Acoustic resonators in the coupler and in the ear

The acoustic effect of four resonators on the output of a single hearing aid was measured on ten subjects. The purpose was to compare the effect of each of the resonators in a 2 cc (2 cm3) coupler and in real ears. Two of the resonators were special earhook resonators and the other two were contained in the earmolds. The output of the hearing aid with a standard earhook-earmold configuration was compared to the output of the hearing aid through each of four earmold-earhook configurations. One resonator was present in each of the nonstandard systems. Each of the four comparisons was made in (1) the real ears using a probe microphone in a sound-treated test booth and (2) in the coupler with the hearing aid placed in a sound-treated test box. Predictable, systematic differences were found between the 2 cc coupler measurements and the real-ear measurements. Therefore, a reliable transfer function for each resonator can be expected when 2 cc coupler specifications are used to fit resonators for specific hearing losses.