|These illustrations were drawn by Frank L. Vanni, Visual Information Specialist of the Scientific and Technical Publications Section. Mr. Vanni followed several sources, particularly Kenneth W. Berger's 1970 classic The Hearing Aid: Its Operation and Development.|
Hearing enhancement is as old as cupping a hand behind an ear, a method that provides some 10 dB of gain in the region of 1000 Hz, is easy to use, and costs nothing. It is supposed that seashells and horns have been in use since time out of mind to extend sound gathering still further. Horn, in particular, is easily shaped and worked by heating and scraping; it was as generally useful to societies of antiquity as plastics are to ours. This drawing of a multisegmented hearing trumpet faced Chapter One.
Hand-held trumpets tended to deprive the user of the use of one hand as the price for improved hearing. Here a conical trumpet is attached to spectacle frames in an attempt to solve this problem. This drawing faced Chapter Two (1).
Space did not permit the inclusion of this lovely binaural acoustic device that left the hands free while providing amplification; otherwise, it would have faced Chapter Three (2).
One problem with acoustical instruments was that amplification is dependent upon size: the larger the trumpet, the more sound it could gather. The problem of concealing such devices prompted some ingenious solutions. Here, the entire table is the aid: sound is gathered through grillework in the neck of the "urn". It is directed down through the urn's body into the pedestal of the table, where it enters the ear tube. This Acoustic Urn faced Chapter Four (3).
At the opposite pole from concealment is flaunting what you have. The London Dome was a compound trumpet; its "stem" is actually part of an inner horn that faces the base of the outer shell, achieving the effect of a longer device in a compressed form. Made of brass or even silver, handsomely engraved examples exist that were obviously made to be admired. This one faced Chapter Five (4).
Electronics, particularly the transistor, made concealment of aids practical and affordable. Here a binaural aid dating from the 70s encloses all circuitry, including microphones and batteries, in the frames of eyeglasses. Only the earmoulds are exposed in this illustration facing Chapter Six (5).
Largely concealed beneath the pinna, the behind-the-ear (BTE) aid remains the device of choice for some users, particularly those needing directional microphones or having difficulty manipulating smaller instruments. This example faced Chapter Seven
Behind-The-Ear Aid. With sufficient size to more than accomodate today's smaller circuitry and batteries, the BTE's larger controls are convenient for those users with manipulation problems in addition to hearing difficulties.
Miniaturization of components, including batteries, means that the auditory channel can house the entire aid. This completely-in-channel aid is scarcely noticeable and effective, providing sound unobtrusively to many users. This illustration faced Appendix 1 of Chapter Eight (6).
Further minaturization of circuitry permits the direct stimulation of cochlea without the danger of infection: sound signals pass the skin barrier via magnetism, rather than via percutaneous wires. This schematic representation of the process faced Chapter Nine (7).
In a glance back at the 19th Century, this illustration of Giovanni Paladino's "Fonifero" of 1876 faced Chapter Ten. Essentially a rod with a smooth fork on the "transmitting" end and a cup on the "receiving" end, the Fonifero relied on bone conduction of sound to work, in addition to taking its signal from direct contact with the larynx region of the speaker. The cup was placed on the forehead, the mastoid area, or against the teeth of the listener (8).
And finally, this metal hearing trumpet faced the Glossary at the end of the book.
Last revised Thu 02/11/1999