There's Keystone in every Great invention

Evolution of the Hearing Aid, Listen and Learn

March 20, 2021

There’s a Keystone in every great invention.

Blindness separates us from things, but deadness separates us from people – Helen Keller

There is an estimated 466 million people worldwide with hearing loss. National Deaf History Month is celebrated from March 13 through April 15 to commemorate the achievements of people who are deaf and hard of hearing. From Beethoven to Hellen Kellen to Thomas Edison, those with hearing impairments have had a great impact on society. However, up until the 16th century it was commonly accepted that people with hearing loss also suffered from other disabilities. This assumption led to mass discrimination towards those with hearing loss. It was not until Pedro Ponce, a Spanish monk, taught a nobleman’s deaf sons how to read, write, speak and do math that this theory was disproven.

Hearing loss is not a new condition, and neither are the devices millions of people use every day to improve their hearing. In this blog, we will review the history of hearing aids.

Ear Trumpets

The use of ear trumpets for the partially deaf dates back to the 17th century. These trumpets came in a wide range of shapes, sizes and materials. Ear trumpets were made of everything from sheet iron to animal horns, and could feature quite ornate designs as a display of wealth.

In 1800, Frederick C. Rein was the first to commercially produce ear trumpets in London. In addition to ear trumpets, Rein also sold hearing fans and speaking tubes. These instruments were also used to help amplify sounds.

Electric Hearing Aid

The advent of the telephone by Alexander Graham Bell in 1876 was the catalyst for the electric hearing aid. Telephones are able to control the volume, frequency, and distortion of sounds. These abilities were used in the creation of the hearing aid.

The first electric hearing aid was invented in 1898 by Miller Reese Hutchison. Called the Akouphone, the design used a carbon transmitter and an electric current to amplify weak signals.

One of the first companies to mass produce electronic hearing aid was Siemens in 1913. Around the size of a cigar box, the hearing aids were bulky and not easily portable.

Vacuum Tube Hearing Aids

In 1920, Naval engineer Earl Hanson patented the first vacuum-tube hearing aid. The Vactuphone used a telephone transmitter to turn speech into electrical signals. The converted signal was then amplified into a receiver. The Vactuphone weighed around seven pounds, which made it more portable than previous versions.

In 1923, Western Electric in the US and Marconi in England began selling vacuum tube hearing aids. During the 1920s and 1930s, the vacuum tube hearing aid became more successful and began to decrease in size with better miniaturization techniques.

Military technological advances that occurred in World War II led to additional miniaturization techniques. This could be seen by Zenith's pocket-sized Miniature 75 hearing aid.

Transistor Hearing Aids

The development of transistors in 1948 by Bell Laboratories led to significant hearing aid improvements. Transistors replaced vacuum tubes and offered many advantages. Transistors are smaller, require less battery power, produce less heat and offer better reception (less distortion) Although battery life was improved, it was still short lived.

To extend battery life, the 1952 Sonotone 1010 used a transistor stage along with vacuum tubes. The size of these transistors led to developments in miniature, carbon microphones. These microphones could be mounted on various items such as eyeglasses.

In 1954, the company, Texas Instruments produced a silicon transistor, which was much more effective than the previous version.

The end of the transistor was marked by the creation of the integrated circuit or IC by Jack Kilby at Texas Instruments in 1958. The integration of the IC into hearing aids was perfected over the next 20 years.

Hybrid Hearing Aids

In the 1970s, a hybrid hearing aid was developed using analog components including amplifiers, filters and signal limiting combined with a separate digital programmable component into a conventional hearing aid case. The audio processing remained analog, but was controlled by a superior digital programmable component. The hybrid version was successful as it required lower power consumption and enabled smaller hearing aids.

Digital Hearing Aids

The development of the microprocessor is the 1970s enabled the miniaturization of digital hearing aids. In addition, Edgar Villchur developed an analog multi-channel amplitude compression device with amplitude compression that enabled the audio signal to be separated into frequency bands. These frequency bands were able to adjust the analog sound non-linearly so that loud sounds could be less amplified and weak sounds could become more amplified. The system of multi-channel amplitude compression would be later used as the fundamental structural design for the first hearing aids that used digital technology.

Technically this was a wearable hearing aid though it was not self-contained and the range the user could use it was limited by the range of the wireless connection and the external minicomputer was extremely heavy.

The creation of high-speed digital-array processors used in minicomputers opened up the door for advances in full digital hearing aids. These minicomputers were able to process audio signals at speeds that were equivalent to real-time.

Using this new technology, the first full digital wearable hearing aid was developed in the early 1980s by a research group at the Central Institute for the Deaf led by faculty members at Washington University in St. Louis MO. Engebretson, Morley and Popelka are credited as the inventors. The first commercial full digital hearing aid was created in 1987 by the Nicolet Corporation. In addition to the Nicolet Corporation, Bell Laboratories expanded upon the hearing aid business by developing a hybrid digital-analog hearing aid.

Modern Hearing Aids

Now, virtually all commercial hearing aids are fully digital and feature advanced digital signal processing capability. Very small and very low power specialized digital hearing aid chips are now used in all hearing aids manufactured worldwide. Many additional new features also have been added with various on-board advanced wireless technology.

Recently, made for iPhone (MFi) hearing aids were introduced by Resound. The MFi hearing aids allow users to stream phone calls, music, and podcasts directly from iOS devices.

Hearing aids must be able to withstand a wide range of environmental conditions, from temperature swings to sweat to drops (shock and vibration). A number of Keystone products can be found in modern hearing aids and the electronics that support them, including Battery lips, Contacts & Holders, PCB Test Points &Terminals; and PCB Pins, Plugs, Jacks & Sockets