SIST EN ISO 3741:2009

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Akustik - Ermittlung der Schalleistungspegel von Geräuschquellen durch Schalldruckmessungen - Hallraumverfahren der Genauigkeitsklasse 1 (ISO 3741:1999, einschließlich Cor 1:2001)Acoustique - Détermination des niveaux de puissance acoustique émis par les sources de bruit à partir de la pression acoustique - Méthodes de laboratoire en salles réverbérantes (ISO 3741:1999, Cor 1:2001 inclus)Acoustics - Determination of sound power levels of noise sources using sound pressure - Precision methods for reverberation rooms (ISO 3741:1999, including Cor 1:2001)17.140.01Acoustic measurements and noise abatement in generalICS:Ta slovenski standard je istoveten z:EN ISO 3741:2009SIST EN ISO 3741:2009en01-november-2009SIST EN ISO 3741:2009SLOVENSKI
STANDARDSIST EN ISO 3741:2001/AC:2002SIST EN ISO 3741:20011DGRPHãþD

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN ISO 3741July 2009ICS 17.140.01Supersedes EN ISO 3741:1999
English VersionAcoustics - Determination of sound power levels of noisesources using sound pressure - Precision methods forreverberation rooms (ISO 3741:1999, including Cor 1:2001)Acoustique - Détermination des niveaux de puissanceacoustique émis par les sources de bruit à partir de lapression acoustique - Méthodes de laboratoire en sallesréverbérantes (ISO 3741:1999, Cor 1:2001 inclus)Akustik - Ermittlung der Schalleistungspegel vonGeräuschquellen durch Schalldruckmessungen -Hallraumverfahren der Genauigkeitsklasse 1 (ISO3741:1999, einschließlich Cor 1:2001)This European Standard was approved by CEN on 13 July 2009.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre:
Avenue Marnix 17,
B-1000 Brussels© 2009 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN ISO 3741:2009: ESIST EN ISO 3741:2009

Relationship between this European Standard and the Essential Requirements of EU Directive 98/37/EC .4Annex ZB (informative)
Relationship between this European Standard and the Essential Requirements of EU Directive 2006/42/EC .5 SIST EN ISO 3741:2009

Relationship between this European Standard and the Essential Requirements of EU Directive 98/37/EC This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association to provide a means of conforming to Essential Requirements of the New Approach Directive 98/37/EC, amended by 98/79/EC on machinery. Once this standard is cited in the Official Journal of the European Communities under that Directive and has been implemented as a national standard in at least one Member State, compliance with the normative clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity with the relevant Essential Requirements of that Directive and associated EFTA regulations. WARNING - Other requirements and other EU Directives may be applicable to the product(s) falling within the scope of this standard. SIST EN ISO 3741:2009

Relationship between this European Standard and the Essential Requirements of EU Directive 2006/42/EC This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association to provide a means of conforming to Essential Requirements of the New Approach Directive 2006/42/EC on machinery. Once this standard is cited in the Official Journal of the European Communities under that Directive and has been implemented as a national standard in at least one Member State, compliance with the normative clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity with the relevant Essential Requirements of that Directive and associated EFTA regulations. WARNING — Other requirements and other EU Directives may be applicable to the product(s) falling within the scope of this standard.
AReference numberISO 3741:1999(E)INTERNATIONALSTANDARDISO3741Third edition1999-08-01Acoustics — Determination of sound powerlevels of noise sources using soundpressure — Precision methods forreverberation roomsAcoustique — Détermination des niveaux de puissance acoustique émispar les sources de bruit à partir de la pression acoustique — Méthodes delaboratoire en salles réverbérantesSIST EN ISO 3741:2009

ISO 3741:1999(E)© ISO©
ISO 1999All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronicor mechanical, including photocopying and microfilm, without permission in writing from the publisher.International Organization for StandardizationCase postale 56 · CH-1211 Genève 20 · SwitzerlandInternetiso@iso.chPrinted in SwitzerlandiiContents1 Scope.12 Normative references.13 Terms and definitions.24 Measurement uncertainty.45 Acoustic environment.65.1 General.65.2 Volume and shape of test room.65.3 Requirements for absorption of test room.65.4 Requirements for background noise level.65.5 Requirements for temperature, humidity and pressure.76 Instrumentation.76.1 General.76.2 Calibration.77 Installation and operation of source under test.87.1 General.87.2 Source location.87.3 Source mounting.87.4 Auxiliary equipment.97.5 Operation of source during test.98 Sound pressure measurements and sound power determination.98.1 Initial measurements.98.2 Additional measurements.148.3 Determination of average sound pressure level in the test room.14SIST EN ISO 3741:2009

© ISOISO 3741:1999(E)iii8.4 Determination of the sound power level of the sound source.148.5 Determination of A-weighted sound power level of the source.169 Information to be recorded.169.1 Noise sources under test.169.2 Acoustical environment.179.3 Instrumentation.179.4 Acoustical data.1710 Information to be reported.17Annex A (normative)
Room qualification procedure for the measurement ofdiscrete-frequency components.18Annex B (informative)
Guidelines for the design of rotating diffusing vanes.23Annex C (informative)
Extension for frequencies below 100 Hz.24Annex D (informative)
Guidelines for the design of reverberation rooms.25Annex E (normative)
Test room qualification procedure for the measurement of broad-band sound.27Annex F (normative)
Procedure for calculating octave band sound power levels and an A-weightedsound power level from one-third-octave band sound power levels.29Bibliography.31SIST EN ISO 3741:2009

ISO 3741:1999(E)© ISOivForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISOmember bodies). The work of preparing International Standards is normally carried out through ISO technicalcommittees. Each member body interested in a subject for which a technical committee has been established hasthe right to be represented on that committee. International organizations, governmental and non-governmental, inliaison with ISO, also take part in the work. ISO collaborates closely with the International ElectrotechnicalCommission (IEC) on all matters of electrotechnical standardization.International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.International Standard ISO 3741 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1,Noise.This third edition of ISO 3741 cancels and replaces ISO 3741:1988 and ISO 3742:1988, which have beentechnically revised and amalgamated.Annexes A, E and F form a normative part of this International Standard. Annexes B, C and D are for informationonly.SIST EN ISO 3741:2009

© ISOISO 3741:1999(E)v0
Introduction0.1
This International Standard is one of the ISO 3740 series, which specifies various methods for determining thesound power levels of machines, equipment, and their sub-assemblies. When selecting one of the methods of theISO 3740 series, it is necessary to select the most appropriate for the conditions and purpose of the test. Generalguidelines to assist in the selection are provided in ISO 12001 and ISO 3740. The ISO 3740 series gives only generalprinciples regarding the operating and mounting conditions of the machine or equipment under test. Reference shouldbe made to the noise test code for a specific type of machine or equipment, if available, for specifications on mountingand operating conditions.0.2
This International Standard specifies laboratory methods for determining the sound power radiated by sources asa function of frequency, using a reverberation test room having specified acoustical characteristics. If a room havingthese characteristics is not available, other documents of the series of basic standards with different environmentalrequirements are offered (see Table 1 and ISO 3744 or ISO 9614).In this International Standard, the computation of sound power from sound pressure measurements is based on thepremise that, for a source emitting a given sound power in the reverberation test room, the mean-square soundpressure averaged in space and time, p2, is directly proportional to the sound power and otherwise depends only onthe acoustical and geometric properties of the room and on the physical constants of air.If a source emits narrow-band or discrete-frequency sound, a precise determination of the radiated sound power levelrequires greater effort. The reasons are as follows:a) the space/time-averaged sound pressure along a short microphone path, or as determined with an array of a smallnumber of microphones, is not always a good estimate of the space/time averaged mean-square pressurethroughout the room;b) the sound power radiated by the sources is more strongly influenced by the normal modes of the room and by theposition of the source within the room.If narrow bands of noise or discrete tones are emitted by a source, a determination of its sound power level in areverberation room requires either the optimization and qualification of the room and test set-up (see annex A) or theuse of a greater number of source locations and microphone positions (or greater path length for a movingmicrophone). These numbers can be reduced by adding low frequency absorbers to decrease the reverberation time. Itis also helpful if one or more diffusers are rotating in the test room during the measurements. Guidelines for the designof suitable rotating diffusers are given in annex B.SIST EN ISO 3741:2009

ISO 3741:1999(E)© ISOviTable 1 — Overview of International Standards for determination of sound power levels of noise sourcesunder reverberation conditions giving different grades of accuracyParameterISO 3741ISO 3743-1ISO 3743-2Precision methodGrade 1Engineering methodGrade 2Engineering methodGrade 2Test environmentReverberation roomHard-walled roomSpecial reverberation testroomCriteria for suitability of testenvironmentRoom volume, V, andreverberation time, Trev,to be qualifiedV > 40 m3 andV > 40 VQSound absorptioncoefficient a< 0,20Special qualificationSpecified requirementsVolume of sound source VQPreferably less than 2 %of test room volumePreferably less than 2,5 % of test room volumeCharacter of noiseSteady, broad-band,narrow-band, discretefrequenciesAny, but no isolated burstsLimitation for backgroundnoiseDL > 10 dBDL > 6 dBDL > 4 dBNumber NM of measuringpositionsNM > 6or a continuousmicrophone traverse,if appropriateNM > 3or a continuousmicrophone traverse,if appropriateNM > 3or a continuousmicrophone traverse,if appropriateInstrumentation:a)Sound level meter atleast complying withb)Integrating sound levelmeter at leastcomplying withc)Frequency band filterset at least complyingwithd)calibrator at leastcomplying witha)type 1 according to IEC 61672b)type 1 according to IEC 61672c)class 1 according to IEC 61260d)class 1 according to IEC 60942Sound power levels to beobtainedIn one-third-octave oroctave bandsIn octave bandsA-weighted and in octavebandsA-weighted (to be calculated)Precision of method fordetermining LWA expressedas standard deviation ofreproducibility sRsR < 0,5 dBsR < 1,5 dBsR < 2,0 dB(for sources which emit noise with a relatively "flat" spectrum)SIST EN ISO 3741:2009

INTERNATIONAL STANDARD
© ISOISO 3741:1999(E)1Acoustics — Determination of sound power levels of noisesources using sound pressure — Precision methods forreverberation rooms1 Scope1.1
This International Standard specifies a direct method and a comparison method for determining the soundpower level that would be produced by a source operating in an environment at
standard meteorological conditionscorresponding to a characteristic impedance of rc = 400 N.s/m3 (where r is the density of air and c is the speed ofsound). It specifies test room requirements, source location and general rules for operating conditions,instrumentation and techniques for obtaining an estimate of mean-square sound pressure levels from which thesound power levels of the source in octave or one-third-octave bands are calculated with a grade 1 accuracy. Thequantities to be measured are time-averaged sound pressure levels in frequency bands. The quantities to bedetermined are sound power levels, A-weighted and in frequency bands. Other quantities, which are optional, aresound power levels with other frequency weightings calculated from the measurements in frequency bands. Thisstandard does not provide the means to determine directivity and temporal variation of sound from a source.In general, the frequency range of interest includes the one-third-octave bands with midband frequencies from100 Hz to 10 000 Hz. Guidelines for the application of the specified methods in an extended frequency range inrespect to lower frequencies are given in annex C. This International Standard is not applicable to frequency rangesabove the 10 000 Hz one-third-octave band. For higher frequencies the use of methods given in ISO 9295 isrecommended.1.2
The method specified in this International Standard is suitable for steady noise with broad-band, narrow-bandand discrete-frequency components as described in ISO 12001. The noise may be emitted from a device, machine,component or sub-assembly.This International Standard is applicable to noise sources with volumes which are preferably not greater than 2 % ofthe volume of the reverberation room used for the test. For sources with volumes greater than 2 % of the roomvolume, the standard deviations given by Table 2 could be exceeded.2 Normative referencesThe following normative documents contain provisions which, through reference in this text, constitute provisions ofthis International Standard. For dated references, subsequent amendments to, or revisions of, any of thesepublications do not apply. However, parties to agreements based on this International Standard are encouraged toinvestigate the possibility of applying the most recent editions of the normative documents indicated below. Forundated references, the latest edition of the normative document referred to applies. Members of ISO and IECmaintain registers of currently valid International Standards.ISO 354, Acoustics — Measurement of sound absorption in a reverberation room.ISO 4871, Acoustics — Declaration and verification of noise emission values of machinery and equipment.ISO 6926, Acoustics — Determination of sound power levels of noise sources — Requirements for the performanceand calibration of reference sound sources.ISO 7574-1:1985, Acoustics — Statistical methods for determining and verifying stated noise emission values ofmachinery and equipment — Part 1: General considerations and definitions.SIST EN ISO 3741:2009

ISO 3741:1999(E)© ISO2ISO 7574-4:1985, Acoustics — Statistical methods for determining and verifying stated noise emission values ofmachinery and equipment — Part 4: Methods for stated values for batches of machines.ISO 12001, Acoustics — Noise emitted by machinery and equipment — Rules for the drafting and presentation of anoise test code.IEC 60942, Sound calibrators.IEC 61183, Electroacoustics — Random-incidence and diffuse-field calibration of sound level meters.IEC 61260, Electroacoustics — Octave-band and fractional-octave-band filters.IEC 61672, Electroacoustics — Sound level meters.3 Terms and definitionsFor the purposes of this International Standard, the following terms and definitions apply.3.1reverberation rooma test room meeting the requirements of this International Standard3.2reverberant sound fieldthat portion of the sound field in the test room over which the influence of sound received directly from the source isnegligible3.3sound pressurepfluctuating pressure superimposed on the static pressure by the presence of soundNOTE 1It is expressed in pascals.NOTE 2The magnitude of the sound pressure can be expressed in several ways, but for this International Standard only thesquare root of the mean-square sound pressure over designated time and space is relevant.3.4mean-square sound pressurep2sound pressure averaged in space and time on a mean-square basisNOTE
In practice, space/time-averaging over a finite path length or a fixed number of microphone positions as well asdeviations from the ideally reverberant sound field lead only to an estimate ofp2.3.5sound pressure levelLpten times the logarithm to the base 10 of the ratio of the square of the sound pressure to the square of the referencesound pressureNOTESound pressure levels are expressed in decibels. The reference sound pressure is 20 mPa (2 ´ 10–5 Pa).SIST EN ISO 3741:2009

© ISOISO 3741:1999(E)33.5.1time-averaged sound pressure levelLpeq,Tlevel of the time-averaged square of the sound pressure, expressed in decibels:LTptptpTTeq,lgddB=éëêêùûúúò1012020()(1)NOTE 1Time-averaged sound pressure levels are expressed in decibels.NOTE 2In general, the subscripts "eq" and "T" are omitted since time-averaged sound pressure levels are necessarilydetermined over a certain measurement time interval.3.5.2measurement time intervalportion or a multiple of an operational period or operational cycle for which the time-averaged sound pressure levelis determinedNOTE
See 8.1.3.3.6sound powerWrate per unit time at which airborne sound energy is radiated by a sourceNOTE
It is expressed in watts.3.7sound power levelLWten times the logarithm to the base 10 of the ratio of the sound power radiated by the sound source under test to thereference sound powerNOTE 1It is expressed in decibels. The reference sound power is 1 pW (10–12 W).NOTE 2For example, the A-weighted sound power level is LWA.3.8background noisenoise from all sources other than the source under test3.9reference sound sourcestable and steady source emitting constant broad-band noise with an adequate sound power level, performing andcalibrated in accordance with ISO 69263.10reverberation timeTrevtime or extrapolated time that would be required for the sound pressure level to decrease 60 dB if a sound source ina space were stopped instantaneouslyNOTE 1It is expressed in seconds (s).NOTE 2In this International Standard, Trev is calculated in accordance with ISO 354 except that the reverberation time isextrapolated from the decay of the first 10 dB or 15 dB, denoted T10 and T15 respectively.SIST EN ISO 3741:2009

ISO 3741:1999(E)© ISO43.11frequency range of interestfrequency range covered by the one-third-octave bands with mid-frequencies from 100 Hz to 10 000 HzNOTE
This is the general case. For special purposes, the frequency range may be extended as low as 50 Hz providedcertain criteria are met (see annex C).3.12sound absorption coefficientaat a given frequency and for specified conditions, the fraction of incident sound power not reflected from a surfacecalculated in accordance with ISO 3543.13equivalent absorption areaAproduct of the surface area and its absorption coefficientNOTE
It is expressed in square metres (m2).4 Measurement uncertaintyMeasurements made in conformity with this International Standard tend to result in standard deviations ofreproducibility which are equal to or less than those given in Table 2. A single value of the sound power level of anoise source determined according to the procedures of this International Standard is likely to differ from the truevalue by an amount within the range of the measurement uncertainty. The uncertainty in determinations of thesound power level arises from several factors which affect the results, some associated with environmentalconditions in the measurement laboratory and others with experimental techniques.
If a particular noise sourcewere to be transported to each of a number of different laboratories, and if, at each laboratory, the sound powerlevel of that source were to be determined in accordance with this International Standard, the results would show ascatter. The standard deviation of the measured levels could be calculated (see examples in ISO 7574-4:1985,annex B) and would vary with frequency. With few exceptions, these standard deviations would not exceed thoselisted in Table 2. The values given in Table 2 are standard deviations of reproducibility, sR, as defined inISO 7574-1. The values of Table 2 take into account the cumulative effects of measurement uncertainty in applyingthe procedures of this International Standard, but exclude variations in the sound power output caused by changesin operating conditions (e.g. rotational speed, line voltage) or mounting conditions.The measurement uncertainty depends on the standard deviation of reproducibility tabulated in Table 2 and on thedegree of confidence that is desired. As examples, for a normal distribution of sound power levels, there is a 90 %confidence that the true value of the sound power level of a source lies within the range ± 1,645 sR of the measuredvalue and a 95 % confidence that it lies within the range ± 1,96 sR of the measured value. For further examples,reference should be made to ISO 7574-4 and ISO 9296.NOTE 1The relationship between the standard deviation of reproducibility and the confidence level given in the ISO 7574 seriesand ISO 9296 is valid for standard deviations which are less than or equal to 2 dB. For larger standard deviations the confidencelevel associated with a given range will be lower. In general, however, the true value can be expected to fall within the range ± 3 sRof the measured value.NOTE 2The largest sources of uncertainty, other than possible deviations from the theoretical model (direct method) and errorsin the calibration of the reference sound source (comparison method) in the test methods specified in this International Standardare associated with inadequate sampling of the sound field and with variations in the acoustic coupling from the noise source to thesound field (for different test rooms and for different positions within a test room). In any laboratory, it may be possible to reducemeasurement uncertainty by one or more of the following procedures:a) use of multiple source locations;b) improvement of spatial sampling of the sound field by increasing the number of microphone positions or the length of themicrophone traverse;c) addition of low-frequency sound absorbers to improve modal overlap;d) use of moving diffuser elements.SIST EN ISO 3741:2009

© ISOISO 3741:1999(E)5Table 2 — Estimated upper values of the standard deviations of reproducibility of sound power levelsdetermined in accordance with this International StandardBand widthMidband frequenciesHzUpper values of standarddeviation of reproducibilitydBOne-third-octave100a2004006 300totototo160
3155 00010 0003,02,01,53,0Octave
125a250500 to 4 000
8 0002,51,51,02,0A-weighted per annex E0,5ba Recommendations for frequencies below 100 Hz are given in annex C.b Applicable to a source which emits noise with a relatively "flat" spectrum in the frequency range 100 Hz to
10 000 Hz.In addition, a large reverberation room may be used to reduce uncertainties at low frequencies although the precision of high-frequency sound power level determinations may be degraded. Conversely, a small room may lead to reduced high-frequencyuncertainties but increased low-frequency uncertainties. Thus, if improved precision is needed, and if two reverberation rooms areavailable, it may be desirable to carry out the low-frequency sound power level determinations in the larger room and high-frequency determinations in the smaller room.NOTE 3If several laboratories use similar facilities and instrumentation, the results of sound power determinations on a givensource in those laboratories may be in better agreement than would be inferred by the standard deviations of Table 2.NOTE 4For a particular family of sound sources, of similar size with similar sound power spectra and similar operatingconditions, the standard deviations of reproducibility may be smaller than the values given in Table 2. Hence, a noise test code fora particular type of machinery or equipment making reference to this International Standard may state standard deviations smallerthan those listed in Table
2, only if substantiation is available from the results of suitable interlaboratory tests.NOTE 5The standard deviations of reproducibility, as tabulated in Table 2, include the uncertainty associated with repeatedmeasurements on the same noise source under the same conditions (for standard deviation of repeatability, see ISO 7574-1). Thisuncertainty is usually much smaller than the uncertainty associated with interlaboratory variability. However, if it is difficult tomaintain stable operating or mounting conditions for a particular source, the standard deviation of repeatability may not be smallcompared with the values given in Table 2. In such cases, the fact that it was difficult to obtain repeatable sound power level dataon the source should be recorded and stated in the test report.NOTE 6The procedures of this International Standard and the standard deviations given in Table 2 are applicable tomeasurements on an individual machine. Characterization of the sound power levels of batches of machines of the same family ortype involves the use of random sampling techniques in which confidence intervals are specified, and the results are expressed interms of statistical upper limits. In applying these techniques, the total standard deviation has to be known or estimated, includingthe standard deviation of production, as defined in ISO 7574-1, which is a measure of the variation in sound power output betweenindividual machines within the batch. Statistical methods for the characterization of batches of machines are described inISO 7574-4.SIST EN ISO 3741:2009

ISO 3741:1999(E)© ISO65 Acoustic environment5.1 GeneralGuidelines for the design of reverberation rooms to be used for determining sound power in accordance with thisInternational Standard are given in annex D. The test room shall be large enough and have a low enough total soundabsorption to provide an adequate reverberant sound field for all frequency bands within the frequency range of interest(see annex D).5.2 Volume and shape of test roomThe minimum volume of the test room shall be as specified in Table 3. For reverberation rooms with volumes less thanthe values shown in Table 3 for the frequency range of interest, or with a volume exceeding 300 m3, the adequacy ofthe room for broadband measurements shall be demonstrated using the procedure of annex E.Table 3 — Minimum volume of the test room as a function of the lowest frequency band of interestLowest one-third-octave-band frequency ofinterestHzMinimum volume of the test roomm3100200125150160100200 and higher705.3 Requirements for absorption of test roomThe absorption of the test room primarily affects the minimum distance to be maintained between the noise source andthe microphone positions. It also influences the sound radiation of the source and the frequency responsecharacteristics of the test space. For these reasons the absorption of the test room shall be neither too large norextremely small (see annex D).The surfaces of the test room closest to the source shall be designed to be reflective with an absorption coefficient lessthan 0,06. The remaining surfaces shall have absorptive properties such that the reverberation time, Trev (formeasurement see 8.4.1) in each one-third-octave band, without the source under test in place, is numerically greaterthan the ratio of V and S:Trev > V/S(2)whereTrevis the reverberation time expressed in seconds (s);Vis the volume of the reverberation room expressed in cubic metres (m3);Sis the total surface area of the test room expressed in square metres (m2).If the requirements for the reverberation time given by equation (2) are not met, the adequacy of the room for broadband measurements shall be established by the procedure described in annex E.5.4 Requirements for background noise levelAveraged over the microphone positions or traverse, the level of background noise in all bands within the frequencyrange of interest shall be at least 10 dB below the sound pressure level due to the source under test.SIST EN ISO 3741:2009

© ISOISO 3741:1999(E)7For low noise equipment, DL > 10 dB may not be achievable in all bands. Any bands in which the A-weighted (seeannex F) sound power level of the source under test is more than 15 dB below the highest A-weighted band soundpower level may be excluded from the frequency range of interest.If the comparison method of 8.4.2 is used, the background noise shall be at least 15 dB below the sound pressure leveldue to the reference sound source in all bands within the frequency range of interest.5.5 Requirements for temperature, humidity and pressureIn the region where the microphones are located, the variations of temperature and relative humidity shall be within thelimits shown in Table 4.Measurements of atmospheric pressure shall be made to within ± 1,5 kPa.The limits of Table 4 are generally sufficient (see reference [9]). However, other temperature and humidity conditionsmay be specified in noise test codes for specific equipment types, especially if the operation of the equipmentconcerned depends on ambient conditions. In such cases, those conditions, together with the measurement procedure,shall be applied.Table 4 — Allowable limits in the variation of temperature and relative humidity during measurements in thereverberation roomRanges of
temperatureq°CRanges of relative humidity%< 30 %30 % to 50 %> 50 %Allowable limits for temperature and relative humidity– 5 < q < 10± 1 °C± 1 °C± 5 %± 3 °C10 < q < 20± 3 %± 3 °C± 5 %± 10 %20 < q < 50± 2 °C± 3 %± 5 °C± 5 %± 5 °C± 10 %6 Instrumentation6.1 GeneralThe instrumentation system, including the microphone, shall fulfil the requirements for a type 1 instrument specified inIEC 61672. The filters used shall meet the requirements of a class 1 instrument specified in IEC 61260. Themicrophones shall be calibrated for random incidence as specified in IEC 61183.6.2 CalibrationBefore each series of measurements, a sound calibrator with an accuracy of class 1 as specified in IEC 60942 shall beapplied to the microphone to verify the calibration of the entire measuring system at one or more frequencies in thefrequency range of interest.The calibrator shall be calibrated at least once a year and the compliance of the instrumentation system with therequirements of IEC 61672 shall be verified at least every 2 years in a laboratory making calibrations traceable toappropriate standards.The date of the last verification of the compliance with the relevant IEC standards shall be recorded.SIST EN ISO 3741:2009

ISO 3741:1999(E)© ISO87 Installation and operation of source under test7.1 GeneralThe manner in which the source under test is installed and operated may have a significant influence on the soundpower emitted by the source. This clause specifies conditions that minimize variations in the sound power output due tothe installation and operating conditions of the source under test. The instructions of a noise test code, if any exists,shall be followed in so far as installation and operation of the source under test are concerned.Particularly for large sources, it is necessary to make a decision as to which components, sub-assemblies, auxiliaryequipment, power sources, etc. are to be considered as part of the source under test.7.2 Source locationThe sound source under test shall be placed in the reverberation room in one or more locations relative to theboundary surfaces that are typical of normal installation. If a particular position is not otherwise specified, the sourceshall be placed on the floor at least 1,5 m from any wall of the room. If two or more source positions are necessaryaccording to 8.1.7, the distance between different positions shall be equal to or larger than the half wavelength ofsound corresponding to the lowest midband frequency of measurement. In the case of a reverberation room having arectangular floor shape, the sound source should be placed asymmetrically on the floor.7.3 Source mounting7.3.1 GeneralIn many cases, the sound power emitted will depend upon the support or mounting conditions of the source under test.Whenever a specified condition of mounting exists for the equipment under test, that condition shall be used, orsimulated, if feasible.If a specified condition of mounting does not exist or cannot be utilized for the test, care shall be taken to avoidchanges in the sound output of the source caused by the mounting system employed for the test. Steps shall be takento reduce any sound radiation from the structure on which the equipment may be mounted.NOTE 1Many small sound sources, although themselves poor radiators of low-frequency sound, may, as a result of the methodof mounting, radiate more low-frequency sound when their vibration energy is transmitted to surfaces large enough to be efficientradiators. In such cases, if practicable, resilient mounting should be interposed between the device to be measured and thesupporting surfaces so that the transmissions of vibration to the support and the reaction on the source are both reduced to anegligible amount. In this case, the mounting base should have a sufficiently high mechanical impedance to prevent it fromvibrating and radiating sound excessively. Such resilient mounts should not be used if the device under test is not resilientlymounted in a typical field installation.NOTE 2Coupling conditions (e.g. between prime movers and driven machines) may exert a considerable influence on thesound radiation of the source under test.7.3.2 Hand-held machinery and equipmentSuch equipment and machinery shall be suspended or guided by hand, so that no structure-borne sound is transmittedvia any attachment that does not belong to the machine under test. If the source under test requires a support for itsoperation, the support structure shall be small, considered to be a part of the source under test, and described in themachine noise test code.7.3.3 Base-mounted and wall-mounted machinery and equipmentSuch machinery and equipment shall be placed on a reflecting (acoustically hard) plane (floor, wall). Base-mountedmachines intended exclusively for mounting in front of a wall shall be installed on an acoustically hard floor surface infront of an acoustically hard wall. Table-top equipment shall be placed on the floor at least 1,5 m from any wall of theroom, unless a table or stand is required for operation according to the test code for the equipment under test. Suchequipment shall be placed in the centre of the top surface of the test table.SIST EN ISO 3741:2009

© ISOISO 3741:1999(E)97.4 Auxiliary equipmentCare shall be taken to ensure that any electrical conduits, piping, or air ducts connected to the source under test do notradiate significant amounts of sound energy into the test environment.If practicable, all auxiliary equipment necessary for the operation of the source under test and which is not a part of thesource (see 7.1) shall be located outside the test environment. Otherwise, the auxiliary equipment shall be includedand its operating conditions described in the test report.7.5 Operation of source during testDuring the measurements, the operating conditions specified in the relevant noise test code, if one exists for theparticular type of machinery or equipment under test, shall be used. If there is no test code, the source shall beoperated, if possible, in a manner which is typical of normal use. In such cases, one or more of the following operatingconditions shall be selected:a) device under specified load and operating conditions;b) device under full load (if different from above);c) device under no load (idling);d) device under operating conditions corresponding to maximum sound generation representative of normal use;e) device with simulated load operating under carefully defined conditions.The test conditions shall be selected beforehand and shall be held constant during the test. The source shall be
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