Induction loops, a closer look…..

“Sorry, did you say something?”

Hearing loss is a growing concern not only in the UK but globally. It is now the third most common physical condition after heart disease and arthritis.

We are all aware that hearing loss is common in older people (1 in 3 people over 65 experience hearing loss). This does not necessarily mean school age children and young adults have good hearing. Almost 15% of school age-children have some degree of hearing loss and 2-3 in every 1000 children are born with detectable hearing loss in at least one ear.

So what can be done to assist those with limited hearing?

People with significant hearing loss will typically have a hearing aid, but that is only half the story.

Hearing aids only amplify the sounds they pick up with their microphones and that means everything. Many hearing aid users switch them off/or remove them when they are in noisy environments because the noise is amplified just as much as the things they need to hear like conversational speech and it becomes irritating.

To achieve a better hearing experience for users it is necessary to provide a better source of audio to amplify and not the noisy background.

Most hearing aids function in two modes, one for the amplification of the normal surrounding environment. A second setting, T loop, is used to pick up sound from an induction loop.

The loop is a very simple device. It is copper tape or wire with an electric current passing through it. It is normally arranged in a circuit (or loop) around a listening area either above the ceiling or under the flooring.

The electric current passing through the loop creates a fluctuating magnetic field which in turn induces another electric current in the coils of the hearing aid.

Speech from an induction loop is often clearer to user than directly from the room environment.

In a presentation space, classroom or lecture theatre the sound heard through the induction loop is typically the audio that comes from the speaker’s microphone. The microphone is normally placed in close proximity to the speaker to avoid capturing a lot of background noise itself.  Consequently, the listener can experience reduced background noise and clearer audio from the speaker.

There are two main types of induction loop: perimeter and phased array. Perimeter loops as the name suggests are simply positioned around the perimeter of the listening area. They are easiest and cheapest to install. However with simplicity comes complications.

The main aim of any listening system is to achieve an even coverage across the listening plane. That plane is between 1.2m above the floor for seated listeners to 1.8m for those who are standing. Simple loops cannot always achieve this.

One problem with induction loops is the limited means by which you can control where the induced field is created. Care needs to be taken to ensure that occupants of neighbouring rooms cannot hear what is going on next door. In some organisations this security risk is not acceptable

To achieve a good listening experience over a large area a phased array is recommended. The phased array is in fact a number of loops which are intertwined with each other. The interweaving of loops (and phase shifting of the signal) not only creates an even listening field but also limits spillage to neighbouring spaces.

It is worth noting that whilst it is possible to control spillage horizontally, spaces directly above and below will be affected by the installed loop also.

So what are the alternatives to induction loops?

Infra-red transmitter systems are a simple and effective way of transmitting audio throughout a space using invisible light which is picked up and converted by a receiver, usually worn around the neck.

The system relies on users having a suitable receiver (often given out by the host) and a headset or neck loop to work with their hearing aids T-loop setting. These same systems may be used to transmit multiple channels of audio, for example different languages, as part of a simultaneous interpretation system.

The main disadvantages of IR systems are:

  • Receivers need to be in line of sight with the transmitter. If they are covered up or blocked by other people they will not work.
  • Users are often made to feel self-conscious about wearing the receiver and headphones or neck loop.

Mobile phone based systems are under development too. Smart phones, running an app, connected to the local Wi-Fi network are able to receive an audio stream and play it out through the headphone jack. Unfortunately there is a significant delay between the spoken word and the received signal. Users often rely on a combination of limited hearing and lip reading to understand what is being said. The delay in this case would be unacceptable.

What about the sources?

In most cases the audio source is a microphone. Careful choice of microphone type is vital in achieving the best audio available. Noise rejection is important here.

Ensuring that the speaker’s mouth is as close to the microphone as possible and maintaining that distance will achieve a clear and consistent level of sound.

The sad truth is most hard of hearing don’t bother complaining about the poor quality of sound.  We know this for a fact having worked on many projects where, unknown to management, the systems are not functioning properly. Without thorough initial commissioning followed up by regular checks the technicians have no way of knowing!

So whether you are building a new lecture theatre in a university or a conference room in a hotel getting good advice on assisted listening systems is important, to make sure your system is as inclusive as possible.


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