1、Designation: E1124 10Standard Test Method forField Measurement of Sound Power Level by the Two-Surface Method1This standard is issued under the fixed designation E1124; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the field, or in situ measurementof sound power level by the two-surface method. The testmethod
3、is designed to minimize the effects of reverberantconditions, directivity of the noise source under consideration,and the effects of ambient noise from other nearby equipmentoperating at the same time.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with it
4、s use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C634 Terminology Relating to Building and EnvironmentalAcoustics2.2 ANS
5、I Standard:3S1.4 Specification for Sound Level Meters3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology C634.43.2 Definitions of Terms Specific to This Standard:3.2.1 conformal surfacethe locus of points which lie at afixed distance from the reference
6、 surface of a piece ofequipment. Two conformal surfaces are used in this testmethod. These are surfaces over which the measuring micro-phones are swept. They are located at two different distancesfrom the equipment. Fig. 1 shows a typical arrangement ofthese surfaces for a generalized piece of equip
7、ment.3.2.2 constituent surface areaa portion of the conformalsurface.4. Summary of Test Method4.1 The average one-third or full octave band sound pres-sure levels are measured over two different conformal surfaceswhich envelop the equipment. These conformal surfacesshould be selected to consist of r
8、ectangular, cylindrical, andhemispherical constituent surfaces so that the surface areasmay be easily calculated. From the difference between the twoaverage sound pressure levels taken at each surface and fromthe areas of the surfaces, the sound power level may becalculated. The calculation accounts
9、 for both the effect of thereverberant field and the noise of other equipment. It ispermissible to define conformal surfaces that completely en-velope the source, yet only measure over a portion of theconformal surface due to restrictions from process connectionsor accessibility.5. Significance and
10、Use5.1 The function and operation of equipment in the fieldoften preclude the measurement of the free-field sound pres-sure levels of a single piece of equipment in the absence ofinterfering sound from other equipment operating at the sametime. The two-surface method will provide, in most cases, are
11、liable estimate of the normal sound power levels of aspecimen operating in an adverse environment.5.2 This test method is intended for use in the field in thepresence of what is normally regarded as interfering back-ground noise. This test method is based upon the work ofHubner5,6and Diehl,7but diff
12、ers from all other current soundpower measurement procedures by requiring simultaneous1This test method is under the jurisdiction ofASTM Committee E33 on Buildingand Environmental Acoustics and is the direct responsibility of SubcommitteeE33.08 on Mechanical and Electrical System Noise.Current editi
13、on approved May 1, 2010. Published June 2010. Originallyapproved in 1986. Last previous edition approved in 1997 as E1124 97. DOI:10.1520/E1124-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandard
14、s volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.Available from American National StandardsInstitute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036,
15、http:/www.ansi.org.4Terminology C634 85 was the edition used during the development of thistest method.5Hubner, G., “Analysis of Errors in Measuring Machine Noise Under Free FieldConditions,” Journal of the Acoustical Society of America, Vol 54, No. 4, 1973, pp.967977.6Hubner, G., “Qualification Pro
16、cedures for Free Field Conditions for SoundPower Determination of Sound Sources and Methods for the Determination of theAppropriate Environmental Correction,” Journal of the Acoustical Society ofAmerica, Vol 61, No. 2, 1977, pp. 456464.7Diehl, G. M., Machinery Acoustics, J. Wiley and Sons, New York,
17、 NY, 1973,pp. 97103.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.measurement at both conformal surfaces and by resolvingtime-averaged sound pressure levels at both surfaces to within0.1 dB. These two features, simultaneous recordi
18、ng and 0.1dBresolution, enable source sound power to be calculated whenthe direct sound field of the source is actually lower in levelthan the ambient noise.5.3 The use of this test method is expected to be primarilyfor the relative assessment of the sound power from similarsources or for the predic
19、tion of sound levels in a plant basedupon measurements of similar sources in another plant. Thistest method is believed to be capable of yielding a reasonablygood estimate of absolute power level with proper care ofapplication and full conformance to the provisions of thisprocedure.5.4 The two-surfa
20、ce method is applicable only when the twomeasurement surfaces can be physically selected to producepositive values of the difference in average sound pressurelevel. That is, the inner surface sound pressure level minus theouter surface sound pressure level must be at least +0.1 dB.This limitation ap
21、plies to each frequency band and eachconstituent surface area investigated. Only the frequency bandin which a zero or negative difference occurs is it consideredinvalid and usually adjacent bands will be valid. In practice,only rarely will all three one-third octave bands of a givenoctave yield inva
22、lid data at all constituent areas. Therefore, lessthan complete results are permissible when one-third octaveanalysis is used and full octave results are reported.5.5 The two-surface method may not produce results whentesting some very large machines in very reverberant rooms orin rooms having a vol
23、ume less than about 20 times the spaceenclosed by an envelope around the larger dimensions of themachine. In such cases, the sound pressure level close to themachine may not decrease in any regular way with increasingdistance from a machine surface, making it impossible to selecttwo measurement surf
24、aces producing positive differences ofsound pressure level.6. Operating Conditions6.1 Whenever possible, equipment under test must be oper-ating in a mode acceptable to all parties involved in the test.Otherwise operating conditions must at least be monitored inorder that the test results are proper
25、ly qualified in terms ofrunning speeds, flow rate, production rate, etc.7. Apparatus7.1 Due to the amount of data which must be gathered andprocessed, the following are considered to be the minimumequipment necessary to meet the requirements of this testprocedure.7.1.1 Microphones, that are matched
26、in terms of frequencyand pressure response. Begin by calibrating each data channel,using the same calibrator on each channel. Connect bothmicrophone channels to the cables, connectors, amplifiers, andrecorder to be used in data gathering. Then arrange themicrophones side by side in the presence of b
27、road bandambient noise and record for 60 s on both channels. Thedifferences in the averaged sound pressure levels in eachfrequency band are calibration corrections which may beapplied to either channel prior to any calculation.7.1.2 Recording Device, two-channel instrumentation grade.7.1.2.1 A magne
28、tic tape recorder using either AM or FMformat having the prescribed frequency response called for in7.1.5 would be regarded as instrumentation grade.7.1.2.2 A digital format recorder with two channel capabil-ity, using magnetic tape media, such as DAT (Digital AudioTape) will satisfy this instrument
29、ation grade requirement.FIG. 1 Configuration of Conformal Surfaces, General CaseE1124 1027.1.2.3 Digital recording devices using linear pulse codemodulation (LPCM) using digital storage media will satisfythis instrumentation grade requirement.7.1.2.4 It is recognized that even high-quality Amplitude
30、Modulation (AM) tape recorders cannot maintain channel-to-channel frequency response within 0.1 dB. It is believed,however, that the requirement for determining the correctionsin 7.1.1 based on 60 s average readings sufficiently compen-sates for expected instabilities, channel-to-channel.7.1.2.5 If
31、digital frequency modulation (FM or DAT) orpulse code modulation (PCM) tape recorders are used, theprocedure of 7.1.1 should still be used.NOTE 1The frequency response and accuracy of the acousticalinstruments are different from the interchannel resolution of the recordingdevice. Both the frequency
32、response discussed in 7.1.1 and the accuracyof the acoustical calibrators are distinctly different from the 0.1dBresolution discussed in 5.2.7.1.3 Microphone Mounting FixtureAsuggested fixture isshown in Fig. 2.7.1.4 Spectrum Analyzer, real-time one-third or full octave,having a resolution of 0.1 dB
33、 with a digital storage capability,digital display, or printing capabilities. Modern dual-channeldigital sound level meters with one-third octave band or fulloctave band capability and digital storage capability willeliminate the need for the recording device of 7.1.2.7.1.5 Regardless of the specifi
34、c microphones, recordingdevice and spectrum analyzer used, the entire system must becalibrated so as to ensure a uniform dynamic response of 6 1dB over the frequency range of interest, as measured inone-third octave bands or full octave bands, as applicable. Adescription of the system calibration pr
35、ocess shall be includedin the test results.NOTE 2Real-time analyzers having a resolution of 0.25 dB may alsobe used. However, because of the requirement for a positive sound leveldifference, as discussed in 5.4, these analyzers may yield less completeresults compared with what could be obtained with
36、 an analyzer with betterresolution. In addition, the precision of the results will be reduced if onlydifferences greater than 0.25 dB can be obtained.7.2 Optional equipment may include:7.2.1 Programmable Calculator or Computer.7.2.2 Data Processing, direct from output of real-timeanalyzer.8. Procedu
37、re8.1 Selection of Measurement Surfaces:8.1.1 Conduct a preliminary survey of the sound field toestimate the two optimum conformal measurement surfacesthat will yield a measurable drop in average sound pressurelevel between the two surfaces for the frequency range ofinterest. As stated in Section 5,
38、 merely a 0.1dB difference inaverage sound pressure levels constitutes a measurable drop.However, the surfaces should be chosen so as to maximize thedifference since the overall accuracy of the estimated soundpower levels will be thereby improved. Obviously, the closerthe inner surface is to the equ
39、ipment, the easier it will be toobtain a large positive difference, but possible near-field effectsdictate an inner surface farther from the equipment. Suchnear-field effects cannot be quantified by this test method norcan their effect on the calculated power levels be determined,so that this proced
40、ure can only suggest that the inner surfacemicrophone be always at least 0.15 m, and for larger machinesat least 0.3 m, from the equipment surface thereby avoidingmost of these effects.8.1.2 If the locations of the two conformal surfaces are tooclose together, measurable differences in average sound
41、 pres-sure levels will be difficult to obtain. On the other hand, noFIG. 2 Example of Suggested Measurement SystemE1124 103advantage is gained by using progressively larger outer sur-faces once the outer surface microphone is in the fullyreverberant field since the sound level, and therefore thediff
42、erential, will be constant. No clear optimum ratio betweenthese two surface areas can be prescribed for all equipment.Asa guide, however, experience has shown that an area ratio ofabout 1.4 to 2.0, between the outer and inner surfaces, is areasonable range that may be used in most cases.8.1.3 Select
43、 simple geometric shapes for conformal sur-faces. Fig. 1 shows an example of a generalized situation. InFig. 1, even though the equipment itself can be approximatedby rectangular or cylindrical surfaces which just enclose theequipment, the reference surface is chosen so that the twoconformal measure
44、ment surfaces are convex. It may be helpfulto imagine the major equipment reference surfaces to bedefined by a membrane stretched over the equipment after theremoval of minor projections, gages, tubes, and cables notexpected to be noise sources themselves. Ideally, the soundintensity vector would be
45、 normal to both measurement surfacesat all points.Although this cannot be determined using this testmethod, it may be helpful if the surveyor will attempt tovisualize the expected sound field and so might adjust theselection of conformal surfaces accordingly.8.1.4 It is permissible to subdivide the
46、conformal surfacesinto several constituent surface areas for ease of data collectionor because of inaccessibility. Any number of constituentsurface areas may be used to cover the conformal surface.Since the conformal surfaces will be measured simultaneouslywith the inner and outer microphones, care
47、should be taken thatthe constituent surface area boundaries define related regionson the inner and outer surfaces. These constituent surface areaswill not necessarily be composed of geometrically similar innerand outer surfaces because of the usually complex shape of theequipment sources themselves.
48、8.1.5 Fig. 3 is an example of the application of theseguidelines for the selection of measurement surfaces. A largecoal pulverizer was measured using this test method. Theactual shapes of conformal surfaces are shown as well as anindication of the extent of measurement coverage. Constituentsurface a
49、reas were used for the dome, grinding zone, and upperand lower pedestal. Less than 100 % coverage was used andwas accounted for as discussed in 9.4.8.1.6 No optimum distances from the equipment surface toeither conformal surface can be prescribed for all equipment.However, for sources whose smallest dimension is 1 m, it isrecommended the inner surface distance be at least 0.2 m.Also,for sources whose smallest dimension is 3 m, it is recom-mended the outer surface distance be less than 2 m.8.2 Data Acquisition:8.2.1 Obtain simultaneous measurements of the sound pres-sur
