1、 Reference number ECMA-123:2009 Ecma International 2009 ECMA-108 5th Edition / December 2010 Measurement of High-frequency Noise emitted by Information Technology and Telecommunications Equipment COPYRIGHT PROTECTED DOCUMENT Ecma International 2010 Ecma International 2010 i Contents Page 1 Scope 1 2
2、 Normative references 1 3 Conformity requirements 1 4 Requirements for measurements in a reverberation test room . 1 4.1 General . 1 4.2 Meteorological conditions 2 4.3 Instrumentation . 2 4.4 Installation and orientation of microphone 2 4.5 Installation and orientation of equipment . 3 4.6 Calibrat
3、ion of measurement system . 3 4.7 Measurement of sound pressure level 3 5 Method using measured reverberation time. 4 5.1 General . 4 5.2 Measurement of reverberation time 4 5.3 Calculation of room absorption . 5 5.4 Installation of microphone and equipment . 5 5.5 Measurement of sound pressure leve
4、l 5 5.6 Calculation of sound power level 5 6 Method using calculated air absorption . 6 6.1 General . 6 6.2 Calculation of room constant . 6 6.3 Installation of microphone and equipment . 6 6.4 Measurement of sound pressure level 6 6.5 Calculation of sound power level 6 7 Method using a reference so
5、und source 8 7.1 Reference sound source. 8 7.2 Installation of microphone and equipment . 8 7.3 Installation of reference sound source . 8 7.4 Measurement of sound pressure level 8 7.5 Calculation of sound power level 8 7.5.1 Equipment emitting broad-band noise 8 7.5.2 Equipment emitting discrete fr
6、equency tone(s) . 9 8 Method using a free field over a reflecting plane . 9 8.1 General . 9 8.2 Meteorological conditions 9 8.3 Instrumentation . 10 8.4 Installation and orientation of microphone 10 8.5 Installation of equipment 10 8.6 Calibration of measurement system . 10 8.7 Measurement of sound
7、pressure level 11 8.8 Calculation of surface sound pressure level and sound power level 11 9 Information to be recorded . 11 9.1 Equipment under test 11 9.2 Acoustic environment . 11 9.3 Instrumentation . 12 9.4 Acoustical data 12 10 Information to be reported 12 ii Ecma International 2010 Annex A (
8、normative) Calculation of air absorption coefficient . 15 Ecma International 2010 iii Introduction In September 1981 ECMA issued Standard ECMA-74 for the Measurement of Airborne Noise Emitted by Computer and Business Equipment. This Standard was contributed to ISO/TC 43; it formed the basis for Inte
9、rnational Standard ISO 7779. ECMA-74 and ISO 7779 are newly revised and have expanded scope to cover all information technology and telecommunications equipment. This Standard ECMA-108 specifies methods for the determination of the sound power levels in the frequency range covered by the octave band
10、 centred at 16 kHz. Some information and telecommunications 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. noise of switching power supplies and video display units). The measured levels are n
11、ot freq uency-weighted. The principal objective of this Standard is to prescribe methods for measuring the levels and frequencies of tones which are contained within the 16 kHz octave band. The first edition of this ECMA Standard was published in December 1986. It has been adopted by ISO under the f
12、ast-track procedure as International Standard ISO 9295. The text of the second edition of Standard ECMA-108 has been adapted to the final wording of ISO 9295:1988. The text of the third edition of this Standard has been adapted to eliminate ambiguity in the determination of the A-weighted sound powe
13、r levels of sounds that contain contributions in the octave band centred at 16 kHz, and to align with the fourth edition of ECMA-74 (1996). Like ECMA-74, the scope of ECMA-108 now covers all information technology and telecommunications equipment. The fourth edition of this ECMA Standard was publish
14、ed in December 2008. The primary change is to incorporate changes in the tenth edition of ECMA-74, which limits the frequency range of interest for determining A-weighted sound power levels to one-third-octave bands with centre frequencies from 100 Hz to 10 000 Hz. With the fourth edition of ECMA-10
15、8, noise in the 16 kHz octave band is no longer used to determine overall A-weighted sound power level of the unit under test; only contributions in the 100 Hz 10 000 Hz one-third-octave bands determined in accordance with the tenth edition of ECMA-74 are used to determine A-weighted sound power lev
16、el. The fifth edition of this ECMA Standard was published in December 2010. The primary change was to expand Table 1 Values of the air absorption coefficient to include a wider temperature range. Also the equations to calculate the air absorption coefficient were aligned with ISO 9613-1. This Ecma S
17、tandard has been adopted by the General Assembly of December 2010. iv Ecma International 2010 “DISCLAIMER This document and possible translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared,
18、 copied, published, and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this section are included on all such copies and derivative works. However, this document itself may not be modified in any way, including by removing the copyright
19、 notice or references to Ecma International, except as needed for the purpose of developing any document or deliverable produced by Ecma International (in which case the rules applied to copyrights must be followed) or as required to translate it into languages other than English. The limited permis
20、sions granted above are perpetual and will not be revoked by Ecma International or its successors or assigns. This document and the information contained herein is provided on an “AS IS“ basis and ECMA INTERNATIONAL DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRA
21、NTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY OWNERSHIP RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.“ Ecma International 2010 1 Measurement of High-frequency Noise emitted by Information Technology and Telecommunications Equipment 1 Scop
22、e This Standard ECMA-108 specifies four methods for the determination of the sound power levels of high-frequency noise emitted by information technology and telecommunications equipment in the frequency range covered by the octave band centred at 16 kHz, which includes frequencies between 11,2 kHz
23、and 22,4 kHz. They are complementary to the methods described in Standard ECMA-74. The first three methods are based on the reverberation test room technique. The fourth method makes use of a free field over a reflecting plane. The test conditions which prescribe the installation and operation of th
24、e equipment are those specified in ECMA-74. While the four methods described in this Standard are particularly suitable for information technology and telecommunications equipment, they may also be applied to other types of equipment. NOTE The sound power level in the 16 kHz octave band determined i
25、n accordance with this Standard typically is subject to a standard deviation of approximately 3 dB. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the late
26、st edition of the referenced document (including any amendments) applies. ECMA-74, Measurement of Airborne Noise Emitted by Information Technology and Telecommunications Equipment ISO 6926, Acoustics Requirements for the performance and calibration of reference sound sources used for the determinati
27、on of sound power levels ISO 9613-1Acoustics Attenuation of sound during propagation outdoors Part 1: Calculation of the absorption of sound by the atmosphere 3 Conformity requirements A method for the measurement of high-frequency noise is in conformance with this Standard if it satisfies all the m
28、andatory requirements of one of the four methods described herein specified in Clause 4 and if the information recorded and reported is that specified in Clauses 10 and 11, respectively. 4 Requirements for measurements in a reverberation test room 4.1 General Three methods are described using the re
29、verberation test room technique of Standard ECMA-74. The first and the second method 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 t
30、he sound power levels of the equipment are determined by comparison. 2 Ecma International 2010 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 summ
31、arized in 4.3 to 4.7 below. Additional requirements specific to each method are given separately. For additional information on instrumentation, see ECMA-74. 4.2 Meteorological conditions The air absorption in the reverberation test room varies with temperature and humidity, particularly at frequenc
32、ies above 1 000 Hz. The temperature in C and the relative humidity hr, expressed as a percentage, shall be controlled during the sound pressure level measurements. The product hr ( + 5) shall not vary by more than 10 % during the measurements. For equipment whose noise emissions vary with ambient te
33、mperature in a deliberate manner (e.g., by varying the speeds of air moving devices), the room temperature during the test measurement shall be 23 C 2 C or, if the room temperature is outside these limits, then the fan shall be adjusted to the speed for an ambient temperature of 23 C 2 C. The follow
34、ing conditions are recommended: Barometric pressure : 86 kPa to 106 kPa Temperature : 15 C to 30 C Relative humidity : 40% to 70 % 4.3 Instrumentation The microphone shall have a flat frequency response for randomly incident sound in the 16 kHz octave band. The tolerances shall be within 2,0 dB in t
35、he frequency range 11,2 kHz to 22,4 kHz. NOTE 1 To meet this requirement a microphone with a diameter of 13 mm or less is usually required. 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
36、 the equipment under test contains discrete frequencies, a narrow-band analyser which provides bandwidths of 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 2 For narrow-band analysis, an analyser with a bandw
37、idth 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. 4.4 Installation and orientation of microphone The microphone shall
38、 be mounted at 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 pointing in such a way that the normal to its diaphragm is parallel to the axis of
39、 rotation and the microphone faces away from the equipment under test. The period of rotation shall be at least 30s. 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 t
40、o 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 determ
41、ine the electrical background level. Ecma International 2010 3 4.5 Installation and orientation of equipment Place the equipment on the floor of the reverberation test 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
42、equipment shall be used as follows. Operator side facing the centre of the microphone path. Equipment turned clockwise by 90 from its initial position about a vertical axis through its centre. Equipment turned clockwise by 180. Equipment turned clockwise by 270. Alternatively, place the equipment on
43、 a turntable and revolve it during the measurements. The motion of the turntable shall not be synchronous with the rotation of the microphone boom. 4.6 Calibration of measurement system Before the measurement of the equipment noise, the measurement set-up shall be calibrated in accordance with ECMA-
44、74. 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 intervals of not more than two years. If an FFT analyser is calibrated with a single-frequency calibrator, care shall be taken to
45、have all major sideband levels included in the calibration level. 4.7 Measurement of sound pressure level The sound pressure level is measured in one-third-octave bands or, if discrete tones are present, in narrow bands which include the discrete tones. Measurements of the sound pressure level along
46、 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 sound pressure level with the equipment in operation, b) the band sound pressure levels of the background noise (including noise produc
47、ed by ancillary equipment, if any), c) the band sound pressure levels of the reference sound source (if required: see Clause 7). 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
48、periods, each time period shall correspond to one revolution. The influence of measurement duration and corrections for background noise shall be taken into account in accordance with ECMA-74. When FFT analysers are used, the analysis time is typically greater than the individual time window. For th
49、is 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 Lp of N measurements of the sound pressure level shall be calculated using Equation (1): NiLp iNL11,0101lg10 (1) where Li is the band sound pressure level, in decibels (reference: 20 Pa) for the i-th measurement. 4 Ecma International 2010 For the four orientations of the equipment under test, the average value of Lp is obtain
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