FAQs Loop Systems

People who are hearing impaired, find it difficult to hear in large venues because of poor room acoustics. The problem is made worse by the distance that sound has to travel before it reaches the listener, background noise and competing sounds. Induction loop systems help to reduce unwanted background noise so that sound can be heard more clearly with the hearing aid set to the ‘T’ position.

We have dedicated a whole page to the topic of how an induction loop works, for more information, please click on the link below... How induction loops (or inductive loops) work

A majority of loop amplifier manufacturers specify the coverage area based on 100mA/m instead of the 400mA/m. Therefore it is truly impossibly to compare different amplifiers with the manufactory claimed coverage area. An amplifier configured for 400mA/m need be 16 times as powerful!! And since power output is costly this 16 times difference are likely to come up in the price tag. This is therefore not a popular subject amongst most manufactories. In addition the coverage is highly dependent on loop figuration and metallic environment and is always less than the theoretical free field value.

The new revised IEC 60118-4 with 400mA/m as the new reference overrides the old vastly misunderstood 100mA/m standard. A level of 400mA/m must be achieved in a loop system according to the new standard. It is NOT sufficient with only 100mA/m which is a widely spread misunderstanding of the old standard. This has caused and is causing many weak and noisy installations based on cheap and under-powered amplifiers. The 100mA/m has therefore been removed in the revised standard and should not be referred to any longer.

Using a loop system with a television, hi-fi, microphone or other sound source means a hearing person can hear sound at a level that is comfortable for them. The hearing impaired person using the loop system can get louder sound by adjusting the volume on the hearing aid. Sound from a TV speaker is unaffected by a loop system.

Hearing aid users (with hearing aid on the ‘T’ position) may hear magnetic interference from electrical equipment and wiring, such as fluorescent lights, light dimming circuits or 3 phase power cables. In extreme cases this manifests itself as a continuous loud hum or buzz. Clearly this is unacceptable for the hearing aid user. It is important that any site allocated for an induction loop system is checked for electro-magnetic background interference (in accordance with BS6083 Part 4). It is advisable that test is carried out before the equipment is fitted. A Field Strength Meter (FSM) is used for the purpose of testing for electro-magnetic background interference. An induction loop system must not be installed or be in use if the electro-magnetic background interference exceeds the critical level of -20dB across the majority of the loop area.

If just a small proportion of the looped area has electro-magnetic background interference above the critical level of -20dB then a loop system can be installed but signs must be displayed clearly marking the area that has interference.

Using a Field Strength Meter (FSM) will determine the level of electro-magnetic background noise. A Field Strength Meter can be hired from us to carry out this test prior to fitting one of our kits. Full instructions on how to test for electro-magnetic background interference are supplied with the meter.

Field Strength Meter (FSM) operation.

You can install the induction loop cable yourself - or you may want to ask someone who is good at DIY to do it for you. Full instructions for installation are included with every kit that we supply. The loop amplifier is normally placed close to the source of sound (e.g the stage area) and connected directly to it via a plug-in lead or microphone. Installing the loop cable itself is the trickiest part of the installation as it is usually placed round the edge of the room at skirting board level (or you can hide it under the carpet if there is one). Take care to install the cable securely - especially round door frames, window frames or openings (staple pitch < 15cm). You can route the loop cable up and down over door frames, window frames and openings as this will have little effect on the overall system performance.

Once the induction loop system has been installed it must be calibrated to the correct output level of +12dB on peak signals using a Field Strength Meter (FSM) in the middle of the room at 1.5 metres above floor level. Instructions for set up are supplied with all our loop induction kits.

You will need to check if the existing public address (PA) system has an auxiliary or tape output socket. This would normally be found on the rear of the PA amplifier. An audio lead (supplied with the loop kit) is connected from the auxiliary or tape output socket on the PA amplifier to the loop audio input socket. If the PA amplifier does not have an auxiliary or tape output socket, a separate microphone will be required for use with the loop.

If the area for the induction loop system does not have public address system, a microphone will be required. The microphone is probably the most important part of the induction loop system - get this wrong and any good induction loop system can sound poor. With this in mind each of our induction loop kits has the correct type of microphone to be used for each particular venue.

The induction loop amplifiers in each of our kits have been designed to be left on continuously including the home induction loop system that has a DC power supply. We would advise that a dedicated fused spur be used for the mains supply to all of the induction loop system kits (except home loop system). The installation of a dedicated mains fused spur removes the chance of the induction loop system being switched off deliberately or inadvertently. You will also not have to remember to turn your system on before each use or performance. If customers cannot use the system because it has not been switched on, then you could be in breach of the Disability Discrimination Act (DDA).

Microphone techniques.

An induction loop system must not be installed if the electro-magnetic background interference exceeds the critical level of -20dB across the majority of the loop area. If this is the case then we can supply an alternative method of meeting your requirement, for example by using our Infra-Red (IR) systems.

Metalwork, particularly aluminium, can have an unpredictable effect on loop system performance. Other external factors can affect the performance of an induction loop system. Reinforced concrete floors, steel lintels, corrugated steel cladding and other types of metalwork all have an effect on the performance of the induction loop system. Any aluminium based building product extensively used throughout the building may have a dramatic effect up on the performance of the induction loop system. In extreme cases it may prohibit the installation of a loop system because its effect has degraded the sound quality and strength to an unacceptable level. If you are in any doubt of the construction of the building it is advisable to run a temporary loop around the venue and test it first. This saves having to deal with problems after the loop has been installed. You may want to use our test system hire service.

Overspill is the magnetic field outside the area of the loop system. Induction loop systems are designed for hearing aid users to be present within the area of the loop. As the magnetic field will travel through walls, ceilings and floors there will always be some overspill. This means that hearing aid users outside the looped area may be able to overhear conversations if their hearing aids are switched to 'T' position. The magnetic field of a simple one loop system will overspill into adjoining rooms and rooms directly above and below. If you are fitting more than one loop please use our consultation service.

In some circumstances, an induction loop may cause interference in other circuits within a sound system (e.g. a public address system). This is likely to happen if the induction loop cable is installed parallel to, and in close proximity to, audio input cables. Microphone cables are especially vulnerable to this kind of interference. Carefully routing of all cables so as not to run in parallel or cross/touch normally prevents this problem.

Ideally, you should use a Field Strength Meter (FSM) with level indicator LED’s and speaker output to check the system (available as an optional extra). This lets you check magnetic field strength (+12B on peaks of sound) and quality of the sound. Non hearing aid users are unable to hear the loop system unless they use a hearing aid set to the ‘T’ position or use a FSM. We would advise that any venue that has an induction loop system should use an FSM on a regular basis.

Portable induction loop systems can be used when required in any venue and packed away after use. They are useful if you do not need a permanent system or if you need to use the loop in different rooms or venues. The loop cable on an easy to use drum makes the temporary loop set up quick and easy.

You must let your staff know you have had an induction loop system installed for people who are hearing impaired using a hearing set to the ‘T’ position and make sure they know how to use it. If customers cannot use the system because your staffs have not been trained how to use it, then you could be in breach of the Disability Discrimination Act (DDA).

Make sure that at least one named person is responsible for keeping the system working to its optimum performance in your building. With an induction loop system, designated staff should be responsible for looking after the loop system and auxiliary components such as radio microphones. In major venues, it is good practice for users to be able to contact at least one member of staff if there is a problem during performances. All staff who have contact with customers should also know about the system.

No, you do not need a licence to operate an induction loop system.

Omni-directional and uni-directional microphones explained: Omni-directional mics pick up sound with equal sensitivity from all directions. This is not normally useful for PA work, because in PA work each mic is targeted at a single sound source (so that the amplification given to that sound can be controlled separately from others, and so that pick-up of unwanted sounds can be minimised). Their application is generally limited to recording work (particularly of ambient sounds) and to sound-level measurement. Uni-directional mics pick up sound with greater sensitivity from the front than from other directions. There are several variations on this theme: Cardioid mics have a gradually reducing sensitivity from the front to the back, with very little sensitivity at the back. Super-cardioid mics reduce their sensitivity from the front to the sides at a faster rate than cardioid types, reaching a minimum sensitivity at an angle of around 120-140°, measured from the front. The sensitivity then increases again towards the back, but the sensitivity at the back is still very much less than at the front. Hyper-cardioid mics provide even less sensitivity at the sides than do super-cardioid types, at the expense of a little more sensitivity at the back. Therefore, a monitor speaker should never be placed directly behind this type of mic. Their minimum sensitivity is at an angle of around 100-120°, measured from the front. 'Rifle' or 'shotgun' mics are the most directional type, so-called because of their long rifle-like barrels. They are generally used only for long-distance miking (more than 2 metres from the source), e.g. for theatrical work, and should be located such that the back of the mic is not exposed to unwanted sounds.