Candidates for multiple frequency response characteristics.

This study examined what types of subjects may benefit from the use of multiple memory hearing aids that offer variation in their frequency response characteristics. Thirty subjects with varied degrees and configurations of hearing loss compared an individually prescribed frequency response (NAL) and two variations in which the real-ear response slope was either increased (more high-frequency emphasis) or decreased by about 3 dB/octave over the range from 500 Hz to 4000 Hz. The evaluations consisted of paired comparison judgments of pleasantness and of ease of understanding speech, in quiet and in three background noises with substantially different acoustic spectra (traffic noise, speech babble, and high-frequency noise). Twelve of the 30 subjects selected different frequency responses for different background noises and/or for different response criteria. These subjects were characterized as having the more severe high-frequency hearing losses (averaged across 2000, 3000, and 4000 Hz). They also tended to be those for whom the three frequency responses provided the greatest variation in real-ear low-frequency gain. (Despite substantial electronic variations, some subjects received only small variations in real-ear gain at the low frequencies). When subjects chose a different response for different conditions, they tended to prefer responses for which the slope was negatively related to the spectrum of the stimulus. This was true for both response criteria. The conclusion is that hearing aid users with substantial high-frequency losses, and who can be fitted with sufficient variation in the low-frequency real-ear gain, have the potential to benefit from having a choice of frequency response characteristics.