Telecoil

[rich...@webtv.net]

Exactly, what is a telecoil all about when it comes to hearing aids and
phones?

[jim]

A telecoil is just a very miniature coil wound on a ferrite or iron core.
Its is used to pick up audio frequency magnetic fields and converting them
to a small electrical signal that you hearing aid uses in the same way it
uses the signal from the microphone. These magnetic audio signals can come
from a variety of sources.

In the case of a conventional (older styles particularly) telephones the
earpiece generates a fairly strong audio magnetic field while it is in the
process of creating the audible sound. This magnetic "by-product" makes it
possible to recreate the electrical wirelessly by just placing a coil near
the telephone receiver. Coupling to the signal this was is also called
inductive coupling. The process is called magnetic induction.

Some hearing aids use this useful mechanism to get the caller's voice into
the hearing aid by picking up the field with a telecoil instead of a
microphone. This will let you turn off the microphone and still hear the
caller. The advantage for doing this is to avoid the likelihood of feedback
and "singing" (oscillation) that often happens when you hold something close
to your hearing aid. It also is a fairly high quality way to get the sound
to your ear without distorting the frequency response.

Telecoils are also pretty inexpensive.

Although they were probably created for telephone use, once they appeared
they got used in all kinds of other applications. Anything that can make an
audio magnetic field can talk to the telecoil in your hearing aid and
thereby talk to you.

People found that wearing a neckloop (that was really a big wire coil) made
it possible to hear audio from electronic devices connected to it. So there
are all kinds of gadgets that attach to neckloops (auxiliary microphones, FM
receivers etc.).

Places like churches create huge coils encircling the whole church and
thereby are able to broadcast to all in the church with telecoil equipped
hearing aids.

While telecoils are a cost effective wireless solution, they do sometimes
suffer from some limitations:

1. If they are pointed 90 degrees relative to the field, they get no signal.
2. Things like computers and other electronic devices can generate inductive
interference that sometimes makes telecoils unusable.
3. As implemented in hearing aids there is no automatic controlling of
level. That means the further you get fro the source the quieter it gets.

Recently companies like Phonak and Unitrom have started to use telecoil-like
devices that are built like little radios. In this case the telecoil doesn't
detect voice signals directly but the telecoils is tuned to a higher
frequency (AM radio style) and electronics recreates the audio signal. They
do this at 374 KHz.

Siemens has used this same mechanism at about 117 KHz to form a 2-way data
radio for letting one hearing aid compare notes with the other and for
sending data (not voice) to and from a remote control.

jim

<rich...@webtv.net> wrote in message
news:920-4220...@storefull-3238.bay.webtv.net...

[rich...@webtv.net]

Thank you very much JIm. You really went all out in explaining
telecoils. I will look in to it.

[Bill M]

Richard48 explained it better than me, but here is my explaination of
t-coils:

T-coils exist to make the Nokia cell phone neck loop work. The neck loop is
worn invisiably under clothing. The neck loop makes the cell phone
perfectly loud and clear. The neck loop has mysterious jacks to plug things
into, but I have no idea what or how. I just know that it can make the cell
phone brilliant. Richard explains better.

Bill M

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