Hugh Hetherington Hearing Aid Museum
Hugh Hetherington Hearing Aid Museum

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T-Coils—General Information

History of T-Coils—General Information

by Neil Bauman, Ph.D.

A lot of people think that t-coils and loop systems are a relatively new invention. I’ll bet you’ll never guess just how long t-coils have been available in hearing aids.

If you’re like most people, you probably guessed some time in the 1970s or 1980s. If you guessed that, you’d be way off base.

The truth is, 2011 will mark the 75th anniversary of the first t-coil-equipped hearing aid!

T-coils Have Been Around Since When?

The very first known hearing aid with a t-coil was made by Tel-Audio of Washington, DC in 1936. This hearing aid was a vacuum-tube, table-top model that used A/C power and thus needed to be plugged into a wall socket. The t-coil was a large external device measuring 4½" long x 3" wide x 1¾" thick! (Compare that with the tiny t-coils shown in the above picture.)

Tel-Audio apparently only made this one hearing aid. It couldn't have been that successful because they went out of business in 1938.

In 1937,  Joseph Poliakoff of Great Britain received an early patent for an induction-loop hearing assistance system.

(Incidentally, Joseph had founded the Multitone Electric Co. Ltd of London, England in 1931. They produced their first hearing aid, a desk-top model, in 1933.)
 

 


Examples of modern t-coils

Photo courtesy
www.tibbettsindustries.com

 

In 1937 Multitone came out with a wearable hearing aid (as opposed to their earlier desk-top models) which they called the VPM (Vest Pocket Model). In 1938 they modified this VPM model to have an optional t-coil. Thus the first wearable hearing aid with a t-coil was the 1938 version of the Multitone VPM.

It took another 8 years until a company in the USA produced a wearable hearing aid with a t-coil. In December, 1946, RadioEar Corp, who were located at Mt. Lebanon, PA at that time, produced their Permo-Magnetic Multipower hearing aid (sometimes referred to as the “PhoneMaster”). This was the first wearable American hearing aid with a t-coil. (It was also the first vacuum-tube hearing aid to use a magnetic microphone.)

Since the 1950s, t-coils have been standard features on a number of hearing aids.

Click picture for larger view

 

The original 1937 Multitone Model VPM vacuum-tube hearing aid
without the t-coil

View of the inside of the Acousticon Model A-310 transistor body hearing aid (1953) showing the t-coil. The t-coil is the large coil of wire along the bottom. This t-coil is enormous by today's standards (see below).

 

 

Click picture for larger view

 
Picture showing several passive t-coils of more modern vintage (~2000) for use in behind-the-ear hearing aids.

Photo courtesy www.tibbettsindustries.com

 

 

Picture of a preamplified Tibbetts t-coil. The amplifier is the black bump on the top.

Photo courtesy www.tibbettsindustries.com

 

 

In 1956 Sonotone came out with their Model 200 transistor body-style hearing aid with a built-in t-coil. They also produced a miniature loop pad that you could hook up to your radio or TV and so listen via this loop pad. This is the earliest example of a loop pad I've found.

You hooked the loop pad to your radio or TV by simply clipping two alligator clips to the speaker wires. Then you set the loop pad down beside you and placed the body of your hearing aid on the loop pad (as shown) and turned the mic/t-coil switch to the t-coil position.

 

Click picture for larger view

 

The Sonotone Model 200 Transistor Body Hearing Aid (1956) on the Miniature Loop Pad
 

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