History of hearing aids
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.
Collapsible conical ear trumpets were made by instrument makers on a one-off basis for specific clients.
[2][3] Rein was commissioned to design a special acoustic chair for the ailing King John VI of Portugal in 1819.
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.
[4] 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.
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.
[3] 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.
[1] The first wearable hearing aid using vacuum tube technology went on sale in England in 1936, and a year later in the United States.
[1] Military technological advances that occurred in World War II helped the development of hearing aids.
Transistors were created to replace vacuum tubes; they were small, required less battery power and had less distortion and heat than their predecessor.
After coming to this conclusion, the first "all-transistor" hearing aids were offered in 1952, called the Microtone Transimatic and the Maico Transist-ear.
[3] Moreover, researcher Edgar Villchur developed an analog multi-channel amplitude compression device that enabled an audio signal to be separated into frequency bands.
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.
[citation needed] The hybrid device was effective from a practical point of view because of the low power consumption and compact size.
A little later, Stephan Mangold and Arne Leijon[7] created a programmable multi-channel hybrid hearing aid.
[9] The creation of high-speed digital-array processors used in minicomputers opened up the door for advances in full digital hearing aids.
In 1982, at the City University of New York, a real-time full digital experimental hearing aid was created based on the digital array processor in an external, standalone minicomputer and an FM radio transmitter that allowed a wireless connection between the minicomputer and individual wearing a transmitter on the body.
Also in the early 1980s a research group at Central Institute for the Deaf headed up by faculty members at Washington University in St. Louis created the first full digital wearable hearing aid.
[10][11] They were the first to design and manufacture a full miniaturized digital hearing aid to be powered by battery and be fully wearable.
The external sound from microphones positioned in an ear module identical to a BTE was first converted into binary code, digitally processed and digitally controlled in real time, then converted back to an analog signal sent to miniature loudspeakers positioned in an ITE ear module.
Over the years, specialized hearing aid chips continued to become smaller, increased in computational ability and required even less power.
The hearing aid contained a body-worn processor that had a hardwire connection with an ear mounted transducer.
[2] One of the major contributions of these chips was the ability to process both speech and other types of noises in real time.
[14] 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.
