Interactions between hearing aid and patient in the individual fitting situation.

Due to individual variations in the auricle, meatus, middle ear, and the ear mould, identical hearing aids will yield different insertion gain in different ears. The present experiment was performed in order to introduce an adjusting factor for the individual ear mould-supplied patient compared with KEMAR data as a basis for the selection and fitting of the hearing aid. For different hearing aids tested on the same person the variation in the insertion gain compared with KEMAR data was, however, of such an extent that such a factor cannot be immediately introduced. The variation reflects differences in the sensitivity of the hearing aids with respect to the acoustic load represented by the ear mould-fitted individual ear. In order to predict the effect of a certain hearing aid on one specific patient it is necessary to know the sensitivity for the acoustic load impedance in advance.