Effects of peaks in hearing aid frequency response curves on comfortable listening levels of normal hearing subjects

For normal hearing subjects, MCLs were measured for speech presented through an amplifying system having a smooth frequency response and for 12 conditions in which a peak was added to the base response. Low, mid, and high frequency peaks were tested for 4 bandwidths ranging from one twenty-third of an octave to over one octave. All peak conditions caused a reduction in MCL, relative to the smooth response condition. The amounts of reduction agreed closely with predictions based on Zwicker's loudness model. The presence of peaks in a hearing aid frequency response curve would result in less signal being delivered than for a smooth response, when the hearing aid volume control has been set for comfortable listening. This is consistent with research which shows that peaks adversely affect speech intelligibility and supports the view that response curves should be made as smooth as possible.