corridors,entrance halls and stairwellsThe absorption treatment in the corridorshas been assessed in accordance withMethod A, as described in Appendix 7. It is proposed to install acousticallyabsorbing material in the form of asuspended ceiling, to provide an areaequal to the total floor area. The ceilingsystem has an absorption class equal to, orbetter than, Absorption Class C accordingto manufacturers literature XYZ.

A10.7 Rain Noise Laboratory measurement data for rainnoise on the proposed lightweight metalroof construction is currently unavailable.However, the same roof construction hasbeen used in another school, School X, inwhich field measurements were carriedout. These tests are described in field testreport XYZXYZ. These measurementsdemonstrate that the rain noise is notaudible when the roof constructioncomprises a suspended plasterboardceiling (10 kg/m2) with a 150 mm void.Hence, the same roof construction withthe suspended ceiling will be used.

The submission shouldreference the source(s) ofall absorption data forproducts (eg ceiling tiles)used in corridors, entrancehalls and stairwells. Thefollowing options aresuitable: copies oflaboratory sound insulationtest certificates in theappendices of thesubmission, reference totest report number andlaboratory accreditationnumber, or reference tobooks or papers.

The submission shouldreference the source(s) ofrain noise measurement orprediction data.


Bibliography

203

Government Documents

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A full list of all relevant DfES publicationsis onwww.teachernet.gov.uk/sbdupublications.Many of the publications are available freeeither on the DfES website or from DfESPublications, P O Box 5050,Nottinghamshire, NG15 0DJ, Tel: 084560222 60.

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Department for Education and Employment(1998). Fume cupboards in schools,Building Bulletin 88. London: TheStationery Office. ISBN 0112710271.

Department for Education and Employment(1998). Art accommodation in secondaryschools, Building Bulletin 89. London: TheStationery Office. ISBN 0112710298.

Department for Education and Employment(2000). Modern foreign languagesaccommodation, Building Bulletin 92.London: The Stationery Office. ISBN011271093X.

Department for Education and Skills(2002). Schools for the future, designs forlearning communities, Building Bulletin 95.London: The Stationery Office. ISBN0112711286.www.teachernet.gov.uk/schoolbuildings

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Special Educational Needs

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Department for Education andEmployment (1999). What the DisabilityDiscrimination Act (DDA) 1995 means forschools and LEAs: DfEE Circular 20/99.

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Department for Education and Skills(2002). Accessible schools: summaryschools, ref: DfES/0462/2002.www.dfes.gov.uk/sen

Department for Education and Skills(2002). Accessible schools: planning toincrease access to schools for disabledpupils, ref: LEA/0168/2002.www.dfes.gov.uk/sen

Department for Education and Skills(1998). Meeting special educationalneeds, A programme of action. London:The Stationery Office. ISBN 0855229063.

Department for Education andEmployment (1992). Designing for pupilswith special educational needs: specialschools, Building Bulletin 77. London: TheStationery Office. ISBN 0112707963.

Department for Education andEmployment (1999). Access for disabledpeople to school buildings, BuildingBulletin 91. London: The Stationery Office.ISBN 011271062X.

Department for Education and Skills(2001). Inclusive school design:accommodating pupils with specialeducational needs and disabilities inmainstream schools, Building Bulletin 94.London: The Stationery Office. ISBN011271109X.

National Grid for Learning. Inclusionwebsite. inclusion.ngfl.gov.uk

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Classroom Acoustics

Finitzo-Hieber, T. and Tillman, T.W. (1978).Room acoustics effects on monosyllabicword discrimination ability for normal andhearing-impaired children. J. Speech Hear.Res. 21(3), 440-458.

Miller, J. (1993). Design standards for thesound insulation of music practice rooms.Acoustics Bulletin of the Institute ofAcoustics 18(6), 54-58.

Mills, J. (1993). Music in the primaryschool. 2nd ed. Cambridge: CambridgeUniversity Press. ISBN 0521448255.

Picard, M. and Bradley, J.S. (2001).Revisiting speech interference inclassrooms. Audiology 40(5), 221-244.

Shield, B. and Dockrell, J. (2003). Theeffects of noise on children at school: areview. Building Acoustics 10(2), 97-116.

General Acoustics

Association of Noise Consultants (2001).ANC guidelines: Measurement andassessment of groundborne noise andvibration. Fresco. ISBN 0953951618.

Association of Noise Consultants (1997).ANC guidelines: Noise measurement inbuildings, Part 1: Noise from buildingservices. Association of NoiseConsultants. www.association-of-noise-consultants.co.uk

Association of Noise Consultants (1998).ANC guidelines: Noise measurement inbuildings, Part 2: Noise from externalsources within buildings. Association ofNoise Consultants. www.association-of-noise-consultants.co.uk

Barron, M. (1993). Auditorium acousticsand architectural design. London: SponPress. ISBN 0419177108.

BBC Engineering (1990). BBC guide toacoustic practice. 2nd ed. London: BBC.ISBN 0563360798.

BRE Digest 337, Sound insulation: basicprinciples, October 1988. ISBN0851253652. CRC Ltd.

Bibliography

BRE Report BR 358, Quiet homes, A guideto good practice and reducing the risk ofpoor sound insulation between dwellings,1998. CRC Ltd. ISBN 1860812562.

BRE Report BR 406, Specifying dwellingswith enhanced sound insulation: a guide,2000. CRC Ltd. ISBN 1860814344.

BRE information paper IP6/94, The soundinsulation provided by windows, 1994.CRC Ltd.

BRE and CIRIA (1993). Sound control forhomes. BRE report 238, CIRIA report 127.BRE ISBN 08512555900, CIRIA ISBN0860173623, CIRIA ISBN 0305408X.

Chu, W.T. and Warnock, A.C.C. (2002).Detailed directivity of sound fields aroundhuman talkers. National Research CouncilCanada RR-104.http://irc.nrc-cnrc.gc.ca/fulltext/rr104/

CIBSE (2002). Guide B5: Noise andVibration Control for HVCA. CIBSE. ISBN1903287251.

Craik, R.J.M. (1996). Sound transmissionthrough buildings using statistical energyanalysis. Aldershot: Gower. ISBN0566075725.

Egan, M.D. (1988). Architecturalacoustics. New York: McGraw-Hill. ISBN0070191115.

Fry, A. ed. (1988). Noise control inbuilding services. Oxford: Pergamon. ISBN0080340679.

Harris, C.M. (1993). Noise control inbuildings. New York: McGraw-Hill. ISBN0070268878.

Lord, P and Templeton, D. (1996).Detailing for acoustics. 3rd ed. London:Spon Press. ISBN 0419202102.

McLoughlin, J., Saunders, D.J. and Ford,R.D. (1994). Noise generated by simulatedrainfall on profiled steel roof structures.Applied Acoustics 42, 239-255.

Morfey, C.L. (2001). Dictionary ofacoustics. London: Academic Press. ISBN0125069405.

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Templeton, D. ed. (1993). Acoustics in thebuilt environment. Oxford: ButterworthArchitecture. ISBN 0750605383.

Standards

BS EN ISO 140-1:1998 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part 1. Requirements forlaboratory test facilities with suppressedflanking transmission. British StandardsInstitution.

BS EN 20140-2:1993 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part 2.Determination, verification and applicationof precision data. British StandardsInstitution.

BS EN ISO 140-3:1995 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part 3. Laboratory measurementof airborne sound insulation of buildingelements. British Standards Institution.

BS EN ISO 140-4:1998 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part 4.Field measurements of airborne soundinsulation between rooms. BritishStandards Institution.

BS EN ISO 140-5:1998 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part 5.Field measurements of airborne soundinsulation of façade elements and facades.British Standards Institution.

BS EN ISO 140-6: 1998 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part 6.Laboratory measurement of impact soundinsulation of floors. British StandardsInstitution.

BS EN ISO 140-7: 1998 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part 7.Field measurement of impact soundinsulation of floors. British StandardsInstitution.

BS EN ISO 140-8: 1998 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part 8.Laboratory measurements of the reductionof transmitted impact noise by floorcoverings on a heavyweight standard floor.British Standards Institution.

BS EN 20140-9:1994 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part 9.Laboratory measurement of room-to-roomairborne sound insulation of a suspendedceiling with a plenum above it. BritishStandards Institution.

BS EN 20140-10:1992 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part10. Laboratory measurement of airbornesound insulation of small buildingelements. British Standards Institution.

BS EN ISO 140-12: 2000 Acoustics -Measurement of sound insulation inbuildings and of building elements. Part12. Laboratory measurement of room-to-room airborne and impact sound insulationof an access floor. British StandardsInstitution.

BS EN ISO 717-1:1997 Acoustics - Ratingof sound insulation in buildings and ofbuilding elements. Part 1. Airborne soundinsulation. British Standards Institution.

BS EN ISO 717-2:1997 Acoustics - Ratingof sound insulation in buildings and ofbuilding elements. Part 2. Impact soundinsulation. British Standards Institution.

BS EN ISO 3382:2000 Acoustics -Measurement of the reverberation time ofrooms with reference to other acousticalparameters. British Standards Institution.

BS 8233: 1999 Sound insulation andnoise reduction for buildings - Code ofPractice. British Standards Institution.

BS EN ISO 11654:1997 Acoustics - Soundabsorbers for use in buildings. Rating ofsound absorption. British StandardsInstitution.

BS EN 12354-1:2000 Building Acoustics -Estimation of acoustic performance inbuildings from the performance ofelements. Part 1. Airborne soundinsulation between rooms. BritishStandards Institution.

BS EN 12354-2:2000 Building Acoustics -Estimation of acoustic performance inbuildings from the performance ofelements. Part 2. Impact sound insulationbetween rooms. British StandardsInstitution.

BS EN 12354-3:2000 Building Acoustics -Estimation of acoustic performance inbuildings from the performance ofelements. Part 3. Airborne soundinsulation against outdoor sound. BritishStandards Institution.

BS EN 20354:1993 Acoustics -Measurement of sound absorption in areverberation room. British StandardsInstitution.

BS EN 60268-16:1998 Sound systemequipment – Part 16: Objective rating ofspeech intelligibility by speechtransmission index. British StandardsInstitution.

BS EN 60804:2001 Integrating-averagingsound level meters. British StandardsInstitution.

ANSI S12.60-2002 American nationalstandard acoustical performance criteria,design requirements and guidelines forschools. American National StandardsInstitute.

ANSI S3.5-1997 (R2002) Methods for thecalculation of articulation index. AmericanNational Standards Institute.

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Department for Education and Skills (DfES)School Buildings & Design Unit7th Floor, Caxton House, 6-12 Tothill Street, London, SW1H 9NAWebsite: www.teachernet.gov.uk/acoustics

Office of the Deputy Prime Minister (ODPM)Building Regulations Division3/D1, Eland House, Bressenden Place, London, SW1E 5DUWebsite: www.odpm.gov.uk

Institute of Acoustics77A St Peter’s Street, St Albans, Herts, AL1 3BNTel: 01727 848195 Fax: 01727 850553Email: [email protected] Website: www.ioa.org.uk

Association of Noise Consultants6 Trap Road, Guilden Morden, Royston, Herts, SG8 0JE Tel: 01763 852958 Fax: 01763 853252Email: [email protected] Website: www.association-of-noise-consultants.co.uk

Voice Care Network UK29 Southbank Road, Kenilworth, Warwickshire, CV8 1LATel: 01926 864000 Fax: 01926 864000Email: [email protected]: www.voicecare.org.uk

National Deaf Children's Society15 Dufferin Street, London, EC1Y 8URTel: 020 7490 8656 (voice & text) Fax: 020 7251 5020Email: [email protected]: www.ndcs.org.uk

British Association of Teachers of the Deaf (BATOD)175 Dashwood Avenue, High Wycombe, Buckinghamshire, HP12 3DBEmail: [email protected] Website: www.batod.org.uk

Royal National Institute for the Deaf (RNID)19-23 Featherstone Street, London, EC1Y 8SLWebsite: www.rnid.org.uk

Association of Building Engineers (ABE)Lutyens House, Billing Brook Road, Weston Favell, Northampton, NN3 8NWTel: 01604 404121Email: [email protected] Website: www.abe.org.uk

Chartered Institution of Building Services Engineers (CIBSE)222 Balham High Road, Balham, London, SW12 9BSTel: 020 8675 5211Fax: 020 8675 5449Website: www.cibse.org

List of organisations

www.teachernet.gov.uk/acoustics

www.odpm.gov.uk

www.ioa.org.uk

www.association-of-noise-consultants.co.uk

www.voicecare.org.uk

www.ndcs.org.uk

www.rnid.org.uk

www.abe.org.uk

www.cibse.org