Author:  Dolly Bhargava, M. Spec. Ed.

What is an Induction Loop Amplification System?

An induction loop amplification (ILA) system is comprised of:

  • one or more microphones to collect the desired sound (such as a teacher’s voice, television),
  • an amplifier to boost the signal, and
  • a loop of wire that surrounds the perimeter of the listening area (such as the classroom or auditorium). (Lewis, 1998)

How Does an Induction Loop Work?

Here is an illustration of how an induction loop works.

The sound signal is transmitted from the microphone worn by the source (e.g. speaker, TV or radio) to a loop amplifier that converts the signal into electrical energy. The electrical signal passes through the wire loop and generates an electromagnetic field.  The electromagnetic energy is received by one of the following devices if it is equipped with a T switch (a telecoil that picks up messages from the magnetic field).:

  • hearing aid
  • cochlear implant
  • loop receiver that the student can connect to using earphones or headphones (Lewis, 1998). 

Induction loops are traditionally used in venues such as lecture halls, theatres, churches and public halls.

Benefits of Induction Loop Systems

  • They can be used with students with a wide variety of hearing impairments 
  • If the receiver is the built-in T coil in the hearing aid or cochlear implant, it means the student with the hearing aid always has a "receiver" with them (Palm, 2004).  If the student does not have the telecoil facility, he/she can use a Loop Receiver and a headset to hear the audio signal provided by the induction loop system.
  • Induction Loop Systems deliver sound directly from the source to the hearing aid, without the interference of background noise, by bridging the distance between the sound source and listener and reducing background noise. 
  • The sound signal received by the student matches his/her needs.

Tips for Teachers using Induction Loop Systems

This section describes some of the limitations associated with use of induction loop systems in classrooms, and provides tips for teachers to use them effectively.

When the hearing aids are switched on to 'T' no other sounds can be heard at all, except what is coming through the "pick up point," so the student will not be able to hear peers’ comments, class discussions, or questions.  To overcome this problem, recent changes in hearing aid technology now provide more options. For example, it is possible to have the option of 'M' and 'T' combined on some hearing aids. This means that the student can access information from the loop system (‘T’) as well as information from the hearing aid microphone (‘M’).

The signal generated by the induction loop system may be affected by interference picked up from metal, electrical equipment such as fluorescent lights, dimmer switches or electric wiring, or video display terminals (Lewis, 1998). Replacing dimmer switches with good quality switches that do not emit interference, reducing the size of the loop, or rearranging the seating away from the source of the interference and reducing the speaker-to-listener distance may help overcome this problem.

Walls, ceilings and floors do not block the magnetic waves from a loop, so loop signals can spill out into other rooms.  According to Gilmore (1995) the spillover distance can be 50 to 100 feet.  Rooms that are next to each other, and rooms directly above and below the loop, can be affected. Hearing aid users whose hearing aids are also switched to T and people using a Loop Receiver outside the room may be able to overhear sounds or conversations (RNID, n.d.).  To overcome this problem it is important that the induction loop system is configured using a low spillover design. Alternatively an infrared system maybe used.

Infra-red Systems.  Another alternative might be to use an Infrared system, as infrared transmissions will not pass through walls.  Infrared listening devices can be supplied that work with the T-switch on the hearing aid, connect directly to the hearing aids (Direct Audio Input) or are used without hearing aids (using headphones). Infrared transmitters convert the sound source into infrared light that is transmitted to a receiver. The receiver must be in line-of-sight to the transmitter. Strong sunlight affects the infrared light, so infrared would be a classroom based solution only (i.e. not suitable for field trips or out in the playground).