Maico Hearing Aids, Minneapolis ~ 1954 NAM; from "Industry on Parade"

more at http://quickfound.net/

Originally a public domain film from the Library of Congress Prelinger Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://en.wikipedia.org/wiki/History_of_hearing_aids

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

The first electronic hearing aids were constructed after the invention of the telephone and microphone in the 1870s and 1880s. The technology within the telephone increased how acoustic signal could be altered. Telephones were able to control the loudness, frequency, and distortion of sounds. These abilities were used in the creation of the hearing aid.

The first electric hearing aid, called the Akouphone, was created by Miller Reese Hutchison in 1898. It used a carbon transmitter, so that the hearing aid could be portable. The carbon transmitter was used to amplify sound by taking a weak signal and using electric current to make it a strong signal. These electronic hearing aids could eventually be shrunk into purses and other accessories.

One of the first manufacturers of the electronically amplified hearing aid was the Siemens company in 1913. Their hearing aids were bulky and not easily portable. They were about the size of a "tall cigar box" and had a speaker that would fit in the ear.

The first vacuum-tube hearing aid was patented by a Naval engineer Earl Hanson in 1920. It was called the Vactuphone and used the telephone transmitter to turn speech into electrical signals. After the signal was converted, it would be amplified when it moved to the receiver. The hearing aid weighed seven pounds, which made it light enough to be carried. Marconi in England and Western Electric in the US began marketing vacuum tube hearing aids in 1923.

During the 1920s and 1930s, the vacuum tube hearing aid became more successful and began to decrease in size with better miniaturization techniques. The Acousticon's Model 56 was created in the mid-1920s and was one of the first portable hearing aid units, although it was quite heavy. The first wearable hearing aid using vacuum tube technology went on sale in England in 1936, and a year later in the United States. By the 1930s, hearing aids were becoming popular to the public. Multitone of London patented the first hearing aid to use automatic gain control. The same company introduced a wearable version in 1948.

Military technological advances that occurred in World War II helped the development of hearing aids. One of the major advances that World War II enabled was the idea of miniaturization. This could be seen by Zenith's pocket-sized Miniature 75...

The development of transistors in 1948 by Bell Laboratories led to major improvements to the hearing aid. The transistor was invented by John Bardeen, Walter Brattain, and William Shockley. Transistors were created to replace vacuum tubes; they were small, required less battery power and had less distortion and heat than their predecessor. These vacuum tubes were typically hot and fragile, so the transistor was the ideal replacement. The 1952 Sonotone 1010 used a transistor stage along with vacuum tubes, to extend battery life. The size of these transistors led to developments in miniature, carbon microphones. These microphones could be mounted on various items, even eyeglasses. In 1951, Raytheon manufactured the transistor and was one of the first companies to mass-produce transistors to throughout America. Raytheon realized that their hearing aid only lasted short-term and began to sell the vacuum-tube hearing aids again along with transistor hearing aids.

The act of putting transistors into hearing aids was so quick that they were not properly tested. It was later found that transistors could get damp. Because of this dampness, the hearing aid would only last for a few weeks and then die. In order to stop this from happening, a coating had to be put on the transistor to protect it from the dampness. This problem had to be fixed in order for transistors in hearing aids to be successful.

Zenith was the first company to realize the problem with transistors was the body heat of individuals. After coming to this conclusion, the first "all-transistor" hearing aids were offered in 1952, called the Microtone Transimatic and the Maico Transist-ear...