1、Reaffirmed by ANSI July 29, 1997 Reaffirmed by ANSI October 29, 2002 Reaffirmed by ANSI October 19, 2007 Reaffirmed by ANSI September 5, 2012 ( J ( J ANSI S12.12-1992 ASA 104-1 922l J( AMERICAN NATIONAL STANDARD Engineering Method for the Determination of Sound Power Levels of Noise Sources Using So
2、und Intensity ACCREDITED STANDARDS COMMITTEE S12, NOISE ABSTRACT This standard describes a method for in situ determination of the sound power level of noise sources in indoor or outdoor environments using sound intensity measure ments. The standard contains informat ion on instrumentation, installa
3、tion and oper ation of the source, procedures for the selection of a measurement surface, methods for the sampling of sound intensity on the measurement surface, procedures for the calculation of sound power level, and techniques that can be used to qualify the mea surement environment. J AMERICAN N
4、ATIONAL STANDARDS ON ACOUSTICS The Acoustical Society of America provides the Secretariat for Accredited Standards Committees S1 on Acoustics, S2 on Mechanical Shock and Vibration, S3 on Bio acoustics, and S12 on Noise. These committees have wide representation from the technical community (manufact
5、urers, consumers, and general-interest representa tives). The standards are published by the Acoustical Society of America through the American Institute of Physics as American National Standards after approval by their respective standards committees and the American National Standa rds Institute.
6、These standards are developed and published as a public service to provide stan dards useful to the public, industry, and consumers, and to Federal, State, and local governments. This standard was approved by the American National Standards Institute as ANSI 512.12-1992 on 27 January 1992. An Americ
7、an National Standard implies a consensus of those substantially concerned with its scope and provisiOns. An American National Standard is imended as a guide to aid the manufacturer, the consumer, and the general public. The existence of an American National Standard does not in any respect preclude
8、anyone, whether he has approved the standard or not, from manufacturing, market ing, purchasing, or using products, processes, or procedures not conforming to the st andard. Ameri can National Standards are subject to periodic review and use are cautioned to obtain the latest editions. Ciwrion Noric
9、e: An American National Standard ma y be revised or withdrawn at any time. The proce dures of the Americln National Standards Institute require that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of publication. The American Nationa l Standards
10、Institute, Inc. (ANSI) is the national coordinator of voluntary standa rds development and the clearing house in the U.s. for information on national and international standards. The Acoustical Society of America (ASA) is an organization of scientists and engineers formed in 1929 to increase and dif
11、fuse the knowledge of acoustics and to promote its practical applications. Published by the Acoustical Society of America through the American Institute of Physics 1992 by Acoustical Society of America. This standard may not be reproduced in whole or in part in any form for sale, promotion, or any c
12、ommercial purpose, or any purpose not falling within the fair use provisions of the Copyright Act of 1976, without prior written permission of the publisher. For permission, address the Sta nda rds Secreta riat of the Acoustical Society of America. FOREWORD This Foreword is nol a part 01 the America
13、n National Standard Engineering Method for the Determination of Sound Power Levels of Noise Sources Using Sound Intensity. ANSI 512 .12- 1992 (ASA Catalog No. 104 1992). This American National Standard contains procedures for the determination of the sound power of noise sources from sound intensity
14、 measurements. Previous sound power determinations required special facilities such as anechoic, hem i-anechoic, or reverberation rooms and the estimation of the sound power of sources from sound pressure measurements which resulted in various errors. Using this new standard, the sound power of nois
15、e sources ca n be directly determined from sound intensity mea surements made in situ even when intrusive background noise is present in the envi ronment. The approaches in this standard are useful also for the relative ranking of machinery noise sources in terms of sound power. This standard was de
16、veloped using the American National Standards Institute (ANSI) Accredited Standards Committee Procedure under the Secretariat of the Acoustical Society of America . Accredited Standards Committee S12, Noise, under whose jurisdiction this standard was developed, has the following scope: Standards, sp
17、ecifications, and terminology in the field of acoustical noise penaining 10 methods of measurement, evaluation, and control, including biological fety. tolerance. and comfort, and phys ical acoustics as related to environmental and occupational noise. At the time this standard was submitted to Accre
18、dited Standards Committee S12, Noise, for approval, the membership was as follows: W . Melnick, Chairman R. Hillquist, Vice-Chairman A. Brenig, Secretary Acousticolil Society of Ameriu. W. Melnick. R. Hillquist (Alf) Air-Conditioning .lind Refrigerolition Institute . R. Harold, H. C. Skarbek (Alt) A
19、luminum Comp.IOY of Americoli (ALCOA) . S. I. Roth Ameriun Audemy of Otoluyngology, Heolid .lind Ned: Surgery, Inc R. F. Naunton. L A. Michael (Aff) Ameriun Industriolil Hygiene Auociolilion. C. D. 80hl Ameriun CkCupolitionolil Medinl Auociolition. T. R. Hatfield. J. Sataloff (Aft) Ameriun Otologiul
20、 Society, Inc I. Tonndorf Ameriun Society of Heolitin;: 1 iOUL P /(N - II L:., IO“ll, D12 - 1010g I +NI 10“,17.,.“ - 10 “ I -(I/N)2; _ 1 1Ou. I7. . r/(N _ I) L; I lOo.17.“,“ , D 1.3 = 10 iogw I + N! I,: _ 1 /“ - ( 1INIL: ,1“, J/(N -IIL.,I“lJ, aod D14 = 101ogw1 + N1 I.;_I /; 0 implies the presence of
21、 signifi can t parasitic noise. With low or moderate values of para sitic noise, D 2 t = o. Indicator D 22 is a measure of the signal-to-noise ra tio, if the room effect noise can be neglected. With this assumption, D 22 10 dB implies that the background noise is negligi ble, while D 22 0 implies sp
22、atial variations of the field. The spa tial variation may be due to source directivity or the presence of parasitic noise. Indicator D 26 is similar to D25, but is less sensiti ve to source directivity. Indicator D27 is similar to 6WN and can be used to con firm that parasitic noise does not influen
23、ce the sound power determination. Provided that the amount of additional absorption introduced into the measure men! environment is significant, values for D 27 less than the tolerance values for 6W N given in Table 5 of this standard imply that the effects of parasitic noise are negligible. When D
24、27 is reported, an estimate of the fractional change in absorption introduced into the test environment must be reported also. To reduce the apparent parasitic noise, one or more of the following steps may be helpful. 1. Reduce the actual background noise by shielding the background noise sources. 2
25、. Reduce reverberant sound by increasing the ab sorption in the measurement environment. (Caution: Do not place absorption ins ide the measurement surface.) 3. Increase the proportion of direct sound from the source by reducing the average measurement distance. 4. Modify the shape of the measure men
26、t surface with the objective that the su rface be everywhere nor mal to the direction of sound propagation from the subject source. 16 AMERICAN NATIONAL STANDARD 8.3 Surface Averaging Accuracy Indicators, D3 The D 3 indicators can be used to demonstrate that the measurement surface has been adequate
27、ly sampled andlor that scanning, if used, gives accurate results: D31=ILw-L1 lr,-r;1 aod D32=ILw-L1 =II, - lil, where Lw and II are the sound power and surface sound in tcnsity levels, respectively, L and L i indicate values obtained using four times as many measurement locations as for Lw and II, L
28、 and I; indicate values obtained using the same number of measurement locations as for Lw and I/ but at dilferent positions on the measurement surface. Both D3 indicators are similar to /)w,“ Values or D 31 and D 32 less than the tolerance values for 8W N given in Table 5 of this standard imply that
29、 the surface averaging is adequate. If sampling at fixed points is used, it is im portant that there be a sufficient number of measurement loca tions to avoid spatial undersampling. This can be checked by evaluating the indicator with a different number of measurement locations. If scanning is used,
30、 the D 31 indicator is preferred over D 32 for evaluating the accuracy of scanning. For either indicator, care must be taken to ensure that the scanning pattern is different for the two sound power level (or surface sound intensity level) determinations. For D 31 it is recommended that the measuring
31、 loca tions for the two determinat ions be selected in such a way that each larger area coincides with four smaller ones, and that these four have equal areas and meet at the centroid of the larger area. 8.4 Sound Power Accuracy Indicators, 04 With the assumption that the sound intensity mea suring
32、instrumentation is functioning correctly, the following indicators may be useful in evaluating the accuracy of the sound power level determined using this standard: D41 = ILw-LI, D 42 = L . lOo.IL . s (see definition of L, given in Sec. 8.2), where Lw and L are the sound power levels determined us i
33、ng two different measurement surfaces, and D42 is an estimate of the level of the normalized stan dard deviation of the sound power over an ensemble of measurement surfaces. It is recommended that the measurement surfaces be as different in size and shape as practicable. The measurement su rfaces mu
34、st be reported with these indicators. B.5 Phase Indicators, 05 Two kinds of phase difference are important in in tensity measurements: (I) the phase difference be tween the acoustic pressure and velocity, and (2) the phase difference between the quantities measured by two instrumentation channels. T
35、hese may, or may not, be identical. They must be compared with the capabil i ty of the instrumentation used. The following indica tors may be useful: D5l = (Lw - L ;“)12, D 52 = 5p; lo - 5p; . D53 = 5p; , ,nd D54 = 510gw ? -ur/l! 12 , where L w is the sound power level and L indicates the sound powe
36、r level determined as for L w but with the intensity probe oriented to measure in the oppo site direction, i.e., the component of intensity nor mal to the measurement surface but in the direction toward the source, 5p; is the pressure-intensity index: 5p; = Lp - L/ - 10 logln(Pcl(p), where Lp = the
37、sound pressure level, L/ = the sound intensity level, pc = the characteristic impedance, 10= the reference intensity, I pW/m2, and Pn = the reference sound pressure, 20,uPa, ANSI 512.12-1992 17 Bpo 10 is the pressure-intensity index measured in a pressure chamber, and pr and i? are the mean-square s
38、ound pressure and particle velocity, respectively. Indicator D 51 is useful when intensity is measured using the “two-microphone method.“ Subject to the usual measurement uncertainties for small phase mis match. indicator D 51 is the error, in decibels, in the sound power level due to instrumentatio
39、n channel phase mismatch. Indicator D 52 is useful to evaluate the capability of certain “two-microphone method“ intensity devices to accurately measure sound intensity. For such devices, if D 52 7 dB, the error in measured sound intensity level for a plane wave due to instrumentation phase mismatch
40、 will be less than 1 dB. Indicator D 53 gives information about the differ ence in phase measured by the two channels of a “two microphone method“ intensity measuring system. This consists of the sum of the actual phase difference at the two microphone locations and the instrumentation channel phase
41、 mismatch. For D 53 to be useful, the in strumentation phase mismatch must be known and re ported. Indicator D 54 can serve a function similar to that of D 53 for certain “pressure-velocity method“ sound in tensity measuring devices. When the instrumentation phase mismatch is negligible, indicator D
42、 54 gives a measure of the phase difference between the sound pressure and the particle velocity. B.6 Averaging Time Sufficiency Indicators, 06 Four indicators, each based on an est imate of a level of normalized temporal standard deviation, may be useful: D62, L,l,), D63=L100,ILpl, and D64. = L IOO
43、IL, ) “ where L, Is I 10 10g,.( 1 + .t, IS. - 1;) l! I IN - )1; 1) , s,. represents an ensemble over time of dummy vari able 5, N is the number of 5 in the ensemble, I is the surface sound intensity, I ,. is the sound intensity at the jth measurement location, I p is the surface sound pressure level
44、, and Lpo is the sound pressure level at the ilh measure ment location. These indicators must be evaluated using the actual measurement averaging time. The measured quantity must be measured a number of times N. which should be as large as practicable and not less than three. If indicator D62,. or D
45、64,. is used, several measurement locations should be sampled to ensure that reported values are typical for the measurement surface. In gen eral, the indicator should be determined with the sub ject source, and all background sources, operating as for a sound power determination. These indicators a
46、re similar to the D I indicators, and the suggestions given in Sec. B.l apply if the D 6 indicator values are excessive. B.7 Measurement Interference Indicators, 07 To obtain an accurate sound power determination, the presence of measurement equipment and/or an op erator must not significantly influ
47、ence the measure ment. Particular care must be taken to ensure that ob jects that are moved during the course of testing do not result in inconsistent acoustical data. Three indi cators may be useful to evaluate the significance of interference: D7t = ILw -LI = II, - I,I, D72,. = IL r; - L 1;1 , and
48、 D73; = 10 logto IMax(/;) - Min(/;) I, 18 AMERICAN NATIONAL STANDARD where Lw. I,. and ii, are the sound power level, surface sound intensity level, and sound intensity level al the ilh measurement location, respectively, ob tained in the usual manner, L;.“ I;, and L;, represent the same quantities
49、ob tained with special care to avoid interference, and I ; is the intensity at the ilh measurement location while various possible interfering objects are moved in the vicinity of the measurement location, and throughout the measurement environment. as they might be during the course of a usual sound power determination. Care should be taken to sample the measurement surface to ensure that values reported for D 72 and D 73 are typical. In general, small values for the D
