Perceived sound quality of hearing aids with varying placements of microphone and receiver

Purpose:
Perceived sound quality was variously compared between either no aiding, or aiding with three models of hearing aid that varied the microphone position around the pinna, depth of the receiver in the auditory meatus, degree of meatal occlusion and processing sophistication. The hearing aids were modern designs, commercially available at time of testing.

Method:
Binaural recordings of multi-channel spatially separated speech and music excerpts were made in a manikin, either open ear or aided. Recordings were presented offline over wide-bandwidth, high quality, insert earphones. Participants listened to pairs of the recordings and made preference ratings both by clarity and externality (a proxy for ‘spaciousness’).
Two separate groups of adults were tested, twenty with audiometrically normal hearing (NH), and twenty with mild-to-moderate sensorineural hearing loss (HI).

Results:
For ratings of speech clarity, the NH group expressed no preference between the open ear and a deeply-inserted occluding aid, both of which were preferred to a low-pass filtered output of the same aid. For the music signal, a small preference emerged for the open ear recording over that of the aid. For the HI group, clarity of the deeply-inserted aid was similar to in-the-ear and behind-the-ear devices for speech, but worse for music.
Ratings of spaciousness produced no clear result in either group, which can be
attributed to study limitations and/or participant factors.

Conclusion:
Based on clarity, a wide bandwidth, particularly to beyond 5 kHz generally, and below 300 Hz for music, is desirable, independent of hearing aid design.