Efficacy of 3 commonly used hearing aid circuits: A crossover trial. NIDCD/VA Hearing Aid Clinical Trial Group.

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

Functional gain.

The concept of functional gain was popularized by Pascoe in 1975, and for some time was one of the most popular hearing aid evaluation techniques. More recently probe tube systems for measuring insertion gain have become popular, and some questions regarding the continued utility of functional gain have been raised. In this paper some of the major advantages and disadvantages of functional gain are reviewed. While functional gain is subject to contamination from noise external or internal to the hearing aid, it does provide subjective information not available from insertion gain.

A comparison of functional gain and 2 cm3 coupler gain.

The amount by which individual functional gain differed from 2 cm3 coupler gain for a single wide-band hearing aid was determined empirically for 20 hearing-impaired adults. Both occluding and non-occluding earmold fittings were evaluated. The amount of this difference accounted for by known measurement differences, such as coupler, real-ear response differences, earmold differences, and sound field pressure differences between the eardrum and hearing aid microphone location, was also established. While it was found that accounting for the known major measurement differences resulted in a reasonable estimate of median differences between measurements of functional gain and measurements of gain in a 2 cm3 coupler, individual variability was quite high.