[Examination in three hearing aids (postaural types) concerning the influence of voltage on the output sound level and on the automatic grain control (author's transl)].

In three modern hearing aids the effect of voltage on the initial sound pressure and the conduct of regulation are examined. The following apparatus were measured: Bosch 66 F AGCI related to the regulation at power entrance, Siemens 274 PP AGCI related to the regulation at power entrance, Microtechnic A 18, related to the regulation at power exit. The examinations show that the hearing aids tested have to operate with that voltage recommended by the producers. The nickel-cadmium accumulators are not efficient. Writing a prescription for an adequate power supply is as important as the prescription of the hearing aid itself.