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Expert Viewpoint: Hearing the Message

Induction-loop basics for houses of worship. 1/01/2008 7:00 AM Eastern

Expert Viewpoint: Hearing the Message

Jan 1, 2008 12:00 PM, By Julian Pieters

Induction-loop basics for houses of worship.




Induction-loop systems are the most commonly used assistive-listening systems in Europe. Products such as the Ampetronic ILC5 combiner system (pictured) allow multiple loop amplifiers to be used to drive one loop.

Induction-loop systems are the most commonly used assistive-listening systems in Europe. Products such as the Ampetronic ILC5 combiner system (pictured) allow multiple loop amplifiers to be used to drive one loop.

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.

LOOP LAYOUTS

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.


Expert Viewpoint: Hearing the Message

Jan 1, 2008 12:00 PM, By Julian Pieters

Induction-loop basics for houses of worship.




STANDARDS AND TRAINING

There is a recently revised international performance standard for induction-loop systems: IEC 60118-4:2006. This standard seeks to ensure that all installed loop systems provide a useful output, and it only applies to the complete installed system — not to individual pieces of equipment. The contractor or installer is usually responsible for ensuring compliance to this standard.

In outline, the loop system must provide:

  • Even field strength: capable of 400mA/m RMS, with variation of +/-3dB over the entire volume in which the hearing aid user may be
  • Flat frequency response: from 100Hz to 5kHz +-3dB over the volume, often requiring the system to have special frequency compensation capability to adjust for frequency-dependent losses when metal structures are present.

It is also necessary to ensure that existing background magnetic interference is not present or is more than 32dB below the signal strength. Loop-system providers should design a system to meet these requirements and provide a certificate of conformity for the installed system.

One of the great benefits of loop systems is the near-invisible installation — no one needs to know that they are there or that they are being used. However, hearing-aid users do need to know that a loop system is installed, obviously. Good, clear, visible signage is very important to let people know that a system is available for them, and it must be provided for in the system specification.

The most common cause of loop-system failure is poor use or insufficient maintenance. Too often, systems are installed without consideration for those who must look after and maintain the systems. There must be someone nominated to be responsible for regularly inspecting and adjusting any loop system — and trained to do so properly.

Every installation must have at least a basic listening device to allow the system to be checked, with a field-strength meter available for larger or critical systems. Training, support, or a maintenance service should be part of the package provided by any loop-system provider.

EXAMPLES

These and other considerations can make installing such systems very challenging. Ampetronic and installation company Scanaudio specialize in overcoming these challenges. Therefore, following are three brief installation examples of recent work we have done together in the United Kingdom, using Ampetronic induction-loop systems.

With its original 12th-century building nowadays forming an adjacent aisle to a bigger 1906 nave, the Grade II-listed Holy Trinity Church in the Southchurch district of Southend-on-Sea, Essex, recently had a new Ampetronic ILD500 amplifier and perimeter-loop system installed to replace an infrared system. Ironically, the infrared system had been installed several years ago to replace an earlier induction-loop technology, with the thought that the infrared system would provide better coverage. But experience at Holy Trinity proved that an induction loop provides superior coverage for that particular facility.

One of the challenges of the installation was that the loop had to cover the whole main body of the church, which meant two very different approaches in the different eras of the building. Because the building was listed, extreme care was also taken to minimize visual intrusion.

“In most church installs, it is a fundamental requirement for the induction loop to cover as much of the main area as possible,” says Scanaudio proprietor Dee Couchman. “There will be members of the congregation who have been attending for years, and they will all have a favorite place to sit. So it is important that nobody is accidentally excluded from the loop's coverage.”

The floor in the 12th-century part of the church is covered with thick carpet, so there the loop comprised copper tape, and it was laid beneath the carpet. However, the more modern part features a stone-flagged floor, so there we used .06in. (1.5mm) tri-rated switch gear cable, which was either glued to the stone work at the interface of the floor and wall or stapled discreetly onto the top edge of a wooden skirting board.

A more modern building that has recently seen an Ampetronic installation is the church of Christ the King in Salfords, Surrey. There, the replacement of a 1980s induction-loop system was carried out. Because this was a late-1950s building, there weren't the strict guidelines of a listed building to deal with in placing the loop.

“We installed an [Ampetronic] ILD300 amplifier and perimeter loop, which was very straightforward,” Couchman says. “The building had a wooden skirting board all round the main part of the church, so we were able to attach the loop to it and install the equipment very quickly.”

Coming right up to date, a new Methodist church in Wimbledon, London, is a brand-new structure that has replaced the church's previous, century-old home on the same site.

Because it was new construction, the technical infrastructure could be designed into the building. The church took the opportunity to contact Scanaudio to install a sophisticated AV system, with an Ampetronic ILD500-powered induction loop as an integral part of the system.

“A new-build project is the easiest type of installation for making the induction loop completely invisible, as you can incorporate it into the fabric of the building before the finishing touches such as flooring are laid,” Couchman says.

The loop at Wimbledon Methodist Church takes its feed from the church's main audio system and is effectively a figure eight; the hall can be divided into two by means of a screen.

As Scanaudio's recent church projects demonstrate, induction-loop systems can be simply integrated into the most modern and the most ancient of buildings.


Julian Pieters holds a B.A. in Engineering and an M.B.A. He spent six years at Cambridge Consultants as head of product engineering, and a further two years as the company's head of diagnostics and instrumentation before taking over his current role of managing director of Ampetronic Limited, a manufacturer of audio induction-loop systems.

Web Exclusives

For more on induction-loop technology, and other types of assistive-listening systems, go to svconline.com/audioplayback/products/avinstall_assistivelistening_systems.


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