Assistive Listening Knowledge Base
  • Peer-reviewed study (electroacoustic bench measurements)

Some effects of FM-system coupling on hearing aid characteristics

From https://assistivelisteningknowledgebase.org/evidence/hawkins-schum-1985/ · record checked 13 October 2026

  • Hawkins DB, Schum DJ
  • Journal of Speech and Hearing Disorders 50(2):132-141 (American Speech-Language-Hearing Association)

Independent (journal study; the archived abstract and metadata give no author affiliation or funder, and the full text was not read)

Summary

Measured four hearing aids alone and connected to two FM systems by direct audio input, a neck loop and a silhouette inductor, comparing frequency response, distortion, noise and input-output functions.

Key findings

  • Measured frequency response, harmonic distortion, noise levels, input-output functions and the taper of the FM receiver's volume wheel for four hearing aids, then repeated the measurements with each aid connected to two FM systems through direct input, a neck loop and a silhouette inductor.
  • Found large differences in some frequency-response comparisons, with no single coupling method consistently closer to the response of the hearing aid alone.
  • Distortion and noise were similar for the hearing aids alone and for the FM-hearing aid combinations, except with the silhouette inductor.
  • Some combinations gave very non-linear volume-wheel curves, and input-output functions differed between the hearing aids and the FM systems; the authors conclude that a hearing aid's electroacoustic characteristics cannot be assumed to be preserved when it is connected to an FM system. Minor changes in the position of the silhouette against the aid were also investigated.

Limits

Read from the PubMed abstract only; the size of the differences and the effect of moving the silhouette are not stated there. Personal classroom FM systems and hearing aids of the early 1980s, so the results describe the coupling methods rather than current products.

Read the original

pubs.asha.org/doi/10.1044/jshd.5002.132

Link checked . We link to the original and do not host copies.

Cited in

Cite this source

Hawkins DB, Schum DJ. Some effects of FM-system coupling on hearing aid characteristics. Journal of Speech and Hearing Disorders 50(2):132-141 (American Speech-Language-Hearing Association). May 1985. https://pubs.asha.org/doi/10.1044/jshd.5002.132 (accessed 13 October 2026).

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