Performance Characteristics of Electrical Hearing Aids for the Deaf

Abstract

There has long existed a need, which has been expressed by otologists and others interested in persons who are hard of hearing, for a disinterested comparison of the performance characteristics of portable commercial carbon microphone hearing aids. In 1934 Dr. Horace Newhart, as chairman of the Committee of Deafness Prevention and Amelioration of the American Academy of Ophthalmology and Otolaryngology, proposed that an investigation be undertaken to determine whether significant differences exist between the hearing aids of various manufacturers. With the help of funds supplied by the Graduate School Research Committee of the University of Minnesota the proposed investigation was commenced in July 1934 as a joint project of the Division of Otolaryngology and of the Electrical Engineering Department.It was the original plan to test the products of the leading and representative manufacturers of portable carbon microphone hearing aids and thereupon to make an attempt to specify easily applied procedures for evaluating their relative worth. Accordingly, seven different stock hearing aid models of the portable carbon microphone type were tested in an extensive preliminary investigation. These tests indicated the nature of the data needed to determine the performance characteristics of the instruments and showed which models were comparable as to amplifying power. A second more extensive series of tests was conducted on the latest product of four of the leading manufacturers. This article is a report on this second series of tests, with an introductory discussion of the general problem.Two general types of hearing aids are in current use, the air conduction type, which is fundamentally similar to the telephone, and the so-called bone conduction type. The first part of the discussion will be confined to the air conduction method of ameliorating deafness.