Some Recent Engineering Developments in Group Hearing Aids
Charles E. Harrison · The Journal of the Acoustical Society of America · 1950
The engineering requirements for group hearing aids to be used with profoundly deaf children are primarily (1) a high level of maximum undistorted acoustic output (roughly 130 db), (2) suitable frequency response, (3) ease of operation by the teacher, (4) suitable acoustic treatment of the school room. The evolution of a series of instruments which attempt to satisfy these requirements will be described. The first instruments met the requirements very satisfactorily but in a subsequent series it was decided to include compression amplification. When this had been achieved it was decided to combine compression amplification with automatic volume control in an attempt to “package” speech in the relatively small auditory area available to the profoundly deaf child. This development raised the important question as to the optimum dynamics of the speech itself within the small area of audibility. The design of the series of instruments will be discussed and problems for the immediate future will be stated.