Response of human skull to bone-conducted sound in the audiometric-ultrasonic range.

Some new therapies for tinnitus employ bone-conducted sound in the high audio and ultrasonic frequencies, but there has been little previous research on sound transmission through the head at these frequencies. The vibrational characteristics of two dry skulls, in comparison to a live human head, were measured in the 2- to 52-kHz range. White noise was played and received through piezoelectric transducers and was Fourier-analyzed. Complex resonances and antiresonances were found in both the dry skulls and the live head and varied with small changes in the position of the transducers. There were also pronounced differences between the skulls. In comparison to the skulls, the live head showed greater attenuation and less prominent resonances and antiresonances, reflecting greater damping. The attenuation of the skulls and the head did not increase consistently with frequency but was dominated by resonances at a variety of frequencies. For designing high audio and ultrasonic tinnitus maskers and hearing aids, these results suggest that wide bandwidth must be used to compensate for the unpredictability of the resonances.