Bone‐Conduction Thresholds for Sonic and Ultrasonic Frequencies

Several investigators have reported that high‐intensity sounds in the ultrasonic region above 20 kc can produce auditory sensations in individuals with normal hearing. The present experiment was performed to establish bone‐conduction thresholds for pure tones from 5 to 100 kc in a group of subjects with no otological abnormalities. Fifty male and fifty female subjects, ranging in age from 18 to 24 years, were tested on only the left or right ear 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 bone. The curve for the mean threshold of hearing (for subjects audiometrically screened by air conduction from 250 to 8000 cps) showed a very sharp rise between 10 and 20 kc with a slope of approximately 50 db/octave, and a gradual rise above 20 to 100 kc with a slope of approximately 18 db/octave. The maximal discrepancy between men and women was approximately 5.5 db (at...