A very useful feature found in most behind the ear hearing aids and some in the ear hearing aids is the telecoil. It's also sometimes known as a t-switch or t-coil. Telecoils allow the hearing aid to receive signals from different electronic sources. They can provide better sound quality and eliminate background noise in certain situations. Telecoils can be used with some telephones, FM radio systems and public address systems.
A telecoil consists of wire wrapped around a metal core. This allows a telecoil to produce through induction an electrical signal when in the presence of an electromagnetic field. Thus telecoils will pick up magnetic signals like a microphone picks up a sound signal. The telecoil will bypass the hearing aid’s microphone and transmit this signal directly to the hearing aid’s processing circuits for amplification.
The telecoil was originally designed to be used with old-style telephones. This is where the name telecoil comes from. These phones produced a strong magnetic field from the speakers in the ear piece. The telecoil would allow its user to hear the telephone better, as it would allow the user to not amplify the background noise.
Newer phones do not produce the same strong magnetic fields as older phones. However, most phones are designated as hearing aid compatible, or HAC. This means that they can produce the signals needed for the telecoil to work properly. In addition, many movie theaters, auditoriums, and sports stadiums provide assistive listening systems to those patrons that require them. These generally take the form of hearing aid compatible headsets or receivers which can be borrowed by those who need them.
There are also a series of loop devices that can produce the magnetic fields needed by telecoils. They are generally hooked directly into a sound source like a television, radio or PA system. The three types of loop devices are room loops, neck loops, and silhouettes. Room loops are built into a room, either in the ceiling, floor or baseboards. The magnetic signal they produce can be used by everyone in the room, making them suitable for areas where there are many hearing aid users, like a church or nursing home. A neck loop and a silhouette are both single user devices, the neck loop being the size of a necklace, and the silhouette being even smaller and designed to fit behind the ear.
The advantage of a telecoil is that you can bypass the microphone on your hearing aid and therefore minimize the effect of background noise. Telecoils made it possible for hearing aid users to hear important communication in difficult situations, like a crowded theater.