Noise Barrier Test Reports Section1

Technical ReportReport Number C/08/5L/20588/R01

Date 22 December 2008

Project The Laboratory Determination of Random Incidence Sound Absorption Coefficient of a Barrier

Prepared for

Tilon Composites LtdUnit 23 Rassau Industrial EstateEbbw ValeBlaenauGwentNP23 5SD

By

Allen Smalls

Sound Research Laboratories LimitedConsultants in Noise & VibrationHead Office & Laboratory: Holbrook House, Little WaldingfieldSudbury, Suffolk CO10 0THTelephone (01787) 247595 Fax (01787) 248420e-mail:[email protected]

This report shall not be reproduced, except in full, without written approval of the laboratory

1.0 Summary

Tests have been done in SRL's Laboratory at Holbrook House, Sudbury,Suffolk, to determine the sound absorption coefficient of a barrier inaccordance with BS EN ISO 354:2003, BS EN 1793-1:1998 and BS EN1793-3:1998. Calculations done in accordance with BS EN 1793-1:1998 arenot UKAS accredited.

From these measurements the required results have been derived and arepresented in both tabular and graphic form in Data Sheet 1.

The results are given in 1/3rd octave bands over the frequency range 50Hz to 10KHz, which is beyond that required by the test standard. Measurementsoutside the standard frequency range are not UKAS accredited.

......................................... ........................................Allen Smalls Trevor HickmanLaboratory Manager Executive ConsultantQuality Manager Deputy Technical Manager

For and on behalf ofSound Research Laboratories Ltd

________________________________________________________________________________________________________________P:\C20000s - Tech Services\C20550\20588\R01© Sound Research Laboratories Ltd C/08/5L/20588/R01 22 December 2008 Page 2 of 14 Tel: 01787 247595

Contents

1.0 Summary

2.0 Details of Measurements

3.0 Description of Test

4.0 Results

Data Sheets 1

Photograph 1

Drawing 1

Appendix 1: Test Procedure

Appendix 2: Measurement Uncertainty


2.0 Details of Measurements

2.1 Location

Sound Research Laboratories LtdHolbrook HouseLittle WaldingfieldSudburySuffolkCO10 OTH

2.2 Test Date

19 December 2008

2.3 Instrumentation and Apparatus Used

Make Description Type

E D I Microphone MultiplexerMicrophone Power Supply Unit

Norwegian Real Time Analyser 830Electronics

Brüel & Kjaer 12mm Condenser Microphones 4166 Windshields UA0237

Pre Amplifiers 2639, 2669CMicrophone Calibrator 4231Omnipower Sound Source 4296

Larson Davis 12mm Condenser Microphone 2560

Thermo Hygro Temperature & Humidity Probe

TOA Graphic Equalizer E-1231Power Amplifier DPA-800


2.4 References

BS EN ISO 11654:1997 Sound absorbers for use in buildings.Rating of sound absorption.

ATSM C423-01 Sound Absorption and sound Absorption Coefficients by the Reverberation RoomMethod

BS EN ISO 354:2003 Measurement of sound absorption in areverberation room

BS EN 1793-1:1998 Road traffic noise reducing devices - BS EN 1793-3:1998 Test method for determining the acoustic

performance.Part 1 - Intrinsic characteristics of soundabsorption.Part 3 - Normalised traffic noise spectrum.

2.5 Personnel Present

S O’Leary TilonJ Elliott Tilon


3.0 Description of Test

3.1 Description of Sample

Tilon Composites sound absorbent barrier, see drawing 1 for construction.

Sampling plan: Enough for test only

Sample condition: New

Details supplied by Tilon

Sample installed by Tilon

3.2 Sample Delivery date

19 December 2008

3.3 Test Procedures

The sample was mounted/located and tested in accordance with the relevantstandards. The method and procedure is described in Appendix 1. Themeasurement uncertainty is given in Appendix 2.

Standards BS EN 1793 parts 1 and 3 have additional requirements formeasurement and these have been fully included in the test procedure.


4.0 Results

The results of the measurements are given in Data Sheet 1. The singlenumber rating and category calculated to BS EN 1793-1:1998 are listed below.

Results relate only to the items tested.

A413Barrier2

CategoryDLa,dB

Single number ratingBS EN 1793-1:1998Description in BriefSRL

Test No.

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ End of Text⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯


Data Sheet 1Data Sheet 1

The Laboratory Measurement of Random Incidence Sound Absorption to BS EN ISO 354:2003

Client: Tilon Composites Ltd

Test Date: 19/12/2008

Empty Room: Temperature: 17.2 °C Humidity: 46 %RH Pressure: 1020 mbar

Room with Sample: Temperature: 15.1 °C Humidity: 43 %RH Pressure: 1020 mbar

Sample Tilon Composites Sound Absorbent Barrier

Description:Mounting Method: A

Sample Area: 10.55 m2

Chamber Volume: 300 m3

Test 2Absorp Practical

Freq T1 T2 Coeff AbsorpHz sec sec Coeff #50* 3.87 3.74 0.0563* 4.08 2.57 0.67 n/a80* 5.27 3.20 0.57100 6.90 5.44 0.18125 7.36 4.78 0.34 0.30160 6.90 4.15 0.45200 7.16 3.61 0.64250 7.03 3.27 0.76 0.75315 6.51 2.89 0.90400 6.07 2.55 1.06500 5.10 2.24 1.17 1.00630 4.94 2.21 1.16800 5.31 2.30 1.151000 5.76 2.43 1.10 1.001250 5.62 2.46 1.051600 5.12 2.42 0.992000 4.61 2.27 1.00 1.002500 3.94 2.09 0.983150 3.23 1.87 0.944000 2.55 1.59 0.93 0.955000 1.95 1.30 0.936300* 1.43 1.03 0.888000* 1.09 0.82 0.89 n/a10000* 0.77 0.61 0.95

1.00

Class ACalculated to EN ISO 11654:1997

NRC 1.00Calculated to ASTM C 423-01

DLa 13dBCategory A4

Calculated to BS EN 1793-1:1998(Not UKAS accredited))

* Denotes frequencies outside the range covered

by BS EN ISO 354:2003 T1, empty room reverberation time

T2, room reverberation time with sample# Practical absorption coefficient, BS EN ISO 11654:1997 v3

100125

160200

250315

400500

630800

10001250

16002000

25003150

40005000

Frequency, Hz

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

Abs

orpt

ion

Coe

ffici

ent

Sound Absorption Coefficient


Photograph 1 - Barrier Being Tested


Drawing 1


Appendix 1

Test Procedure

Measurements of Random Incidence Sound AbsorptionCoefficients to BS EN ISO 354:2003 - TP14 (Plane Absorbers)

In the laboratory, random incidence sound absorption coefficients are determined fromthe rate of decay of a sound field in a reverberation room, with and without a testsample installed. The rate of decay is described by the time a sound field takes todecay by 60dB, known as the reverberation time.

The reverberation room is constructed from 215mm brick, which is internally plasteredwith a reinforced concrete roof and floor. The room is rectangular and has a volumeof 300 cubic metres and a total surface area of 275m2. From the ceiling hang 10randomly positioned diffusers, each measuring 1.2m x 2.14m. The room is isolatedfrom the surrounding structure by the use of resilient mountings and seals, ensuringgood acoustic isolation.

Using at least two omnidirectional loudspeaker positions, broad band random noise isproduced in the room using an electronic generator and power amplifier. When theamplification system is switched off, the decay of sound is filtered into one-third octaveband widths and the reverberation times measured. This process is repeated for eachof six microphone positions and the values arithmetically averaged to obtain a finalvalue for each frequency.

The sample area should normally be between 10m2 and 15.7m2, this may be larger if itis suspected that the absorption properties will be low. The sample is laid on the floorof the reverberation room so that no part of it is closer than one metre from any edge ofthe boundaries. The procedure of measuring the reverberation times then repeated.

The sound absorption coefficients are calculated from the difference in decay rates foreach frequency according to the formula:

=asATS

where

is the random incidence absorption coefficientas is the increase in equivalent sound absorption area of the testAt

specimen (m2)is the area covered by the test specimen (m2)S


The equivalent absorption area of the test specimen is further defined as:

AT = 55.3V 1c2T2

− 1c1T1

− 4V (m2 − m1 )

where

is the volume of the empty reverberation room (m3)Vis the speed of sound in the empty room (m/sec)c1is the reverberation time in the empty room (sec)T1is the power attenuation coefficient calculated according to ISO 9613-1m1using the climatic conditions that have been present in the emptyrooms during the measurement.

and have the same meanings as and but with the testc2,T2 m2 c1,T1 m1specimen in the room.

It is occasionally found that the absorption coefficient derived in this mannerreaches a value greater than unity. This is impossible, by definition, andinvestigation has shown that this anomaly is due to diffraction of the impingingsound waves at the edges of the sample. In practical terms this isinsignificant.

The measured absorption coefficients are used to calculate a single numberrating (DLa) and category, following the method set out in BS EN 1793-1:1998.


Appendix 2

Measurement UncertaintyBS EN ISO 354:2003 - TP14

1. Introduction

The estimated values of uncertainty are based on a standard uncertaintymultiplied by a coverage factor of K = 2, which provides a level of confidence ofapproximately 95%.

Table 1: Uncertainty For Equivalent Absorption Area Measurement

9.08.15.66.74.38.14.65.05.33.23.53.12.82.72.21.81.61.6

10012516020025031540050063080010001250160020002500315040005000

Expanded uncertaintyK = 2, 95%

% of A1 or A2

Frequency, Hz

2. Estimation of Expanded Uncertainty For Sample Equivalent Sound AbsorptionArea

The expanded uncertainty, UA,m2 is estimated by using the following formulae:-

UA =uA1100

2+ uA2

1002


` where UA is the expanded uncertainty for the sampleequivalent sound absorption area, for K = 2,95%, m2

u is the estimated expanded uncertainty for theequivalent sound absorption area, taken fromTable 1 above, K = 2, 95%, % of A1 or A2

A1 is the equivalent sound absorption area of theempty room, m2

A2 is the equivalent sound absorption area of theroom with the sample, m2

3. Estimation of expanded Uncertainty For Sound Absorption Coefficients

The expanded uncertainty for sound absorption coefficients, U , is estimatedsusing the following formulae:-

U =ssUAA

where U is the expanded uncertainty for sounds

absorption coefficients, K=2, 95%

is the sound absorption coefficients

UA is the expanded uncertainty for the sampleequivalent sound absorption area, K=2, 95%,m2

A is the sample equivalent sound absorptionarea, m2


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Noise Barrier Test Reports Section1