The very first hearing aids were invented in the 17th century. They were external and known as ear trumpets. Ear trumpets were useful for directing sounds into the ear canal. Ear trumpets were hand held, acoustic, and only raised the amplification level modestly.
This type of hearing aid was used almost exclusively for over two hundred years but the move towards modern hearing aids began with the invention of the telephone in the late 19th century. The telephone was the first electrical device that could transmit speech. Hearing-impaired persons often found that they could hear a conversation better through the telephone than in person as the sound was subtly amplified directly into their ear. Thomas Edison, who was hard of hearing, didn’t benefit from improved hearing through the telephone so was interesting in improving on the Alexander Graham Bell’s telephone invention. In 1878, Mr Edison invented the carbon transmitter for the telephone which, unlike Bell’s device, amplified the the electrical signal. Some tried to adapt telephones for use as hearing aids but the results were cumbersome, heavy and only offered sound amplification of about 15 decibels. Considering that normal speech is about 60 decibels, this wasn’t much improvement. These early hearing devices were of limited usefulness and really had no commercial viability.
Then came the introduction of the vacuum tube and Western Electric Co. started producing technically superior hearing aids in 1920. These offered sound amplification at 70 decibels and more frequency response. However, these “hearing aids” were as large as a filing cabinet and weight over 200 lbs. Four short years later and Western Electric created hearing aid weighing in at less than 10 lbs and fitting in a small wooden box…still not portable and very conspicuous. These were still not popular with the hearing impaired population due to their unwieldiness and the stigma attached to be visibly pegged as hearing impaired.
By 1938, Aurex Corp. out of Chicago, developed the first wearable hearing aid. The earpiece was connected to a thin wire that lead to the amplifier-receiver clipped to the wearer’s clothes. The battery pack was strapped to the wearer’s leg. Around the same time, 1937 to be precise, Raytheon developed sub-miniature vacuum tubes which allowed for amplifiers that were smaller and required less power. The amplifiers were marketed to hearing aid manufacturers and gained market share even though they still relied on the strap-on battery pack.
By the late 1940s manufacturers combined sub-miniature vacuum tubes with two innovations that rose from WWII; printed circuit boards and button batteries. They were able to produce more compact and reliable models. The battery,
amplifier, and microphone were combined into one unit that could fit in a person’s shirt pocket or even a woman’s hairdo! The unit was connected to an earpiece by a wire. The device was not invisible by any means but the manufacturer did try to camouflage them by hiding the microphones in the hair or on some clothing accessory like a tie tack or brooch. What the hearing impaired really wanted was a truly one-piece, nearly invisible unit that was worn in the ear. So far, this was not possible even with the smallest sub-miniature vacuum tubes.
A solution came in 1948 with the invention of the transistor and by 1952, Raytheon was manufacturing and selling transistors to hearing aid manufacturers. More than 200,000 transistorized hearing aids were sold in 1953. By the late 1950’s Otarion Electronics in Chicago, introduced the first hearing aid worn entirely at the ear….no wires leading to amplifiers and battery packs. This was accomplished by putting all the electronics in the temple pieces of a pair of eyeglasses. By 1959, this type of hearing aid,
known as “hearing glasses” had captured half the market and were even worn by people with near perfect vision. It was a big step towards modern hearing aids but the leap was made in 1964 by Zenith Radio, a longtime hearing aid manufacturer in Chicago who sold a behind-the-ear model using integrated circuit amplifiers and a 1.2 volt button battery. It weighed a mere 7 grams and about 500 times more reliable than hearing aids built with discreet transistors. The microphone was placed inside the ear and was connected by a wire to the amplifier and battery which were clipped to the ear.
In the late 1980s, several companies were applying digital signal-processing chips (DSP) to hearing aids in which digital signals controlled and analog compression amplifier. These were known as hybrid models. The fully digital models debuted in 1996 and a few short years later, programmable models allowing for greater flexibility and fine tuning according to patient’s needs became available.
By 2005, digital hearing aids captured 80% of the market. Despite how far hearing aids have come, there is still room for improvement and manufacturers are still working on some of the issues that face hearing aid wearers. Modern hearing aids excel at amplification and acoustic feedback but researchers are still working on devices to filter out background noise and extraneous sounds that can obscure a conversation.Share This Article: