IEC 61094-2:2009

FOREWORD
1 Scope
2 Normative references
3 Terms and definitions
4 Reference environmental conditions
5 Principles of pressure calibration by reciprocity
  5.1 General principles
      5.1.1 General
      5.1.2 General principles using three microphones
      5.1.3 General principles using two microphones and an
            auxiliary sound source
  5.2 Basic expressions
  5.3 Insert voltage technique
  5.4 Evaluation of the acoustic transfer impedance
  5.5 Heat-conduction correction
  5.6 Capillary tube correction
  5.7 Final expressions for the pressure sensitivity
      5.7.1 Method using three microphones
      5.7.2 Method using two microphones and an auxiliary
            sound source
6 Factors influencing the pressure sensitivity of microphones
  6.1 General
  6.2 Polarizing voltage
  6.3 Ground-shield reference configuration
  6.4 Pressure distribution over the diaphragm
  6.5 Dependence on environmental conditions
      6.5.1 Static pressure
      6.5.2 Temperature
      6.5.3 Humidity
      6.5.4 Transformation to reference environmental conditions
7 Calibration uncertainty components
  7.1 General
  7.2 Electrical transfer impedance
  7.3 Acoustic transfer impedance
      7.3.1 General
      7.3.2 Coupler properties
      7.3.3 Microphone parameters
  7.4 Imperfection of theory
  7.5 Uncertainty on pressure sensitivity level
Annex A (normative) Heat conduction and viscous losses
        in a closed cavity
Annex B (normative) Acoustic impedance of a capillary tube
Annex C (informative) Examples of cylindrical couplers for
        calibration of microphones
Annex D (informative) Environmental influence on the
        sensitivity of microphones
Annex E (informative) Methods for determining microphone
        parameters
Annex F (informative) Physical properties of humid air

IEC 61094-2:2009 is applicable to laboratory standard microphones meeting the requirements of IEC 61094-1 and other types of condenser microphone having the same mechanical dimensions and specifies a primary method of determining the complex pressure sensitivity so as to establish a reproducible and accurate basis for the measurement of sound pressure. This second edition cancels and replaces the first edition published in 1992. This second edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- an update of Clause 6 to fulfil the requirements of ISO/IEC Guide 98-3;
- an improvement of the heat conduction theory in Annex A;
- a revision of Annex F: Physical properties of humid air.