High-frequency audiometry. Accelerometric findings with electric bone-conduction audiometry

The skull vibrations induced by an electrical high-frequency audiometer (Audimax 500) were measured with a sensitive accelerometer in 5 subjects. The measurements included the maximum output levels, the equivalent threshold force level (ETFL) decreases, the distortions over the whole frequency range (0.5-20 kHz) of the audiometer and the effect of different electrode positions. The results showed that there is a real bone-conduction effect with this audiometer throughout the high-frequency range with the different electrode positions. The mean maximum output level ranged between 60 and 70 dB ETFL in the high-frequency range. The ETFL decrease was of the same order, irrespective of the frequency, but the differences in the maximum output levels at different frequencies necessitate a frequency-dependent additive correction so that the equal hearing level at each frequency can be achieved. When the electrodes were placed on both mastoids, the second harmonic distortions were found only at signal frequencies of 2 and 4 kHz. At the other electrode positions the distortions were increased, however, not being audible.