EN 29295:1991

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Akustik - Messung von hochfrequentem Geräusch von Geräten der Büro- und Informationstechnik (ISO 9295:1988)Acoustique - Mesurage du bruit a haute fréquence émis par les matériels informatique et de bureau (ISO 9295:1988)Acoustics - Measurement of high-frequency noise emitted by computer and business equipment (ISO 9295:1988)35.020Informacijska tehnika in tehnologija na splošnoInformation technology (IT) in general17.140.20Emisija hrupa naprav in opremeNoise emitted by machines and equipmentICS:Ta slovenski standard je istoveten z:EN 29295:1991SIST EN 29295:1999en01-november-1999SIST EN 29295:1999SLOVENSKI
STANDARD
INTERNATIONAL STANDARD 9295 First edition 1988-1 l-15 Corrected and reprinted 1989-02-01 ~gf~~~ = 3 = ED = =uJid = L = = E = c ~~ INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOJJHAFI OPI-AHM3A~MR i-l0 CTAHfiAPTM3AuMM Acoustics - Measurement of high-frequency noise emitted by computer and business equipment Acoustique - Mesurage du bruit ;i haute frhquence hmis par les mathriek informatiques et , , I de bureau Reference number IS0 9295 : 1988 (E) SIST EN 29295:1999

IS0 9295 : 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. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. 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 9295 was prepared by the European Computer Manufac- turers Association (as Standard ECMA-108) and was adopted, under a special “fast- track procedure”, by Technical Committee ISO/TC 43, Acoustics, in parallel with its approval by the IS0 member bodies. 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 l Printed in Switzerland SIST EN 29295:1999

INTERNATIONAL STANDARD IS0 9295: 1988 (E) Acoustics - Measurement of high-frequency noise emitted by computer and business equipment 0 Introduction Some computer and business equipment emits high-frequency noise which may be broad-band noise (e.g. paper noise of high- speed printing) or narrow-band noise and discrete tones (e.g. switching power supplies and video display units). The measured levels are not frequency-weighted. However, when there are significant contributions in the octave bands having centre frequencies between 125 Hz and 8 kHz, and, in addition, there is a contribution in the 16 kHz band which is broad-band in character, the A-weighted sound power level may be calculated with the contribution of the 16 kHz octave band in- cluded. The principal objective of this International Standard is to prescribe methods for measuring the levels and frequencies of tones which are contained within the 16 kHz octave band. 1 Scope and field of application This International Standard specifies four methods for the determination of the sound power levels of high-frequency noise emitted by computer and business equipment in the frequency range covered by the octave band centred at 16 kHz. They are complementary to the methods described in IS0 7779. The first three methods are based on the reverberation room technique described in clause 5 of IS0 7779 : 1988. The fourth method makes use of a free field over a reflecting plane as described in clause 6 of IS0 7779 : 1988. The test conditions which prescribe the installation and opera- tion of the equipment are those specified in IS0 7779. While the four methods described in this International Standard are particularly suitable for computer and business equipment, they may also be applied to other types of equipment. This International Standard specifies methods for the determination of sound power levels in the frequency range covered by the octave band centred at 16 kHz which includes frequencies be- tween II,2 kHz and 22,4 kHz. NOTE - The sound power level in the 16 kHz octave band determined according to this International Standard typically is subject to a stan- dard deviation of approximately 3 dB. A method for the measurement of high-frequency noise is in conformance with this International Standard if it satisfies all the mandatory requirements of one of the four methods described herein and if the information recorded and reported is that specified in clauses 8, 9 and IO, respectively. 2 References IS0 6926, Acoustics - Determination of sound power levels of noise sources - Characterization and cafibra tion of reference sound sources. l) IS0 7779, Acoustics - Measurement of airborne noise emitted by computer and business equipment. 3 Requirements for measurements in a reverberation room 3.3 General Three methods are described using the reverberation room technique of clause 5 of IS0 7779 : 1988. The first and the second methods are usually called “direct” methods because they use directly measured or calculated reverberation times. The third method is a so-called comparison method. A calibrated reference sound source is used from which the sound power levels of the equipment are determined by com- parison. All three methods require a determination of the average sound pressure level in the reverberant field. As instrumentation and basic measurement techniques are the same for all three methods, they are summarized in 3.2 to 3.6. Additional requirements specific to each method are given separately. For additional information on instrumentation, refer to IS0 7779. 3.2 Instrumentation The microphone shall have a flat frequency response for ran- domly incident sound in the 16 kHz octave band. The tolerances shall be within + 2,0 dB in the frequency range 1 I,4 kHz to 22,8 kHz. NOTE - To meet this requirement, a microphone with a diameter of 13 mm or less is usually required. 1) To be published. 1 SIST EN 29295:1999

IS0 9295 : 1988 E) When the noise of the equipment under test is broad-band in character, an analyser with a bandwidth of one-third octave or less shall be used. When the noise of the equipment under test contains discrete frequencies, a narrow-band analyser which provides bandwidths less than one-third octave in width shall be used to determine the frequency of the tone(s) and to enhance the signal-to-noise ratio. NOTE - For narrow-band analysis, an analyser with a bandwidth equal to or less than one-twelfth octave is appropriate. Digital analysers using fast Fourier transform (FFT) or equivalent techniques may be useful, particularly when the analyser combines narrow-band analysis and averaging. 33 . Installation and orientation of microphone The microphone shall be mounted on the end of a rotating boom traversing a circle with a diameter of at least 2 m. In order to reduce the influence of the direct field on the measured sound pressure level, the microphone shall be mounted on the end of the boom pointing upwards in such a way that the nor- mal to its diaphragm is parallel to the axis of rotation. The period of rotation shall be at least 30 s. Longer paths and traversing periods than the minimum values may be used to reduce the background noise of the drive mechanism, and to minimize modulation of any discrete tone(s) due to the moving microphone. Care shall be taken to ensure that there is no electrical pick-up by the measurement instrumentation which would interfere with the sound pressure level measurement. NOTE - A test with a dummy microphone, and with the equipment under test in operation, is recommended to determine the electrical background level. 34 . installation and orientation of equipment Place the equipment on the floor of the reverberation room, at least 1 m from any wall, and at least 1,8 m from the point of closest approach of the microphone. Four orientations of the equipment shall be used as follows : a) Operator side facing the centre of the microphone path. b) Equipment turned clockwise by 90°. c) Equipment turned clockwise by 180°. d) Equipment turned clockwise by 270°. Alternatively, place the equipment on a turntable and revolve it during the measurements. The motion of the turntable shall not be synchronous with the rotation of the microphone boom. 35 . Calibration of measurement system Before the measurement of the equipment noise, the measure- ment set-up shall be calibrated according to 5.4.6 of IS0 7779 : 1988. Calibration at a single frequency is sufficient if the frequency response of the entire system, including the frequency range of the 16 kHz octave band, is checked at inter- vals of not more than two years. If an FFT analyser is calibrated with a single-frequency calibrator, care shall be taken to have all major sideband levels included in the calibration level. 36 . Measurement of sound pressure level The sound pressure level is measured in one-third octave bands or in narrow bands which include any discrete tones. Measurements of the sound pressure level along the circular microphone path shall be carried out for each frequency band within the frequency range of interest. The following data shall be obtained : a) The band operation. sound pressure levels with the equipment in b) The band sound pressure levels of the background noise (including noise produced by ancillary equipment, if any). cl The band sound pressure levels sou rce (if required : see clause 6). of the reference sound True integration-averaging during a full sweep of the microphone is the preferred method. When using a narrow- band analyser that performs the analysis in consecutive time periods, each time period shall correspond to one revolution. The influence of measurement duration and corrections for background noise shall be taken into account according to 5.7 of IS0 7779 : 1988. When FFT analysers are used, the analysis time is typically greater than the individual time window. For this reason, the total measurement time shall be increased, or individual measurements shall be repeated for three revolutions of the boom, each for a different starting point. The average value, L,, of IV measu rements of the pressure level shall be calculated using the equation : sound L, = 1Olg [+ $, lo(Vlo] .I’ (1) where Li is the sound pressure level, in 20 PPa) for the ith measurement. decibels reference : For the four orientations of the equipment under test, the average value of L* is obtained with IV = 4. For the three revolutions of the boom, L, is obtained using Iv = 3. When a discrete tone is analysed, the moving microphone distributes the energy of the tone into sidebands of the tone frequency. In order to obtain the total level, the analyser band- width shall not be less than : 2 SIST EN 29295:1999

IS0 9295 : 1988 (E) Af = 2fv . . . c (2) where Af is the minimum value of the analyser bandwidth, in hertz; f is the centre frequency of the tone, in hertz; c is the speed of sound, in metres per second; v is the speed of the traversing microphone, in metres per second. When using FFT or equivalent techniques for the analysis of the discrete tone(s), the bandwidth may be significantly nar- rower than given above. In this case, the levels in the sidebands adjacent to the tone centre frequency which contribute to the tone level shall be added on an energy basis to obtain the total level using the following equation : N L tot = 10 lg lO(V’O) . . . . (3) i=l where L tot is the total sound level, in decibels (reference : 20 PPa); Li is the sound pressure level in an individual band, in decibels (reference : 20 PPa); Iv is the number of sideband levels to be combined. 4 Method using measured reverberation time 4.5 Measurement of sound pressure level 4.1 General A basic assumption of this method is that the reverberant com- ponent dominates the sound field at the microphone positions. Experiments show that in the 16 kHm octave band, the direct field may still be present. However, the microphone orientation specified in 3.3 significantly reduces the direct field contribu- tion, and, therefore, the measured sound pressure level is determined by the reverberant field. From the measured reverberation time which is determined by the absorption in air and by the room surfaces, the total room absorption is calculated. Although air absorption is the major part of the two, wall absorption may contribute to the total room absorption. At frequencies above 10 kHz, the absorption coefficient of the room, a, cannot be considered small compared to unity. Therefore, the Eyring equation [see equation (411 shall be used for the calculation of the room absorption instead of the simpler Sabine equation. 42 . Measurement of reverberation time The reverberation time, T, in seconds, of the reverberation room with the equipment under test present shall be determined in those one-third octave bands with centre frequencies be- tween 125 kHz and 20 kHz which are of interest for the measurement of the equipment noise. When the equipment under test emits discrete tones, the reverberation time shall be measured at those frequencies in narrower bands, e.g. in l/12 octave bands. For each frequency band of interest, the average value of the reverberation times measured at three or more locations, equally spaced on the microphone path, shall be determined. The response time of the measuring instrument (e.g. a level recorder) shall be such that reverberation times shorter than 0,7 s can be measured. 4.3 Calculation of room absorption The room constant R for each band is calculated from the measured reverberation time as follows : Sxa R=r -a a=l-e -0,16 V/(S x T) where . . . (4) . . . (5) S is the total surface area of the room, in square metres; V is the volume of the room, in cubic metres; IF is the measured average reverberation time, in seconds; a is the absorption coefficient of the room. 4.4 Installation of microphone and equipment The microphone and the equipment under test shall be installed as described in 3.3 and 3.4, respectively. Before the measurement of the equipment noise, the measure- ment set-up shall be calibrated as described in
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