EN 23741:1991

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Bestimmung des Schalleistungspegels von Geräuschquellen - Rahmenmeßverfahren der Genauigkeitsklasse 1 für Breitbandspektren in Hallräumen (ISO 3741:1988)Acoustique - Détermination des niveaux de puissance acoustique émis par les sources de bruit - Méthodes de laboratoire en salles réverbérantes pour les sources a large bande (ISO 3741:1988)Acoustics - Determination of sound power levels of noise sources - Precision methods for broad-band sources in reverberation rooms (ISO 3741:1988)17.140.01Acoustic measurements and noise abatement in generalICS:Ta slovenski standard je istoveten z:EN 23741:1991SIST EN 23741:1997en01-april-1997SIST EN 23741:1997SLOVENSKI
STANDARD
INTERNATIONAL STANDARD 3741 INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXP,YHAPO)JHAfl OPI-AHM3A~Mfl IlO CTAH~APTM3A~MM Acoustics - Determination of sound power levels of noise sources - Precision methods for broad-band sources in reverberation rooms Acoustique - Dhtermination des niveaux de puissance acoustique kmis par les sources de bruit - Mthodes de laboratoire en sales r&verb&antes pour les sources ;i large bande IS0 Second edition 1988-12-01 ~ Reference number I IS0 3741 : 1988 (E) SIST EN 23741:1997

Iso 3741 : 1988 (El Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 % approval by the member bodies voting. International Standard IS0 3741 was prepared by Technical Committee ISO/TC 43, A cous tics. This second edition cancels and replaces the first edition (IS0 3741 : 19751, of which it constitutes a minor revision. Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. 0 International Organization for Standardization, 1988 Printed in Switzerland ii SIST EN 23741:1997

IS03741 :1988 (El Contents Page 0.1 Related International Standards . 0.2 Synopsis of IS0 3741 . 0.3 Introduction . 1 Scope and field of application . 2 References . 3 Definitions. . 4 Acoustical environment . 5 Instrumentation. . 6 Installation and operation of source . 7 Measurement of mean-square sound pressure . 8 Calculation of sound power level . 9 Information to be recorded . 10 Information to be reported. . Annexes Test room qualification procedure for the measurement of broad-band sound Characteristics and calibration of reference sound source . . . . . . . . . . . . . . . . . Procedures for calculating A-weighted sound power level from octave or one-third octave-band power levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Guidelines for the design of reverberation rooms. . . . . . . . . . . . . . . . . . . . . . . . . Guidelines for the design of rotating diffusers . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1 3 3 4 4 5 6 7 8 9 10 11 12 13 14 16 . . . III SIST EN 23741:1997

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INTERNATIONAL STANDARD IS0 3741 : 1988 (E) Acoustics - Determination of sound power levels of noise sources - Precision methods for broad-band sources in reverberation rooms 0.1 Related International Standards 0.2.3 Quantities to be measured Sound pressure levels in frequency bands on a specified path or at several discrete microphone positions. This International Standard is one of a series specifying various methods for determining the sound power levels of machines and equipment. These basic documents specify only the acoustical requirements for measurements appropriate for dif- ferent test environments as shown in table 1. 0.2.4 Quantities to be determined Sound pressure levels power levels (optional) in frequency bands; A-weighted When applying these basic documents, it is necessary to decide which one is most appropriate for the conditions and purposes of the test. The operating and mounting conditions of the machine or equipment to be tested are given as general principles stated in each of the basic documents. Guidelines for making these decisions are provided in IS0 3740. If no noise test code is specified for a particular machine, the mounting and operating conditions shall be fully described in the test report. 0.2.5 Quantities which cannot be obtained Directivity cha racteristics of the source; temporal pattern of radiated noise for sources emittin g non-steady noise. 0.3 Introduction This International Standard specifies in detail two laboratory methods for determining the sound power radiated by a device, machine, component, or sub-assembly as a function of fre- quency, using a reverberation test room having specified acoustical characteristics. While other methods could be used to measure the noise emitted by machinery and equipment, the methods specified in this International Standard are particularly advantageous for rating the sound output of sources which produce steady noise and for which directivity information is not required. If the source emits non-steady noise or if direc- tivity information is desired, one of the other methods specified in IS0 3740 shall be selected. 0.2 Synopsis of IS0 3741 0.2.1 Applicability 0.2.1 .I Test environment Reverberation room with specified volume and absorption or qualified in accordance with a test procedure given in annex A. Guidelines for the design of reverberation rooms are given in annex D. The minimum test room volume depends on the lowest frequency band of interest ( I’min = 200 m3 corresponds to 100 Hz for the lowest allowable one-third octave band). Among the reasons for obtaining data national Standard are the following: as described in this Inter- a) rating apparatus according to its sound power output; 0.2.1.2 Size of noise source b) establishing sound control measures; Volume of the source preferably less than 1 % of volume of the test room. c) predicting the sound pressure levels produced by a device or machine in a given enclosure or environment. In this International Standard, the computation of sound power from sound pressure measurements is based on the premise that the mean-square sound pressure averaged in space and time, 9, is 0.2.1.3 Character of noise radiated by the source Steady (as defined in IS0 2204), broad-band. 0.2.2 Precision a) directly source, proportional to the sound power output of the Measurements made in conformity with this International Stan- dard will, with very few exceptions, result in standard devia- tions equal to or less than I,5 dB from 400 to 5 000 Hz, 2 dB from 200 to 315 Hz, increasing to 3 dB below 200 Hz and above 5 000 Hz (see 1.3 and table 2). b) inversely Prop0 of the room, and to the equivalent bsorption area c) otherwise depends only on density and velocity of sound. the physical constants of air SIST EN 23741:1997

Table 1 - International Standards specifying various methods for determining the sound power levels of machines and equipment m Inter- national Standard No.” Classification of Test Volume method** environment of source Character of noise Sound power levels Optional information obtainable available 3741 3742 3743 Precision (grade I) Engineering (grade 2) Reverberation room Steady, broad-band meeting specified In one-third octave or Steady, discrete-frequency A-weighted sound power requirements octave bands level Preferably less than 1 % or narrow-band of test room volume Special reverberation test Steady, broad-band, narrow-band, or discrete- A-weighted and in octave Other weighted sound room frequency bands power levels 3744 Engineering (grade 2) 3745 Precision (grade 1) 3746 Survey (grade 3) Outdoors or in large room Anechoic or semi- anechoic room No special test environment Greatest dimension less than 15 m Preferably less than 0,5 % of test room volume No restrictions : limited only by available test environment AflY Any Any A-weighted and in one- third octave or octave bands A-weighted Directivity information and sound pressure levels as a function of time; other weighted sound power levels Sound pressure levels as a function of time; other weighted sound power levels 3747 Survey (grade 3) No special test environ- ment; source under test not movable No restrictions Steady, broad-band, narrow-band, or discrete- frequency A-weighted Sound power levels in octave bands * ** See clause 2. See IS0 2204. SIST EN 23741:1997

Is0 3741 : 1988 E) 1 Scope and field of application 1.1 General This International Standard specifies a direct method and a comparison method for determining the sound power level pro- duced by a source. It specifies test room requirements, source location and operating conditions, instrumentation and tech- niques for obtaining an estimate of mean-square sound pressure from which the sound power level of the source in oc- tave or one-third octave bands is calculated. 1.2 Field of application 1.2.1 Types of noise This International Standard applies primarily to sources which produce steady broad-band noise as defined in IS0 2264. NOTE - If discrete frequencies or narrow bands of noise are present in the spectrum of a source, the mean-square sound pressure tends to be highly dependent on the positions of the source and the microphone within the room. The average value over a limited microphone path or array may differ significantly from the value averaged over all points in the room. Procedures for determining the sound power radiated by a source when discrete tones are present in the spectrum are described in IS0 3742. 1.2.2 Size of source This International Standard applies only to small noise sources, i.e. sources with volumes which are preferably not greater than 1 % of the volume of the reverberation room used for the test. 1.3 Measurement uncertainty Measurements made in conformity with this International Stan- dard tend to result in standard deviations which are equal to or less than those given in table 2. The standard deviations given in table 2 take into account the cumulative effects of all causes of measurement uncertainty. Table 2 - Uncertainty i n determining sound power levels of broad-band noise sources in reverberation rooms Hz Hz I dB 125 loo to 160 3 250 200 to 315 2 500 to 4 000 400 to 5 000 L5 8000 6300to 10000 3 NOTES 1 The standard deviations given in table 2 are measures of the uncer- tainties associated with the test methods defined in this International Standard. If a stable source of steady broad-band noise were transported to each of a large number of laboratories, and if, at each laboratory, the sound power level of that source were measured in accordance with the provisions of this international Standard, the stan- dard deviation, as a function of frequency, of these many sound power level calculations could be calculated. If a similar inter-laboratory series of measurements were carried out on each of a large number of different specimens of the same type of stable sources of steady broad- band, it would be possible to calculate overall standard deviations that would correspond to the random selection of a noise source and the random selection of a laboratory. It is these standard deviations which have been estimated and given in table 2. 2 If two laboratories use similar facilities and instrumentation, the results of sound power level determinations on a given source in these laboratories may be in better agreement than would be inferred from the standard deviations in table 2. 3 For a particular family of noise sources, of similar size and with similar sound spectra, the standard deviations of sound power level determinations in different laboratories may be significantly smaller than the values given in table 2. Thus, a test code for a particular type of machinery may state standard deviations smaller than those given in table 2 if the results of inter-laboratory tests are available to substan- tiate the smaller values. 4 The largest sources of uncertainty, other than possible deviations from the theoretical model (direct method) and errors in the calibration of the reference sound source (comparison method), in the test methods specified in this International Standard are associated with inadequate sampling of the sound field and with variations in the acoustic coupling from the noise source to the sound field (for different test rooms and for different positions within a test room). In any laboratory, it may be possible to reduce measurement uncertainty by one or more of the following procedures: al b) use of multiple source locations; improvement of spatial sampling of the sound field; c) addition overlap ; of low-frequency sound absorbers to improve modal d) use of moving diffuser elements. In addition, a large reverberation room may be used to reduce uncer- tainties 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-frequency uncertainties but in- creased low-frequency uncertainties. Thus, if improved precision is needed, and if two reverberation rooms are available, it may be desirable to carry out the low-frequency sound power level determina- tions in the larger room and high-frequency determinations in the smaller room. 2 References IS0 266, Acoustics - Preferred frequencies for measure- men ts. IS0 354, Acoustics - Measurement of sound absorption in a reverberation room. IS0 2204, Acoustics - Guide to International Standards on the measurement of airborne acoustical noise and evaluation of its effects on human beings. IS0 3746, Acoustics - Determination of sound power levels of noise sources - Guidelines for the use of basic standards and for the preparation of noise test codes. IS0 3742, Acoustics - Determination of sound power levels of noise sources - Precision methods for discrete- frequent y and narrow-band sources in reverberation rooms. IS0 3743, Acoustics - Determination of sound power levels of noise sources - Engineering methods for special reverberation test rooms. 3 SIST EN 23741:1997

IS0 3741 : 1988 (E) 3.5 sound power level, L *, in decibels: Ten times the logarithm to the base 10 of the ratio of a given sound power to the reference sound power. The width of a restricted frequency band shall be indicated; for example, octave-band power level, one-third octave-band power level, etc. The reference sound power is 1 pW (= lo-12 W). IS0 3744, Acoustics - Determination of sound power levels of noise sources - Engineering methods for free-field conditions 0 ver a reflecting plane. IS0 3745, Acoustics - Determination of sound power levels of ’ noise sources - Precision methods for anechoic and semi- anechoic rooms. IS0 3746, Acoustics - Determination of sound power levels of noise sources - Survey method. 3.6 frequency range of interest: For general purposes, the frequency range of interest includes the octave bands with centre frequencies between 125 and 8 000 Hz or the one-third octave bands with centre frequencies between 100 Hz and 10 000 Hz. Any band may be excluded in which the level is more than 40 dB below the highest band pressure level. IS0 3747, Acoustics - Determination of sound power levels of noise sources - Survey method using a reference sound source. IS0 6826, Acoustics - Determination of sound power levels of noise sources - Characterization and calibration of reference sound sources. 1) For special purposes, other frequency ranges of interest may be defined depending upon the characteristics of the noise source, provided that the test room is satisfactory for use over the ap- propriate frequency range. IEC Pu blication 50(08), International lary - Elec tro-acoustics. Electra technical Vocabu- IEC Publication 225, Octave, half-octave and third-octave band filters intended for the analysis of sound and vibrations. 3.7 direct method: That method in which the sound power level is calculated from the measured sound pressure levels pro- duced by the source in a reverberation room and from the . volume and reverberation time of the room. IEC Publication 651, Sound level meters. 3.8 comparison method: That method in which the sound power level is calculated by comparing the measured sound pressure levels produced by the source in a reverberation room with the sound pressure levels produced in the same room by a reference sound source (RSS) of known sound power output. 3 Definitions For the purposes definitions apply. of this International Standard, the following 3.1 reverberation room : A test room quirements of this International Standard. meeting the re- 4 Acoustical environment 3.2 reverberant sound field: That portion of the sound field in the test room over which the influence of sound re- ceived directly from the source is negligible. 4.1 General Guidelines for the design of reverberation rooms to be used for determining sound power in accordance with this International Standard are given in annex D. 33 . mean-square sound pressure, 3: The sound pressure averaged in space and time on a mean-square basis. In prac- tice, space/time-averaging over a finite path length or a fixed number of microphone positions as well as deviations from the ideally reverberant sound field lead only to an estimate of g, called p& in this International Standard. The test room shall be large enough and have low enough total sound absorption to provide an adequate reverberant sound field for all frequency bands within the frequency range of interest (see annex D). 4.2 Volume of test room 3.4 sound pressure level, L,, in decibels: Ten times the logarithm to the base 10 of the ratio of the mean-square sound pressure of a sound to the square of the reference sound pressure. The width of a restricted frequency band shall be in- dicated : for example, octave-band pressure level, one-third octave-band pressure level, etc. The reference sound pressure is 20 PPa. The minimum volume of the test room shall be as specified in table 3. If frequencies above 3 000 Hz are included in the fre- quency range of interest, the volume of the test room shall not exceed 300 m3. The ratio of the maximum dimension of the test room to its minimum dimension shall not exceed 3: 1. 1) At present at the stage of draft. 4 SIST EN 23741:1997

IS0 3741 : 1988 (E) Table 3 - Minimum volume of the test room as a 4.4 Criterion for adequacy of test room function of the lowest frequency band of interest . Lowest frequency band Minimum volume If the test room does not have an absorption as required by 4.3, of the test room the adequacy of the room shall be established by the procedure of interest m3 described in annex A. 125 Hz octave or 100 Hz one-third octave 200 4.5 Criterion for background noise level 125 Hz one-third octave 160 Hz one-third octave 250 Hz octave or 200 Hz one-third octave and higher 150 100 70 The background noise level including any noise due to motion of the microphone shall be at least 6 dB, and preferably more than 12 dB, below the sound pressure level to be measured in each frequency band within the frequency range of interest. 4.6 Criteria for temperature and humidity 4.3 Criterion for absorption of test room The air absorption in the reverberation room varies with temperature and humidity, particularly at frequencies above 1 000 Hz. The temperature 6, in degrees Celsius, and the relative humidity (r.h.1, expressed as a percentage, shall be controlled during the sound pressure level measurements. The product 4.3.1 General The equivalent absorption area of the test room primarily af- fects the minimum distance to be maintained between the noise source and the microphone positions. It also influences the sound radiation of the source. For these reasons, the ab- sorption area shall be neither too large nor extremely small (see annex D). r.h. x .(0 + 5 “C) shall not differ by more than + 10 % from the value of the pro- duct which prevailed during the measurements of clause 7. The reverberation time, in seconds, shall be greater than v/s where 5 Instrumentation V is the room volume, in cubic metres; 5.1 General S is the total surface area of the test room, in square metres. Instrumentation shall be designed to determine the mean- square value of the sound pressure in octave and/or one-third octave bands averaged over time and space. 4.3.2 Minimum distance The minimum distance between the noise source and the nearest microphone position, dmin, shall not be less than Several alternative procedures for space-averaging are given in clause 7; those involving automatic sampling require in- strumentation with longer integration (averaging) times. d min = C&IT There are two alternative approaches to time-averaging the output voltage of the octave (or one-thi rd octave) band filters: where Cl = 0,08; a) Integration of the squared voltage over interval, rn, by analogue or digital means. a fixed time V is the room volume, in cubic metres; b) Continuous analogue averaging of the squared voltage, using an RC-smoothing network with a time constant r,& This provides only an approximation of the true time average, and it places restrictions on the “settling” time and observation time (see 7.2.2). T is the reverberation time, in seconds. NOTE - In order to minimize the near-field recommended that the value of Cl be 0,16. bias error, it is strongly 4.3.3 Surface treatment 5.2 Indicating device The surfaces of the test room closest to the source shall be designed to be reflective with an absorption coefficient less than 0,06. Except for these surfaces, none of the other surfaces shall have absorptive properties significantly deviating from each other. These other surfaces shall be designed so that for each one-third octave band within the frequency range of interest, the mean value of the absorption coefficient of each surface is between 0,5 and 1,5 times the mean value of the ab- sorption coefficients of all surfaces. 5.2.1 General An estimate of 3 is obtained by determining the mean-square pressure corresponding to the mean-square value of the voltage at the output of the filter set, e,(r). This mean-square pressure is denoted by pz,,, and is determined for a given microphone path traverse (or array) and time (see 7.2.1). SIST EN 23741:1997

Is0 3741 : 1988 (El 5.2.2 Integration over a fixed time interval Table 4 - Relative tolerances for the If this method is used (see 5.11, the normalized variance of the estimates of the level of the mean-square voltage shall be less than 0,25 dB for a steady sine-wave input over the frequency range of interest; the average value of a series of ten estimates of the level of the mean-square voltage shall not differ from the value obtained by continuous integration by more than + 0,25 dB. The integration time, rn [see 5.1 a)], shall be identical to the observation period used (for minimum values of observation periods, see 7.2.2; for relation between integrating time and microphone traversing or scanning period, if applicable, see 7.1.1). 5.2.3 Continuous averaging The time constant, rA [see 5.1 b)], shall be at least O,7 s and long enough to meet the criterion of 7.1 .l . 5.3 Microphone and its associated cable A condenser microphone, or the equivalent in accuracy, stab- ility and frequency response, shall be used. The microphone shall have a flat frequency response for randomly incident sound over the frequency range of interest. NOTES 1 This requirement is met by a microphone of a standardized sound level meter fulfilling at least the requirements for a type 1 instrument in accordance with IEC Publication 651 and calibrated for free-field measurements only if it has a linear random response. 2 If several microphones are used , it is desirable to avoi d the axis of each microphone being oriented in the same direction in space. The microphone and its asociated cable shall be chosen so that their sensitivity does not change by more than 0,5 dB in the temperature range encountered during the measurements. If the microphone is moved, care shall be exercised to avoid in- troducing acoustical or electrical noise (e.g. from gears, flexing cables, or sliding contacts) that could interfere with the measurements. 5.4 Freq system uency respo nse of the i mentation The frequency response of the instrumentation for randomly incident sound shall be determined in accordance with the procedure in IEC Publication 651 with the tolerances given in table 4. instrumentation system (adapted from IEC Publication 651) Frequency Hz 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1 600 2 000 2 500 3 150 4 000 5000 Tolerance limits dB l!I I,5 If: I,5 If: I,5 +1 +1 +1 +I +I +I +1 +1 +I +1 +I +I +I +I +I +I +I + I,5 -2 6 300 + I,5 -2 8 000 + I,5 -3 10 000 +2 -4 12 500 +3 -6 16 000 +3 -a3 20 000 +3 -a 5.6 Calibration During each series of measurements, a
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