ASTM_E_1124_-_10.pdf

Designation:E112410Standard 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 last 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 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 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:2C634 Terminology Relating to Building and EnvironmentalAcoustics2.2 ANSI 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 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 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 consist 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 calculation 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.Significance 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 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 Diehl,7but differs from all other current sound1This test method is under the jurisdiction ofASTM Committee E33 on Buildingand Environmental Acousticsand is the direct responsibility of SubcommitteeE33.08 on Mechanical and Electrical System Noise.Current edition 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 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.Available from American National StandardsInstitute(ANSI),25 W.43rd St.,4th Floor,New York,NY 10036,http:/www.ansi.org.4Terminology C634 85 was the edition used during the development of this testmethod.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 Methods for the Determination of theAppropriate Environmental Correction,”Journal of the Acoustical Society ofAmerica,Vol 61,No.2,1977,pp.456464.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 power measurement procedures by requiring simultaneousmeasurement at both conformal surfaces and by resolvingtime-averaged sound pressure levels at both surfaces to within0.1 dB.These two features,simultaneous recording and 0.1dBresolution,enable source sound power to be calculated whe