Assistive listening systems transmit sound one of three ways:

1. FM systems that transmit sound from a remote microphone (or PA system) to receivers via FM radio frequency, 
2. Infrared systems that transmit sound from a transmitter (emitter) to receivers via infrared light and
3. Induction loop systems that transmit sound from a transmitter directly to hearing aid telecoils via a magnetic induction loop.
   

How an induction loop system works
A thin loop of wire is placed around a listening area and attaches to a special amplifier with microphone (or PA system). Speech signals are amplified and sent through the loop of wire that creates a magnetic energy field.

The magnetic energy field is detected by people who wear hearing aids with telecoils or by special induction receivers that use headphones to get sound to a non-hearing aid user's ears.

How a telecoil works
Hearing aid and CI users have their own built-in receivers, called telecoils.

Telecoils are available on hearing aids and cochlear implants. A telecoil is a receiver built-into the hearing aid or CI and is activated by a switch. When the telecoil is turned on, it picks up the electromagnetic signal from an induction loop and converts it to sound.

The ability to turn off the hearing aid microphone helps reduce background noise so that the cleanest sound signal is processed. Some hearing aids have 'automatic' telecoils that automatically turn on when an induction signal is detected. The automatic telecoil is only useful when using a telephone handset.

How a telecoil works with induction loops
The audio signal from an induction loop system is presented directly to the telecoil but there are other ways to get sound to the telecoil. Neckloops and earhooks used with FM systems, personal listening systems, TV systems and cell phones are 'personal' loop systems working the same way as large area induction loop systems.

History of Induction Loops

Technically speaking, an Induction Loop or Hearing Loop is referred to as an Audio Frequency Induction Loop System (AFILS).

"In Northern Europe (where in some countries 90 percent of hearing aids have telecoils) induction loops … are the common communication access system. For example, in Britain nearly all hearing aids provided by the National Health Service now come with telecoils, and most churches and cathedrals are now looped. In the next several years, all London taxis and all London Underground ticket windows will be looped. So most induction loop systems are manufactured in Europe."  (from www.HearingLoop.org)

Oval Window Audio is the only company in North America manufacturing loop systems.

Telecoils are available on more hearing aids now than ever in the US and induction loop systems are becoming more popular as a means for communication access. There is an initiative spearheaded by David Myers of Michigan to Loop America. His efforts have certainly impacted the use of induction loop systems. Visit his non-profit informational website  www.HearingLoop.org.