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Conversational and whispered voice tests for the determination of hearing impairment, though widely used, are admittedly seriously inaccurate. When such tests are used in the fitting of hearing aids the inaccuracy becomes an even greater problem, since the patient is purchasing an expensive piece of electrical equipment on the basis of these findings. Changing the intensity of one's voice such as whispering is practically impossible to control accurately, and the natural reaction when walking away from a listener is unconsciously to raise one's voice. However, every person maintains a relatively constant loudness for direct conversational speech.
On the basis of this fact the muted megaphone, a detailed drawing of which is appended, is presented as a reasonably accurate method for determining a patient's hearing impairment and the overall gain in speech reception derived from the use of any given hearing aid.
By careful and accurate acoustic measurement it has been
Hughson W, Eva Thompson A. A MUTED MEGAPHONE FOR THE FITTING OF HEARING AIDS. JAMA. 1944;124(9):570. doi:10.1001/jama.1944.62850090005007b