consultancy report ref: 9383-r01 - the woolly...

ISVR Consulting, University of Southampton, Highfield Campus, Southampton SO17 1BJ, United Kingdom

Tel: +44 (0)23 8059 2162 Fax: +44 (0)23 8059 2728 Email: [email protected] Web: www.isvr.co.uk

Consultancy Report Ref: 9383-R01

Submitted to: Mr Tim Simmons The Woolley Shepherd Secret Meadow Weekmoor Milverton Taunton TA4 1QE

Prepared by:

John Fithyan Laboratory Manager Approved for issue by:

Andy Varley (MIOA) Senior Consultant

Sound absorption tests on a range of sheep’s wool based materials

February 2015

9383-R01

mailto:[email protected]

ISVR Consulting Report 9383-R01 / February 2015 Contents

Contents

1. Introduction .................................................................................................................... 3

2. Measurement Method .................................................................................................... 5

3. Results ............................................................................................................................ 6

3.1 Ambient Conditions 6

3.2 Test results 6

Tables 1 to 6: Sound Absorption Coefficients

Figures 1 to 3: Photographs of the test samples inside the reverberation chamber

Appendix 1 Instrumentation and Calibration

Appendix 2 Acoustic Environment

ISVR Consulting Report 9383-R01 / February 2015 of 20

1. Introduction

ISVR Consulting were engaged by The Woolley Shepherd, to undertake

measurements on a range of products to establish their sound absorption coefficient

(aS) or equivalent sound absorption area (Aobjm2) depending on the product being

tested.

The sound absorption measurements were performed in the Reverberant Suite of the

Rayleigh Laboratories of the ISVR, University of Southampton. The tests were

carried out on the 10th

February 2015.

The measurements were carried out in accordance with BS EN ISO 354: 2003

‘Acoustics – Measurement of sound absorption in a reverberation room’.

When a sound source operates in an enclosed space, the level to which reverberant

sound builds up, and the subsequent decay of reverberant sound when the source is

stopped, are governed by the sound-absorbing characteristics of the boundary

surfaces, the air filling the space, and objects within the space. In general, the fraction

of the incident sound power absorbed at a surface depends upon the angle of

incidence. In order to relate the reverberation time of an auditorium, office,

workshop, etc, to the noise reduction that would be effected by an absorbing

treatment, knowledge of the sound-absorbing characteristics of the surfaces, usually in

the form of a suitable average over all angles of incidence, is required. Since the

distribution of sound waves in typical enclosures includes a wide and largely

unpredictable range of angles, a uniform distribution is taken as the basic condition

for the purposes of standardization. If, in addition, the sound intensity is independent

of the location within the space, the sound distribution is called a diffuse sound field,

and the sounds reaching a room surface are said to be at random incidence.

The sound field in a properly designed reverberation room closely approximates a

diffuse field. Hence, sound absorption measured in a reverberation room closely

approximates the sound absorption that would be measured under the basic conditions

assumed for standardization.


BS EN ISO 354: 2003 ‘Acoustics – Measurement of sound absorption in a

reverberation room’ specifies a method of measuring the sound absorption coefficient

of acoustical materials used as wall or ceiling treatments, or the equivalent sound

absorption area of objects, such as furniture, persons or space absorbers, in a

reverberation room.

The materials tested were described as follows:

Standard wall panel

Limpets

Clouds

The standard wall panels are rectangular panels designed to be mounted onto walls.

They can be used individually or combined to cover larger areas of wall.

The limpets are a bit like a scalloped rectangle and are designed to be fitted flush onto

ceilings. They would normally be installed individually but one ceiling might have

multiple limpets fitted.

The clouds are similar to the limpets but they are designed to hang from ceilings.

The materials were tested as either individual (discrete) absorbers or as plane

absorbers depending on their application.

The results obtained can be used for comparison purposes and for design calculation

with respect to room acoustics and noise control.


2. Measurement Method

The averaged reverberation rimes (RT60) in 1/3 octave bands were determined for the

empty chamber in the frequency range 100 Hz to 5000 Hz, as described in the

standard, using an interrupted broad band noise. Thirty two decays were measured,

(eight microphone combinations at each of four sound source locations).

The sample of absorbent material was introduced into the chamber and either laid out

on the floor or hung from the ceiling in accordance with the guidelines given in the

standard. The test arrangement was chosen depending on whether the sample was a

discrete absorber or a plane absorber. In the case of the plane absorbers the edges of

the sample were covered with metal plate to prevent the edges from absorbing any of

the sound waves.

Once the sample was positioned in the chamber, the averaged reverberation time

spectrum was determined as before.

The absorption in the chamber was calculated for the sample and the increase in

absorption due to the absorbent material relative to the empty chamber, was found.

For the plane absorbers the coefficient of absorption (aS) in each 1/3 octave band was

calculated. The results are shown as a value between 0 and 1 where 1 signifies total

absorption and 0 signifies no absorption. NB. In practice the test method can give

values greater than 1 which can be confusing. Where a value of greater than 1 is

given for a plane absorber it has been caused by edge effects of the test sample.

For the discrete absorbers the equivalent sound absorption area (Aobjm2) in each 1/3

octave band was calculated. The sound absorption property of discrete objects is

quantified by the equivalent sound absorption area expressed as m2 per object. This is

the area of a 100% fictive absorbing surface which would absorb the same amount of

sound as the object in question.


3. Results

3.1 Ambient Conditions

Barometric pressure 101.1 kPa

Temperature 15.0 C

Relative Humidity 44 %

3.2 Test results

The results in the tables below are given as either the coefficient of absorption (aS) or

as the equivalent sound absorption area (Aobjm2) depending on the type of sample

being tested.

In the case of the plane absorbers where the results are given as the coefficient of

absorption (aS), BS EN ISO 11654 can be used to express the spectrum of results as a

sound absorption class. The classes range from A to E where A is the top class. The

standard is not applicable to single items, such as the limpets and clouds measured

during these tests.

NB. There are other standards, namely ASTM C4423-09a that can be used to express

the sound absorption test spectrum as a single number. ASTM C423 uses the term

Noise Reduction Coefficient (NRC) although this is being replaced by Sound

Absorption Average (SAA). Both the NRC and SAA terms have values between 0 and

1 where 1 indicates total absorption. ASTM C423 test procedures should be used

when calculating the NRC or SAA value. In this report we have used BS EN ISO 354

to determine the sound absorption coefficient. The methods in the two standards

differ slightly. However for indication purposes I have used the BS EN ISO 354

values to calculate an NRC and SAA value for the materials we tested.

Table 1 shows the results with 20 individual wall panels butted together to form a

large rectangle. The outer edges of the rectangle were covered to prevent them

absorbing more sound.


Table 2 shows the results with 20 individual wall panels butted together to form a

large rectangle. The outer edges of the rectangle were left uncovered and therefore

absorbed more sound.

Table 3 shows the results when the 20 wall panels were tested as discrete absorbers.

The results are given as the equivalent sound absorption area (Aobjm2).

Table 4 shows the results with 25 individual limpets butted together to form a large

sample. The outer edges of the sample were left uncovered and therefore absorbed

more sound.

Table 5 shows the results when the 25 limpets were tested as discrete absorbers. The

results are given as the equivalent sound absorption area (Aobjm2).

Table 6 shows the results when the 8 clouds were tested as discrete absorbers. The

results are given as the equivalent sound absorption area (Aobjm2).

Figures 1 to 3 show photographs of the samples under test.


Table 1: Standard wall panels butted together with outer edges covered

Customer:

Frequency AbsorptionHz as

100 0.28

125 0.30

160 0.42

200 0.52

250 0.75

315 0.90

400 1.00

500 1.01

630 1.01

800 1.03

1000 0.98

1250 1.01

1600 0.99

2000 0.99

2500 0.97

3150 0.97

4000 0.97

5000 0.94

BS EN ISO 11654

Sound absorption

class = A

Test Standard: BS EN ISO 354

Project No: 9383

NRC 0.95

SAA 0.93

All sample panels butted together. Edges covered

Using the ISO 354 test data above to calculate the ASTM C 423-09a

descriptors, which is not strictly correct, you would get these values:

Airborne sound absorption measured in a reverberation chamber.

BS EN ISO 354:2003

Woolly Shepherd

Construction tested

Standard Wall Panel

Highfield, Southampton Test date: 27/01/2015

University of Southampton Tested by: J.Fithyan

0.0

0.2

0.4

0.6

0.8

1.0

1.2

100 1000 10000

Sound A

bsorp

tion C

oeffic

ient a

s

Frequency, Hz

Sound absorption coefficient


Table 2: Standard wall panels butted together with outer edges left uncovered

Customer:


100 0.29

125 0.30

160 0.44

200 0.53

250 0.71

315 0.91

400 1.01

500 1.06

630 1.07

800 1.04

1000 1.04

1250 1.07

1600 1.08

2000 1.08

2500 1.07

3150 1.06

4000 1.08

5000 1.07

BS EN ISO 11654

Sound absorption

class = A


Project No: 9383

NRC 0.95

SAA 0.97



All sample panels butted together. Edges left uncovered

Woolly Shepherd


BS EN ISO 354:2003

Construction tested

Standard Wall Panel



0.0

0.2

0.4

0.6

0.8

1.0

1.2

100 1000 10000

Sound A

bsorp

tion C

oeffic

ient a

s

Frequency, Hz



Table 3: Twenty individual standard wall panels tested as discrete absorbers

Customer:

Frequency AbsorptionHz Aobjm

2

100 0.19

125 0.25

160 0.38

200 0.47

250 0.62

315 0.77

400 0.83

500 0.89

630 0.92

800 0.91

1000 0.91

1250 0.94

1600 0.93

2000 0.94

2500 0.95

3150 0.96

4000 0.97

5000 0.95


Project No: 9383



All sample panels moved apart. Edges left uncovered


BS EN ISO 354:2003

Woolly Shepherd

Construction tested

Standard Wall Panel

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

100 1000 10000

Equiv

ale

nt

sound a

bsorp

tion p

er

wall

panel A

ob

jm2

Frequency, Hz



Table 4: Limpets butted together with outer edges left uncovered

Customer:


100 0.37

125 0.41

160 0.56

200 0.60

250 0.81

315 0.95

400 0.99

500 1.08

630 1.09

800 1.10

1000 1.07

1250 1.08

1600 1.09

2000 1.10

2500 1.08

3150 1.06

4000 1.06

5000 1.04

BS EN ISO 11654

Sound absorption

class = A


Project No: 9383

NRC 1.00

SAA 1.00

All samples butted together. Edges left uncovered




BS EN ISO 354:2003

Woolly Shepherd

Construction tested

Limpets



0.0

0.2

0.4

0.6

0.8

1.0

1.2

100 1000 10000

Sound A

bsorp

tion C

oeffic

ient a

s

Frequency, Hz



Table 5: Twenty-five individual limpets tested as discrete absorbers

Customer:


2

100 0.23

125 0.26

160 0.36

200 0.42

250 0.54

315 0.64

400 0.69

500 0.75

630 0.75

800 0.76

1000 0.75

1250 0.77

1600 0.77

2000 0.76

2500 0.76

3150 0.76

4000 0.76

5000 0.72


Project No: 9383



All samples moved apart. Edges left uncovered


BS EN ISO 354:2003

Woolly Shepherd

Construction tested

Limpets

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

100 1000 10000

Equiv

ale

nt

sound a

bsorp

tion p

er

limpet

Ao

bjm

2

Frequency, Hz



Table 6: Eight individual clouds tested as discrete absorbers

Customer:


2

100 0.22

125 0.28

160 0.42

200 0.44

250 0.73

315 1.01

400 1.18

500 1.34

630 1.43

800 1.50

1000 1.50

1250 1.52

1600 1.49

2000 1.46

2500 1.43

3150 1.42

4000 1.36

5000 1.29


Project No: 9383




BS EN ISO 354:2003

Woolly Shepherd

Construction tested

Clouds

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

100 1000 10000

Equiv

ale

nt

sound a

bsorp

tion p

er

clo

ud A

ob

jm2

Frequency, Hz



Figure 1: Standard wall panels


Figure 2: Limpets


Figure 3: Clouds


Appendix 1: Instrumentation and Calibration

1.1 Measuring Equipment

1.1.1 Noise Generation

Instrument Manufacturer Type Ser No Cal Due

Amplifier Cambridge Audio A1 V2.0 1201-1711 Not required

Loudspeaker - - - Not required

1.1.2 Noise Measurement

Instrument Manufacturer Type Ser No Cal Due

Microphone Brüel & Kjær 4165 1297127 August 15






Pre-amplifier Brüel & Kjær 2669 2552964 September 15






Freq Analyser Brüel & Kjær 3560C 2447709 October 15

Freq Analyser Brüel & Kjær 3560B 2609169 October 15

Mic Calibrator Brüel & Kjær 4231 2594478 September 15

1.2 System Calibration

The noise measuring system was calibrated by applying the microphone calibrator (type

4231) to the transducer and adjusting the analyzer to the reference level at the beginning

of the measurement session. The level was also checked at the end of the session to

ensure that no drift or fault had occurred.

The above equipment is calibrated against the transfer standards below.


1.3 Traceability

1.3.1 Microphones and Calibrators

Microphones and Calibrators

ISVR Consulting hold two transfer standard Microphones, type 4145, serial numbers

375091 and 375617. The most recent calibration was carried out by Campbell

Associates. This is fully documented in Certificates 17840 and 17841, dated 22nd

January 2015. A transfer standard Pistonphone, type 4220, serial number 1297434

and a transfer standard calibrator, type 4231, serial number 2162524 are also held.

These were calibrated by Campbell Associates and are documented in certificate

numbers 17844 and 17842, dated 22nd

January 2015.

1.3.2 Additional Instrumentation

A Digital Voltmeter (Fluke type 8050A) and a Frequency Counter (Marconi type

2430A) are used with these Transfer Standards to calibrate the above equipment.

Both instruments were calibrated by Southern Calibration Laboratories and carry

certificates numbered 14111199 and 14111200 respectively and both are dated 25th

November 2014.

The instrumentation complies with the requirements for a type 1 instrument, as

specified in BS EN 61672:2003, BS EN 60942:2003 and BS EN IEC 61260:1996.

The Standards are traceable to the National Physical Laboratory, Teddington,

England.


Appendix 2: Acoustic Environment

2.1 Large Reverberation Chamber

2.1.1 Construction

The chamber is constructed of reinforced concrete and is separated from the

foundations and neighbouring walls by rubber vibration isolators. It is designed with

an inclined ceiling and non-parallel walls to ensure a uniform distribution (with

frequency) of the normal acoustic modes of the room.

2.1.2 Dimensions

Mean edge lengths 9.15 m

6.25 m

6.10 m - height

Volume 348 m3

Surface Area 302 m2

2.1.3 Walls and Ceiling

All inside surfaces of the chamber are finished with a hard gloss paint to give a high

reflection coefficient. The walls are 305 mm thick, and the ceiling, which is 460 mm

thick, includes two removable sections (1.75 m x 0.86 m) which provide access for a

chain hoist capable of carrying loads up to 2000 Kg, and an entry for a 4000 Watt

siren driven horn. Connections to the equipment in the chamber may be made via any

of five cable ports in the walls. A glazed window (305 mm x 305 mm) permits visual

observation from the control area.

2.1.4 Diffusers

Ten diffusers are hug from the ceiling of the chamber. These diffusing elements are

plywood sheets painted with gloss paint so that they have a low sound absorption.

The diffusers, which are of varying sizes are orientated at random and positioned at

different heights within the chamber. The total surface area of the diffusers is

43.2 m2.


2.1.5 Floor Area

The floor is 305 mm thick and has a steel vibration isolated pad (2.1 m x 3.6 m) set

into it. This pad may be used for mounting test rigs or vibrators without structural

vibrations being transmitted to the chamber.

2.1.6 Doors

One set of double doors connects the chamber and the corridor, another set opens into

the small reverberation chamber and incorporates removable panels (1.07 m x 1.07 m)

for transmission loss measurements. The doorway (2.4 m x 2.0 m) may be used for

testing larger panels. The doors (2.56 m x 2.26 m x 130 mm thick) are a sandwich

construction of wood wool, wood and steel, and have an average transmission loss in

excess of 50 dB.

2.1.7 Ventilation and Lighting

At each corner of the floor there is an air inlet vent, and there are four outlet vents

situated high up on one wall. With all vents open the air is changed at a rate of

100 m3 per minute. When not required the vents are covered by steel plates and these

have diagonal stiffeners to reduce panel vibrations. The chamber is lit by six sodium

discharge lights mounted on the wall at 3 m above the floor.

consultancy report ref: 9383-r01 - the woolly...

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