Overspill counter loop magnetic field diagram (Image: Ampetronic)

Designing for the Hearing Impaired: Induction Loops

10 million people in the UK live with hearing loss. The Equality Act 2010 stipulates that businesses have a legal obligation to make reasonable adjustments to their services to make them accessible for the deaf and hard of hearing people. Equipping a business with the appropriate products is not only the socially responsible thing to do: it also makes sound business sense. If a business fails to take accessibility for the hard of hearing into account, 1 in 6 potential customers will understandably take their custom elsewhere.

Induction loops are the most commonly used assistive listening systems. What follows is a brief overview of what these are, how they work and how to install them.

What is a loop system?

Loop systems have been internationally available in theatres, cinemas, banks and other public places since the 1970’s when ‘behind the ear’ hearing aids were introduced, and are becoming more and more prevalent. Loop systems work by connecting a microphone and amplifier to a cable or wire which is placed in a loop around the perimeter of a room. When the hearing-aid wearer switches to telecoil or ‘T’ setting, the hearing-aid will pick up a magnetic wireless signal from the loop cable allowing the person to hear the spoken word or music with background noise eliminated, as if on a one-to-one basis.

Induction loop signage

Installation

The loop consists of few components: a microphone or other audio source, amplifier and a cable to form the ‘loop’. The audio source and amplifier will be connected to the rest of the audio-visual equipment used in the public place. The cable can often simply be installed around the perimeter of a room, under the carpet or skirting board, in a suspended ceiling, or, in a commercial setting, around the desk or kiosk. The measure of quality is conformity to International Electrotechnical Commission (IEC) standard IEC 60118-4 (revised in 2006).

RIBA CPD Providers Network members Ampetronic list 8 key requirements including values for the correct field strength, frequency response and background noise decibels.

Design considerations

Vivid Acoustic Systems provide a well-explained list of specific considerations for the design and installation of loop systems. Some of these include:

  • The size, shape and function of the space (e.g. classroom, theatre, church, bank kiosk)
  • The requirement for audience participation. If this is needed, other audio-visual equipment or microphones may need to be integrated with the system
  • Proximity to metal structures or components. Girders, rebars in reinforced concrete, metal roofing components etc. can all affect the magnetic field generated by the loop cable and dictate specific solutions (explained below)
  • Proximity to other equipment. Underfloor heating, fire alarm systems, lighting and air conditioning systems may all create electromagnetic interference
  • Locations containing some types of medical or laboratory equipment may not be suitable for a magnetic loop system.

Other general but important things to consider when designing for the hearing impaired include:

  • The acoustic properties of the materials in a room
  • Lighting levels and direction such that a hard of hearing person is not prevented from being able to lipread the other people
  • The appropriate positioning of fittings (for example, a reception desk or bank counter) such that the user is not inconvenienced or obstructed when trying to communicate
  • If an induction loop is installed, appropriate signage indicating that a loop system is available to use (and ideally the venue will actually turn the loop system on!)

Induction loop diagram for hearing aid wearers

Ultimately, when designing for the hard of hearing, compliance with the following legislation should be achieved:

Performance problems and solutions

‘Dead’ areas. The magnetic field strength generated by the loop must be appropriate for the shape, location of the room and the construction materials used in the building. If not designed correctly, this can result in a ‘dead’ area in the centre of a room if the loop is located around the perimeter. The specification of an appropriate amplifier and loop cable layout is critical to avoiding this problem. The most common solution for very large rooms or buildings with steel construction is to use a low loss phased array.

A low loss phased array system utilises two loop cables operating out of phase, each loop cable laid out to form a series of smaller loops within the given space. These system require amplifiers with 2 output channels and integrated phase shifting capability, or two separate amplifiers and a phase shifter. These systems not only offer coverage over large spaces and mitigate the effects of metal construction, but also reduce overspill.

Loop Spill. Within the loop of cable, the magnetic field strength should offer consistent coverage. Outside of the loop the magnetic field decreases, however with a standard rectangular loop, the signal will still be audible up to 4 times away from the coil, both horizontally and vertically. This creates a problem not only with confidentiality but in areas where multiple loops are needed, for example school classrooms or even semi-detached houses were the signal from each loop will spill over to others in proximity.

If the spill issue is limited to a single direction, such as a stage where electric guitars will be used that will pick up interference from the loop, a cancellation loop may be a suitable solution. A cancellation loop is a smaller loop positioned in the direction where the spill needs preventing, installed to ensure no users will be in the vicinity of this extra loop. If the spill issue is not limited to a single direction, or the size and construction of the room prevents a perimeter loop being used,  a low spill array is needed

Cancellation loop diagram

Cancellation loop layout (Image: Ampetronic. Ampetronic colour plots show the distribution of magnetic field around a loop system, from the side or from above)

A low loss array system is a series of loops positioned within the main loop, on top of one another, with two amplifiers which not only offers coverage over large spaces, also reduces overspill.

Low spill phased array loop layout (Image: Ampetronic)

Confidentiality. Since a hearing aid wearer is able to ‘tap into’ any nearby loop system that is not installed in the ‘low spill’ format, in situations where confidentiality is required (meeting rooms, courtrooms, banks etc.) this can present a problem.

One solution is emerging Infrared (IR) technology. The wearer is provided with a neck loop with a built in infrared receiver which communicates with the telecoil. The speaker will use a microphone with an infrared transmitter. If the room has internal windows, these should be fitted with blinds or curtains to prevent the infrared signal ‘spilling’ through glass or the daylight interfering with the intra-red signal. Vivid Acoustics provide a well explained definition of this technology.

Infra-red systems offer a wider bandwidth of sound and so the audio quality can be better than with an induction loop system, although listening to the signal using hearing aids rather than a receiver with headphones cancels out this advantage. Infra-red systems are ideal where there may be interference from other systems with magnetic fields such as stage lights. Infra-red systems are not affected by the metal in a building and do not overspill outside the walls, floor and ceiling in the same way that an induction loop system does. The main disadvantage is that anybody wishing to use the facility must identify themselves has having a disability and ask for a a specialist receiver which the operator of the venue will provide, but is often perceived to be unsanitary by the potential user. Care must be taken that these are returned after use as replacement is a costly exercise.

Cost and practicality. Occasionally loop systems can be expensive and time consuming to install, depending on the type of system and size, layout and function of the rooms. However the benefits to the hearing aid wearer far outweigh the initial outlay and the overall lifetime costs are often more economical than other solutions due to the lack of required maintenance and extra receivers.

Ultimate benefits

Regardless of installation challenges, the benefits of the system are self-evident. The hard-of-hearing person will be able to hear the person using the microphone clearly in a similar way to listening to sound through a headset or earphones, but far less conspicuously. Domestic loop systems are also available for use with telephones, televisions and other appliances. making day to day home-life far easier too. There are no real excuses today not to allow for this sort of simple system in public places.

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