A comparison of functional gain and 2 cm3 coupler gain.

The amount by which individual functional gain differed from 2 cm3 coupler gain for a single wide-band hearing aid was determined empirically for 20 hearing-impaired adults. Both occluding and non-occluding earmold fittings were evaluated. The amount of this difference accounted for by known measurement differences, such as coupler, real-ear response differences, earmold differences, and sound field pressure differences between the eardrum and hearing aid microphone location, was also established. While it was found that accounting for the known major measurement differences resulted in a reasonable estimate of median differences between measurements of functional gain and measurements of gain in a 2 cm3 coupler, individual variability was quite high.