BS 5677:1979 BRITISH STANDARD IEC 327:1971 Method (precision) for pressure calibration of one-inch standard condensermicrophones by the reciprocity technique UDC 621.395.616.089.6:534.612.5 BSi NOCOPYINGWITHOUTBSIPERMISSIONEXCEPT BS 5677:1979 Cooperating organizations The Electronic Equipment Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following BSI Government department and scientific and industrial organizations: British Broadcasting Corporation* British Electrical and Allied Manufacturers' Association (BEAMA) British Radio Equipment Manufacturers' Association Cable and Wireless Limited Cable Television Association of Great Britain Electricity Supply Industry in England and Wales Electronic Components Industry Federation Electronic Engineering Association Institution of Electronic and Radio Engineers* Ministry of Defence* Post Office* Post Office Engineering Union Scientific Instrument Manufacturers' Association The organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: British Association of Otolaryngologists British Medical Association British Society of Audiology Department of Health and Social Security Department of Industry - National Physical Laboratory Health and Safety Executive Hearing Aid Industry Association Institute of Physics Institute of Sound and Vibration Research Medical Research Council Royal Aeronautical Society Royal National Institute for the Deaf Royal Society of Medicine Society of Hearing Aid Audiologists Limited This British Standard, having been prepared under the direction of the Electronic Copy: Equipment Standards Committee, was published under the authority of the Executive Board on Amendments issued since publication Licensed 29 December 1978 Amd. No. Comments Date of issue CBSI 01-2000 The following BSI references relate to the work on this standard: Committee reference EEL/24 Draft for comment 78/24931 DC ISBN0580106004 BS 5677:1979 Contents Page BSI Cooperating organizations Inside front cover National foreword ii 1 Scope 1 2 Object 1 3 Explanation of terms 1 3.1 Open-circuit voltage 1 3.2 Pressure sensitivity of a microphone 1 3.2.1 Pressure sensitivity level of a microphone 1 3.2.2 Pressure sensitivity phase angle of a microphone 1 3.3 Electrical impedance of a microphone 1 3.4 1 Acoustic impedance of a microphone 3.5 2 Equivalent volume of a microphone 3.6 Coupler 2 3.7 2 Electrical transfer impedance 3.8 Acoustic transfer impedance 2 3.9 Reciprocal microphone 2 4 Principles of pressure calibration by reciprocity 3 4.1 General 3 4.1.1 General principles using three microphones 3 4.1.2 General principles using two microphones and an 3 auxiliary sound source 4.2 3 Coupler requirements 4.3 Reciprocity procedure 3 Evaluation of Zab 4.4 4 4.5 Heat-conduction correction 5 4.6 Capillary correction 5 4.7 Final expressions for the pressure sensitivity level 4.7.1 Method using three microphones 5 4.7.2 Method using two microphones and an auxiliary 6 sound source 5 6 Absolute accuracy of calibration 5.1 General 6 5.2 Factors influencing the accuracy of calibration 6 5.2.1 Polarizing voltage 6 5.2.2 Static pressure 6 5.2.3 Frequency 6 5.2.4 Electrical transfer impedance 6 5.2.5 Heat conduction correction 6 5.2.6 Capillary correction 6 5.2.7 Cross-sectional area of the coupler 6 5.2.8 6 Effective length of the coupler 5.2.9 Effective volume of the coupler 6 5.2.10 6 Temperature of the coupler and microphones 5.2.11 Pressure distribution over the diaphragm 6 5.2.12 Acoustic losses 7 5.3 7 Over-all accuracy 6 Calibration methods and equipment 7 6.1 7 Coupler 6.2 Reference configuration of ground-shield 7 CBSI 01-2000 i