INTELLIGIBILITY OF TELEPHONE SPEECH FOR THE HEARING-IMPAIRED WHEN VARIOUS MICROPHONES ARE USED FOR ACOUSTIC COUPLING

This study set out to systematically measure the effect of using various candidate microphones for acoustic coupling of hearing aids to a telephone receiver. Intelligibility of words was determined for three microphones and three levels of interfering noise for a total of nine conditions. The subjects all had moderate hearing loss. It was found that microphones that exhibit pressure gradient sensitivity can, when properly positioned relative to the telephone receiver, increase intelligibility scores significantly. Results show that comparable listening performance is achieved with a pressure gradient microphone at a 10 dB higher level of interfering noise than with a microphone that is only sensitive to pressure. The results quantify the effect of microphones in acoustic coupling of hearing aids to telephones and point to a possible means for improving some types of hearing aids to facilitate telephone use for the hearing-impaired.