1、Designation: E 1124 97 (Reapproved 2004)Standard Test Method forField Measurement of Sound Power Level by the Two-Surface Method1This standard is issued under the fixed designation E 1124; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 me
3、thod. The testmethod 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 an
4、y, associated with its 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:2C 634 Terminology Relating to Environmental Acoust
5、ics2.2 ANSI Standard:3S1.4 Specification for Sound Level Meters3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology C 634.43.2 Definitions of Terms Specific to This Standard:3.2.1 conformal surfacethe locus of points which lie at afixed distance from th
6、e reference 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 pie
7、ce of equipment.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 c
8、onsist of rectangular, 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 calculati
9、on accounts 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. Signif
10、icance and 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
11、 cases, areliable 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 Dieh
12、l,7but differs from all other current soundpower measurement procedures by requiring simultaneousmeasurement at both conformal surfaces and by resolving1This test method is under the jurisdiction of ASTM Committee E33 onEnvironmental Acoustics and is the direct responsibility of Subcommittee E33.08
13、onMechanical and Electrical System Noise.Current edition approved April 1, 2004. Published April 2004. Originallyapproved in 1986. Last previous edition approved in 1997 as E 1124 97.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.
14、org. For Annual Book of ASTMStandards 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 10036.4Terminology C 634 85 was the edition used during the development of th
15、istest 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 Procedures for Free Field Conditions for SoundPower Determination of Sound Sources and Metho
16、ds 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, NY, 1973,pp. 97103.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, We
17、st Conshohocken, PA 19428-2959, United States.time-averaged sound pressure levels at both surfaces to within0.1 dB. These two features, simultaneous recording and 0.1-dBresolution, enable source sound power to be calculated whenthe direct sound field of the source is actually lower in levelthan the
18、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 prediction of sound levels in a plant basedupon measurements of similar sources in another plant. Thistest method is believed to be capable of yieldi
19、ng a reasonablygood estimate of absolute power level with proper care ofapplication and full conformance to the provisions of thisprocedure.5.4 The two-surface method is applicable only when the twomeasurement surfaces can be physically selected to producepositive values of the difference in average
20、 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 applies to each frequency band and eachconstituent surface area investigated. Only the frequency bandin which a zero or negative difference occur
21、s 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 invalid data at all constituent areas. Therefore, lessthan complete results are permissible when one-third octaveanalysis is used and full octave r
22、esults 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 volume less than about 20 times the spaceenclosed by an envelope around the larger dimensions of themachine. In such cases, the sound pressure lev
23、el close to themachine may not decrease in any regular way with increasingdistance from a machine surface, making it impossible to selecttwo measurement surfaces producing positive differences ofsound pressure level.6. Operating Conditions6.1 Whenever possible, equipment under test must be oper-atin
24、g 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 properly qualified in terms ofrunning speeds, flow rate, production rate, etc.7. Apparatus7.1 Due to the amount of data which must be gathered andpro
25、cessed, the following are considered to be the minimumequipment necessary to meet the requirements of this testprocedure.7.1.1 Microphones, that are matched in terms of frequencyand pressure response. Begin by calibrating each data channel,using the same calibrator on each channel. Connect bothmicro
26、phone channels to the cables, connectors, amplifiers, andrecorder to be used in data gathering. Then arrange themicrophones side by side in the presence of broad bandambient noise and record for 60 s on both channels. Thedifferences in the averaged sound pressure levels in eachfrequency band are cal
27、ibration corrections which may beapplied to either channel prior to any calculation.7.1.2 Magnetic Tape Recorder, two-channel instrumentationgrade having a frequency response of 61 dB over thefrequency range of interest.7.1.2.1 It is recognized that even high-quality AmplitudeModulation (AM) tape re
28、corders 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. If digitalfrequency modulation (F
29、M) or pulse code modulation (PCM)tape recorders are used, the procedure of 7.1.1 should still beused.FIG. 1 Configuration of Conformal Surfaces, General CaseE 1124 97 (2004)2NOTE 1The frequency response and accuracy of the acousticalinstruments are different from the interchannel resolution of the t
30、aperecorder. Both the frequency response discussed in 7.1.2 and the accuracyof the acoustical calibrators are distinctly different from the 0.1-dBresolution discussed in 5.2.7.1.3 Microphone Mounting FixtureA suggested fixture isshown in Fig. 2.7.1.4 Spectrum Analyzer, real-time one-third or full oc
31、tave,having a resolution of 0.1 dB with a digital display or printingcapabilities.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 co
32、mpared with what could be obtained with 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 Desktop Computer.7.2.2 Data Processing, dir
33、ect from output of real-timeanalyzer.8. Procedure8.1 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 freq
34、uency range ofinterest. As stated in Section 5, merely a 0.1-dB 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. Obvi
35、ously, the closerthe inner surface is to the equipment, 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 calculate
36、d power levels be determined,so that this procedure 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 t
37、ogether, measurable differences in average sound pres-sure levels will be difficult to obtain. On the other hand, noadvantage 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 thedifferentia
38、l, 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 ofFIG. 2 Example of Suggested Measurement SystemE 1124 97 (2004)3about 1.4 to 2.0, between the outer and inner surfaces, is area
39、sonable range that may be used in most cases.8.1.3 Select 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 ref
40、erence surface is chosen so that the twoconformal measurement 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 source
41、s themselves. Ideally, the soundintensity vector would be 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 surf
42、aces accordingly.8.1.4 It is permissible to subdivide the 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
43、 simultaneouslywith the inner and outer microphones, care 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
44、 usually complex shape of theequipment sources themselves.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 o
45、f the extent of measurement coverage. Constituentsurface areas 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 prescr
46、ibed 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
47、measurements of the sound pres-sure level at the two microphone positions along a line normal,that is perpendicular to, the inner conformal surface. See 7.1.3for a suggested microphone mounting fixture. Determine theaverage sound pressure level over each constituent surface areausing a continuous un
48、iform microphone sweep as indicated inFig. 4.8.2.2 If the inner and outer measurement surfaces aresubdivided into smaller constituent areas for the survey, theaverage sound pressure levels over the entire inner and outerconformal surfaces are determined by summing the valuesobtained for the respecti
49、ve constituent areas, as shown in 9.3.8.2.3 The microphone sweeping speed shall be sufficientlyslow, continuous, and uniform that when the data are continu-ously recorded, a representative average sound pressure level isobtained for each constituent area swept by the microphone(s).A reasonable averaging period is usually between 30 and 60 sfor each constituent area. A reasonable sweeping speed isusually about 0.5 m/s.8.2.4 Fig. 5 illustrates an alternate data collection techniquein which a large number of uniform constituent surface areasare measured by moving the microp
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