This Report describes an interim reference coupler for loading an earphone with a specified acoustic impedance, when calibrating audiometers, in the frequency range of 125 Hz to 8000 Hz.
The sound pressure developed by an earphone is not, in general, the same in the coupler as in a person's ear. However, the IEC recommends its use as a simple and ready means for the exchange of specifications on audiometers and for the calibration of earphones used in audiometry.
IS 10779-1984 history
1985IS 10779-1984 Reference coupler specification for headphone calibration in audiometry