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A Comparison of Four Hearing Aid Measurement Systems

Daniel M. Schwartz
Walter Reed Army Medical Center, Washington, D.C.

Measurements of hearing aid performance were made using four different electroacoustic systems. Nine hearing aids were evaluated three times in each of the four systems: a standard Bruel and Kjaer apparatus, a Fonix 5000, and both a Phonic Ear HC 1000 and HC 2000. Tests included frequency response and, when possible, total harmonic distortion, second harmonic distortion, and third harmonic distortion. Results were equivalent for frequency response and second harmonic distortion, whereas significant differences occurred for total harmonic distortion and third harmonic distortion at both the low and high frequencies. The degree to which the sum of second harmonic distortion and third harmonic distortion fails to equal the total harmonic distortion was also examined. In the low frequency region, second harmonic distortion plus third harmonic distortion yielded values considerably less than the total harmonic distortion, although good agreement was found in the midfrequencies.