Effect of ear canal occlusion on pure-tone threshold sensitivity

This study sought to quantify the effects of varying the degree of ear canal occlusion on pure-tone threshold sensitivity. Thresholds were obtained from each ear of five normal-hearing adults without occlusion, with complete occlusion, and with partial occlusion estimated to be 40-60% and 60-80%. A commercial lubricant was used in the completely occluded condition to eliminate possible acoustic leakage. Results showed a reduction of threshold sensitivity in all occluded conditions, with the greatest effect in frequencies above 1000 Hz. Only in the completely occluded condition were frequencies below 1000 Hz affected. In the partially occluded conditions, thresholds decreased by an average 7.5 dB and 13.0 dB across frequency for the 40-60% and 60-80% conditions respectively. At frequencies above 1000 Hz, the average threshold shifts for the two partially occluded conditions were 10.0 dB and 16.8 dB respectively. The implications of these findings on routine pure-tone audiometric procedures, with specific relevance for industrial hearing conservation programs, are discussed.