Variations in the feedback of hearing aids

Variations in the loop response of hearing aids caused by jaw movements, va riations in acoustics outside the ear, and variations of vent size have bee n identified. Behind The Ear (BTE) and In The Ear Canal (ITEC) hearing aids were considered. The largest variations among the variations of the acoust ics outside the ear, except when the hearing aid was partly removed, were f ound with the ITEC when a telephone set was placed by the ear. The variatio ns of the loop response caused by changes in vent size were compared with t he variations of a theoretical model of the feedback path. The theoretical model was also used to compare the feedback of:different designs of the ven t that gives the same acoustic impedance at low frequencies. The calculated feedback was less with the short vents (12 mm) than the long vents (24 mm) . (C) 1999 Acoustical Society of America. [S0001-4966(99)05811-7].