Induction Loop Systems

Cost-effective induction loop systems suitable for many applications

Induction Loop Systems

Cost-effective induction loop systems suitable for many applications

Key Features

  • Designed to meet and exceed the requirements of BS7594 and BS-EN60118-4 when correctly installed
  • Available in a variety of cost-effective kit formats suitable for use in ticket offces, meeting rooms, lecture theatres, nursing homes, GP surgeries, churches and shops
  • Allows hearing aid users to participate fully in general conversation and other social or work related activities
  • Can be used to help building managers and service providers comply with BS8300 and the Equality/Disability Discrimination Act
  • All amplifiers are compatible with Outreach plate audio input extension system, a range of wall, ceiling and desk mountable single gang audio input plates specifically designed to increase the audio input capability of an induction loop system (and many other systems besides)
  • A comprehensive range of amplifiers, microphones, connector plates and test equipment covering virtually every conceivable AFILS application are available
  • Induction loop test kits include everything required to test an AFILS system to current British standards

Specification / Technical Information

What is an Audio-Frequency Induction Loop System?
Audio-frequency induction loop systems allow hearing impaired people to hear more clearly. Most hearing aids have a ‘T’ or ‘MT’ switch which allows them to pick up the electromagnetic field generated by an induction loop system. The hearing aid converts this signal into a sound suited to its user’s specific hearing requirements. Any person with a hearing aid positioned within or near the loop can hear the loop signal by switching their hearing aid to the correct position, allowing them to participate more effectively in general conversation, ordering goods or services, listening to public performances, etc.

An induction loop system therefore comprises the following main elements:
  • The audio source - typically a microphone, television or other audio input (sometimes more than one).
  • The induction loop amplifier
  • The loop - typically 1 or 2 turns of wire usually run around the perimeter of the room or a special counter loop fixed to the underside of a table/desk.
  • The receiver(s) - any hearing aid with a ‘T’ or ‘MT’ switch or a specially designed loop listening device.

How Does an Audio-Frequency Induction Loop System Work?
Audio-frequency induction loop systems do not use radio frequencies; they operate at audio frequencies. The signal from an audio source is fed into an induction loop amplifier, which amplifies and sets the signal level in the same way as a conventional amplifier. The amplified signal, instead of going to a loudspeaker, is fed to a closed loop of cable that is normally placed around the perimeter of the room (although other, more sophisticated ‘loop patterns’ can be employed). Using a constant current amplifier ensures the current is maintained at the set level whilst providing a flat frequency response without the need for equalisation circuitry. The current flowing through the loop generates a magnetic field that radiates in the space around the loop cable. Any lines of magnetic flux that pass through the telecoil in a receiver, such as a hearing aid, will generate a current in the coil that is then converted back to audio and fed into the listener’s ear.

It is important to remember that the magnetic field will ‘bleed’ outside the perimeter of the loop and therefore a loop system cannot be considered confidential. Induction loop systems are popular because:
  • Unwanted sounds such as other conversations and background noise are not picked up.
  • No special receivers are required - telecoils are fitted as standard in most hearing aids or are an inexpensive option.
  • Magnetic induction tends to be more reliable and effective than other systems (infrared, for example, is line of sight only).
  • Modern hearing aids amplify different bands by different amounts to suit a user’s specific hearing requirements.

In the UK, the installation of induction loop systems is governed by BS7594 (The Code of Practice for Audio-Frequency Loop Systems) and EN60118-4 (Magnetic field strength in audio frequency induction loop systems for hearing aid purposes). This system is designed to meet or exceed these requirements.

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