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Audio induction loops for hearing aids
Churches and some other places use audio induction loop to feed the sound from the PA system directly to the hearing aids.
That audio loop is basically a simple loop round the hall fed from an audio amplifier with the same sound that is sent to hall audio system speakers. The loop then converts the sound to a magnetic field which the hearing aid system.
One simple idea to make such loop is to take length of 25 pair telephone 'Inside Wire' that's long enough to go around the perimeter. Then get a 66 block (or some other kind of puch down block) and punch down the wires so they connect in a multiple turn loop. In this way you can add or subtract turns as you wish if you need that later.
You can feed this loop with an audio amplifier. When doing this you need to make sure that the wire resistance does not go to too low values or your amplifier will not like this. It is a good idea to keep the wire resistance in around same figure (or more) than the nominal spaker impedannce of the amplifier you are using is designed to drive. If the wire itself has too low resistance, use a suitable series resistor to increase the load resistance seen by the amplifier (pick up a power resistor which can dissipate enough power if you use this method).
I don't know how much power audio loop will need or take exactly, but this isn't a real problem nowadays. You can get a cheap amplifier that can put out a hundred watts, which should be ebough for even quite large loops.