1、 SURFACE VEHICLE RECOMMENDED PRACTICE J2883 APR2015 Issued 2015-04 Laboratory Measurement of Random Incidence Sound Absorption Tests Using a Small Reverberation Room RATIONALE This recommended practice discusses a test methodology to measure the random incidence sound absorption coefficient of absor
2、ption materials and parts and components for automotive and other transportation applications in a small reverberation room. Currently there are no standards for this type of test. 1. SCOPE This SAE Recommended Practice describes a laboratory test procedure for measuring the random incidence sound a
3、bsorption performance of a material or a part in a small size reverberation room by measuring decay rates. The absorption performance may include sound absorption coefficient of the test sample and or the amount of energy absorbed by the test sample. Materials for absorption treatments may include h
4、omogeneous materials, nonhomogeneous materials, or a combination of homogeneous, nonhomogeneous, and/or inelastic impervious materials. These materials are commonly installed in the mobility products and in the transportation systems such as ground vehicles, marine products, aircraft, and commercial
5、 industry (in industrial and consumer products) to reduce reverberant sound build-up and thus reduce the noise level in the environment by minimizing reflections off of hard surfaces. The test method described herein was developed also to describe a way to measure the absorption performance of a par
6、t or a sound package system that will relate to an application. It can be used to rank order materials for application on panels using general automotive steel but also may be applicable to other situations or conditions. This test procedure has been developed for measurements made in rooms between
7、6m 3to 25m 3in volume. The absorption performance for most materials and systems varies as a function of frequency. Accordingly, this test procedure includes provisions for measuring absorption over a frequency range found applicable to many transportation systems. Samples that are used typically in
8、 the transportation industry are not thick enough to provide any significant absorptive properties below 250 Hz and in many cases below 400 Hz 1/3 rdoctave band frequency. Combining the size of the sample and the frequency range of interest for automotive and related applications, this test method h
9、as been developed for conducting measurements using a small reverberation room where the frequency range of interest would be from as low as 250 Hz to 8000 Hz 1/3 rdoctave band frequency, depending on the volume of the room. The recommended volume of the room for this test method is from 6m 3to 25m
10、3 . The test method described here differs from the ASTM C423 and the ISO 354 methods in that the SAE method is based on using a significantly smaller size reverberation room than the recommended size room in the ASTM C423 or ISO 354 methods. This aids not only to testing a small size sample, but al
11、so allows testing a typical component, part, or a subsystem (that approximates closely to a small size sample as mentioned above) of a vehicle and other transportation systems, or products for other applications more conveniently and easily than the ASTM C423 or the ISO 354 test method. This test is
12、 appropriate to rank order a specific size material and/or part sound absorption properties and not intended to duplicate the results of other size samples. The results obtained by the SAE method may be different from that of the ASTM C423 or the ISO 354 as the room volume and the sample size may si
13、gnificantly impact the measured absorption. This recommended practice is not intended to replace the ASTM C423 or the ISO 354 test standard. _ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of thi
14、s report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabili
15、zed, or cancelled. SAE invites your written comments and suggestions. Copyright 2015 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or oth
16、erwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-4970 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical
17、 Report, please visit http:/www.sae.org/technical/standards/J2883_201504 SAE INTERNATIONAL J2883 Issued APR2015 Page 2 of 21 2. REFERENCES 2.1 Applicable Publications The following publications form a part of this specification to the extent specified herein. The latest issue of publications shall a
18、pply. 2.1.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or +1 724-776-4970 (outside USA), www.sae.org. SAE TSB 003 Rules for SAE Use of SI (Metric) Units SAE J1355 Test Method for Measuring Thickness
19、of Resilient Insulating Pads SAE J2629 Standard Formats for Presenting Acoustical Data 2.1.2 ANSI Publications Available from American National Standards Institute, 25 West 43rd Street, New York, NY 10036-8002, Tel: 212-642-4900, www.ansi.org. ANSI S1.1 Acoustical Terminology ANSI S1.11 Specificatio
20、n for Octave Band and Fractional Octave Band Filter Sets ANSI S1.26 Method for Calculation of the Absorption of Sound by the Atmosphere 2.1.3 ASTM Publications Available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, Tel: 610- 832-9585, www.astm.org
21、ASTM E691 Conducting an Interlaboratory Study to Determine the Precision of a Test Method ASTM C423 Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method ASTM E795 Practices for Mounting Test Specimens During Sound Absorption Tests 2.1.4 ISO Publications Available from
22、American National Standards Institute, 25 West 43rd Street, New York, NY 10036-8002, Tel: 212-642-4900, www.ansi.org. ISO 354 Acoustics - Measurement of Sound Absorption in a Reverberation Room ISO 3382-2 Acoustics - Measurement of room acoustic parameters - Part 2: Reverberation time in ordinary ro
23、oms ISO 18233 Acoustics - Application of new measurement methods in building and room acoustics ISO 3741 American National Standard ANSI S12.51 Acoustics - Determination of Sound Power Levels and Sound Energy Levels of Noise Sources Using Sound Pressure Precision Method for Reverberation Rooms”, App
24、endix A Guidelines for the Design of Reverberation Test Rooms. SAE INTERNATIONAL J2883 Issued APR2015 Page 3 of 21 3. TEST METHOD The test method for this measurement is based on determining the sound absorption of an empty reverberation room (with any accessories required to seal the perimeter side
25、s of a test sample as discussed later) and the sound absorption of the same room but with a test sample in the room. The difference of these two sound absorption values provides the sound absorption provided by the sample alone. This is known as the amount of energy absorbed by the sample. This quan
26、tity divided by the area of the test sample provides the sound absorption coefficient of the test sample. The absorption of the bare reverberation room is computed using the equation: A1 = 0.921*(V*D1/c) (Eq. 1) or, A1 = 55.3 *V/(c*T1) (Eq. 2) The absorption of the reverberation room with the test s
27、ample in place is computed using the equation: A2 = 0.921*(V*D2/c) (Eq. 3) or, A2 = 55.3 *V/(c*T2) (Eq. 4) Where, A1 = Sound absorption of the bare reverberation room, m 2A2 = Sound absorption of the reverberation room with the test sample in place, m 2V = Volume of the reverberation room, m 3T1 = R
28、everberation time of the bare reverberation room, s T2 = Reverberation time of the reverberation room with the test sample in place, s D1 = Decay rate of the bare reverberation room, dB/s D2 = Decay rate of the reverberation room with the test sample in place, dB/s D1=60/T1 D2=60/T2 c = speed of sou
29、nd, m/sec, is a function of temperature, humidity, and barometric pressure, and can be expressed as 1 = 4.5513 , m/s (Eq. 5) Where, c d = the speed of sound in dry air w = specific heat ratio for moist air M w = Total average molecular weight See Appendix A at the end for step by step calculation of
30、 the speed of sound as a function of temperature, humidity, and barometric pressure. 1Ref: Bohn, D., A., “Environmental Effects on the Speed of Sound” J. Audio Eng. Soc., Vol. 36, No. 4, 1988 April. SAE INTERNATIONAL J2883 Issued APR2015 Page 4 of 21 Therefore, the amount of sound energy (A) absorbe
31、d by the sample alone is given by: A = A2 A1 =0.921*(V*D2/c) - 0.921*(V*D1/c) (Eq. 6) The sound absorption coefficient () of the sample is given by: = A/S (Eq. 7) Where, S is the surface area of the sample in m 2 . 3.1 Measurements shall be conducted in a humidity controlled room as the absorption m
32、easurements are very susceptible to humidity. Test samples shall be conditioned in the humidity controlled room for at least 12 hours prior to testing. 3.2 The sound absorption coefficient of a test sample may be affected significantly due to sound absorption by air (air absorption). Excessive absor
33、ption could take place at high frequencies and at low relative humidities due to the changes in temperature and relative humidity (changes in environmental factors) during the course of the measurement. 3.3 At and above 1000 Hz 1/3 rdoctave band frequency, the effects of temperature and relative hum
34、idity are adjusted by subtracting the decay rate of the air absorption from the decay rate of the measurements. The decay rate of the air absorption is calculated following equations provided in the ANSI S1.26 see Appendix B at the end. The correction due to air absorption is given by dair = (air*c)
35、 (Eq. 8) where, dair = decay rate due to sound absorption by air, dB/s air = Attenuation coefficient due to air absorption and obtained from ANSI S1.26 Therefore, at and above 1000 Hz, the decay rate to use in Equations 1 and 3 is: D 1 d air and D 2 d air, respectively 2 . Here, D 1 d air = Adjusted
36、 decay rate of the bare reverberation room, dB/s D 2 d air = Adjusted decay rate of the reverberation room with the test sample in place, dB/s 3.4 During all measurements the average test temperature shall be no less than 15 C, and the average relative humidity in the room shall be at least 50%. How
37、ever, it is strongly recommended to have 60% relative humidity for consistent measurements above 6.3 kHz. Although the effect of change in temperature and relative humidity on air absorption is addressed by the equations discussed in Section 3.3, it is best practice if: The temperature between tests
38、 of a bare room and the room with a test sample does not vary more than 5 C The relative humidity between tests of a bare room and the room with a test sample does not vary more than 5%. 2Although the adjustment in environmental factors is necessary at and above 1000 Hz 1/3 rdoctave band, it is enco
39、uraged to using these adjustments for all frequencies. SAE INTERNATIONAL J2883 Issued APR2015 Page 5 of 21 If the temperature and the relative humidity exceed these variations, a new bare room decay rate measurement is recommended such that the environmental conditions of the measurements made with
40、the bare room and the test sample are within these deviations. It is encouraged that devices that are used to measure the temperature, relative humidity, and barometric pressure have the following accuracy: 1 C for temperature 2% for relative humidity 30 kPa for barometric pressure. 4. REVERBERATION
41、 ROOM SHAPE, SIZE, AND DIFFUSION 4.1 The test method is based on the fact these measurements are made in a reverberation room. A reverberation room is defined as a room where the sound field is diffuse and uniform throughout the room. Diffuse means sound waves approach from any direction at any time
42、 with equal probability, and therefore the sound field is the same everywhere. For sound absorption measurements, the diffusion has one more challenge. This has to do with the fact the decay signal is transient and not steady state, where normally the diffusion is best understood. Therefore the reve
43、rberant sound field needs to closely approximate the diffuse sound field not only for steady state sound with the source on, but also for the decay of sound when the source is turned off. 4.2 Both the design and construction of a reverberation room are very critical to the success of obtaining reaso
44、nably good sound absorption data of a material. There are four parameters to the proper design of a reverberation room: Cut-off frequency Schroeder frequency Room dimensions Axial/normal modes The details of the design of a reverberation room are provided in Appendix C. 4.3 A reverberation room may
45、be constructed of a massive masonry, concrete materials, massive steel panels, as well as light weight building construction materials. Walls should be painted to seal any pores and to increase diffusion in the room. In addition, external sound reflecting panels or objects (commonly called diffusers
46、) are required to achieve adequate diffusion in the room for stationary and transient sound signals in the room. Attention needs to be paid so the absorption coefficient of the room surfaces is low enough to provide proper diffusion. These are discussed further in Appendix C. 4.4 The reverberation r
47、oom volume has the potential to establish the cut-off frequency for acceptable diffusivity of the reverberation room and therefore to have some confidence on the data. Table 1 provides the cut-off frequencies for different size small reverberation rooms. Room sizes should be established based on the
48、 assurance that there are at least twenty (20) natural frequency modes within the lowest 1/3 rdoctave band frequency of interest for good diffusion of sound. SAE INTERNATIONAL J2883 Issued APR2015 Page 6 of 21 TABLE 1 - TABLE FOR DETERMINING THE LOWEST (CUT-OFF) FREQUENCY OF MEASUREMENT FOR A GIVEN
49、ROOM VOLUME Room volume, m 31/3 rdOctave Band Cut-off Frequency, Hz 6 400 10 315 15 250 25 250 Calculations used air temperature of 20 C to compute the speed of sound. Ref: Saha, P., Pan, J., and Veen, J. R., “Thoughts behind Developing SAE Standard J2883 Random Incidence Sound Absorption Tests Using a Small Reverberation Room,” SAE Technical Paper 2009-01-2141, 2
