This study investigated three issues involving corrections for individual ear acoustics in hearing aid prescriptions: (a) the extent to which inconsistencies in the sound-field reference position can affect comparative corrections for the real-ear unaided response (REUR); (b) the extent to which individual variability in the real-ear-to-coupler level difference (RECD) supports the use of individual measurements as opposed to an average-ear estimate; and (c) the adequacy of using KEMAR estimates of the effects of the location of the hearing aid microphone. In Experiment 1, KEMAR REURs using over-the-ear and under-the-ear reference positions were compared with KEMAR REURs using a center-of-head reference position. Maximum differences of 4–9 dB were found in the 1500- to 5000-Hz range, depending on test conditions. In Experiment 2, the ear canal response of an insert earphone was compared to the 2-cc coupler response of the same earphone to calculate the RECD. Individual RECDs for a population of hearing aid candidates were compared to the RECD for KEMAR. For 8 of the 15 subjects (9 of 18 ears), the RECD was more than 4 dB different from KEMAR at two or more third-octave frequencies between 500 and 4000 Hz. In Experiment 3, the effect of the location of the hearing aid microphone for in-the-ear (ITE) and in-the-canal (ITC) locations was compared with the over-the-ear (OTE) location for 18 ears and for KEMAR. The effects varied across individual ears, but all ears and KEMAR showed positive gain in the high frequencies for the ITE and ITC locations. The relevance of these results to hearing aid prescription practices is discussed.

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The present investigation examined the effect of different compression ratios (compression ratios of 2:1, 3:1, 8:1 and wide-dynamic-range compression) on speech intelligibility and quality in compression-limiting systems. Speech intelligibility and quality were evaluated for sentences in four-talker babble. Sentences were presented at a signal-to-noise ratio of 7.5 dB at six different input levels, and at two of these levels (80 and 100 dB SPL) four different signal-to-noise ratios. Speech intelligibility was evaluated in terms of percent correct words and the quality of the conditions was rated on a scale of 0 to 100%. Across subjects, across input levels, and across signal-to-noise ratios, different compression ratios did not differ in terms of speech intelligibility and quality. Individual subject analysis revealed that for three of the subjects 8:1 compression ratio conditions gave the best speech intelligibility and quality results. One of the subjects achieved his best speech intelligibility performance with the wide-dynamic-range compression condition. For four of the subjects, different compression ratios did not effect speech intelligibility and quality differently. Overall, results indicated that there were considerable variations in performance with different compression ratios among individuals with similar hearing sensitivity. [Work partly supported by Northwestern Univ. Doctoral Student Research Grant.]