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.
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.
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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