SIST EN 23742:1997
(Main)Acoustics - Determination of sound power levels of noise sources - Precision method for discrete-frequency and narrow-band sources in reverberation rooms (ISO 3742:1988)
Acoustics - Determination of sound power levels of noise sources - Precision method for discrete-frequency and narrow-band sources in reverberation rooms (ISO 3742:1988)
This International Standard specifies the special requirements necessary for accurate determinations of the sound power when discrete frenquencies or narrow bands of noise are radiated by a source.
Akustik - Bestimmung des Schalleistungspegels von Geräuschquellen - Methoden der Genauigkeitsklasse 1 im Hallraum für Quellen mit Reinton- und Schmalbandanteilen (ISO 3742:1988)
Acoustique - Détermination des niveaux de puissance acoustique émis par les sources de bruit - Méthodes de laboratoire en salles réverbérantes pour les sources émettant des bruits a bande étroite (ISO 3742:1988)
Akustika - Ugotavljanje ravni zvočnih moči virov hrupa - Precizijska metoda za vire hrupa s črtastimi in ozkopasovnimi spektri v odmevnicah (ISO 3742:1988)
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Akustik - Bestimmung des Schalleistungspegels von Geräuschquellen - Methoden der Genauigkeitsklasse 1 im Hallraum für Quellen mit Reinton- und Schmalbandanteilen (ISO 3742:1988)Acoustique - Détermination des niveaux de puissance acoustique émis par les sources de bruit - Méthodes de laboratoire en salles réverbérantes pour les sources émettant des bruits a bande étroite (ISO 3742:1988)Acoustics - Determination of sound power levels of noise sources - Precision method for discrete-frequency and narrow-band sources in reverberation rooms (ISO 3742:1988)17.140.01Acoustic measurements and noise abatement in generalICS:Ta slovenski standard je istoveten z:EN 23742:1991SIST EN 23742:1997en01-april-1997SIST EN 23742:1997SLOVENSKI
STANDARD
SIST EN 23742:1997
SIST EN 23742:1997
SIST EN 23742:1997
INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOAHAR OPTAHM3A~Mfl I-l0 CTAH,lJAPTM3AL/MM Acoustics - Determination of sound power levels of noise sources - Precision methods for discrete- frequency and narrow-band sources in reverberation rooms Acoustique - bruit D&termination des niveaux de puissance acoustique e’mis par les sources de - M&bodes de laboratoire en salles r&verb&antes pour les sources kmettant des bruits ;i composantes tonales et 5 bande ktroite IS0 3742 Second edition 1988-12-01 Reference number IS0 3742 : 1988 (E) SIST EN 23742:1997
IS0 3742 : 1988 (E) 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 3742 was prepared by Technical Committee ISO/TC 43, A cous tics. This second edition cancels and replaces the first edition (IS0 3742 : 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 23742:1997
IS0 3742 : 1988 0 Contents - Page 0.1 Related International Standards . 0.2 Synopsis of IS0 3742 . 0.3 Introduction . 1 Scope and field of application . 2 References . 3 Determination of the significance of discrete-frequency components and narrow bands of noise . 4 Number of microphone positions and source locations. . Annex - Alternative qualification procedure for the measurement of discrete- frequencycomponents . . . . III SIST EN 23742:1997
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INTERNATIONAL STANDARD- ’ IS0 3742 : 1988 (E) Acoustics - Determination of sound power levels of noise sources - Precision methods for discrete- frequency and narrow-band sources in reverberation rooms . 0.1 Related International Standards 0.2.3 Quantities to be measured 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. 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 Synopsis of IS0 3742 0.2.1 Applicability 0.2.1 .I Test environment Specified reverberation room which is to be qualified in ac- cordance with a test procedure given in clause 3 of the main part of this International Standard and in the annex; additional test room requirements are given in IS0 3741. 0.2.1.2 Size of noise source Volume of the source preferably less than 1 % of volume of the test room. 0.2.1.3 Character of noise radiated by the source Steady (as defined in IS0 22041, discrete-frequency and/or narrow-band. 0.2.2 Precision Measurements made in conformity with this International Stan- dard will, with very few exceptions, result in standard devia- tions equal to or less than 1,5 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). Sound pressure levels in frequency bands on a specified path or at several discrete microphone positions. 0.2.4 Quantities to be determined Sound pressure levels in frequency bands; A-weighted sound power levels (optional). 0.2.5 Quantities which cannot be obtained Directivity characteristics of the source; temporal pattern of radiated noise for sources emitting non-steady noise. 0.3 Introduction This International Standard specifies in detail two laboratory methods for determining the sound power of small sources using a reverberation test room. The procedure specified in IS0 3741 applies to sources which produce steady, broad-band noise. This International Standard gives additional precautions that have to be observed if discrete frequencies or narrow bands of noise are present in the spec- trum of the noise radiated by the sound source. If a source emits narrow-band or discrete-frequency sound, a precise determination of the radiated sound power requires greater effort. The accuracy objectives for characterizing broad-band sound sources (table 2 of IS0 3741) cannot be achieved with a microphone traverse of 3 m (or with only three microphones in a fixed array) and with only one source location in the reverberation room. The reasons are as follows: a) the space/time-averaged sound pressure along the microphone path (see 7.1 in IS0 3741), or as determined with an array of three microphones, is not always a good estimate of the space/time-averaged mean-square pressure throughout the room; b) the sound power radiated by the source is more strongly influenced by the normal modes of the room and by the position of the source within the room. If narrow bands of noise or discrete frequencies are emitted by a source, a determination of its sound power level in a reverberation room requires the use of a greater number of source locations and microphone positions (or a greater path length for a moving microphone). The required numbers of locations and positions depend on the desired accuracy, the spectrum of the radiated noise, and the properties of the test SIST EN 23742:1997
SIST EN 23742:1997
IS0 3742 : 1988 (El room. These numbers can usually be reduced if one or more diffusers are rotating in the test room during the measurements. Guidelines for the design of suitable rotating diffusers are given in annex E in IS0 3741. The use of rotating diffusers considerably reduces the effort required to make measurements on sources that emit discrete-frequency com- ponents. 1 Scope and field.of application 1.1 General This International Standard specifies the special requirements that are necessary for accurate determinations of the sound power when discrete frequencies or narrow bands of noise are radiated by a source. 1.2 Field of application This International Standard applies to sources which radiate discrete frequencies or narrow bands of noise. The spectrum of the source can include broad-band components upon which the prominent discrete frequencies or narrow bands of noise are superimposed. These methods are often complex and time- consuming for measurements on sources which primarily radiate discrete frequencies below 200 Hz. For such sources, measurements in a free field as described in IS0 3745 are likely to be more appropriate. 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. NOTE - A more detailed description of the meaning of the standard deviations in table 2 is given in 1.3 in IS0 3741. Table 2 - Uncertainty in determining sound power levels of discrete-frequency noise sources in reverberation rooms Octave-band One-third octave-band Standard centre frequencies centre frequencies deviation Hz Hz dB 125 1OOto 160 3 250 200 to 315 2 500t04000 400 to 5 000 115 8000 6300to 10000 3 1.4 Principal requirements To meet the accuracy objectives of table 2, additional microphone positions and source locations are usually required as determined in clause 4. First, however, a determination may be made concerning the presence and significance of discrete- frequency components or narrow bands of noise in the spec- trum of the sound emitted by the source (see clause 3). Alternatively, it may be assumed that the spectrum of the sound emitted by the machine or equipment under test does - contain significant discrete-frequency components. In this case either the precautions described in clause 4 should be followed or the test set-up should be qualified as described in the annex. If the room qualifies according to the requirements of the annex, additional source locations are not required. Qualifica- tion of the test set-up according to the annex is usually possible only if a rotating diffuser and additional microphone positions are used in the room. 1.5 Other requirements All other requirements for determining the sound power emit- ted by discrete-frequency and narrow-band sound sources are the same as for broad-band sources described in IS0 3741. 2 References IS0 266, Acoustics - Preferred frequencies for measure- men ts. IS0 354, Acoustics - Measurement of sound absorption in a reverberation room. IS0 1680, Acoustics - Test code for the measurement of air- borne noise emitted by rotating electrical machinery - Part 7: Engineering method for free-field conditions over a reflecting plane. Part 2: Survey method. IS0 2204, Acoustics - Guide to International Standards on the measurement of airborne acoustical noise and evaluation of its effects on human beings. IS0 3740, 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 3741, Acoustics - Determination of sound power levels of noise sources - Precision methods for broad-band sources in reverberation rooms. 1) IS0 3743, Acoustics - Determination of sound power levels of noise sources - Engineering methods for special reverberation test rooms. 1) Cross-references to specific clauses, sub-clauses, etc. in IS0 3741 apply to the second edition published in 1988. 3 SIST EN 23742:1997
IS0 3742 : 1988 (El IS0 3744, Acoustics - Determination of sound power levels of noise sources - Engineering methods for free-field conditions over 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. IS0 3747, Acoustics - Determination of sound power levels of noise sources - Survey method using a reference sound source. IEC Publication 50(08), International Hectrotechnical Vocabu- lary - Electra-acoustics. IEC Publication 225, Octave, half-octave and third-octave band filters intended for the analysis of sound and vibrations. IEC Publication 651, Sound level meters. 3 Determination of the significance of discrete-frequency components and narrow bands of noise 3.1 General If a discrete-frequency component is present in the spectrum of a source, the spatial variations in the sound pressure level usually exhibit maxima separated by minima having an average spacing of approximately 0,8 ;1, where A is the wavelength cor- responding to the frequency of the sound. 3.2 Qualitative procedure The presence of a significant discrete-frequency component can often be detected by a simple listening test or by narrow- band analysis (e.g. by means of a fast Fourier transform analyser). If such a component is audible or if narrow-band analysis clearly indicates the presence of a discrete-frequency component, the measurements described in 3.3 may be omit- ted. In this case, either the provisions of the bottom row of table 3 shall be applied or, alternatively, the test set-up shall be qualified as described in the annex. Discrete-frequency components may be present in the spec- trum even if these components are not audible or if narrow- band analysis does not clearly indicate the presence of a discrete-frequency component. A conclusion that no discrete- frequency components are present can only be reached by per- forming the test described in 3.3. 3.3 Estimate of standard deviation 3.3.1 Obtain an estimate of the standard deviation of the sound pressure levels produced by the source under test in the room by following the procedure described in 3.3.2 and 3.3.3. 3.3.2 Select an array of six fixed microphones (or six microphone positions) s
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