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1、BRITISH STANDARD BS 4669:1971 Specification for An artificial ear of the wide band type for the calibration of earphones used in audiometry Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4669:1971 This British Standard, having been appro
2、ved by the Telecommunication Industry Standards Committee, was published under the authority of the Executive Board on 26 February 1971 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference TLE/24/2 Draft for comment 69/11935 ISBN 580 06267 8 Co-operating
3、organizations The telecommunication Industry Standards Committee under whose supervision this British Standard was prepared consists of representatives from the following Government departments and scientific and industrial organizations: British Broadcasting Corporation*Electronic Valve and Semi-co
4、nductor British Electrical this is described in BS 4668 “An acoustic coupler (IEC reference type) for calibration of earphones used in audiometry”. Type 2 artificial ear has not been specified by IEC Technical Committee 29 Electro-acoustics, as in their opinion Type 3 should be used for the objectiv
5、e calibration of earphones for telephonometric purpose where no acoustic leakage is present. NOTEIEC Technical Committee 29 recognizes that calibration made in this manner takes no account of the acoustic leak that may occur between the earphone and the real ear in normal telephone use. Type 3 artif
6、icial ear for wide band audiometric applications evolved from agreement on the mean impedance of the human ear. Type 4 artificial ear for calibrating insert earphones is under consideration but in the meanwhile use should be made of the insert acoustic coupler described in BS 3171 “Methods of test o
7、f air conduction hearing aids”. Type 5 artificial ear should be the ideal measuring device but at the present time no work is being carried out on the development of this type of artificial ear. This British Standard specifies the design and construction of an artificial ear Type 3 which may be used
8、 directly for the comparison of super-aural earphones used in audiometry. The standard is technically identical with IEC Publication 318 Recommendation “An IEC artificial ear, of the wide band type, for the calibration of earphones used in audiometry”. This artificial ear should allow one set of val
9、ues for audiometric zero to be specified in place of the different values associated with the acoustic coupler in BS 4668. Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4669:1971 BSI 10-1999iii A British Standard does not purport to inc
10、lude all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, page
11、s i to iv, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+0
12、0:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4669:1971 BSI 10-19991 1 Scope This British Standard specifies requirements for an artificial ear which covers the audiometric frequency band f
13、rom 80 Hz to 10 000 Hz. This artificial ear is intended for the calibration of super-aural earphones which are applied with minimum leakage to human ears. 2 Explanation of terms For the purposes of this British Standard the following terms apply: 1) Audiometric artificial ear. A device to permit cal
14、ibration of earphones, used in audiometry consisting of an acoustic network designed to approximate to the acoustic characteristics of the human ear and a microphone to measure the sound pressure developed. 2) Super-aural earphone. An earphone in which the earcap is applied directly to the pinna. NO
15、TE 1Other types of earphone include those which are sealed by a cushion which surrounds the ear (circumaural) and those which connect directly to the external auditory meatus (insert). NOTE 2The term supra-aural is sometimes used in place of super-aural. 3) Equivalent volume of a microphone. It is c
16、onvenient to express the acoustic impedance of the microphone in terms of an equivalent complex volume Vc of a gas enclosed in a rigid cavity according to the following equation. NOTE 1The equivalent volume will generally be a complex quantity and a function of frequency. NOTE 2For dry air at 20 C a
17、nd Pa= 105N/m2, k = 1.402. 3 Description of the artificial ear for audiometric measurements 3.1 Basic design. The artificial ear is composed of three cavities coupled acoustically. The shape and volume of the primary conical cavity but only the volumes of the remaining cavities are defined (see Figu
18、re 1). The lumped parameter values of the coupling elements shall be adjusted as follows. L2= 500 N s2 m5 L3= 104N s2 m5 R2= 6.5 106N s m5 R3= 2 107N s m5 These values relate to normal atmospheric conditions (N.T.P.). The inductive elements shall be in or near the microphone end of the conical cavit
19、y. NOTEThe 32 slope section of the artificial ear may be removable as shown for example in Figure 2 and should be removed when calibrating earphones in which the sloped section of the earcap is greater than 30. 3.2 Tolerances. The linear dimension specified shall be within a tolerance 0.02 cm, the v
20、olumes within 1 % and the magnitude of the coupling elements 5 %. The angular dimensions 33 30 shall have a tolerance of 00 30 the angular dimension 32 (see Figure 1) shall have a tolerance + 3 1. 3.3 Pressure-equalizing leak. A leak provided to equalize the pressure shall have an acoustic resistanc
21、e R1 greater than 5 108N s m5 and less than 109N s m5. This leak can be coupled to any one of the three volumes. 3.4 Microphone. A microphone shall form the base of cavity V1. The acoustical impedance of the microphone shall be high, the equivalent volume being less than 0.02 cm3 over the specified
22、range of frequencies. The overall pressure sensitivity of the microphone and associated measuring system over the specified frequency range shall be known within 0.4 dB. The microphone shall be coupled with the volume V1 without leakage. NOTEThe equivalent volume of the microphone is usually specifi
23、ed by its manufacturer. 3.5 Material. The artificial ear shall be constructed of a hard, stable non-magnetic material such as brass. 3.6 Example of design. One specific example of the artificial ear is shown in Figure 2. 4 Method of use The earphone to be calibrated shall be applied symmetrically to
24、 the artificial ear without acoustic leakage with a force of between 4 N and 5 N, excluding the weight of the earphone itself. NOTEThe earcap should not rest on the sloping side of the artificial ear, but only on the upper edge (or rim). If the earcap of an earphone to be calibrated is made of a ver
25、y hard material, a wax or grease film of minimal thickness shall be used between earcap and artificial ear in order to eliminate leakage. where:k=the ratio of the specific heats Ps=the static pressure j6=the angular frequency Za=the acoustic impedance of the microphone Unit: cubic metre. Licensed Co
26、py: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4669:1971 2 BSI 10-1999 5 Calibration For an artificial ear complying with the above requirements, the calibration depends on a knowledge of the overall pressure sensitivity of the microphone and assoc
27、iated measuring system. NOTEIt is recommended that manufacturers of artificial ears conforming to this British Standard should describe a method for determining overall stability. 6 Lumped-parameter electrical network analogue of the artificial ear In this analogue, one electrical ohm corresponds to
28、 105 M.K.S. acoustical ohms (N s m5). NOTEThree independent determinations of the acoustical impedance of the human ear under no-leakage conditions were available, covering the various earcap contours used on audiometric earphones. In each case an analogue network of the type shown in Figure 3 was d
29、evised with values of the elements adjusted to produce optimum fit to the experimental impedance data. The values of the lumped parameters shown in Figure 3 are average values and define the impedance at the input plane of the artificial ear. The impedance values are shown in Figure 4 and Figure 5.
30、Figure 1 Basic design Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4669:1971 BSI 10-19993 NOTEThe three adjusting screws are set so that corresponding flow resistance is 6.5 106N s m5. All linear dimensions are in millimetres. Figure 2
31、 Example of one specific design of the artificial ear Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4669:1971 4 BSI 10-1999 Figure 3 Analogue network Figure 4 Imaginary component of the impedance of the electrical analogue network Licen
32、sed Copy: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4669:1971 BSI 10-19995 Figure 5 Real component of the impedance of the electrical analogue network Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+00:00 2006, Uncontrolled Cop
33、y, (c) BSI 6 blank Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 30 08:36:42 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4669:1971 BSI 10-1999 British Standards Institution The following are available on application: YEARBOOK Including subject index and numerical list of British Standards SE
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