Acoustical characterization of impermeable membranes: hearing aid applications

This investigation explored the feasibility of utilizing impermeable membranes to develop an easy to clean, water resistant hearing aid. A common problem with hearing aids is the accumulation of earwax in the small conduit that communicates the loudspeaker with the exterior of the device. This problem could be overcome by placing an impermeable membrane at the hearing aid surface to prevent earwax (as well as other substances) from entering the device. Placing a membrane between the loudspeaker and the ear canal will probably distort the sound generated by the loudspeaker, since the membrane will attenuate and possibly reflect some of the sound. A microphone and a loudspeaker similar to those utilized for hearing aid applications were used to determine the acoustic transfer characteristics of several types of impermeable membranes. Digital signal processing techniques were employed to compensate for the deleterious effects that the membrane can impart to the sound generated by the loudspeaker.