An equivalent input noise level criterion for hearing aids

The purpose of this project was to establish a maximum acceptable equivalent input noise level (EINL) for hearing aids. It was found that, if the version of the National Acoustic Laboratories (NAL) procedure for selecting the gain and frequency response of hearing aids, which includes modifications for severe and profound hearing loss is used, the EINL criterion can be relaxed for higher gain hearing aids, as a function of the gain of the aid. The relationship between relaxation of the criterion and 2-cc coupler gain is nonlinear, in different amounts, at the various frequencies, so no simple rule can be used to describe the manner in which the criterion can be relaxed.