Journal of the American Medical Association has an article on the results of
clinical trials of 3 common hearing aid circuits. Full text is available at
web site to paid subscribers or in the Oct 11 paper edition of the journal
Vol. 284 No. 14,
October 11, 2000
Efficacy of 3 Commonly Used Hearing Aid Circuits, A Crossover Trial
Context: Numerous studies have demonstrated that hearing aids provide
significant benefit for a wide range of sensorineural hearing loss, but no
carefully controlled, multicenter clinical trials comparing hearing aid
efficacy have been conducted.
Objective: To compare the benefits provided to patients with sensorineural
hearing loss by 3 commonly used hearing aid circuits.
Design Double-blind, 3-period, 3-treatment crossover trial conducted from May
1996 to February 1998.
Setting: Eight audiology laboratories at Department of Veterans Affairs
medical centers across the United States.
Patients: A sample of 360 patients with bilateral sensorineural hearing loss
(mean age, 67.2 years; 57% male; 78.6% white).
Intervention: Patients were randomly assigned to 1 of 6 sequences of linear
peak clipper (PC), compression limiter (CL), and wide dynamic range compressor
(WDRC) hearing aid circuits. All patients wore each of the 3 hearing aids,
which were installed in identical casements, for 3 months.
Main Outcome Measures: Results of tests of speech recognition, sound quality,
and subjective hearing aid benefit, administered at baseline and after each
3-month intervention with and without a hearing aid. At the end of the
experiment, patients ranked the 3 hearing aid circuits.
Results: Each circuit markedly improved speech recognition, with greater
improvement observed for soft and conversationally loud speech (all 52-dB and
62-dB conditions, P.001). All 3 circuits significantly reduced the frequency of
problems encountered in verbal communication. Some test results suggested that
CL and WDRC circuits provided a significantly better listening experience than
PC circuits in word recognition (P = .002), loudness (P = .003), overall liking
(P = .001), aversiveness of environmental sounds (P = .02), and distortion (P =
In the rank-order ratings, patients preferred the CL hearing aid circuits more
frequently (41.6%) than the WDRC (29.8%) and the PC (28.6%) (P = .001 for CL vs
both WDRC and PC).
Conclusions: Each circuit provided significant benefit in quiet and noisy
listening situations. The CL and WDRC circuits appeared to provide superior
benefits compared with the PC, although the differences between them were much
less than the differences between the aided vs unaided conditions.