The earliest hearing aid was simplicity itself and is still in use: a cupped hand behind the ear. But today's technology has made hearing aids much less obtrusive and much more helpful.
While early hearing aids tried to improve upon the external ear, with devices to direct the sound coming from the front into the ear of the listener and block noise from the sides and rear, modern devices fit surreptitiously behind or into an ear while augmenting the sound coming in.
In the 17th century, artisans made metal "ears" to fit over the natural ears. Ear trumpets, cones that could be aimed at the source of a sound, came into use in the early 1800s.
By the late 1800s, the acoustic horn became available. It was a flexible tube with two ends _ one cone shaped to catch the sound, the other gently tapered to fit inside the ear.
The approach changed from art to engineering in this century. In 1913, Siemens became one of the first companies to offer electronically amplified hearing aids. These early units were large and not very portable _ about the size of a tall cigar box _ but they had a speaker that fit into the ear.
Acousticon's Model 56 in the mid-1920s was one of the first really portable units, although it was quite heavy. Some of the technological advances of World War II showed up after the war in hearing aids. Zenith's pocket-sized Miniature 75 helped set a trend toward smaller and more effective prosthetics.
Transistors led to startling improvements in hearing aids. Tiny transistors in newly developed miniature microphones could be built into the frames of eyeglasses along with better, smaller batteries.
Mounting a hearing aid behind the ear, as in Zenith's Diplomat of the late 1950s, is called BTE in the industry. The next step was to put hearing aids in the ear (ITE), then, as they got even smaller, partly into the ear canal (ITC). Now hearing aids can fit completely into the ear canal (CIC).
Until the early 1990s, most hearing aids were analog and consisted of a microphone, an amplifier and a speaker (transducer). But with the availability of miniature computer components, as well as the audio-processing technology found in CD and DVD players, the digital hearing aid was born.
Most hearing aids now have some digital components, and all-digital hearing aids are becoming popular.
Using the power of computer chips, or microprocessors, digital hearing aids are able to manipulate the incoming sound to amplify the specific frequencies that a user is having trouble hearing. This feature, called equalization control, was rarely available with analog devices.
One example of this kind of technology is the Senso, a fully digital unit that fits completely in the ear and is made by the Danish company Widex. A number of other companies also make digital hearing aids, including Siemens, a German company, and Telex, based in the United States.
Settings on digital hearing aids can be adjusted for specific environments. Going to a chamber music concert? Select setting No. 1. Meeting the boss for a business lunch in a noisy restaurant? Select setting No. 4.
What these settings do is adjust the equalization, volume and signal-processing functions. If you cannot hear high frequencies well but love chamber music, the appropriate setting would emphasize the high frequencies (for the violins) and give you a moderate increase in volume.
Lunch with the boss would require an emphasis on the middle range (for the human voice), a decrease in the high frequencies and some form of extraneous noise reduction.
In the 1940s, the cost of a hearing aid started at about $150, a great expense at the time. Today's units can range from $700 for an analog unit worn behind the ear to $1,200 for an analog model completely in the ear canal or up to $3,000 or more for digital devices worn completely in the canal.
Several companies are beginning to offer products with greater processing power that they say will provide a better match for a user's pattern of hearing loss. And, taking a cue from science fiction, cochlear implants are beginning to be used.
These implants bypass some of the faulty nerve circuitry in the cochlea, a spiral-shaped structure in the inner ear that contains the cells that transmit nerve impulses representing sound toward the brain. That allows some people who are deaf or who have severe hearing loss to have some degree of hearing.
A number of companies, like the Cochlear Corp., have developed cochlear implants, which are surgically connected to the cochlea. Researchers are studying the possibility of brain implants or nerve regeneration as future remedies for hearing loss.
As the American population ages, hearing loss afflicts a growing number of people. Although some of the causes of hearing loss (loud music and noisy environments) can be avoided, some cannot (heredity, accidents, disease and aging).
Many people try to avoid dealing with the problem, but the evidence is clear: Hearing loss does not reverse itself and generally gets worse. If you think your hearing may be impaired, see an audiologist or other doctor. Hearing aids may not give you perfect hearing, but at least you'll be able to hear the music. And the children. And the car alarms.