Evaluation of high-fidelity hearing aids.

An essential building block for any high-fidelity hearing aid is an amplifier-transducer-coupling combination that does not audibly degrade the sound, that is, provides high-fidelity sound reproduction as judged by someone with normal hearing. To demonstrate that such a combination is possible, two binaural pairs of hearing aids were assembled using available hearing aid transducers and electronic components, one pair of Over-The-Ear hearing aids with 8-kHz bandwidth and one pair of In-The-Ear hearing aids with 16-kHz bandwidth. Objective insertion-gain measurements on these aids, obtained with a KEMAR manikin in a diffuse sound field, revealed a frequency-response accuracy comparable to that available in expensive high-fidelity loudspeakers. Subjective fidelity ratings obtained from three groups of listeners judging prerecorded A-B-A comparisons (made from equalized eardrum-position microphones in a KEMAR manikin) produced a similar conclusion. We conclude that the important question for hearing aid research is no longer "What can a hearing aid be designed to do?" but "What should a hearing aid be designed to do for the hearing impaired?"