Reference Zero for the Calibration of Audiometric Equipment using ‘Clicks’ as Test Signals

Intended as an input to international standardisation, this study investigated reference hearing thresholds for the calibration of audiometric equipment, which have been determined using 'clicks' as test signals, several kinds of earphones, and two types of transducers (a loudspeaker and a bone vibrator). The threshold measurements were carried out with groups of 25 test persons with normal hearing capability following as far as possible the ISO-preferred test conditions. The influence of different parameters on the results, such as click duration, polarisation mode, repetition rate, gender and age of the test persons, or type of ear simulator, was studied. The results mainly depend on the type of ear simulator used to calibrate corresponding audiometers. Together with the results of another investigation carried out in Denmark, the data of the present study shall form the basis for the coming International Standard ISO 389-6 on reference hearing thresholds for acoustic test signals of short duration.