The Master Hearing Aid

Abstract

As early as the 1930s the term Master Hearing Aid (MHA) described a device used in the fitting of hearing aids. In their original form, the MHA was a desktop system that allowed for simulated or actual adjustment of hearing aid components that resulted in a changed hearing aid response. Over the years the MHA saw many embodiments and contributed to a number of rationales for the fitting of hearing aids. During these same years, the MHA was viewed by many as an inappropriate means of demonstrating hearing aids; the audio quality of the desktop systems was often superior to the hearing aids themselves. These opinions and the evolution of the MHA have molded the modern perception of hearing aids and the techniques used in the fitting of hearing aids. This article reports on a history of the MHA and its influence on the fitting of hearing aids. Keywords hearing aid, master hearing aid, audiologyCurran and Galster 109 various ways since, not always favorably, but in a general sense, it describes rather well the many alternative versions that have surfaced since the introduction of the electrical hearing aid.Figures 1, 2, and 3 show examples of MHAs from early to more recent times. The design and function of each succeeding version reflected the state-of-the-art of its era, adapting appropriately as technologies and fitting schemes evolved. The Nature of the ProblemThe problem of how-to-fit was recognized by the early pioneers in hearing aid development. In their search for an answer, they turned naturally to inventing "fitting machines," for their backgrounds were in engineering and manufacturing. The notion of using a specifically designed mechanical or electrical apparatus to execute a corrective prescription for a sensory deficit is not novel. An obvious example is the use of the phoropter, an effective adjunct in the field of visual correction. The phoropter calculates the correct lens prescription according to the patient's responses as lenses are being compared. The autorefractor is an automated expression of the phoropter, a computer controlled device that provides an objective account of refractive error without the need for patient input.However, with regard to compensating for hearing loss, there is one significant difference. Franks (1978), in commenting on the contrast between the instrumentation used by the optometrist in fitting eyeglasses and master hearing aids used by hearing aid professionals in the past, makes a telling observation:The optometrist is trying to prosthetically remedy a conductive problem, light transmission through the lens of the eye, and would never attempt to use a device . . . to attempt to remedy a receptor problem such as deterioration of the retinal structure. The audiologist is trying to prosthetically remedy a receptor problem, deterioration of the cochlear mechanisms . . . Trends in Amplification 17(2)The diminished transmission of the acoustic signal through the impaired middle ear is equivalent to the diminished transmission of visual stimuli through the defecti...

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