A Short History of Hearing Aids

 

Since hearing loss is one of the oldest of the known disabilities, attempts to amplify sound go back several centuries. Over time, hearing-aid producers have tried to improve the quality of sound, to develop a smaller device, and in some instances to conceal the device.

Some of the first hearing aids are described by Giovanni Battista Porta in Natural Magick in 1588. These hearing aids were made of wood and shaped like the ears of animals known to have acute hearing.

Several centuries ago, speaking tubes were used to collect sounds of people’s voices and confine them to the narrow diameter of the tube so that the sounds did not diffuse but traveled through the tube with less loss of energy. Speech went from the speaker to the listener in concentrated form.

Sailors and others who needed to communicate over considerable distances popularized the use of ear trumpets to improve their hearing. Resembling small megaphones, ear trumpets collected and concentrated sound waves at the ear. Wealthy, hearing-impaired individuals then began to purchase custom-made ear trumpets to aid their own hearing in normal circumstances.

At the beginning of the nineteenth century, companies began to manufacture a great variety of hearing devices, some stylishly designed and constructed of valuable materials and others built of cheap tin or rubber. Most did not work very well.

If a person cups his hand behind his ear, he can increase the strength of sound waves by 5 to 10 decibels (dB). The best ear trumpets could do better than that but could still only help people with mild hearing impairments. Depending on their size and shape, ear trumpets could amplify by about 10-20 dB, with most of this in the range of 500-1000 Hertz (Hz) – — only a small part of the 300-3000 Hz range of human speech. Large trumpets could amplify sound in this range by up to 40 dB, but were heavy and difficult to use.

Auricles and cornets were developed as an alternative to the ear trumpet with the hope that the devices would be less observable on the wearer. A. R. Auricle invented the implement which was smaller than an ear trumpet and which people could wear around their ear. The device resembled a musical instrument, the cornet.

Some aids such as the Audi-Ear and the Super Ear, developed in the 1920s, had headbands and were designed to fit over and under the ear. People thought that these aids would do the same job as placing the hand behind the ear and cupping it to receive sound.

Sounds are transmitted to the ear not only by vibrations in the air but also by vibration of the bones in the skull. This process is called bone conduction, and for some people in need of hearing aids it was the best way to transmit amplified sound. Bone-conduction devices had been tested since the 16th century. The first practical one was the 1879 Rhodes Audiophone, which used a vulcanite fan to pick up air vibrations and transmit them to the teeth. Electric bone-conduction hearing aids appeared in 1923 and were a major improvement. Today most bone-conduction hearing losses are corrected surgically.

The transition to battery-powered hearing aids occurred in the early 1900s, bringing sound amplification to a broader audience. The earliest electric aids offered the same amplification as ear trumpets did but covered a wider frequency range — sometimes as much as 500 to 1800 Hz. Initially the battery packs were large and were carried in separate boxes or strapped to the user’s leg. These early aids were carbon type. Later models with multiple microphones provided 25-30 dB of amplification. The introduction of amplifiers in the 1920s increased the range to 45-50 dB.

Vacuum-tube aids were introduced in 1939. In 1944, the first vacuum-tube hearing aid was developed which contained the battery inside the aid. The first transistor hearing aid was introduced in 1953. With the development of the transistor, hearing aids were able to become smaller and more powerful. In 1985 the use of microchips for programming hearing aids was introduced. Hearing aids today can provide substantially more amplification than before and can be individually tailored to address each wearer’s particular hearing loss.