Comparison of two hearing aid receiver-amplifier combinations using sound quality judgments

Sound quality judgments were obtained on two binaural pairs of laboratory hearing aids with similar battery drain. One pair had a traditional low-current-drain "starved Class A" output stage. The other had a new (at the time) "Class D" output stage. Speech and music reproduction was rated, for seven input levels between 70 and 100 dB SPL, on an overall quality scale by juries of normal-hearing and hearing-impaired subjects. The same subjects also were asked to assign a dollar value to each condition by answering the question "What would you pay for a hearing aid that sounded like that?" Both subject groups rated the hearing aids with the Class D output stage as having superior sound quality across a variety of input levels and test materials, consistent with objective distortion measurements. On the average, each one-percentage point increase in sound quality rating corresponded to a $6.75 increase in perceived value in these experiments.