This International Standard describes an acoustic coupler for loading supra-aural audiometric earphones as specified in ISO 389-1 (to be published) 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 specified earphones used in audiometry.