Reference zero for the calibration of bone-conduction audiometric equipment using short-duration signals

OBJECTIVE: Clicks and tonebursts used in auditory brainstem responses (ABRs) are calibrated using a standardised reference, published in ISO 389-6 (2007). However, the standardised reference contains toneburst values for air-conduction (AC) but not bone-conduction (BC) transducers. Therefore, BC values are usually estimated in clinical practice as an interim measure until empirical values become available. Here we offer such empirical values. DESIGN: Equivalent Threshold Vibratory Force Levels (ETVFLs) closely to preferred test procedures described in ISO 389-9 (2009). The transducer was a RadioEar B81 bone vibrator, and levels were characterised using the peak-to-peak equivalent method. STUDY SAMPLE: 27 otologically normal adults (14 female and 13 male) with a mean age of 22 years (range 18-25). RESULTS: Median thresholds corresponding to 0 dB HL for a range of stimulus frequencies and listening conditions are provided. Toneburst values at the commonly used centre frequencies of 0.5, 1, 2 and 4 kHz are respectively 68 dB, 60.5, 47.5 and 44.5 dB re: 1 µN with contralateral masking. The click reference, with contralateral masking, is 58 dB re: 1 µN. CONCLUSIONS: These data could serve as a basis upon which to address the incomplete suite of values in ISO 389-6 (2007).