BS DD IEC TS 61094-7-2006 Measurement microphones - Values for the difference between free-field and pressure sensitivity levels of laboratory standard microphones《计量扩音器 实验室标准扩音器的自.pdf

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2、easurement microphones Part 7: Values for the difference DRAFT FOR DEVELOPMENTDD IEC/TS 61094-7:2006DD IEC/TS 61094-7:2006This Draft for Development was published under the authority of the Standards Policy and Strategy Committee on 31 July 2006 BSI 2006ISBN 0 580 48976 0comments will be welcomed. T

3、hese should be sent to the Secretary of BSI Technical Committee EPL/29, Electroacoustics, at British Standards House, 389 Chiswick High Road, London W4 4AL, giving the document reference and clause number and proposing, where possible, an appropriate revision of the text.A list of organizations repr

4、esented on this committee can be obtained on request to its secretary.Cross-referencesThe British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”,

5、 or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Summary of pagesThis document comprises a front cover, an insid

6、e front cover, the IEC/TS title page, pages 2 to 9 and a back cover.The BSI copyright notice displayed in this document indicates when the document was last issued.Amendments issued since publicationAmd. No. Date CommentsA review of this Draft for Development will be carried out not later than 2 yea

7、rs after its publication.Notification of the start of the review period, with a request for the submission of comments from users of this Draft for Development, will be made in an announcement in the appropriate issue of Update Standards. According to the replies received, the responsible BSI Commit

8、tee will judge whether the Draft for Development can be converted into a British Standard or what other action should be taken.Observations which it is felt should receive attention before the official call for National forewordThis Draft for Development reproduces verbatim IEC/TS 61094-7:2006. It s

9、upersedes BS 5941:1980 which is withdrawn.This publication is not to be regarded as a British Standard.It is being issued in the Draft for Development series of publications and is of a provisional nature. It should be applied on this provisional basis, so that information and experience of its prac

10、tical application can be obtained.IECTECHNICAL SPECIFICATION TS 61094-7First edition2006-05Measurement microphones Part 7: Values for the difference between free-field and pressure sensitivity levels of laboratory standard microphones Reference number CEI/IEC/TS 61094-7:2006 DD IEC/TS 61094-7:2006 2

11、 CONTENTS 1 Scope 3 2 Normative references .3 3 Terms and definitions .3 4 Reference environmental conditions3 5 Background 4 6 Difference values of free-field and pressure sensitivity levels.4 6.1 General .4 6.2 Data sources .4 6.3 Expression for the difference between free-field and pressure sensi

12、tivity levels 4 6.4 Uncertainty on the calculated free-field sensitivity level 5 Annex A (informative) Source data .7 Annex B (informative) Acknowledgements 8 Annex C (informative) Historical data .9 DD IEC/TS 61094-7:2006 3 MEASUREMENT MICROPHONES Part 7: Values for the difference between free-fiel

13、d and pressure sensitivity levels of laboratory standard microphones 1 Scope This part of IEC 61094 gives a polynomial function derived from a least square fit to data from several laboratories, for the differences between free-field and pressure sensitivity levels of laboratory standard microphones

14、 as specified in IEC 61094-1, enables determination of the free-field sensitivity level of a laboratory standard microphone for zero-degrees incidence in air by adding values of these differences to the pressure sensitivity level, gives tabulated values for the polynomial function for a range of fre

15、quency and temperature, is applicable when a suitable free-field calibration is not available. 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 latest ed

16、ition of the referenced document (including any amendments) applies. IEC 61094-1, Measurement Microphones Part 1: Specifications for laboratory standard microphones IEC 61094-2:1992, Measurement Microphones Part 2: Primary method for pressure calibration of laboratory standard microphones by the rec

17、iprocity technique IEC 61094-3:1995, Measurement Microphones Part 3: Primary method for free-field calibration of laboratory standard microphones by the reciprocity technique 3 Terms and definitions For the purpose of this part of IEC 61094, the following definition applies in addition to the defini

18、tions given in IEC 61094-1, IEC 61094-2:1992 and IEC 61094-3:1995. 3.1 zero-degrees incidence for a frontal incident sound wave, direction perpendicular to the diaphragm of the microphone 4 Reference environmental conditions The reference environmental conditions are: temperature 23,0 C static press

19、ure 101,325 kPa relative humidity 50 % DD IEC/TS 61094-7:2006 4 5 Background According to the definitions of the free-field and pressure sensitivities of a microphone, the two sensitivities will differ from each other for the following reasons: owing to diffraction and reflection, the introduction o

20、f a microphone into a free progressive sound wave disturbs the sound field. Thus the sound pressure at the microphone diaphragm is not the same as that of the undisturbed free field, owing to diffraction and reflection the sound pressure over the diaphragm of the microphone is not uniform and, for a

21、 specific microphone, is affected by the acoustic impedance of its diaphragm. The values given have been derived from theoretical considerations combined with measurements of the pressure and free-field sensitivity levels of a number of microphones carried out in accordance with IEC 61094-2 and IEC

22、61094-3, respectively, to which reference should be made concerning terminology, microphone preamplifier configurations, etc. 6 Difference values of free-field and pressure sensitivity levels 6.1 General The difference between free-field and pressure sensitivity is determined by two factors, see 5.4

23、 of IEC 61094-3:1995. The major part is determined by the geometrical diffraction around the microphone and its support. This is a wavelength phenomenon and thus a function of temperature. A minor part is determined by the interaction between the impedance of the microphone diaphragm and its radiati

24、on impedance. As the radiation impedance depends on the static pressure and temperature this part will be a function of both these variables. Although this part also depends on the individual microphone impedance, the variations between microphones of the same model can be neglected in comparison wi

25、th the overall uncertainty on the difference values. For type LS2 microphones the interaction between the impedance of the microphone diaphragm and its radiation impedance is insignificant. 6.2 Data sources Values for the difference between free-field and pressure sensitivity levels have been derive

26、d experimentally and by calculation at a number of institutions. The average of the individual results, together with further details is reported in Annex A. A weighted average of these results forms a basis of the expressions for the difference values given in 6.3. 6.3 Expression for the difference

27、 between free-field and pressure sensitivity levels Due to its physical nature the difference values between the free-field and pressure sensitivity levels will be a smooth function of frequency, which has no discontinuities and tends to zero at low frequencies. Thus the difference values can be exp

28、ressed by a polynomial function in terms of normalized frequency. The dependence on temperature can also be accounted for by including this parameter in the polynomial function. DD IEC/TS 61094-7:2006 5 The difference values between the free-field and pressure sensitivity levels in dB for zero-degre

29、es incidence ff, can then be expressed by ()nnc R ft+ , dB (1) () () ()c R ft c R ft c R ft = + + +123ff 1 2 3,where ()Rft=, ft +296,15273,15; f frequency, kHz; t temperature, C; cnpolynomial coefficients given in Table 1. When Equation (1) is used to obtain the free-field sensitivity level of a lab

30、oratory standard microphone at arbitrary environmental conditions it should be recalled that the pressure sensitivity level of the microphone shall refer to the same environmental conditions. The pressure sensitivity level of the microphones is a function of static pressure and temperature, see 6.5

31、of IEC 61094-2:1992. When the polynomial coefficients in Table 1 are used, Equation (1) is valid from 200 Hz to 12,5 kHz for type LS1 microphones and from 400 Hz to 25 kHz for type LS2 microphones. Below these frequency ranges the difference values are less than 0,01 dB and can be neglected. The coe

32、fficients shall be used with the precision shown in Table 1 during the calculation, in which case the maximum deviation on the estimate derived from Equation (1) is within 0,05 dB from a weighted average of the source data given in Annex A. Tabulated values, derived from Equation (1) for a number of

33、 temperatures, are given in Table 2 for type LS1 and LS2a microphones. 6.4 Uncertainty on the calculated free-field sensitivity level When Equation (1) is used to obtain the free-field sensitivity level of a laboratory standard microphone, the resulting uncertainty is the combined uncertainty derive

34、d from the uncertainties of the pressure sensitivity level of the microphone at the relevant environmental conditions, the source data for the difference values, see Table A.1, the uncertainty, 0,05 dB, on the polynomial approach, see 6.3. DD IEC/TS 61094-7:2006 6 Table 1 Polynomial coefficients for

35、 calculation of the difference between the free-field and pressure sensitivity of laboratory standard microphones for zero-degrees incidence Coefficient Microphone type LS1 (without protection grid) Microphone type LS2a c10,007 7 0,038 2 c20,311 6 0,104 94 c30,056 26 0,012 918 c40,020 861 0,002 105

36、8 c50,004 656 1 0,000 218 5 c60,000 484 13 1,189 645 105c7 2,372 15 1053,480 9 107c8 4,471 1075,238 03 109c90 3,196 42 1011Table 2 Difference values of free-field and pressure sensitivity levels in dB for different ambient temperatures and for zero-degrees incidence, calculated from Equation (1) Mic

37、rophone type LS1 (without protection grid) Microphone type LS2a Temperature C Temperature C Frequency kHz 18 23 28 33 18 23 28 33 0,500 0,069 0,068 0,067 0,066 0,006 0,006 0,005 0,005 0,630 0,109 0,108 0,106 0,104 0,015 0,015 0,014 0,014 0,800 0,174 0,172 0,169 0,166 0,032 0,031 0,030 0,029 1,000 0,

38、269 0,264 0,260 0,256 0,057 0,056 0,055 0,053 1,250 0,412 0,406 0,399 0,393 0,097 0,096 0,094 0,092 1,600 0,661 0,650 0,640 0,630 0,169 0,166 0,163 0,160 2,000 1,010 0,994 0,978 0,963 0,272 0,267 0,263 0,258 2,500 1,538 1,514 1,490 1,467 0,429 0,422 0,415 0,408 3,150 2,360 2,323 2,288 2,254 0,679 0,

39、667 0,657 0,646 4,000 3,602 3,550 3,500 3,451 1,076 1,058 1,041 1,025 5,000 5,158 5,093 5,029 4,966 1,637 1,612 1,587 1,563 6,300 7,008 6,940 6,873 6,807 2,500 2,462 2,425 2,390 8,000 8,664 8,617 8,569 8,522 3,788 3,734 3,682 3,632 10,00 9,463 9,448 9,432 9,416 5,376 5,309 5,245 5,181 12,50 9,210 9,

40、254 9,293 9,328 7,152 7,086 7,021 6,956 16,00 8,721 8,683 8,645 8,606 20,00 9,138 9,141 9,144 9,144 25,00 8,714 8,738 8,761 8,784 DD IEC/TS 61094-7:2006 7 Annex A (informative) Source data Values for the difference between free-field and pressure sensitivity levels have been determined by experiment

41、s and calculations by a number of institutions. Table A.1 gives values for the difference between free-field and pressure sensitivity levels in decibels for two microphone types. It refers to a plane progressive wave incident at an angle of zero-degrees relative to the normal of the microphone diaph

42、ragm (“zero-degree incidence”). The values given in the table are the mean values of the data presented and the quoted uncertainties refer to the experimental standard deviation of the mean values of these data using a coverage factor 2. NOTE 1 The free-field sensitivity of a microphone refers to a

43、microphone mounted on the end of a long cylinder, whose diameter is equal to the nominal diameter of the microphone (see 6.4 of IEC 61094-3:1995). The values quoted are derived for cylinder lengths in excess of five times the diameter. NOTE 2 The tabulated values are derived at the prevailing enviro

44、nmental conditions at the participating institutions. Thus the temperature dependence of the geometrical diffraction has not been accounted for and therefore is included in the uncertainty of the quoted average value. NOTE 3 The experimental data were all derived for microphones of Brel & Kjr Type 4

45、160 and Brel & Kjr Type 4180 only. Slightly different values may be found for other type LS1 microphones if the acoustic impedance of the diaphragm is significantly different from that of Brel & Kjr Type 4160. Table A.1 Source data for the difference between free-field and pressure sensitivity level

46、s in dB for zero-degrees incidence Frequency kHz Microphone type LS1 (without protection grid) Microphone type LS2a Difference Uncertainty U (k = 2) Difference Uncertainty U (k = 2) 0,500 0,070 0,032 0,630 0,125 0,044 0,800 0,186 0,045 1,000 0,279 0,056 0,080 0,060 1,250 0,432 0,056 0,120 0,044 1,60

47、0 0,680 0,064 0,192 0,071 2,000 1,019 0,054 0,281 0,097 2,500 1,548 0,062 0,422 0,112 3,150 2,331 0,058 0,662 0,123 4,000 3,526 0,094 1,032 0,120 5,000 5,063 0,096 1,562 0,108 6,300 6,911 0,081 2,394 0,122 8,000 8,491 0,226 3,619 0,170 10,00 9,382 0,230 5,125 0,272 12,50 9,147 0,294 6,924 0,333 16,0

48、0 8,569 0,229 20,00 9,037 0,167 25,00 8,642 0,172 DD IEC/TS 61094-7:2006 8 Annex B (informative) Acknowledgements The data used for deriving the values quoted in Table A.1 in Annex A have kindly been contributed by the institutes listed in alphabetical order below. Danish Primary Laboratory of Acous

49、tics, Denmark, Danish Technical University, Department of Acoustic Technology, Denmark, Japan Quality Assurance Organization, Japan, Laboratoire national de mtrologie et dessais, France, National Physical Laboratory, United Kingdom, Physikalisch-Technische Bundesanstalt, Germany. DD IEC/TS 61094-7:2006 9 Annex C (informative) Historical data The previous standard IEC 655 (1979), which has been withdrawn, contained sim