Designing Induction Loop Systems

Designing a loop system can be very simple, but it is also easy to make a mistake and end up with an inadequate system.  Ashton Audio can give you advice and guidance at any stage of your specification and design process to ensure your system works first time.

However you approach the design of your system you should also understand there are 6 basic types of loop layout for an audio induction loop system:

Overspill (counter) Loop
One to one communications
Counters, reception desks, intercoms etc.
1 small amplifier

Perimeter Loop
Area coverage, spaces up to 25m wide with NO METAL LOSS
Area coverage, spaces up to 2-6m with metal loss (depends on level)
Spill allowed up to 4x width away
1 loop amplifier required 

Single Array
Areas with metal loss but wider than 2-6m maximum
Only for fixed seating areas, e.g. theatre, classroom
1 loop amplifier required

Cancellation Loop
Areas suitable for a perimeter loop where spill control is required on one side only
Adjacent classrooms etc.
1 loop amplifier required

Low Loss Array
Large areas with metal loss
Areas in excess of 25m wide
Balconies in theatres

Ultra Low Spill Array
Adjacent rooms
Confidentiality
Nearby interfering systems
Large areas with metal loss / in excess of 25m wide

Loop Spill Explained
Induction loops create a magnetic field that is fairly consistent within the loop and reduces outside of the loop. Outside of a simple rectangular loop there is still an audible signal as far as 4 times the width of the room away from the loop, shown in the graphic on the left below. Spill is also vertical by approximately the same distance, as shown in the second graphic. If another loop system is used with this ‘spill’ area the systems will interfere with each other.

Spill is a problem in many environments where induction loops are useful, for example adjacent classrooms and lecture theatres, cinemas etc.

The solution is usually to use a low spill array, or a cancellation loop. These loop solutions are a little more complex, but are used widely in theatres, educational establishments, cinemas and conference centres around the world. The dramatic improvement in performance can be seen in the third graphic below.

Ampetronic was the first company to develop array systems and continues to lead the industry in design of array systems for a wide range of environments. Ampetronic’s highly skilled and experienced Support team use our proprietary design and analysis tools to produce designs tailored for your application to ensure that spill is not an issue for you and your loop systems.

Metal Structures
Metal in buildings - the impact on Induction Loops

The importance of designing Induction Loop systems to cope with losses due to metal structures within the fabric of buildings cannot be over-emphasised. It is absolutely critical to allow for signal loss caused by metal structures during the system planning phase of any installation. If this is not done, the installed loop system is most likely to suffer from a range of problems - insufficient signal strength, uneven signal strength - loud in places and inaudible in others, lack of high frequency detail / clarity or other problems. Metal loss problems can be overcome, but only by proper design and attention to detail.

The Ampetronic Support team can help you to assess and compensate for the metal structures in your application – contact us if you would like some assistance.

Principles

The magnetic field generated by an induction loop system, induces a current in any closed path of a metal structure placed in the vicinity of the induction loop. Further Information.

These induced currents tend to weaken the magnetic field and cause loss. This loss is dependant on the type and thickness of metal and its position in relation to the induction loop.

Examples of Metal Structures

Reinforced concrete floors – often containing a mesh. Further information about reinforcing meshes.
Lightweight floor construction with a (usually profiled) metal sheet under a thin reinforced concrete slab
Metal floor tiles - System floors
Suspended ceiling grid - 600mm x 600mm (2' x 2') or 1200mm x 600mm (4' x 2') metal grids with acoustic or metal tiles
Foil backed plasterboard - Vapour barrier
Girders, beams, constructional metalwork
Metal cladding, walls and roofs
Metal counters - Whole or part metal
Metal box construction - Elevators / lifts

Ashton Audio in conjunction with Ampetronic can design your induction loop system for you.  Simple induction loop designs are free, complex array systems will be charged for at a nominal rate.  You can request a design through our 'Contact Us' Enquiry Form.

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