ASA 124th Meeting New Orleans 1992 October

4pPPa10. Digital feedback suppression in open-ear hearing aids.

Timothy H. Ruppel

Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677

Lisa Lucks Mendel

F. Douglas Shields

Univ. of Mississippi, University, MS 38677

Some preliminary studies into the effectiveness of digital feedback correction schemes for open-ear hearing aids have been conducted. Three different hearing aids were used: (1) a commercially available behind-the-ear (BTE) hearing aid with an open earmold modified so that its internal filters and amplifiers were bypassed and the microphone and receiver connected directly to a digital signal processor, (2) the same BTE hearing aid with a closed earmold for comparison, and (3) a specially designed hearing aid with the microphone placed at the entrance to the ear canal and the receiver placed directly inside the ear canal. Off-line probing was used to determine the characteristics of the feedback path. In this experiment, the subjects had normal hearing. The addition of digital feedback control showed significant improvement in the available insertion gain from the open ear devices, as demonstrated in real ear measurements of the subjects.