When the ear canal is occluded with an earmould, then own voice might sound different and loud sounds are generated when eating and walking. Other effects such as mist and itch do also appear. Hear an investigation is reported which included 48 hearing aid users. The users were asked to fill in a questionnaire based on their daily experience with their personal hearing aid. It turned out that 73% of these persons experienced a change in own voice, but both occlusion effects of acoustic, mechanical and biological origin were experienced. The same persons came into Oticon's clinic, where their hearing aid fitting and occlusion effect were evaluated. Occlusion effect was measured as the difference in real ear sound pressure level with and without hearing aid while the person was speaking. It was done both with the hearing aid turned off and with the hearing aid turned on. Relations between their experienced annoyances and the objective measurements were analysed. Persons suffering from tinnitus behaved differently than person without tinnitus. The latter group showed significant relations between the measured occlusion effect, hearing loss and the personal of occlusion. The actual sensation level is also significantly correlated with annoyance for subjects without tinnius. It could also be concluded that the objectively measured occlusion effect varies a lot between subjects and that it is not possible to calculate the exact occlusion effect only based on the vent size and insertion gain.
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Poulsen, Torben, Lundh, Peter
Department of Acoustic Technology, Technical University of Denmark, 1997