Loop systems consist of three basic parts—a microphone or other input device, a loop amplifier and a loop of wire. That's it for the transmitting side. Your own hearing aids equipped with telecoils make up the receiving side.
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. The wire loop is used instead of regular loudspeakers. 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. At this point, the loop system's job is done.
Now, it is your hearing aids' job to convert this magnetic signal into sound you can hear. When you switch your hearing aid from its microphone to its telecoil, all you are doing is connecting a small coil of wire 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.
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