The Occlusion Effect and Ear Canal Sound Pressure Level

Comparisons were made between changes in the audibility of bone-conduction stimuli to differences in the sound pressure present in the external auditory canal when ears were occluded. Fifteen listeners with normal middle ear function were tested using pure tones of 250, 500, and 1000 Hz, delivered via a bone-conduction oscillator placed on the mastoid process and the frontal bone. At all three frequencies, and both sites of stimulation, ear canal sound pressures were greater in the occluded than in the unoccluded conditions. Concurrently, the test signals were detected at lower intensities, although the changes in audibility and external canal sound pressure levels were not unity. The occlusion effect was attenuated slightly when the skull was vibrated from the frontal bone.