Frequency response and output variations of Radioear B-71 and B-72 bone vibrators

Frequency response curves were obtained for a Radioear B-71 and a B-72 bone vibrator with a revised Bruel and Kjaer model 4930 artificial mastoid. The curves for each vibrator were characterized by three resonant peaks which decreased in amplitude as frequency increased. The maximal output voltage variations of the artificial mastoid were less than or equal to 2 dB for each vibrator at all audiometric frequencies (+/- 3%), except for the B-72 at 4000 Hz where the variation was 6.9 dB. Overall, the findings were interpreted to question the use of a +/- 3% frequency tolerance for the generation and calibration of reference bone conduction thresholds.