The History of Hearing Aids: A Look at Hearing Aid Technology

From their size to their shape to they way in which they function, the hearing aid technology that is used today is far different from what hearing aids used 100, 50, or even five years ago. The history of hearing aids is far reaching and colorful--the earliest hearing aids worked without electricity, while the earliest electric models were simply too large to be portable. Today, digital hearing aids are discrete, lightweight, and have the capability to be adjusted for different environments and to amplify sound without distortion. And the future holds many exciting improvements to hearing aid technology as a whole. But it's important to review the history of hearing aids in order to understand just where the industry is headed.

The Early History of Hearing Aids

We start our look at the history of hearing aids two hundred years ago, when aids came in the form of ear trumpets--large horn-shaped devices used to direct sound into the ear of a hearing-impaired person and provide very basic sound amplification without electricity. These trumpets were large and awkward, although some models could be worn on the head attached to a harness. They performed one basic function--sound amplification--and they could also improve the signal-to-noise ratio in a noisy environment, but they weren't able to do much else. In fact, cupping your hand behind your ear gives a similar (but smaller) amplification. Hearing aid technology has certainly come a long way since this time.

The Advent of Electric Hearing Aids

Hearing aid technology started to change rapidly with two important milestones in the history of hearing aids--the advent of electricity and Alexander Graham Bell's work on the telephone, which was essentially a machine that could electronically amplify sound via a carbon microphone in combination with a battery. Modern hearing aid technology still utilizes the concept of a receiver, a telephone component, to describe the tiny speaker inside the hearing aid.

In the early 1920s, hearing aid technology incorporated the use of vacuum tubes, which allowed a much more efficient method for amplifying sound. But the early electrical hearing aids were still far too unwieldy to be carried around easily--many were as large as desk radios, and just as heavy. Luckily, an important development in the history of hearing aids was just around the corner.

Smaller Batteries, Smaller Hearing Aids

One of the first major changes in the history of hearing aids that led to a decrease in their size was the miniaturization of batteries. Previously, batteries were large, heavy, and could not hold a charge for very long, making them impractical for hearing aid use. Battery packs had to be worn on the hearing-impaired person's body. By the 1930s, hearing aid technology had progressed so that aids could be portable.

The Transistor Changes Everything

However, the most important event in the history of hearing aids was yet to come. It was the invention of the transistor in the 1950s that changed hearing aid technology completely. A transistor is simply a switch that has no moving parts and that has only two settings: on or off. Put multiple transistors together, however, and you can get incrementally larger combinations of on/off switches--the basis for binary code, and essentially a computer in its simplest form. Additionally, a transistor's conductivity can be manipulated based on the purity of the silicon with which the transistor is made, providing an infinite number of possibilities for which the transistor can be used. Silicon transistors allowed hearing aids to shrink in size so that they could become "body aids," eventually leading to hearing aid technology available in a size that we are familiar with today--with aids that can be worn discretely behind the ear or even within the ear canal.

The Digital Age

By the mid-1990s, digital hearing aid technology was in common use. Digital hearing aids allowed for more precise shaping of the sound into the wearer's ear. With digital circuitry, the sound could be amplified or dampened as needed. Programs could be created that could be utilized depending upon the user’s location or needs--more amplification for quiet settings, for example, or specific amplification of certain frequencies in loud situations so that the user could clearly hear speaking voices, even when surrounded by other noises. Digital products also took advantage of compression technology, eliminating an annoying side effect that had plagued users throughout the history of hearing aids--the distortion of very loud sounds.

Today's Hearing Aid Technology

Today, we are still shaping the history of hearing aids, and hearing aid technology is constantly being updated. For example, new technologies are being introduced that allow the user to be directly involved with the fitting of his or her hearing aids. Instead of using basic prescriptions based on a user's audiogram, testing can be performed, analogous to the optical testing done in an ophthalmologist's office, to hone the hearing aid's settings for the specific user. From listening to a narrow band of sounds and making loudness judgments to filling out a questionnaire with specific information, end users are able to modify their hearing aid settings to suit their needs.

Rules that utilize "fuzzy logic" (a system of computer instructions enabling the computer to deal with ambiguities¹) are built into some of today's hearing aids. This allows use of these customized settings to ensure that the hearing aid output is constantly optimized to the listener's needs for every sound in every environment. Clinical studies show that this new generation of hearing aid technology can provide consistently improved intelligibility of speech in quiet and noisy environments, more comfort for the user in the presence of loud sounds, greater audibility of soft sounds, and improved sound quality over conventional amplification schemes.

This hearing aid technology is not offered by all manufacturers, but it is worth seeking out because it can greatly improve a user's hearing when using the aid. Newer hearing aids are also being offered with limited ear occlusion, making them nearly invisible and allowing the user's hearing to be further improved.

In addition, a brand new hearing aid technology known as ADRO (adaptive dynamic range optimization) is starting to become available from some manufacturers. This is one of the most significant changes in the recent history of hearing aids, as it is a major update from traditional compression circuits that were most often used with digital hearing aids.

ADRO allows the hearing aid to make constant adjustments to its algorithms using fuzzy logic, delivering to the user a higher level of sound quality and eliminating louder nuisance sounds more readily. Echoes are also eliminated. The latest generation of ADRO, which goes one step beyond what was originally offered, is presented by some companies in an ultra low delay product that delivers up to 32 channels, a large increase over earlier products that only offered seven or eight. Some products in this new generation of hearing aids also incorporate a newer, adaptive directional microphone. This exciting new hearing aid technology gives us a glimpse into what the future holds.

The Future of Hearing Aid Technology

Just as the history of hearing aids has seen many developments, the future of hearing aids will bring extremely exciting new options for all users, just in time for the aging baby boomer generation. Transducers are getting smaller, and at the same time, circuitry is shrinking rapidly. This means that ever smaller, increasingly more powerful hearing aids will be able to be produced. And consumers will find themselves in control of their own hearing again, as they become even more involved with the fitting and adjusting of their hearing aids. We've come a long way from ear trumpets, but hearing aid technology is continuing to evolve with time, and we still have a long way to go.

¹"fuzzy logic." Dictionary of Business Terms. Barron's Educational Series, Inc, 2000. Answers.com 04 Aug. 2006. http://www.answers.com/topic/fuzzy-logic

About the Author

Henry Smith is the founder of America Hears, a leading manufacturer and distributor of hearing aids online for over 26 years. The company recently rolled out its new FreedomAD product line, which utilizes the latest generation of ADRO hearing aid technology. Henry started the company in 1979, following a 15-year career at the Pennsylvania School of the Deaf, including his work as an Acoustic Technician. Henry is a pioneer in the use of computers and the Internet to allow customers to have a hands-on approach to the tuning and adjusting of their digital hearing aids. He strives to be customer-centric in all aspects of his work.