WG 5 - TC 29/WG 5

IEC TR 61904-10:2022
- is applicable to laboratory standard microphones meeting the requirements of IEC 61094-1 and other types of measurement microphones,
- describes one possible absolute method for determining the complex pressure sensitivity, based on a device capable of generating a known sound pressure, especially at low frequencies, and
- provides a reproducible and accurate basis for the measurement of sound pressure at low frequencies.
All quantities are expressed in SI units.

IEC 61094-3:2016 specifies a primary method of determining the complex free-field sensitivity of laboratory standard microphones so as to establish a reproducible and accurate basis for the measurement of sound pressure under free-field conditions. It is applicable to laboratory standard microphones meeting the requirements of IEC 61094-1. It is intended for use by laboratories with highly experienced staff and specialized equipment. This second edition cancels and replaces the first edition published in 1995. This edition constitutes a technical revision.
The contents of the corrigendum of December 2016 have been included in this copy.

IEC 61094-5:2016 is applicable to working standard microphones with removable protection grids meeting the requirements of IEC 61094-4 and to laboratory standard microphones meeting the requirements of IEC 61094-1. This part of IEC 61094 describes methods of determining the pressure sensitivity by comparison with either a laboratory standard microphone or another working standard microphone with known sensitivity in the respective frequency range. This edition cancels and replaces the first edition published in 2001. This edition constitutes a technical revision.

IEC 61094-8:2012 applicable to working standard microphones meeting the requirements of IEC 61094-4. It describes methods of determining the free-field sensitivity by comparison with a laboratory standard microphone or working standard microphone (where applicable) that has been calibrated according to either; IEC 61094-3; IEC 61094-2; IEC 61094-5; IEC 61094-6; or this part of IEC 61094. Methods performed in an acoustical environment that is a good approximation to an ideal free-field (e.g. a high quality free-field chamber), and methods that use post processing of results to minimise the effect of imperfections in the acoustical environment, to simulate free-field conditions, are both covered by this part of IEC 61094. Comparison methods based on the principles described in IEC 61094-3 are also possible but beyond the scope of this part of IEC 61094.

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.

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 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 frequency and temperature, - is applicable when a suitable free field calibration is not available.

This part of IEC 61094 - gives guidelines for the design of actuators for microphones equipped with electrically conductive diaphragms; - gives methods for the validation of electrostatic actuators; - gives a method for determining the electrostatic actuator response of a microphone. The applications of electrostatic actuators are not fully described within this standard but may include - a technique for detecting changes in the frequency response of a microphone, - a technique for determining the environmental influence on the response of a microphone, - a technique for determining the free field or pressure response of a microphone without specific acoustical test facilities, by the application of predetermined correction values specific to the microphone model and actuator used, - a technique applicable at high frequencies not typically covered by calibration methods using sound excitation.

Specifies mechanical dimensions and certain electroacoustic characteristics for condenser microphones used as laboratory standards for the realization of the unit of sound pressure and for sound pressure measurements of the highest attainable accuracy. The specifications are intended to ensure that primary calibration by the reciprocity method can be readily carried out. Establishes a system for classifying laboratory standard condenser microphones into a number of types according to their dimensions and properties.