1、ECMA EUROPEAN COMPUTER MANUFACTURERS ASSOCIATION STANDARD ECMA-160 DETERMINATION OF SOUND POWER LEVELS OF COMPUTER AND BUSINESS EQUIPMENT USING SOUND INTENSITY MEASUREMENTS; SCANNING METHOD IN CONTROLLED ROOMS 2nd Edition - December 1992 _ ,ECMA ECMA*160 92 3404593 0015051 428 mI I Free copies of th
2、is document are available from ECMA, European Computer Manufacturers Association, 114 Rue du Rhne - CH-1204 Geneva (Switzerland) Phone: +41 22 735 36 34 Fax: 41 22 786 52 31 ECMA ECMA*360 92 m 3404593 0035052 364 m ECMA EUROPEAN COMPUTER MANUFACTURERS ASSOCIATION STANDARD ECMA-160 DETERMINATION OF S
3、OUND POWER LEVELS OF COMPUTER AND BUSINESS EQUIPMENT USING SOUND INTENSITY MEASUREMENTS; SCANNING METHOD IN CONTROLLED ROOMS 2nd Edition - December 1992 ECMA ECMA*LbO 92 3404593 0015053 2TO Brief History This ECMA Standard specifies methods for the measurement of sound power levels of the however th
4、ey may be used for installation planning (see ECMA TR/27). The purpose of this measurement procedure is to obtain sound power levels in “controlled“ environments using sound intensity procedures with an engineering grade accuracy that is comparable to that of the methods of clauses 5 and 6 of ECMA-7
5、4. The measurements performed using this Standard are made in less restrictive environments than special acoustical rooms; however, if the source is closer to a wall than specified in ECMA-74, the sound power emitted from the source may be different from that emitted in a reverberation room or in an
6、 hemi anechoic room, although this difference is not expected to be significant. The scanning sound intensity technique in this Standard to determine sound power levels is an alternative to the two procedures in ECMA-74; however, ECMA-74, clause 7 must be used to determine the A-weighted sound press
7、ure level at the bystander or operator position. This scanning method can be used for checking whether the declared noise emission values reported in specification sheets, for example, according to ISO/IEC 11159 and IS0 11160 are, indeed, met by installed equipment. The advantage of this method is t
8、hat this check can be made in ordinary rooms, which reduces the time and cost involved considerably. This measurement procedure is not intended for the identification of noise sources within the equipment under test. This standard gives requirements for the acoustical environment, extraneous noise,
9、measurement surface, and scanning technique for the intensity measurement. The procedure for calculating sound power from sound intensity is given. The noise of the equipment under test has to be stationary so that proper time and spatial integration is obtained while scanning over the measurement s
10、urface. The measurement of isolated bursts of sound energy is thus not covered by the method, unless the isolated bursts are repeatable and special precautions are utilized during the scanning. Surface integration of the intensity component normal to the measurement surface is approximated by subdiv
11、iding the measurement surface into contiguous segments, and scanning the pmbe over each segment along a continuous path which covers the extent of the segment. The measurement instmment continuously time-integrates the normal intensity component and squared sound pressure over the duration of each s
12、can. The scanning operation may be performed either manually or by means of a mechanical system. The one octave, one-third octave or band-limited weighted sound power level is calculated from the measured values. The method is applicable to any computer and business equipment for which a physically
13、stationary measurement surface can be defined, and on which the noise generated by the source is stationery in time, as defined in 4.12. This Standard specifies certain ancillary procedures, described in annex B, to be followed in conjunction with the sound power determination. The results are used
14、to indicate the quality of the determination, and hence the grade of accuracy. If the indicated quality of the determination does not meet the requirements of the Standard, the test procedure must be modified in the manner indicated in this Standard. ECHA ECHA*lbO 92 9 3404593 0035058 882 -2- 1.2 Fi
15、eld of Application This Standard is suitable for type tests of computer and business equipment and provides methods for manufacturers and testing laboratories to obtain comparable results. The methods specified in this Stanard allow the determination of noise emission levels (sound power levels) for
16、 a unit tested individually. The sound power and the sound pressure levels obtained may serve noise emission deciaration and comparison purposes (see ECMA-109). They are not to be considered as installation noise immission levels; however they may be used for installation planning (see ECMA TR/27).
17、If sound power levels obtained are determined for severai units of the same production series, they can be used to determine a statistical value for that production series. Character of noise radiated by the source The noise radiated by the source shali be stationary in time, as defined in 4.12. If
18、a some operates according to a duty cycle, within which there are distinct continuous periods of steady operation, for the purposes of application of this Standard an individual sound power level is determined and reported for each distinct period. Action shall be taken to avoid measurement during t
19、imes of operation of non-stationary extraneous noise sources of which the occurences are predictable (see table B.3) 1.3 1.4 Measurement uncertainty For the purpose of application of this Standard engineering grades of accuracy are defined in table 1. The stated uncertainties account for random erro
20、rs associated with the measurement procedure, together with the maximum measurement bias error which is limited by the selection of the bias error factor K appropriate to the required grade of accuracy (see table 2). They do not account for tolerances in nominal instrument performance which are spec
21、ified in IEC 1043. Nor do they account for the effects of variation in source installation, mounting and operating conditions. NOTE 1 For the purpose of this Standard, the normal range for A-weighted data is covered by the one octave bands from 125 Hz to 4 wlz, and the one-third octave bands from 10
22、0 Hz to 63 wlz. The A-weighted value which is computedfrom one octave band levels in the range 125 Hz to 4 kHz, and one-third octave band levels in the range 100 Hz to 63 kHz is correct if there are no signijicantly high levels in the band from 8 kiiz to 10 kHz. For the purpose of this assessment, s
23、ignijcant levels are band levels which afrer A-weighting are no more than 6 dB below the A-weighted value computed. if A-weighted measurements and associated sound power level determinations are made in a more restrictedfrequency range, this range must be stated in accordance with 10.6 The uncertain
24、ty of determination of the sound power level of a noise source is related to the nature of the sound field of the source, to the nature of the extraneous sound field, to the absorption of the source under test, and to the form of intensity field sampling and measurement procedure employed. For this
25、reason this Standard specifies initial procedures for the evaluation of indicators of the nature of the sound field which exists in the region of the proposed measurement surface (see annex A). The results of this initial test are used to select an appropriate course of action according to table B.2
26、. If only an A-weighted determination is required any single-A-weighted band level of 10 dB or more below the highest A-weighted band level shall be neglected. If more than one band level appear insignificant, they may be neglected if the level of the sum of the A-weighted sound powers in these band
27、s is 10 dB or more below the highest A-weighted band level. If only a frequency-weighted overall sound power level is required, the uncertainty of determination of the sound power level in any band in which it is 10 dB or more below the overail weighted level, is irrelevant. 4. ECMA ECflA*lbO 92 m 3
28、404593 0035059 739 m -3- Octave band One third octave band centre frequencies centre frecluencies Hz Hz 125 50 to 160 200 to 630 1 000 to4ooO 800t05000 6 300 A-weighted (125 Hz - 4 kHz or 100 Hz - 63 kHz) 250 to 500 Standard deviations (s*) Engineering (grade 2) dB 3 2 135 295 195 *) The true value
29、of the sound power level is to be expected with a certainty of 95% in the range off 2 s about the measured value. NOTE 2 The stated uncertainty of the A-weighted estimate does not apply if the total A-weighted power in the one-third octave bands outside the range 800 Hz to 5000 Hz exceeds the total
30、within this range: individual band uncertainties apply. 2 Conformance Measurements are in conformance with this Standard if they meet the following requirements: - The measurement procedure, the installation, and the operaing conditions specified by this Standard are fully taken into account. - The
31、engineering accuracy requirements are met as specified in 1.4. It is recommended that personnel performing sound intensity measurements according to this Standard are trained and experienced in performing acoustical and sound intensity measurements. NOTE 3 To insure the quality of measurements perfo
32、med to this Standard, it is recommended that the person responsible for pelfonnng measurements for the purpose of determning or verfiing declared values be accredited to perform such measurements by a national accreditation body certified to IS0 9000. 3 References ECMA-74 ECMA- 109 ECMATRJ27 IS0 220
33、4: 1979 Acoustics - Guide to International Standards on the measurement of airborne IS0 6926 1990 IS0 7779: 1988 IS0 92961988 ISO/DIS 9614-1:“ ISO/DIS 9614-2:* Measurement of Airborne Noise Emitted by Computer and Business Equipment (1992) Declared Noise Emission Values of Computer and Business Equi
34、pment (1992) Method for the Prediction of Installation Noise Levels (1985) acoustical noise and evaluation of its effects on human beings Characterization and calibration of reference sound sources Acoustics - Measurement of airborne noise emitted by computer and business equipment Acoustics - Decla
35、red noise emission values of computer and business equipment Acoustics - Determination of sound power levels of noise sources using sound intensity - Measurement at discrete points Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 2: Measurement by scannin
36、g ECMA ECNA*160 92 W 3404593 0015060 430 -4- ISO/IEC 11 159: 1992 IS0 1116Ck1993 IEC 9421988 Sound calibrators Information technology - Office equipment - Minimum information to be included in specification sheets - Copying machines Information technology - Minimum information to be included in spec
37、ification sheets - Printing machines IEC 1043:* * : under development Instruments for the measurement of sound intensity 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Definitions For the purpose of this Standard the definitions in ECMA-74 and the following additional definitions apply. Dynamic capability index, Ld
38、Ld = 6, - K = 6, - 7 The value of K is selected according to the grade of accuracy required (see table 2). Table 2 - Bias error factor K Grade of accuracy Bias error factor K dB Engineering (grade 2) 10 Field indicators F+,- and FpI Field indicators are defined in annex A. Measurement distance The s
39、hortest distance between the physical surface of the equipment under test and the measurement surface. Measurement surface A hypothetical surface on which intensity measurements are made, and which either completely encloses the noise source under test, or, in conjunction with an acoustically rigid,
40、 continuous surface, encloses the noise some under test. In cases where the hypothetical surface is penetrated by bodies possessing solid surfaces, the measurement surface terminates at the lines of intersection between the bodies and the surface. Measurement segment For the purpose of this Standard
41、 a measurement surface is subdivided into a set of smaller areas known as segments. probe That part of the intensity measurement system which incorporates the sensors. Pressure-residual intensity index, 6, The difference between indicated Lp and indicated LI, when the intensity pmbe is placed and or
42、iented in a sound field such that the sound intensity is zero. Details for determining 6 the subscript n indicates the direction of the probe axis. are given in IEC 1043. In this is the associated instantaneous particle velocity at the same point; 4.9.2 Sound intensity, Z The time-average value of Z
43、(t) in a temporally stationary sound field: where: T is the integration period. also: Z VI is the signed magnitude of I: the sign is an indication of directional sense, and is dictated by the choice of positive direction of energy flow; is the unsigned magnitude of Z. 4.93 Normal sound intensity, In
44、 The component of sound intensity in the direction normal to a measurement surfxe defined by unit normal vector n. I, =Ion (5) where: n is the unit normal directed out of the volume enclosed by the measurement surface. 4.9.4 Normal sound intensity level, L The logarithmic measure of the unsigned val
45、ue of the normal sound intensity I I, I, given by: In ECMA ECNA*360 72 H 3404593 0035062 203 -6- I where: Io is the reference sound intensity Wm-2. Where I, is negative, the level is expressed as (-) xx dB, except when used in the evaluation of 8p,o (see 4.7). 4.9.5 Extraneous intensity The contribu
46、tion to the sound intensity which arises from the operation of sources external to the measurement surface (source mechanisms operating outside the volume enclosed by the measurement surface). 4.10 Sound power 4.10.1 Padl sound power, Wi The time-averaged rate of flow of sound energy through an elem
47、ent (segment) of a measurement surface, given by: where: 42 Si and lWjl is the magnitude of Wi. The total sound power generated by a source as determined by this Standard, given by: is the signed magnitude of the estimated spatial average normal sound intensity component measured on the segment i of
48、 the measurement surface; is the area of the segment i 4.10.2 Sound power, W, N i=l WI = C y., and N i=l YI= CY where: N NOTE 4 During a scan, an intensity measurement instrument performs a temporal average which is made equivalent to a spatial average by the movement of the probe along the path of
49、the scan. is the total number of segments of the measurement surface. 4.10.3 Parthl sound power level, L, Ii The logarithmic measure of the sound power passing through segment i of the measurement surface: lKl = 1Olg-dB WO ECMA ECMA*LbO 92 W 3404593 0035063 L4T W -7- 4.10.4 Sound power level, L, I The logarithmic measure of the sound power generated by a source, as determined using this Standard, given by* = 101g- Iwil dB WO iqi WO is the reference sound power, Watts. Where W, is negative, the level is expressed as (-) xx dB for record purposes only. This Standard does
