INDUCTION LOOP SYSTEMS

What is an Audio Frequency Induction Loop System (AFILS) ?

How does an Induction Loop System work ?

When a current flows through an electrical conductor, a magnetic field is created around it.
If another conductor is immersed in this magnetic field, an electrical signal identical to the first appears at its terminals.
This is called an “induced” signal, hence the term induction. This principle is notably used in transformers.

STANDARDS NF-EN 60118-4

The type of site and surface to be equipped are very important, as they will determine all the guidelines to be followed in terms of :

• • The type of loop cabling: “single” loop or “figure-of-eight” loop,
  • Crosstalk to be taken into account or not (if adjacent but independent rooms are to be equipped, or if a microphone is to be used),
  • Choice of amplifier,
  • Choice of cable cross-section.

1- The surface/typology of the place

All surfaces can be equipped, but certain parameters need to be taken into consideration.

• • For a room whose width is less than or equal to 15m and whose length is less than or equal to 4 times the width, a “Simple” loop can be installed :

Caution : The magnetic field is cancelled out by overlaps within the loop. You must therefore ensure that this overlap is not located in a “useful” zone.

2- Crosstalk ?

If several contiguous rooms are to be equipped, crosstalk must be taken into account. In other words, the influence of one loop on another. The magnetic field does not stop abruptly. The isolation distance between 2 loops is about 1/2 the width of the loop.

The segment width of an area (1/8) shall not be less than 0,8m.

Horizontal crosstalk :

If you want to use stage microphones, in order to limit the effect of feedback on a zone, you can adopt the following principle :

3- Amplifier

The amplifiers to be used for a Magnetic Induction Loop must comply with NF EN60118-4.

Amplifier power depends on the surface area of the site to be equipped. Our range includes several references for coverage areas ranging from 56 to 3,400m².

PROLOOP NX7 LOS and PROLOOP NX15 LOS amplifiers are recommended when low crosstalk is required.

4- Induction loop cable

The cable to be used for Induction Loop Systems will be unshielded, with the cross-section depending on the surface area of the site to be equipped and the distance between the amplifier and the loop.

5- Installation

WARNING : The influence of the magnetic field (background noise) must be less than 32 dB (EN 60118-4) to ensure good intelligibility.

Sources of interference may be :

• • Transformers
  • Three-phase power cables
  • Electric lighting
  • Nearby magnetic loops

The magnetic loop cable should ideally be laid on the floor or ceiling if it is not too high (<2m40).

The loop can be embedded in concrete if it is not reinforced. In addition,  this loop must not be near metal (exclude metal cable trays, for example).

Keep the magnetic loop cable at a safe distance (min. 0.25 m or more) from other electrical cables.

The cable between the amplifier and the magnetic loop must be twisted.

6- Testing Induction Loop Systems

The magnetic fields generated by the loop are controlled by Majorcom the system is commissioned.

We use a test tool to ensure that the intensity complies with the EN60118-4 standard and that the audio signal perceived by the hearing-impaired person is correct (no saturation or distortion).