Infrared systems tend to be more expensive than loops because a stock of receivers has to be supplied with the system. An induction loop is a cable that goes round the audience area. It is fed by a loop amplifier. This gets its signal from a microphone placed in front of the person speaking or by means of a direct connection from a sound system or other sound source. The inductive signal is then picked up by anyone within the area of the loop with a hearing aid switched to the 'T' setting.
Listeners adjust their own hearing aids for volume.
Their hearing aids also ensure that the range of tones is right. Receivers can be supplied for people who do not have a suitable hearing aid. The loop wire is usually run around the edges of the room so that it serves the entire audience area. Sometimes, however, it encircles only a particular seating area. It can be routed over doors and arches.