Amplification bandwidth and intelligibility of speech in quiet and noise for listeners with sensorineural hearing loss.

The intelligibility of speech mixed with noise (+6 dB S/N) and in quiet was measured as a function of its audible bandwidth for 7 listeners with moderate sensorineural hearing losses. Words were presented at three levels in the field (50, 60 and 70 dB SPL) and amplified with a Limiting Master Hearing Aid (LMHA) which allows independent control of gain and maximum power output in each of nine, half-octave channels. The frequency gain characteristics were chosen so the speech spectrum (60 dB SPL) at the input was shaped to approximate the individual listener's contour of most comfortable listening levels at the output. At each level and for the words in noise as well as quiet, the LMHA was set for four bandwidths (266-6 000, 375-4 242, 530-3 000 and 750-2 121 Hz). For these conditions, the listeners all obtained the highest mean score with the LMHA set for the widest bandwidth. The listener's ability to understand the words, after adjustment for individual differences, was well correlated (0.77-0.91) with the articulation index. Preliminary observations on the acceptability of amplified sounds, that is, loud speech, impact noise, an air-horn blast, and a party ratchet, are included.