**2. The history of hearing aids**

When we cannot hear what someone nearby is saying, we cup our hand behind our ears. This is actually a type of hand reflector, which can aid hearing by emphasizing in the middle and high frequency range (>500 Hz) between 5 and 10 dB and by blocking unnecessary noise from extraneous directions. The first documented evidence of a hearing aid dates back to the sixteenth century [6] and describes wooden panels that imitated animal auricles and were meant to be worn behind the ear. **Figure 1** shows a 1673 sketch depicting a hearing device called the "*Ellipsis Otica.*" This is one of the oldest illustrations of a hearing aid and was published in *Phonurgia nova*, the first known book to deal with the nature of sound, acoustics, and music in 1673 [7]. Horn-shaped hearing aids called "*Ear Trumpets*" (**Figure 2**) became a common remedy for hearing loss for the next 300 years [8] until the development of electric hearing devices. Before the twentieth century, hearing aids were always thought of as sound collectors. The narrow end of the ear trumpet was inserted in the user's ear, and the broad end faced toward the speaker. Thus, like a cupped hand, the ear trumpet was used between two people standing at close range.

Early on, ear trumpets were made from animal horn, but over time people began making them from wood and metal. The preferred color was black because it blended in with the dark clothes that were often worn by European people of that time. This was perhaps an effort to avoid drawing attention to the horn for fear that one's hearing loss would be exposed. In the eighteenth and nineteenth centuries, hearing aids were designed to be hidden from public view, as can be seen in **Figure 3**. For females, the hearing aid body was placed into a hair band (**Figure 3a**, *Aurolese Phones*) or a handy fan (**Figure 3b**, air conduction fan), which they used in daily life. For men, the hearing aid body was covered by their own beard (**Figure 3c**). The

desire to hide hearing aids has not changed with new technology, as evidenced by the current

**Figure 3.** (a) *Aurolese Phones* simulated in hair bands (F. C. Rein co.) from the 1810s. (b) Acoustic fan with ear trumpet

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**Figure 2.** Illustrations of *Ear Trumpets* in *A clinical manual of the diseases of the ear* (1887) [8].

In contrast to the wearable hearing aids described earlier, larger types of hearing aids were placed or mounted on furniture. **Figures 4a** and **b** show a flower-vase-type hearing aid that was placed in the center of a table to collect sound from a number of people conversing during a meal, while the user put the end of tube on his ear. **Figure 4c** shows a chair that was designed to function as a hearing aid. The mouths of the lions carved at the front of the wooden armrests gathered sound, and hollow cavities running through the armrests transmitted the amplified sound to the end of the tube that the user inserted into his ear. Because wearable hearing aids required the speakers to be at very close proximity, those in high positions or peerage used these types of acoustic thrones to keep a suitable distance from unknown speakers that might

In the latter part of the nineteenth century, the invention of the telephone and microphone had a tremendous impact on hearing aid design. Once sound signals (longitudinal wave in air) could be converted into electric signals, hearing aids changed from classical sound collectors

popularity of small, skin-colored hearing aids.

from the 1850s. (c) Beard receptacle (Hawksley co.) from the 1830s.

make them uncomfortable.

**Figure 1.** Speaking tubes (*Ellipsis Otica*) from *Phonurgia nova* (1673) [7].

**Figure 2.** Illustrations of *Ear Trumpets* in *A clinical manual of the diseases of the ear* (1887) [8].

hearing impairment and dementia was published in 1989 [2], and several longitudinal studies that included auditory and nonauditory cognitive testing have shown that people with hearing loss have a 30–40% rate of accelerated cognitive decline [3] and an increased risk of incident allcause dementia [4, 5]. The implications are that auditory stimulation that reaches the brain can delay aging of the brain and allow communication with family and society to continue. Thus, the earlier that people can receive audiological treatment and hearing aid prescriptions, the better.

When we cannot hear what someone nearby is saying, we cup our hand behind our ears. This is actually a type of hand reflector, which can aid hearing by emphasizing in the middle and high frequency range (>500 Hz) between 5 and 10 dB and by blocking unnecessary noise from extraneous directions. The first documented evidence of a hearing aid dates back to the sixteenth century [6] and describes wooden panels that imitated animal auricles and were meant to be worn behind the ear. **Figure 1** shows a 1673 sketch depicting a hearing device called the "*Ellipsis Otica.*" This is one of the oldest illustrations of a hearing aid and was published in *Phonurgia nova*, the first known book to deal with the nature of sound, acoustics, and music in 1673 [7]. Horn-shaped hearing aids called "*Ear Trumpets*" (**Figure 2**) became a common remedy for hearing loss for the next 300 years [8] until the development of electric hearing devices. Before the twentieth century, hearing aids were always thought of as sound collectors. The narrow end of the ear trumpet was inserted in the user's ear, and the broad end faced toward the speaker. Thus, like a cupped hand, the ear trumpet was used between two people

Early on, ear trumpets were made from animal horn, but over time people began making them from wood and metal. The preferred color was black because it blended in with the dark clothes that were often worn by European people of that time. This was perhaps an effort to avoid drawing attention to the horn for fear that one's hearing loss would be exposed. In the eighteenth and nineteenth centuries, hearing aids were designed to be hidden from public view, as can be seen in **Figure 3**. For females, the hearing aid body was placed into a hair band (**Figure 3a**, *Aurolese Phones*) or a handy fan (**Figure 3b**, air conduction fan), which they used in daily life. For men, the hearing aid body was covered by their own beard (**Figure 3c**). The

**2. The history of hearing aids**

152 An Excursus into Hearing Loss

standing at close range.

**Figure 1.** Speaking tubes (*Ellipsis Otica*) from *Phonurgia nova* (1673) [7].

**Figure 3.** (a) *Aurolese Phones* simulated in hair bands (F. C. Rein co.) from the 1810s. (b) Acoustic fan with ear trumpet from the 1850s. (c) Beard receptacle (Hawksley co.) from the 1830s.

desire to hide hearing aids has not changed with new technology, as evidenced by the current popularity of small, skin-colored hearing aids.

In contrast to the wearable hearing aids described earlier, larger types of hearing aids were placed or mounted on furniture. **Figures 4a** and **b** show a flower-vase-type hearing aid that was placed in the center of a table to collect sound from a number of people conversing during a meal, while the user put the end of tube on his ear. **Figure 4c** shows a chair that was designed to function as a hearing aid. The mouths of the lions carved at the front of the wooden armrests gathered sound, and hollow cavities running through the armrests transmitted the amplified sound to the end of the tube that the user inserted into his ear. Because wearable hearing aids required the speakers to be at very close proximity, those in high positions or peerage used these types of acoustic thrones to keep a suitable distance from unknown speakers that might make them uncomfortable.

In the latter part of the nineteenth century, the invention of the telephone and microphone had a tremendous impact on hearing aid design. Once sound signals (longitudinal wave in air) could be converted into electric signals, hearing aids changed from classical sound collectors

In 1920, a new type of hearing aid was developed using vacuum tubes to amplify sound by 70–130 dB. The vacuum tube aid contains a filament (heated electron-emitting cathode) and a plate (the anode), and the amount of applied voltage can control the current traveling from cathode to anode. Although the vacuum tube hearing aid was able to have a high gain and accurate frequency response, it was quite large because two batteries were needed for heating the filament and controlling the electric circuit, and batteries at that time were not small. **Figure 5b** shows the earliest vacuum tube hearing aid, called the "*Vactuphone*" (1921). Because the body was about the same size as the box camera of its day, the "*Vactuphone*" included an

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Over time, advances in vacuum tube and battery technology allowed hearing aids to be made much smaller, until eventually the vacuum tube hearing aid was small enough to be worn. However, the invention of the transistor 1952 put an end to the vacuum tube era. The transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. The transistor was much smaller than the vacuum tube, consumed much less power, and thus allowed for much smaller battery sizes. A predecessor of a current behind-theear (BTE) hearing aid appeared in this period (**Figure 5c**). By wearing it on the head, noise from moving clothes was avoided, the direction of sound could be partially perceived, and the cord could be as short as possible. As technology advanced further with the integrated circuit (IC) and button-sized zinc-air battery (1960s–1970s), miniaturization and technical performance were further improved. The end of the twentieth century saw a steady progression of innovation from in-the-ear (ITE) hearing aids that fit into the concha (1980s) to in-the-canal (ITC) and completely-in-the-canal (CIC) hearing aids (1990s). ITC and CIC hearing aids allowed maximized sound collection from the auricle and sound insulation from environmental noises, as well as cut out wind noise. With these inventions, sound could be amplified by more than 100 dB and people with hearing loss could completely hide their

After achieving this level of hearing aid output gain and miniaturization, scientists and engineers began looking for further ways to improve hearing-aid convenience. For example, analog hearing aids amplify sound from all frequency ranges, which means that both speech and unnecessary background noises are amplified equally. Another problem was that the small size of the devices caused the speaker and microphone to be too close, and acoustic feedback generated uncomfortable levels of amplified sound. In 1996, these problems began to be addressed when hearing aids entered the age of digital sound. The digital hearing aid converts sound into a binary digital signal, which can then be modified by computer software. This type of signal modification is called digital signal processing (DSP) and is the biggest

**Figure 6** shows a computer interface through which the DSP installed in a hearing aid can be controlled after connecting the hearing aid to the computer. The most beneficial aspect

unnecessary lens that helped disguise it as a box camera.

problem with an invisible hearing aid.

advantage of the digital hearing aid.

**3. Digital hearing aid**

**Figure 4.** (a) and (b) Flower-vase-type hearing aid for gathering multiple speakers' voices (F. C. Rein Co.) in 1810. (c) Acoustic throne for European royalty in 1819.

to devices that could amplify sound through an electric circuit. The history of the electronic hearing aid is thus very similar to that of the technological evolution of the microphone, amplifier, and battery cell. Between 1989 and 1900, the Akouphone Company produced the first electronic hearing aids called "*Akoulallion*" and "*Akouphone,*" introducing a carbon microphone technique. The carbon transmitter was able to use an electric current to amplify weak signals by 20–30 dB [9]. The *Akoulallion* was large and was used on a table, while the *Akouphone* was portable. Miler Reese Hutchison—one of the company's founding presidents—established the Hutchison Acoustic Company in 1903 and produced "*Acousticon,*" an improved electric hearing aid that was further miniaturized (**Figure 5a**). Users wore the microphone and main body, put the battery in a bag, and held the earphone in their hands. The Danish company *Oticon* and the German company *Siemens* are two current makers of hearing aids that begun operations during this period.

**Figure 5.** (a) Early electronic hearing aid with carbon components: *Acousticon* model A (Hutchison Acoustic Company, 1905). (b) Early vacuum tube hearing aid: *Vactuphone* (Globe Ear-phone Company, 1921). (c) Behind-the-ear hearing aidembedded transistor amplifier (Zenith Diplomat Company, 1956).

In 1920, a new type of hearing aid was developed using vacuum tubes to amplify sound by 70–130 dB. The vacuum tube aid contains a filament (heated electron-emitting cathode) and a plate (the anode), and the amount of applied voltage can control the current traveling from cathode to anode. Although the vacuum tube hearing aid was able to have a high gain and accurate frequency response, it was quite large because two batteries were needed for heating the filament and controlling the electric circuit, and batteries at that time were not small. **Figure 5b** shows the earliest vacuum tube hearing aid, called the "*Vactuphone*" (1921). Because the body was about the same size as the box camera of its day, the "*Vactuphone*" included an unnecessary lens that helped disguise it as a box camera.

Over time, advances in vacuum tube and battery technology allowed hearing aids to be made much smaller, until eventually the vacuum tube hearing aid was small enough to be worn. However, the invention of the transistor 1952 put an end to the vacuum tube era. The transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. The transistor was much smaller than the vacuum tube, consumed much less power, and thus allowed for much smaller battery sizes. A predecessor of a current behind-theear (BTE) hearing aid appeared in this period (**Figure 5c**). By wearing it on the head, noise from moving clothes was avoided, the direction of sound could be partially perceived, and the cord could be as short as possible. As technology advanced further with the integrated circuit (IC) and button-sized zinc-air battery (1960s–1970s), miniaturization and technical performance were further improved. The end of the twentieth century saw a steady progression of innovation from in-the-ear (ITE) hearing aids that fit into the concha (1980s) to in-the-canal (ITC) and completely-in-the-canal (CIC) hearing aids (1990s). ITC and CIC hearing aids allowed maximized sound collection from the auricle and sound insulation from environmental noises, as well as cut out wind noise. With these inventions, sound could be amplified by more than 100 dB and people with hearing loss could completely hide their problem with an invisible hearing aid.
