The first

hearing aid A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers su ...

was created in the 17th century. The movement toward modern hearing aids began with the creation of the

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

, 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 The carbon microphone, also known as carbon button microphone, button microphone, or carbon transmitter, is a type of microphone, a transducer that converts sound to an electrical audio signal. It consists of two metal plates separated by granu ...

transmitters In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to th ...

, digital signal processing chip or

DSP DSP may refer to: Computing * Digital signal processing, the mathematical manipulation of an information signal * Digital signal processor, a microprocessor designed for digital signal processing * Yamaha DSP-1, a proprietary digital signal ...

, and the development of

computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...

technology helped transform the hearing aid to its present form.

Ear trumpet

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 Sir Joshua Reynolds (16 July 1723 – 23 February 1792) was an English painter, specialising in portraits. John Russell said he was one of the major European painters of the 18th century. He promoted the "Grand Style" in painting which depend ...

) 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 tube A speaking tube or voicepipe is a device based on two cones connected by an air pipe through which speech can be transmitted over an extended distance. Use of pipes was suggested by Francis Bacon in the ''New Atlantis'' (1672). The usage for tel ...

s. 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 trumpet An ear trumpet is a tubular or funnel-shaped device which collects sound waves and leads them into the ear. They were used as hearing aids, resulting in a strengthening of the sound energy impact to the eardrum and thus improved hearing for a dea ...

s and cones were used as hearing aids.Levitt, H. "Digital hearing aids: wheelbarrows to ear inserts." ASHA Leader 12, no. 17 (December 26, 2007): 28-30.Mills, Mara. "Hearing Aids and the History of Electronics Miniaturization." IEEE Annals of the History of Computing 33.2 (2011): 24-44. Rein hearing aid catalog

Rein was commissioned to design a special acoustic chair for the ailing King

John VI of Portugal , house = Braganza , father = Peter III of Portugal , mother = Maria I of Portugal , birth_date = , birth_place = Queluz Palace, Queluz, Portugal , death_date = , death_place = Bemposta Palace, Lisbon, 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 or her problem.

Electronic hearing aids

Museum of Medicine Berlin Germany Telephone hearing aids

The first electronic hearing aids were constructed after the invention of the

and

microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...

in the 1870s and 1880s. The technology within the telephone increased how acoustic signal could be altered. Telephones were able to control the

loudness In acoustics, loudness is the subjectivity, subjective perception of sound pressure. More formally, it is defined as, "That attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud". The rel ...

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

, 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 Miller Reese Hutchison (August 6, 1876 – February 16, 1944) was an American electrical engineer and inventor. He developed some of the first portable electric devices, such as a vehicle horn and a hearing aid. His father was William Hutchison ...

in 1898. It used a carbon transmitter, so that the hearing aid could be portable. The

carbon transmitter The carbon microphone, also known as carbon button microphone, button microphone, or carbon transmitter, is a type of microphone, a transducer that converts sound to an electrical audio signal. It consists of two metal plates separated by granul ...

was used to amplify sound by taking a weak signal and using

electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...

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 Siemens AG ( ) is a German multinational conglomerate corporation and the largest industrial manufacturing company in Europe headquartered in Munich with branch offices abroad. The principal divisions of the corporation are ''Industry'', '' ...

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 A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...

hearing aid was patented by a Naval

engineer Engineers, as practitioners of engineering, are professionals who invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considering the l ...

Earl Hanson in 1920. It was called the Vactuphone and used the telephone

transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna (radio), antenna. The transmitter itself generates a radio frequency alternating current, which i ...

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 The Western Electric Company was an American electrical engineering and manufacturing company officially founded in 1869. A wholly owned subsidiary of American Telephone & Telegraph for most of its lifespan, it served as the primary equipment ma ...

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 Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the inpu ...

. 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

The development of

transistors upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...

in 1948 by

Bell Laboratories Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...

led to major improvements to the hearing aid. The transistor was invented by

John Bardeen John Bardeen (; May 23, 1908 – January 30, 1991) was an American physicist and engineer. He is the only person to be awarded the Nobel Prize in Physics twice: first in 1956 with William Shockley and Walter Brattain for the invention of the tran ...

Walter Brattain Walter Houser Brattain (; February 10, 1902 – October 13, 1987) was an American physicist at Bell Labs who, along with fellow scientists John Bardeen and William Shockley, invented the point-contact transistor in December 1947. They shared the ...

, and

William Shockley William Bradford Shockley Jr. (February 13, 1910 – August 12, 1989) was an American physicist and inventor. He was the manager of a research group at Bell Labs that included John Bardeen and Walter Brattain. The three scientists were jointly ...

. Transistors were created to replace vacuum tubes; they were small, required less battery power and had less

distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...

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 Raytheon Technologies Corporation is an American multinational aerospace and defense conglomerate headquartered in Arlington, Virginia. It is one of the largest aerospace and defense manufacturers in the world by revenue and market capitaliza ...

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. In 1954, the company,

Texas Instruments Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globall ...

, produced a

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

transistor, which was much more effective than the previous version. The end of the transistor was marked by the creation of the

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

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 digital processing for creating both speech and audio signals on a large

mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterpris ...

. Because of the slow processing ability of these large digital computers of the era, the process of simulating hearing aids was extremely slow. The processing of the audio speech signal took longer than the length of the duration of the speech signal itself preventing the processing of speech in real time. This made it nearly impossible to conceive the idea that a self-contained, wearable digital hearing aid could be made small enough to fit onto an ear like a conventional analog hearing aid. However, this digital processing research was important for learning about how to develop sounds for those with hearing disabilities. In the 1970s, the

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

was created. This microprocessor helped to open up the door to miniaturization of the digital hearing aid. Moreover, researcher

Edgar Villchur Edgar Marion Villchur (28 May 1917 – 17 October 2011) was an American inventor, educator, and writer widely known for his 1954 invention of the acoustic suspension loudspeaker which revolutionized the field of high-fidelity equipment. A sp ...

developed an analog multi-channel amplitude compression device with amplitude compression that enabled the

audio signal An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals, or a series of binary numbers for digital signals. Audio signals have frequencies in the audio frequency range of r ...

to be separated into

frequency band A frequency band is an interval in the frequency domain, delimited by a lower frequency and an upper frequency. The term may refer to a radio band or an interval of some other spectrum. The frequency range of a system is the range over which i ...

s. 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 Digital technology may refer to: * Application of digital electronics * Any significant piece of knowledge from information technology Information technology (IT) is the use of computers to create, process, store, retrieve, and exchange a ...

. Also in the 1970s the creation of a hybrid hearing aid was possible in which the analog components of a conventional hearing aid consisting of amplifiers, filters and signal limiting were combined with a separate digital programmable component into a conventional hearing aid case. The audio processing remained analog but was able to be controlled by the digital programmable component. The digital component could be programmed by connecting the device to an external computer in the laboratory then disconnected to allow the hybrid device to function as a conventional wearable hearing aid. The hybrid device was effective from a practical point of view because of the low power consumption and compact size. At that time, low-power analog amplifier technology was well developed in contrast to the available semiconductor chips able to process audio in real time. The combination of high performance analog components for real time audio processing and a separate low power digital programmable component only for controlling the analog signal led to the creation several low power digital programmable components able to implement different types of digital control of analog circuits. A hybrid hearing aid was developed by Etymotic Design. A little later, Mangold and Lane created a programmable multi-channel hybrid hearing aid. Graupe with co-authors developed a digital programmable component that implemented an adaptive noise filter that could be added to a hybrid hearing aid. The creation of high-speed digital-array

processors A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, ...

used in

minicomputers A minicomputer, or colloquially mini, is a class of smaller general purpose computers that developed in the mid-1960s and sold at a much lower price than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, ...

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. In 1982, at the

City University of New York The City University of New York ( CUNY; , ) is the Public university, public university system of Education in New York City, New York City. It is the largest urban university system in the United States, comprising 25 campuses: eleven Upper divis ...

, 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 In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...

that allowed a wireless connection between the minicomputer and individual wearing a transmitter on the body. The FM transmitter on the body was connected by a wire to an ear microphone and loudspeaker. 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 and nearly impossible to move Oticon Bluetooth hearing aids

preventing it from being used as conventional hearing aid in real world environments. However, this was a major breakthrough in the creation of a full digital hearing aid. 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 MO created the first full digital wearable hearing aid. They first conceived a complete, comprehensive full digital hearing aid, then designed and fabricated, miniaturized full digital computer chips using custom digital signal processing chips with low power and very large scale integrated (VLSI) chip technology able to process both the audio signal in real time and the control signals yet able to be powered by a battery and be fully wearable as a full digital wearable hearing aid able to be actually used by individuals with hearing loss in any environment similar to a conventional hearing aid. Engebretson, Morley and Popelka were the inventors of the first full digital hearing aid. Their work resulted in

US Patent Under United States law, a patent is a right granted to the inventor of a (1) process, machine, article of manufacture, or composition of matter, (2) that is new, useful, and non-obvious. A patent is the right to exclude others, for a limited ...

4,548,082, "Hearing aids, signal supplying apparatus, systems for compensating hearing deficiencies, and methods" by A Maynard Engebretson, Robert E Morley, Jr. and Gerald R Popelka, filed in 1984 and issued in 1985. This full digital wearable hearing aid also included many additional features now used in all contemporary full digital hearing aids including a bidirectional interface with an external computer, self-calibration, self-adjustment, wide bandwidth, digital programmability, a fitting algorithm based on audibility, internal storage of digital programs, and fully digital multichannel amplitude compression and output limiting. This group created several of these full digital hearing aids and used them for research on hearing impaired people as they wore them in the same manner as conventional hearing aids in real-world situations. In this first full DHA all stages of sound processing and control were carried out in binary form. The external sound from microphones positioned in an ear module identical to a BTE was first converted into binary code, then digitally processed and digitally controlled in real time, then converted back to an analog signal sent to miniature loudspeakers positioned in the same BTE ear module. These specialized hearing aid chips continued to become smaller, increase in computational ability and require even less power. Now, virtually all commercial hearing aids are fully digital and their digital signal processing capability has significantly increased. 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. The first commercial full 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 among hearing aid manufacturers to create more effective full digital hearing aids. Two years later, in 1989, the commercial behind-the-ear (BTE) full 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 AT&T Inc. is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the world's largest telecommunications company by revenue and the third largest provider of mobile tel ...

, the parent company to Bell Laboratories, pulled out of the hearing aid market and sold its rights to Resound Corporation in 1987. When the hybrid hearing aid was put on in the market, it helped bring major changes to the world of the hybrid hearing aid. After the success of the Resound Corporation, other hearing aid manufacturers 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 that included storing parameter settings, having a capability for paired-comparison testing, having settings for different acoustic environments, and having more advanced methods of signal processing that included multi-channel compression. The next major milestone was creating a commercial full digital hearing aid. The Oticon Company developed the first commercial full 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, full 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 full digital 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) were 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.Jacoti, BVBA, "Jacoti ListenApp" https://www.jacoti.com/listenapp/ (accessed January 28, 2016).

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 in 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 Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...

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 down fall of these chips was that they were massive and used up a lot of battery, which made them nearly impossible to be worn.

References

External links

* {{cite web, url=http://beckerexhibits.wustl.edu/did/, title=Deafness in Disguise: Concealed Hearing Devices of the 19th and 20th Centuries, publisher=Washington University School of Medicine, date=15 June 2009, accessdate=4 December 2011 Hearing aids

Hearing aids A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers su ...