Acoustic and hearing aid circuit variables affecting the tolerability of aided impulsive-type sounds

The tolerability of aided impulsive-type stimuli was investigated in a group of 13 hearing-impaired listeners. Two linear circuits (one with a class A and one with a class D output stage) and one adaptive frequency response (AFR) circuit (with a class D output stage) were investigated. In a three-way paired-comparison task, subjects chose the hearing aid that was most tolerable when 75 dB sound pressure level (SPL) impulsive-type sounds were presented. Real-ear measurements of rms SPL, peak SPL, crest factor, and spectral distribution were made to determine which of these variables was most closely associated with behavioral tolerability scores. Results indicated significant differences across hearing aids for tolerability scores, rms sound pressure levels, and spectral peak frequencies. Highest tolerability scores were associated with the hearing aid that produced the lowest rms sound pressure levels in the ear canal (class D AFR). Significant correlations were found between tolerability and both rms SPL and peak SPL. Results are discussed in terms of circuit algorithm and in terms of the possible effects of hearing aid saturation.