Threshold of hearing by bone conduction. A contribution to international standardization.

Threshold measurements with a Präcitronic KH 70 bone vibrator were carried out on 25 young, otologically normal subjects (50 ears) in the frequency range between 125 Hz and 8 000 Hz. The vibrator was applied to the human mastoid as well as to the forehead. The non-test ear was masked. Equivalent threshold force levels were determined on an artificial mastoid type B & K 4930. Between 125 Hz and 2 000 Hz, the equivalent threshold force levels for mastoid placement decrease steadily by about 13.5 dB/octave, they then increase again by about 10 dB and remain constant between 4 000 Hz and 8 000 Hz. The equivalent threshold force levels for forehead application were found to be higher by about 11 dB in the whole frequency range.