A loop system is a special type of sound system for people who use hearing aids. The loop system provides a magnetic wireless signal that is picked up by a hearing aid when it is set to the T-setting (telecoil). Many hearing aids are equipped with a telecoil (t-coil).
Typically, loop systems are found in meeting rooms, auditoriums, theatres, cinemas, places of worship such as churches and mosques and public service areas. Loop systems can also be found in London taxies.
The system filters out unwanted background noise and can be used by any number of users at the same time.
A microphone, an amplifier and a cable
The loop system consists of a microphone to pick up the sound (e.g. spoken words) and an amplifier which processes the signal, which is then sent to a loop cable. A loop cable is a fixed wire that is placed around the perimeter of a specific area. This area can be quite large, e.g. a theatre or a church, or quite small, a person's living room for example or even down to a chair. A loop can even be fitted around the person's own head (neck loop). The wire then sends the signal directly to the hearing aids of those who are in the room when their hearing aids are set in T-mode.
The telecoil in a hearing aid (also called t-switch or t-coil) is a tiny coil of wire around a core that will induce an electric current in the coil when it is in the presence of an activated loop system. Normally, a hearing aid picks up sound with a microphone and then amplifies the sound. With a telecoil, the hearing aid “hears” the magnetic signal from the loop system and then amplifies that signal.
Loop systems are also called audio-induction loops, audio-frequency induction loops (AFIL) or hearing loops.
A loop system cannot be used by hearing aids without telecoil.
Sources: www.hearinglink.org and www.wikipedia.org