Expert Viewpoint: Hearing the Message
Jan 1, 2008 12:00 PM, By Julian Pieters
Induction-loop basics for houses of worship.
Because of the huge variety in age and construction of various types of houses of worship, the installation of modern induction-loop technology into those facilities is a continuously diverse challenge. But before we examine loop systems, it is fundamental to consider what constitutes hearing loss and the effect that can have on a person's day-to-day life.
Suffering from hearing loss can be a traumatic and isolating experience because it reduces the ability to understand what you are hearing, particularly speech. Initially, it becomes difficult to distinguish the sounds that you want to hear from surrounding background noise. Then, as hearing loss advances, you lose your ability to hear the high-frequency sounds that make speech intelligible — and it becomes muffled, incoherent, and impossible to understand. This can change a person's life dramatically, and it can become impossible to interact normally with other people, either socially or in public places.
ASSISTIVE-LISTENING AND INDUCTION-LOOP SYSTEMS
Many people who experience high levels of hearing loss wear some type of hearing aid to help improve their situation. However, hearing aids form only part of the solution.
Even with the best digital hearing aid, background noise is disruptive and has a strong impact on intelligibility. To allow hearing-aid users to hear clearly in noisy public environments, assistive-listening systems need to be installed — systems that are often part of an AV infrastructure aimed at, among other things, extending accessibility to the hard-of-hearing.
In the United States, the Americans with Disabilities Act (ADA) calls for suitable assistive-listening systems to be installed anywhere sound amplification is used. In Europe, directive 2000/78/EC requires member states to adopt legislation to prevent disability discrimination.
An assistive-listening system will transmit sound to a receiver that allows the user to hear that sound clearly and effectively, removing background noise completely. Systems include infrared or FM radio transmitters with dedicated headsets that can be provided to individual users and induction-loop systems that use a magnetic field to transmit sound directly to the users' hearing aids.
Induction loops are the most widely used systems in Europe, and they are becoming increasingly popular in the United States — largely because of the direct use of the hearing aid. Hearing aids create many benefits, not least of which is the fact that the user does not require any additional equipment to be able to use a loop system because they are always carrying the receiver with them in their hearing aid.
ISSUES TO CONSIDER
An induction-loop system transmits an audio signal directly into a hearing aid via a magnetic field — greatly reducing background noise, competing sounds, reverberation, and other acoustic distortions that reduce clarity of sound. The magnetic field is created by driving a loop, or series of loops, with a specialized audio amplifier.
For anyone considering a loop system, there are several issues to consider before proceeding. First among these is the seemingly obvious: Will the system actually help?
While the answer would seem obvious, in actuality, some assistive-listening systems provide no benefit. To be useful, the loop system must be able to provide better separation of the signal audio from background noise. This means there must be suitable audio input, from an AV system or directional microphone, that will separate out background noise and pick up the required sound. If there is no background noise and the normal audio is clear, then an assistive-listening system is likely to be of no benefit. Simple perimeter loops can interfere with other loop systems up to three times the width of the room away in any direction. It is, therefore, important to check whether there are any other systems, or planned systems, in the area. The spill from a loop system can be dramatically reduced — down to 5ft. (1.5m) from the edge of the loop — by using a special low-spill design, which some manufacturers can provide. Ampetronic claims to be the only manufacturer with this ultra-low-spill approach. Other manufacturers can provide improved spill performance, but they will not get close to the mentioned 1.5m.
Magnetic fields can also be distorted by metal structures. Most modern buildings have substantial metal structural components, and metal floors and ceiling grids, particularly, can have a very strong effect on loop performance. Where metal is present, it is common for the amplifier to need to be two to three times more powerful to compensate. Often, the loop layout needs to use smaller loop segments to provide a flat, undistorted field over the required area. Losses tend to reduce the critical high frequencies more, so amplifiers need to have frequency compensation control to give flat frequency response.
Many different loop layouts can be used to give a particular shape and evenness to the magnetic field. Systems providers should be able to select and design the appropriate loop layout if they know enough about your application.
But practical installation of loop cable, or flat copper tape, requires careful evaluation of the site. In some environments, it may not be possible to run cables on the floor, so ceiling voids might be an option either above or below the volume of use. Special cables can be buried within concrete screeds or directly buried in ground outside the building. It is also necessary to avoid other signal cables, ensuring separation of at least 24in. (60cm) where cables are parallel.
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