Bone-Conduction Thresholds for Sonic and Ultrasonic Frequencies

Abstract

Several investigators have reported that high-intensity, bone-conducted sounds in the ultrasonic region above 20 kc/sec can produce auditory sensations in individuals with normal hearing. The present study was performed to establish the curve of audibility for bone conduction from approximately 5 to 100 kc/sec in a group of subjects with no audiometric or otological abnormalities. Fifty-three male and 50 female subjects, ranging in age from 17 to 24 years, were tested on the left or right ear only by a modified method of limits, with all tests being conducted in an anechoic chamber. A crystal transducer, calibrated in a water medium, was used to transmit the acoustic energy to the mastoid portion of the temporal bone. For 38 male and 37 female subjects screened from the larger sample by means of an otological examination and an air-conduction audiometric test from 250 cps to 8 kc/sec, the curve for the mean threshold of hearing showed a very sharp rise between 10 and 20 kc/sec with a slope of approximately 50 dB/octave, and a gradual rise from 20 to 100 kc/sec with a slope of approximately 15 dB/octave. The maximal discrepancy between men and women was approximately 5.5 dB (at 14 kc/sec). The standard deviations ranged from approximately 2 to 15 dB, with the maximal value for each group occurring at 16 kc/sec. In general, the results of the present study are in agreement with earlier fragmentary reports.