Free-field sensitivity level of audiometric earphones to be used for speech audiometer calibration

Speech audiometric test results strongly depend on the frequency response of the equipment used for speech transmission. For the comparison of data measured with different kinds of acoustic transducers, e.g. earphones and loudspeakers, a common reference basis for the specification of the frequency response of speech audiometers is therefore needed. The most obvious basis is the free sound field. In order to provide data for earphone specification in terms of the equivalent free-field response, which are to be included in an IEC standard on speech audiometers under preparation, comprehensive loudness comparison measurements with free progressive sound waves were performed on various audiometric earphones. When these data are used, calibration and testing of speech audiometers are as simple as in the case of puretone audiometers.