Internal circuit noise of hearing aids and speech intelligibility.

The circuit noise generated internally by various components of a hearing aid is influenced mostly by circuit gain and frequency response. The measurement of this variable and its effect, if any, on the listener's ability to unders-and monosyllabic words through a hearing-aid system was investigated. The overall circuit noise of 10 behind-the-ear hearing aids of different brands with comparable gain and frequency response was measured. Based on these measurements, a low-noise and a high-noise hearing aid were selected as the test aids. The internal circuit noise of each test aid was then measured automatically by utilizing a 1/3-octave-band tracking filter. Monosyllabic words were recorded through the test aids at two gain settings. The prerecorded test tapes were presented to 32 normal-hearing listeners. Findings indicate that different amounts of circuit noise generated internally by a hearing aid do exist among various aids. However, the noise generated by the hearing aids used in this study does not affect significantly the intelligibility of monosyllabic words.

Intelligibility of speech transduced via classroom-installed FM and conventional audio induction loop amplification systems.

This study was designed to investigate the intelligibility of speech transduced through a classroom-installed FM system and a conventional induction loop amplification (ILA) system and to examine the applicability of an FM adapter when used with commercially available hearing aids. Findings indicate that speech reproduced via the FM system is significantly better than that of the conventional audio induction loop used in this study. It seems likely that the irregular high-frequency response of the ILA system was responsible for this difference. When an FM adapter was used in conjunction with body-type hearing aids, the frequency response of the telecoil along with the positioning of the adapter determine the total performance of the aid.

Performance of hearing aids with an induction loop amplification system: laboratory versus classroom setting.

This study was designed to investigate the acoustic response of ten body-type hearing aids when used with an induction loop amplification (ILA) system in the laboratory and in the actual classroom setting. Undesirable frequency response characteristics were discovered in the classroom ILA system used in this study. These consist of a slightly poorer low-frequency response and a deep notch at about 2,500 Hz. Had the frequency response of the classroom ILA system been flat, differences between laboratory and classroom measures would have been minimized. Findings of this study support the practicality of measurement in the classroom of the operating characteristics of ILA systems.

Directional microphone in hearing aids. Effects on speech discrimination in noise.

This study was designed to investigate the amount of directionality among three directional aids of different brands and to compare speech discrimination ability of hearing-impaired persons using directional and nondirectional hearing aids in competing background noise. For each hearing aid under study, the full-on gain curves were obtained at 45, 135, 225,, and 315 degree azimuths in an anechoic chamber. Thirty-two hearing aid users were included. Discrimination ability was assessed, using commercially available W-22 disc recordings. Findings indicate directionality varies among directioalaids. The hearing aid that shows the greatest directional effect was found to provide the listeners with best speech discrimination ability under relatively difficult listening conditions. However, it is inadvisable to recommend just any directional aid without careful evaluation of its directional capability under competing noise.