History of hearing aids

The first hearing aid was created in the 17th century. The movement toward modern hearing aids began with the creation of the telephone, and the first electric hearing aid was created in 1898. By the late 20th century, the digital hearing aid was distributed to the public commercially. Some of the first hearing aids were external hearing aids. External hearing aids directed sounds in front of the ear and blocked all other noises. The apparatus would fit behind or in the ear.

The invention of the carbon microphone, transmitters, digital signal processing chip or DSP, and the development of computer technology helped transform the hearing aid to its present form.

Ear trumpets

The use of ear trumpets for the partially deaf, dates back to the 17th century. By the late 18th century, their use was becoming increasingly common. Collapsible conical ear trumpets were made by instrument makers on a one-off basis for specific clients. Well known models of the period included the Townsend Trumpet (made by the deaf educator John Townshend), the Reynolds Trumpet (specially built for painter Joshua Reynolds) and the Daubeney Trumpet.

The first firm to begin commercial production of the ear trumpet was established by Frederick C. Rein in London in 1800. As well as producing ear trumpets, Rein also sold hearing fans, and speaking tubes. These instruments helped amplify sounds, while still being portable. However, these devices were generally bulky and had to be physically supported from below. Later, smaller, hand-held ear trumpets and cones were used as hearing aids.

Frederick Rein Ltd.’s catalog, displaying evolving 19th century designs.

Rein was commissioned to design a special acoustic chair for the ailing King of Portugal, John VI of Portugal in 1819. The throne was designed with ornately carved arms that looked like the open mouths of lions. These holes acted as the receiving area for the acoustics, which were transmitted to the back of the throne via a speaking tube, and into the king’s ear. Finally in the late 1800s, the acoustic horn, which was a tube that had two ends, a cone that captured sound, and was eventually made to fit in the ear.

Toward the late 19th century, hidden hearing aids became increasingly popular. Rein pioneered many notable designs, including his ‘acoustic headbands’, where the hearing aid device was artfully concealed within the hair or headgear. Reins’ Aurolese Phones were headbands, made in a variety of shapes, that incorporated sound collectors near the ear that would amplify the acoustics. Hearing aids were also hidden in couches, clothing, and accessories. This drive toward ever increasing invisibility was often more about hiding the individual’s disability from the public than about helping the individual cope with his problem.

Electronic hearing aids

A 1933 ad for early vacuum tube hearing aids.

These German hearing aids date from around 1920 to 1950. They include an attachment similar to a telephone receiver. Museum of Medicine, Berlin, Germany.

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.

Transistor hearing aids

This early 1980s photo shows a hearing aid with a transistor that is worn over the chest with shoulder straps. It would sometimes have a problem with static interference, even if the wearer laughed or smiled.

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 Transit-ear. 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 and the technique was perfected in hearing aids over the next 20 years.

Elmer V. Carlson, the author of thirty patents, was instrumental in inventing many of the components of the modern hearing aid.

Digital hearing aid

Beginning in the early 1960s, Bell Telephone Laboratories created a process for creating both speech and audio signals on a large mainframe computer. Because of the size of digital computers, the process of simulating hearing aids was extremely slow. The progression of the audio speech signal took longer than the length of the duration of the signal itself. In order to get the power needed to process the sound, a large mainframe computer was needed. This made it nearly impossible to conceive the idea that hearing aids could be made into something that could be made to fit onto an ear. This research was important for learning about how to develop sounds for those with hearing disabilities.

In addition, in the 1970s, the microprocessor was created. This microprocessor helped to open up the door to miniaturization of the hearing aid. Moreover, researcher Edgar Villchur developed multi-channel amplitude compression. Amplitude compression enabled audio signal to be separated into frequency bands. These bands were able to adjust sounds so that sounds that were more intensive were weakened and sounds that were weakened would become more intensified. 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.

Some hearing aids from the early 21st century with traditional designs.

Another pioneer in hearing aid development was Daniel Graupe, who developed the six-channel hearing aid. The six-channel hearing aid in 1975 had digital control of the frequency in all channels. In 1979, electro-acoustic features of hearing aids were able to be changed by a simple button. The pressing of this button caused the amplification to be altered to appropriate levels for the environment in which the individual was present. This technique of controlling the hearing aid for the environment is used in some manner throughout all digital hearing aids.

The creation of high-speed digital-array processors used in minicomputers opened up the door for advances in digital hearing aids. These minicomputers were able to process audio signals at speeds that were equivalent to real-time. In 1982, at the City University of New York, the first real-time all-digital hearing aid was created. The equipment contained a digital array processor and minicomputer. This consisted of an FM radio transmitter and receiver. The radio made a connection between the individual through a transmitter on the body to the radio on top of the computer. The transmitter on the body was connected by a wire to the ear microphone and the receiver. Even though this was a major breakthrough in the creation of hearing aids, there were still a few problems. One of these major problems was that while the hearing aid worked, it was extremely heavy and nearly impossible to move.

Oticon hearing aids to be used with Bluetooth wireless devices.

The first commercial digital hearing aid was created in 1987 by the Nicolet Corporation. The hearing aid contained a body-worn processor that had a hardwire connection with an ear mounted transducer. While the Nicolet Corporation’s hearing aid was not publicly successful and the company shortly folded, it was able to start a competition between companies to create more effective hearing aids. Two years later, in 1989, the behind-the-ear (BTE) digital hearing aid was launched in addition to the Nicolet Corporation, Bell Laboratories expanded upon the hearing aid business by developing a hybrid digital-analog hearing aid. This hearing aid used digital circuits to handle a two-channel compression amplifier. Even though early research on this hearing aid was successful, AT&T, the parent company to Bell Laboratories, pulled out of the hearing aid market and sold its rights to Resound Corporation in 1987. When the hearing aid was put on in the market, it was instantaneously successful. This development helped bring major changes to the world of the hearing aid

After the success of the Resound Corporation, other hearing aid companies began putting out hybrid hearing aids that included analog amplifiers, filters, and limiters that were managed digitally. There were many benefits to these hearing aids; which included storing parameter settings, having a capability for paired-comparison testing, having settings for different acoustic environments, and having more advanced methods of signaling; this which included multi-channel compression.

The next major milestone was creating an all-digital hearing aid. The Oticon Company developed the first digital hearing aid in 1995, but it was only distributed to audiological research centers for research on digital technology in the realm of acoustic amplification. The Senso was the first commercially successful, all-digital hearing aid, and was created by Widex in 1996. After the success of the Senso, Oticon began marketing their own hearing aid, the DigiFocus.

Current digital hearing aids are now programmable which enables digital hearing aids to regulate the sound on their own, without using a separate control. The hearing aid can now adjust itself depending on what environment it is in and often does not even need a physical volume control button.

Recently, “Made for iPhone hearing aids” (MFi) was introduced by Resound, which enables users of MFi digital hearing aids to stream phone calls, music, and podcasts directly from iOS devices. 

Directly leveraging the audio processing power potential in smartphones, Jacoti BVBA from Belgium developed ListenApp, the first digital hearing aid application to win CE certification and FDA approval as a medical device. 

Hearing aid chips

One of the first digital chips was created by Daniel Graupe. The digital chip, referred to as the Zeta Noise Blocker, routinely adjusted the gain in the frequency channels to help control high levels of noise. The chip was integrated into a number of hearing aids in the 1980s. In addition to the Zeta Noise Blocker, there was a development of digital chips that were devoted to high-speed digital signal processing or DSP. DSP chips became available in 1982 and began to be implemented into hearing aids. By 1988, chips were produced in hearing aids. One of the major contributions of these chips was the ability to process both speech and other types of noises in real time. One major downfall of these chips was that they were massive and used up a lot of battery, which made them nearly impossible to be worn.

Source from: WIKI