sfm/j002872/4281/02 14 may 2020 acoustic ......sfm/j002872/4281/02 14 may 2020 architectural...

SFM/J002872/4281/02 14 May 2020

architectural

environmental

occupational

industrial

noise control at source

project management

planning

legal services

expert witness

ACOUSTIC CONSULTANTS

Philip Dunbavin A coustics Ltd.

3 Bridgewater Court · Barsbank Lane · Lymm · Cheshire WA13 0ER

Tel: 01925 759380 · www.pdaltd.com Directors: P. R. Dunbavin • J. A. Dunbavin • M. de Salis • E. Evenden • R. Grant

Registered Number 2302847 England

Registered Office: 3 Bridgewater Court· Barsbank Lane· Lymm · Cheshire WA13 0ER

Report Prepared For: Wynne Construction [email protected] Report Prepared By: R D Cookson PhD, BSc(Hons), MIOA

INITIAL DESIGN SPECIFICATION ADVICE

YSGOL GLANRAFON

MOLD

CH7 1PS

SFM/J002872/4281/02 2 14 May 2020 ___________________________________________________________________________

___________________________________________________________________________ Philip Dunbavin Acoustics Ltd. – Tel (01925) 759380

Email: [email protected]

Document Control

Revision 1 2 3 4

Remark First issue

Added mechanical services noise egress

Date 10/03/2020 14/05/2020

Report prepared by

Stefan Fox Marshall MSc, BSc (Hons), AMIOA

Richard Cookson PhD, BSc(Hons), MIOA

Position Acoustic Technician

Principal Consultant

Report checked by

Richard Cookson PhD, BSc(Hons), MIOA

Position Principal Consultant

SFM/J002872/4281/02 3 14 May 2020 ___________________________________________________________________________



Contents

1.0 SUMMARY ............................................................................................. 4

2.0 BRIEF FOR CONSULTANCY ................................................................ 5

3.0 PERFORMANCE STANDARDS ............................................................ 6

4.0 INTERNAL AMBIENT NOISE LEVELS .................................................. 7

4.1 Design Specification ..................................................................................................... 7

5.0 NOISE SURVEY ................................................................................... 10

5.1 Site noise consideration ............................................................................................. 10 5.2 Survey Details .............................................................................................................. 10

5.2.1 Survey times .......................................................................................................... 10 5.2.2 Measurement Location .......................................................................................... 10 5.2.3 Measurement equipment ....................................................................................... 11 5.2.4 Weather ................................................................................................................. 11 5.2.5 Measured Noise Results ........................................................................................ 11 5.2.6 Typical ambient noise level during the measurement period ................................ 12

5.3 Discussion of external noise levels ........................................................................... 12 5.4 Mechanical Services Noise with full mechanical ventilation system ..................... 13 5.5 External Mechanical Services Noise Egress ............................................................ 13

6.0 INTERNAL SOUND INSULATION ....................................................... 14

6.1 Sound Insulation between spaces ............................................................................. 14 6.2 Corridor walls and doors ............................................................................................ 15

7.0 REVERBERATION TIMES ................................................................... 16

7.1 Design Specification ................................................................................................... 16 7.2 Kitchen / Servery ......................................................................................................... 17

8.0 CONCLUSION ...................................................................................... 18

SFM/J002872/4281/02 4 14 May 2020 ___________________________________________________________________________



1.0 SUMMARY

A design specification report has been made which discusses the required ventilation and glazing strategy needed to achieve specified internal ambient noise levels by BB93. Data from a noise survey was used to make a comment on the suitability of using a natural / hybrid ventilation strategy for the development of the school. A preliminary outline of the required internal sound insulation between rooms and reverberation times for new and remodelled spaces is also made in accordance with the recommendations of Building Bulletin 93 - Acoustic Design of Schools.

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2.0 BRIEF FOR CONSULTANCY

A. Noise Survey

We will travel to the site and carry out an ambient environmental noise survey to assess the level of noise incident upon the proposed development. The measurement and assessment will include for noise from the adjacent road network, and other local noise sources. We would propose to undertake manned measurements during periods representative of the normal school day. We will carry out all noise surveys in accordance with the provisions of BS7445 Description and Measurement of Environmental Noise”. The measurements made will include both dBA and octave band noise levels including Leq, L1, and L90 parameters.

B. Consulting - Design Specification

We will prepare a design specification indicating the required acoustic performance in terms of unoccupied internal ambient noise level, internal sound insulation and reverberation times for each new and remodelled space in accordance with the recommendations of Building Bulletin 93 - Acoustic Design of Schools. We will also comment on the suitability of natural or hybrid ventilation systems based on the outcome of the ambient noise survey of part A). The design specification will be presented in a short technical report.

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3.0 PERFORMANCE STANDARDS

Requirement E4 of Schedule 1 to the Building Regulations 2010 states;

1. Each room or other space in a school building shall be designed and constructed in such a way that it has the acoustic conditions and the insulation against disturbance by noise appropriate to its intended use.

2. For the purposes of this Part – ‘school’ has the same meaning as in Section 4

of the Education Act 1996[4]; and ‘school building’ means any building forming a school or part of a school.

Further to the above, the guidance contained within Section 0.12 of Approved Document E 2010 states;

In the Secretary of State’s view the normal way of satisfying Requirement E4 will be to meet the values for sound insulation, reverberation time and indoor ambient noise which are given in Section 1 of Building Bulletin 93 The Acoustic Design of Schools: performance standards, published by the Department for Education and available on the internet at www.gov.uk.

From the above statements it can be seen that compliance with the performance standards of Building Bulletin 93 (BB93) also ensures compliance with the acoustic requirements of the Building Regulations.

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4.0 INTERNAL AMBIENT NOISE LEVELS

BB93 specifies the indoor ambient noise levels (IANL) in unoccupied teaching spaces in terms of LAeq,30min which is the 30 minute energy averaged sound pressure level within the unoccupied classroom. The limit applies to noise break-in from ambient noise external to the school and also noise from internal building services, but does not apply to noise generated by the operation of the school itself (i.e. noise from equipment, pupils and staff within or external to the building). Internal ambient noise levels are specified in order to provide a suitable ambient noise climate for clear communication of speech between teacher and student, clear communication between students, and for work and study.

4.1 Design Specification

The design guidance within Building Bulletin 93 Acoustic Design of Schools: Performance Standards for the internal ambient noise levels for the rooms within this development are as follows. Table 1 – Maximum unoccupied internal ambient noise levels in spaces

Room Name Upper limit for the indoor

ambient noise level LAeq,30mins dB

KS2 Classroom1 35

KS2 WC1,2 50

Head Office1, 2 40

KS1 Classroom 40

SEN group 35

Staffroom / Exam ST2 45

Hall 45

Studio 40

MI / SEN Therapy 35

Quiet Area 45

Early Years Office2 45

Early Years WC2 55

Notes 1. These rooms are included in the New Build development scheme for the school. Table 1

of BB93 gives a more stringent upper limit of the IANL’s which are given in the above

table for these spaces.

2. Section 0.3.6 of BB93 suggests Administration and Ancillary areas are exempt from the

requirements of Building Regulations E4. For these areas the performance standards

are for guidance only.

Storerooms and Plantrooms have been assumed to be non-acoustic rooms and have not been assessed.

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In addition to the average noise level criteria (LAeq) above, BB93 also suggests, ‘in order to protect students from regular discrete noise events, e.g. aircraft or trains, indoor ambient noise levels should not exceed 60 dB LA1,30mins’. This is achieved by default for internal ambient noise levels up to 40dB LAeq,30min.

Building services and indoor ambient noise levels Noise from building services under normal conditions should meet the limits for indoor ambient noise levels (IANL) given in Table 1. However, BB93 gives some allowance for increase in indoor ambient noise levels where a natural or hybrid ventilation strategy is employed. BB93 suggests that for natural ventilation systems the internal noise levels may be increased from the IANL limit from Table 1 by 5dB. The +5dB does not apply to teaching and learning spaces where the Table 1 IANL is greater than or equal to 45dB. Therefore, the internal ambient noise levels of Table 1 including the allowance for natural ventilation are as follows: Table 2 – Internal ambient noise levels in spaces with natural ventilation allowance

Notes

1. These rooms are included in the New Build development scheme for the school. Table 1 of

BB93 gives a more stringent upper limit of the IANL’s which are given in the above table for

these spaces.


requirements of Building Regulations E4. For these areas the performance standards are for

guidance only.

Room Name

Upper limit for the indoor ambient noise level

including mechanical services during normal ventilationLAeq,30mins dB

Allowance if Natural / Hybrid ventilation strategy

is employed dBA

KS2 Classroom1 35 40

KS2 WC1,2 50 -

Head Office1, 2 40 45

KS1 Classroom 40 45

SEN group 35 40

Staffroom / Exam ST2 45 -

Hall 45 -

Studio 40 45

MI / SEN Therapy 35 40

Quiet Area 45 -

Early Years Office2 45 -

Early Years WC2 55 -

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Note that the criteria are given in terms of dBA, whilst mechanical services noise is typically denoted by NR. Whilst there is no direct relationship between dBA and NR values, as a conservative rule of thumb mechanical services should be designed to NR values at least 6 dB lower than the dBA values given in Table 2. This is the total mechanical services noise including both break-out and down-duct noise. Summertime Ventilation and Intermittent Boost BB93 requires that for summertime ventilation (ventilation under local control of teacher to prevent overheating – allowable during the hottest 200 hrs of the year) and Intermittent Boost (ventilation under local control of teacher for dilution of fumes during practical activities as in practical spaces for science, art, food technology and design and technology), using a natural ventilation system the internal ambient noise level may be increased to ≤55 dBA. For mechanical systems, the IANL for Summertime Ventilation and Intermittent Boost may be increased from that in Table 1 by 5dB. Noise from Ventilator Actuators and Dampers In order to comply with the requirements of the Building Regulations, the noise from the normal operation of automatic systems measured in accordance with ISO 16032 in terms of LAeq,T (T is the duration of a normal operating cycle and the actuator should be operating throughout the measurement) should be no more than 5 dB above the IANL specified for the space in Table 1.

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5.0 NOISE SURVEY

The indoor ambient noise levels are assessed by first establishing the typical outdoor noise levels of the site.

5.1 Site noise consideration

The school is located within a residential area, the dominant noise sources being from occasional car passes surrounding the school. Steady, residual noise can also be heard from roads A5119, B5444 and the Mold Bypass. Figure 1 – Dominant noise sources

5.2 Survey Details

The ambient noise levels were measured at the site to establish the noise impact expected from the surrounding area while the school is in operation.

5.2.1 Survey times

The ambient noise survey measurements were made between 11:15 and 14:00 on Tuesday 3rd March 2020 to establish the noise climate of the area during a typical school day. Measurements were taken using an attended sound level meter set-up by Mr Stefan Fox Marshall MSc, BSc (Hons), AMIOA, of PDA Ltd.

5.2.2 Measurement Location

Measurements were taken from a single location on the property of Ysgol Glanrafon.

A5119 B5444 Mold Bypass Ysgol Glanrafon

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Figure 2 – Noise survey location

5.2.3 Measurement equipment

The noise survey was conducted with an NTI XL2-TA sound level meter.

The NTI XL2 is a class 1 sound level meter in accordance with IEC 61672-1:2002 capable of operating as an integrating sound level meter with frequency weighting and statistical functions. The meter was placed on a tripod which set the height of the microphone to approximately 1.5m above the ground to measure noise levels in line with the guidelines for measurement in BS 7445-1.

5.2.4 Weather

Weather conditions were dry for the duration of the survey. Conditions were slightly overcast in the morning, gradually becoming more sunny into the afternoon. Temperatures varying from 6 to 8°C and windspeeds below 5 m/s.

5.2.5 Measured Noise Results

The noise was measured continuously and averaged over 15-minute periods between 11:15 and 14:00 on the 3rd of March 2020. Note that children of the school had playtime between 12:00 and 13:00. Noise measurements during the assessment were not included for the assessment as the noise from children would be measured to be much higher than the residual sound from the nearby roads and the IANL’s specified in BB93 are not inclusive of noise generated from activity in the school itself.

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Figure 3 – Measured noise results

5.2.6 Typical ambient noise level during the measurement period

In order to assess the indoor ambient noise levels of the primary school, LAeq,30mins

parameters need to be established from the survey data to identify the noise level at the school. This is done by collecting consecutive pairs of LAeq,15mins values from the survey and converting to LAeq,30mins before comparing each combination to establish the worst-case scenario for the site. The worst-case LAeq,30min was found between 11:30 and 12:00 at 54dBA, which will be used for the existing ambient noise level at the survey measurement position. The biggest contributors to the residual sound at the school are due to the roads highlighted in section 5.1. Due to the nature of distance propagation from a line source, it is reasonable to assume that the residual sound level will not change significantly around the school building. Therefore the ambient noise level at the survey measurement position is deemed to be representative of the typical external levels at each façade of the school.

5.3 Discussion of external noise levels

BB93 states that for single sided natural ventilation the internal criteria can normally be achieved where the external noise levels do not exceed the internal noise criterion by more than 16 dB, and for cross ventilated or roof ventilated buildings the internal criteria can normally be achieved where the external noise levels do not exceed the internal noise criterion by more than 20dB.

In this case, for natural ventilation, the internal noise criterion in the new classrooms is 40 dB(A) LAeq [35 dB(A) + 5]. This suggests that the internal criterion will be achievable using single sided natural ventilation, with a predicted internal noise level of 38 dBA LAeq,30mins. For intermittent boost or summertime cooling ventilation with a natural or hybrid ventilation system under the control of the teacher noise may increase to no more than

0

10

20

30

40

50

60

70

80

90

Level dB

Time

Survey Measurement 3rd March 2020

LAFmax

LAeq

LAF90.0%

SFM/J002872/4281/02 13 14 May 2020 ___________________________________________________________________________



55 dB(A) during the boost ventilation. As the typical maximum outdoor level is 54 dB(A) this criterion will be achieved even with wide open windows and doors.

5.4 Mechanical Services Noise with full mechanical ventilation system

Noise levels from mechanical services in classrooms in a fully mechanically ventilated system should not exceed the unoccupied ambient noise criteria of BB93 [35 dB(A) LAeq for new-build or 40 dB(A) LAeq for refurbished classrooms]. For intermittent boost or summertime cooling ventilation with a fully mechanical system under the control of the teacher mechanical services noise may increase by 5 dB [40 dB(A) LAeq in new-build or 45 dB(A) LAeq in refurbished classrooms] for the duration of the boost operation.

5.5 External Mechanical Services Noise Egress

It is proposed to install a new kitchen supply and extract fan, new plant room incorporating a boiler and water heater and also new mechanical ventilation for new toilets. Noise egress from the new kitchen supply and extract fans has been calculated to the nearest noise sensitive house using the un-attenuated manufacturer’s noise data for the typical operating duty of the kitchen fans. The calculated noise egress based on hemispherical propagation over a reflecting plane is detailed in Table below. A 5dB shielding attenuation has been applied as the flat kitchen roof area is shielded from direct propagation to the houses by the pitched roofs of the surrounding school buildings which are higher than the kitchen roof.

Table 3 – Kitchen supply and extract noise egress to nearest noise sensitive properties

As indicated above the total sound pressure due to the kitchen extracts at the nearest residence is predicted to be 42 dB(A). As indicated in Figure 3, the minimum typical background sound level is 46 dB(A), hence, the sound pressure due to the kitchen extract is 4dB below the existing background sound level and is unlikely to cause disturbance at nearby noise sensitive properties. With respect to the proposed toilet extract vents and the proposed boiler and water heater, the noise levels due to these items are well below those indicated for the kitchen supply and extract fans and as such these items are unlikely to be significantly audible at the nearby houses.

Kitchen extract terminal sound power 84.3 LWA

Kitchen supply terminal sound power 83.1 LWA

Kitchen extract casing break-out sound power 74.5 LWA

Kitchen supply casing break-out sound power 62.5 LWA

Distance to nearest house 40 m

Extract terminal attenuation 0 dB

Supply terminal attenuation 0 dB

Shielding attenuation (roof of school building) 5 dB

Total sound pressure level at nearest house 42.0 LAeq dB

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6.0 INTERNAL SOUND INSULATION

Specifying the correct value of internal sound insulation ensures that noise disturbance from one space to another within the building is minimised for noise sensitive spaces, whilst reducing costs for less noise sensitive areas by specifying lower performance partitions. The required sound insulation is dependent on both the amount of noise likely to be generated in the source room, and the noise sensitivity of the activity in the receiving room.

BB93 specifies the airborne internal sound insulation in terms of DnT,w which is a weighted standardised noise level difference between rooms, where T is the upper limit for the mid-frequency reverberation time, Tmf,max for the receiving room type. The required sound insulation between adjacent rooms ranges from 35 to 55 dB DnT,w depending on the use of the rooms. BB93 also separately specifies a standard for partitions between teaching and circulation spaces of 40 dB Rw for normal classrooms and 45 dB Rw for music classrooms, drama rooms and multi-purpose halls, with a standard for internal doorsets of 30 dB Rw for normal classrooms and 35 dB Rw for music classrooms, drama rooms and multi-purpose halls. BB93 also indicates that where there is an essential need for a connecting doorset between two teaching spaces then this should be specified to achieve 35 dB Rw, with the surrounding wall selected to achieve not less than 45 dB Rw.

Please note that sound insulation in terms of dB DnT,w is an on-site tested parameter that depends upon the separating wall performance, flanking sound transmission and room characteristics. The dB Rw parameter represents a laboratory tested value of sound insulation, for the separating element alone. Therefore on site a partition or floor rated at a certain Rw is unlikely to achieve the same value when tested and assessed in terms of dB DnT,w; in most cases the on site tested value will be less than the laboratory Rw value.

6.1 Sound Insulation between spaces

The required airborne sound insulation for noise sensitive room pairings in the school are outlined in the table below:

Table 3 – BB93 specified sound insulation between adjacent rooms

Source Room Adjacent, Noise-

Sensitive Receiver Room

Sound insulation of Party Walls [dB]

DnT(Tmf,max),w (minimum values)

Early Years WC Early Years Classroom 40

Staff Kitchen Early Years WC 2 35

Staff Kitchen Accessible WC 2 35

Nursery WC Early Years Office 2 40

Nursery Nursery Group 40

MI / SEN Therapy Reception 2 45

KS1 Classroom SEN Group 40

KS1 Classroom KS1 Classroom 40

KS1 Classroom Specialist Practical 40

Accessible WC Sick Bay 2 451

Interview General Office 2 401

Head Office General Office 2 401

KS2 Classroom Specialist Practical 451

KS2 Classroom KS2 Classroom 451

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Notes 1 Values specified here are the minimum sound insulation of party walls DnT(Tmf,max),w for

rooms that are part of the new build development scheme.

2 Section 0.3.6 of BB93 suggests Administration and Ancillary areas are exempt from the



Store-rooms, etc. do not have a designation within BB93, and therefore have no requirements. It is assumed that these spaces are not occupied and are generally low noise generating. A standard partition is considered suitable for these spaces.

6.2 Corridor walls and doors

The sound insulation of corridor walls and doors is specified in BB93 in terms of laboratory Rw values. It has been assumed that there are no ventilators in the wall between the classrooms and the corridor (within the corridor wall).

Table 4 – BB93 specified sound insulation between circulation spaces and other spaces used

by students

Type of space used by students

Minimum Rw dB

Wall including any glazing Doorset

New build Refurbishment

Multi-purpose hall, Drama room or Teaching spaces intended specifically for use by students with special hearing or communication needs

45 40 35

All other rooms used for teaching or learning

40 35 30

KS2 WC KS2 Classroom 451

Accessible WC KS2 Classroom 451

KS2 Classroom KS2 Group 451

KS1 WC KS1 WC 2 30

KS1 WC Accessible WC 2 30

Accessible WC Staff Workroom 2 40

Staff WC Staffroom / Exam ST 2 40

Staff WC Staff WC 2 30

Staff Meeting Staffroom / Exam ST 2 30

Staff WC Staff Meeting 2 40

Shared WC's Hall 40

Hall Studio 45

Accessible WC Studio 40

SFM/J002872/4281/02 16 14 May 2020 ___________________________________________________________________________



7.0 REVERBERATION TIMES

The objective is to provide suitable reverberation times for clear communication of speech between teacher and student, clear communication between students, and music teaching and performance.

High reverberation times in internal spaces cause the following problems.

• Increased noise levels due to internal sources. This is particularly an issue in education where teachers must continuously use increased vocal effort to be heard above background noise in teaching areas.

• Reduced speech intelligibility and clarity. Again, reduced speech intelligibility is a particular problem in rooms used for teaching.

Rooms will be assessed in the detailed report in terms of the mid-frequency reverberation time, which is the arithmetic average of the reverberation times in the 500Hz, 1kHz and 2kHz octave bands. BB93 suggests the target values are for rooms that are finished, furnished for normal use, but unoccupied.

The classrooms will be be assessed in accordance with Sabine’s method for determining reverberation time as detailed within Appendix 6 of BB93. Please note that there are limitations with this method of calculation in rooms of significant height, volume or complex geometry, therefore some fine tuning of absorptive treatment (such as absorbent wall linings) may be necessary upon project completion. Where larger spaces (such as Assembly Halls) require assessment for reverberation we will use more detailed ray tracing software models as Sabine method calculations are not sufficiently accurate for these spaces.

7.1 Design Specification

BB93 gives the following maximum values of reverberation time for internal spaces relevant to this development.

Table 5 - BB93 specified maximum values of reverberation time for internal spaces

Room Name BB93 Reverberation Time requirement

Tmf, seconds

Studio ≤1.0

Reception ≤2.0

Hall 0.8 – 1.5

Interview / Meeting rooms ≤0.8

Servery ≤1.5

KS2 classroom ≤0.61

KS1 and nursery classrooms ≤0.8

Open plan: Early Years Classroom ≤0.5

KS2 WC ≤1.51, 2

Notes 1. These spaces are included in the new build development for the school, which has a

separate criteria set out in BB93 than spaces involved in a refurbishment.




SFM/J002872/4281/02 17 14 May 2020 ___________________________________________________________________________



7.2 Kitchen / Servery

We note that the drawings indicate that the partition between the Servery and Hall is to be opened up with a roller shutter added to store tables. With regard to Kitchens adjacent to Halls BB93 states:

Serving hatches between kitchens and multi-purpose halls used for dining should be avoided where practicable, and serveries placed between kitchens and dining areas wherever possible to avoid noise transfer during meal preparation. Where this is not possible, serving hatches should be designed to have as high a level of sound insulation as practicable (not less than 18 dB R w ) and, if necessary, use of the dining hall space timetabled so that noise sensitive activities, eg exams, do not take place in the hall when the kitchen is in use. Where the space is used solely for dining purposes, a sound insulated serving hatch between kitchen and dining space is not necessary.

Whilst we note that the servery is to be retained and will form a buffer between the kitchen and hall, the introduction of a roller shutter will likely reduce the sound insulation between the servery and the hall. We would recommend that the use of a reasonably high sound insulation shutter between the servery and hall is considered to ensure that noise from the Kitchen does not disturb activity within the hall during meal preparation times in the mornings.

SFM/J002872/4281/02 18 14 May 2020 ___________________________________________________________________________



8.0 CONCLUSION

A design specification report has been made which discusses the required ventilation and glazing strategy needed to achieve specified internal ambient noise levels by BB93. Data from a noise survey was used to make a comment on the suitability of using a natural / hybrid ventilation strategy for the development of the school. A preliminary outline of the required internal sound insulation between rooms and reverberation times for new and remodelled spaces is also made in accordance with the recommendations of Building Bulletin 93 - Acoustic Design of Schools.

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Appendix A – Definition of Acoustic Terms The decibel This is the basic unit of noise, denoted dB. A-Weighting This is a weighting process which simulates the human ear’s different sensitivity at different frequencies. A weighting can be shown two typical ways, 50 dB(A) Leq or 50 dB LAeq. Both mean the same thing. (See below for a definition of Leq). The dB(A) level can be regarded as the overall level perceived by human beings. Leq and Leq(s) This is the equivalent continuous noise level which contains the same acoustic energy as the actual time-varying sound. In other words it is a kind of average noise level. It is denoted dB Leq or, for A-weighted figures dB(A) Leq or dB LAeq. It can also be expressed in terms of frequency analysis (see later). Leq(s) is the sample Leq level. Ln This is the level exceeded for n% of the time. It is denoted dB Ln or, for A-weighted figures dB(A) Ln or dB LAn. It can be expressed in terms of frequency analysis (see later). L90 is the level exceeded for 90% of the time and is a measure of the lowest level typically reached. L10

is the level exceeded for 10% of the time and is the highest level typically reached. L50 is the level exceeded for 50% of the time and, mathematically, it is the median. Lmax This is the maximum level reached during a measurement period. The “time constant”, or the ability of the equipment to respond to impulses is usually expressed along with it, e.g. “Fast”, “Slow”, etc. It is denoted dB Lmax or, for A-weighted figures dB(A) Lmax, dB LAmax, etc. It can also be expressed in terms of frequency analysis. Frequency Analysis Whereas dB(A) gives a very useful overall figure, it has its limitations in that it cannot be used to model or predict the effect of noise control and mitigation as this nearly always has radically different performance at different frequencies. Frequency analysis expresses an overall noise level at each frequency or band of frequencies in the audible range. Octave band analysis divides the audible range into 10 bands from 31.5 Hz to 16 kHz and the noise level in each band can be expressed in any form e.g. Leq, L90, Lmax etc. One third octave band analysis uses 30 bands. Narrow band analysis takes the process to resolutions of less than 1 Hz. This is useful for identifying the existence of tones (whines, hums, etc.) and in pin-pointing the sources.

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