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.
SIS SS IEC 303:1985 history
1985SIS SS IEC 303:1985 Acoustics - IEC provisional reference coupler for the calibration of earphone used in audiometry