DISABILITY DISCRIMINATION ACT (DDA)
Many countries are begining to take the issue of disability very seriously and some like the UK and US have legislation in place to make it a criminal offense NOT to cater for such ones. In the context of hearing, the DDA (UK) has major implications for anyone involved in the design or running of areas used by either the general public or specific meeting places. So for example if you are say one of the trustees of your local church or meeting hall, you have a responsibility, in law, to ensure the disabled are not discriminated against. In other words that they have an equal chance to hear what is happening just the same as a normal hearing person.
In a meeting hall context, this is achieved easier and cheaper than any other comparable method by using an AFILS (Audio Frequency Induction Loop System) tied into the sound system. Anyone with a hearing aid can switch to the T position and hear the sound direct with no distracting background noises. Even better, there are no extra receivers or headphones to carry around advertising that a person is hard of hearing - AFILS are very discreet and effective.
However, just having a loop system is not enough - it MUST meet the appropriate standards (EN60118-4 formerly BS6083 or IE118-4) otherwise there is no point in having it! The standards ensure that loop signals are a uniform volume across all the area contained by the loop wiring, are loud enough to meet a defined standard and can be heard clearly by users. In general terms, old fashioned voltage loops with multiple turns of wire just DO NOT meet the standards and need to be replaced or upgraded immediately. Trustees or building designers have a responsibility enshrined in law to ensure compliance with the standards under the terms of the DDA.
Factors to consider when designing a loop system
Inputs to a loop system can be from almost anything - a microphone, Public Address (PA) system, music mixer or TV / home theatre system. However, the quality of signal heard through the loop system is only as good as that going in through the input. So for example sticking a boundary (plate) microphone on a wall or ceiling in a room and expecting it to pick up all conversations in the room just will not work!! It will pick up everything - all conversations, noises from outside, noises transmitted through the building fabric, air con systems and anything else. In short - lots of unwanted sound. The result will be a jumble which gets transmitted through the loop system - no good. Some thought must go into where the sound sources are and then picking up the specific bits. Usually the best solutions to this puzzle are a few well placed microphones feeding through an automatic mixing system and then into the loop amplifier. Then just the wanted sounds are amplified and the loop system works really well.
For the home type environment, loop systems can be a real boon as the volume is no longer determined by the person with the worst hearing in the room! Volume levels can be restored to normal and anyone hard of hearing can listen as loud as they wish via the loop system....more.
OLD FASHIONED VOLTAGE LOOPS NB - As supplied in ALL current quickly built KH sound kits
In the early days of AFILS and before specialist equipment was available, the accepted method of fitting a loop system was to throw a multicore cable around the perimeter of a room or building, wire all the turns in series and then connect it to an ordinary hi-fi amplifier. NO GOOD!!! Due to various factors (cable inductance, lack of current, reactive amplifier loads, building metal content etc.) this sort of worked in places and not in others. Such systems almost always fail to meet the standards and have been almost universally replaced by SINGLE turn loops fed from CURRENT amplifiers - specially designed equipment.
BUILDING CONSTRUCTION....Back to Top
It is essential that you understand the relationship between metalwork and induction loops otherwise you may install a system that simply does not work, sounds poor or fails to meet standards. The amount of metalwork (if any) decides how the loop will be designed and is absolutely fundamental to achieving a workable system.
Metalwork: - Critical to understand this
Any metal (grid or sheet) that is contained within the area where the loop is to be installed will have an effect on loop design and performance if:
- It is arranged in electrically conductive paths ie reinforced concrete floors, metal ceiling or floor tiles, foil backed plasterboard and some suspended / false ceilings. Each of these contains metal arranged into closed circuits and any magnetic field crossing it will generate a current within that closed circuit. Lots of metal - lots of circuits. Each circuit drains energy from the loop system - and so more energy has to be applied to overcome these losses. Compounded with this is the fact that energy losses are frequency selective - in other words high frequencies tend to be absorbed more quickly. The effect is for the audio received through the loop to sound as though you had placed a thick blanket across your hi-fi speakers - muffled and indistinct.
So to recap - The main consideration is the amount of metalwork containing closed paths within the area covered by the loop. Any metalwork that is away from the area enclosed by the loop cables can be ignored. Open ended metal structures such as supports or beams can also be ignored (no closed circuit).
In simple terms, the less metal the better.
Interference: Are there any potential sources of interference which may be picked up by a hearing aid switched to the T position?
Very infrequently, a particular location has a problem with interference which can be picked up by a hearing aid user. Sources of interference are: electrical supply sub-stations, large motors, High Voltage wiring, electric railways, CRT monitors or various other sources including poor mains supply wiring technique (split wiring using single cables). The best test is to get someone with a hearing aid switched to T to listen in the proposed loop area. If no hum or interference is apparent at normal listening levels when all normal electrical services are operating, then it is unlikely that any problem will arise. Otherwise, investigate further and isolate / remove the source of interference.
Other Close Proximity Loop Systems:
It is possible to hear a typical loop system up to three times the loop area away. If there is another loop system within the distance and both loops are to be used at the same time, special arrangements need to be made which fall outside this design service. You need to seek additional assistance.
Confidentiality: In some situations ie interview booths, it may be desirable to limit the distance the loop signal travels to prevent overhearing. If this is the case, you need to seek further assistance.
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