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Timothy C. Hain, MD. 
Page last modified:
June 18, 2009
Loop systems and telecoils work together with hearing aids to help hard of hearing people hear better. They consist of an transmitting antenna that converts sound into radio waves, and a reciever "telecoil" placed inside of ones hearing aid. This system allows you to have sound -- such as from the radio, TV, telephone, or public speaker -- sent directly to your hearing aid with greater clarity. Loop systems resemble the "blue tooth" headsets used for cell-phones, but interface with your hearing aid rather than a separate ear-transducer.
Permanent loop systems are often installed in public buildings and churches. In Europe, they are now installed in many forms of public transportation—taxis, busses, trains and ships. You will also find loop systems in some schools and offices where there are hard of hearing people.
The main advantage of loop systems is that they are inexpensive ways to hear things like the telephone or TV. The main problem with them is that they may pick up hum or static from electrical equipment and wiring. FM systems are a solution to this problem, but they cost more money.
Loop systems consist of three parts—a microphone or other transmitting device, a loop amplifier, and a loop of wire. That's the transmitting side. Your own hearing aids equipped with telecoils make up the receiving side.
To set up a loop system, plug the loop amplifier into a wall socket, plug the input device or microphone into the loop amplifier, string a loop of wire around the perimeter of the room or area you want looped and connect the ends of the wire to the loop amplifier and turn it on.
Audio signals are picked up by the microphone or directly from some sound source like your TV or stereo. They are amplified by the loop amplifier and then travel through a loop of wire that surrounds the listening area. When the sound signal travels through the loop of wire, it produces a magnetic field in the looped area that mirrors the frequency and intensity characteristics of the original sound signal.
Your hearing aid converts this magnetic signal into sound you can hear. When you switch your hearing aid from its microphone to its telecoil, it connects a small coil of wire (t-coil) to the input of the hearing aid's amplifier instead of its microphone. This tiny coil of wire is sensitive to nearby magnetic fields such as the one produced by the loop system. The changing magnetic field in the room loop induces a corresponding electrical signal into the telecoil. The hearing aid amplifier then amplifies this signal and you hear a faithful reproduction of the original speech signal.
This process of inducing an electrical current in one wire as a result of current flowing in a nearby wire is called induction—hence the term induction loop system—or just "loop system" for short.
Since any electrical current will result in a magnetic field, depending on their location, loop systems may be prone to interference. This interference is usually a buzzing or humming sound. This resulting buzz or hum may be so loud that you can't use the loop system in certain places. Typically, interference can come from nearby electrical wires, fuse boxes, TVs, computer monitors and fluorescent light fixtures.
In order to tell if the area you want to loop is free from interference, all you need to do is switch on your telecoils, turn up the volume on your hearing aids and listen. If you hear loud buzzing, that is not a good place for a loop system. As you move around, you will notice that the interference level changes. Set up your loop system where the interference is non-existent or negligible.
The loop wire is the transmitting half of the loop system. The receiving half is the telecoils in your hearing aids.
A telecoil is just a tiny coil of wire inside your hearing aid that picks up electromagnetic signals given off by various devices including loop systems and telephone handsets.
There are a variety of names by which people refer to telecoils. They may call them T-coils, T-switches, telecoils, telephone coils or audio coils.
In order to use a loop system, you must have hearing aids equipped with telecoils. Unfortunately, a good number of hard of hearing people do not even know whether their hearing aids have telecoils installed or not. Before you buy a hearing aid, you should insist that it have good amplified telecoils installed.
Ideally, your hearing aids should have a three position switch (for analog aids) or three programmable modes (for digital aids). These three modes are "M" for microphone only, "T" for telecoil only and "MT" for both microphone and telecoil together.
This combined microphone/telecoil mode is important. When you have your hearing aids in the "T" mode, you can only hear what comes through your telecoils. For example, if you are in a meeting and the person sitting next to you asks you a question, you won't hear him at all. You'd have to switch your hearing aids back to the "M" setting and have the person repeat the question. In the meantime, you'll be missing anything coming through the loop system.
With the "MT" position, you'll be able to hear both through the loop system and people talking around you through your hearing aids' microphones. This is a nice feature. For example, you may be listening to your TV at home though a loop system. If it is quiet and you have your hearing aids set to the "MT" position, you can listen for the baby crying or the doorbell or phone ringing at the same time you are hearing the TV.
Later, if there is a lot of noise around you (the kids are up making a racket near you), you can switch to the "T" position and cut out all this interference and just hear through the loop system. This way you can have the best of both worlds!
If you cannot get hearing aids equipped with a "MT" function, all is not lost. At home you can work around this by hooking both a microphone and a TV, for example, into your home loop system. The loop system's microphone will pick up the kids crying, the doorbell ringing or any other sounds around you and superimpose these sounds on top of those from the TV and you will hear both though your hearing aids' telecoils.
When you buy new hearing aids, it is a good idea to insist they have telecoils installed. However not all telecoils are created equal. Some are good and some not so good. Also, you may notice that when using your telecoils, if you tilt your head while listening to a room loop the sound changes in volume.
If there is a strong loop signal, this may not matter at all—especially if you have amplified telecoils (telecoils with a tiny amplifier attached). However, if you are sitting where the signal is weaker, you may notice that you hear better with your head held at a certain angle. Experiment a bit—tilt your head at different angles and discover the best angle at which to hold your head for the strongest signal. The same thing can happen when using a phone. How you hold a phone up to your telecoils makes a difference in how loud you hear the person talking.
At home, run a wire loop around the edge of a room—stringing it over doorways or you can place it under the edge of a carpet. If you loop your whole house, the easy way to do this is to staple the loop around the edge of the ceiling in the basement. That way you will be able to hear anywhere, both on the main floor and in the basement. Hook both ends of the loop wire to the loop amplifier.
Setting up a portable loop at a meeting or gathering is done as follows: String a loop of wire around the room and tape it down with masking tape or duct tape wherever people may walk so they won't trip over it. Attach both ends of the loop wire to the loop amplifier.
For either type of loop, plug a microphone, or the output of your TV or telephone into the loop amplifier. Turn the amplifier on. Now anything going into the loop amplifier will be transmitted through the loop to anyone wearing hearing aids equipped with telecoils.
Depending on the power of your loop amplifier, you can loop a room, several rooms or your whole house. That way you can move around in the looped area and still hear what you want to hear.
If you just want to loop your favorite chair (or car seat), setting up a personal loop system is as simple as putting a special loop pad under the cushion of your favorite chair or under the seat of your car and plugging it into the loop amplifier.
Home loop systems, as shown in the above table, are relatively inexpensive—in the neighborhood of $200.00.
Neal Bauman. Loop Systems—The Best-Kept Secret in Town. http://www.hearinglosshelp.com/articles/loopsystems.htm
http://www.hearingloop.org/places_hometv.htm
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