Vents in hearing aids have two major effects on the insertion gain of a hearing aid: they let low-frequency sound in without amplification, and they reduce the low-frequency gain of sound transmitted through the hearing aid. Their net effect on low-frequency gain can thus be either negative or positive. This paper shows how to allow for both of these effects. One of the results is that for many hearing-impaired clients, there is a range of coupler gain curves which will result in the required insertion gain. The tables in this article are arranged to enable the user to specify a desired vent, and then determine the allowable range of coupler gains that will achieve a desired insertion gain to within a specified tolerance. The results of various studies comparing coupler gain and insertion gain are also compared and combined. The calculation method outlined in this paper can predict low-frequency real ear insertion gain for the individual subject with a prediction accuracy (root-mean-square-error) of 3.6 dB.
Address reprint requests to Harvey Dillon, Ph.D., National Acoustic Laboratories, 126 Greville Street, Chatswood, 2067, Australia.
Received February 25, 1991; accepted August 16, 1991.
© Williams & Wilkins 1991. All Rights Reserved.