Sound pressure in the external auditory canal during bone-conduction testing

Sound pressure levels (SPLs) were measured in the external auditory canals (EACs) of 16 subjects with normal hearing and normal middle ear immittance. SPLs were the result of bone-conduction (BC) stimulation at 500, 1000, 2000, and 4000 Hz, with the oscillator placed either on the forehead or on the mastoid process. At 1000, 2000, and 4000 Hz, significantly higher SPLs were measured when the head was stimulated from the mastoid than from the forehead. When SPLs were compared between right and left EACs, forehead placement of the oscillator produced no interaural differences, while mastoid placement resulted in significantly greater EAC SPLs ipsilateral to the oscillator at 2000 and 4000 Hz. We conclude that forehead placement of a BC vibrator may help to lessen the (unwanted) contribution of the EAC to measurements of hearing sensitivity by BC.