Using an inductive loop system, hearing-aid wearers can pick up the signals emitted by electric/electronic audio sources (microphone or hi-fi systems) directly in their hearing aids or CI systems. As a result, they hear the sound without any annoying background noise, echo or reverberation. An outstanding advantage of using induction loop systems: no special receivers are required. All that’s needed is the hearing aid.
Most modern hearing aids are now equipped with adjustable »M« and »T« functions. »M« stands for microphone, i.e. hearing the sound in the room via the integrated microphone, and »T« (telecoil) means that the audio signals are transmitted inductively and directly via a telecoil integrated in the hearing aid. Some hearing aids are also equipped with an »MT« function, which combines both types of reception, microphone and telecoil so that the listeners are able to hear the sound in the room as well as the inductively transmitted signals.
During the planning, design and installation of acoustic transmission systems often have special knowledge required. That is why we offer a comprehensive consulting planners and operators and service package for this sector. From the information through a qualified expert design assistance to installation and commissioning, we accompany you with our consultancy service for the effective use of professional audio transmission equipment.
Alternating current creates a magnetic field in a wire/a loop. If a second wire is introduced into this magnetic field (here: the telecoil in a hearing aid), a correspondingly alternating current will also be
created in it: the electrical impulses are »induced« into the second wire without any actual electrical connection.
An induction loop system consists of a loop and an amplifier. The loop, an insulated wire, runs around the outside of the listening area. The amplifier, connected with an audio source (hi-fi system, speaker’s microphone, etc.), transmits the acoustic signals converted into alternating current to the loop.
The magnetic field inside the loop allows the listeners to move freely in the room and pick up the audio signals fed directly into their hearing aids.
In order to install induction loop systems correctly, it is necessary to take into account many different factors – with respect to the architecture as well as the area in which they are used. Some areas of use with special requirements include:
Loop position: In order to create a uniform magnetic field, the distance between the loop level to the normal listening level should be between approx. 1.2 and 2 metres.
The position and size of the loop can also be determined by the position of the listening area (often much smaller than the size of the room) or the position of the microphones as well as other technical equipment that affects the magnetic field.
If possible, avoid using dynamic microphones in combination with induction loop systems. If they cannot be avoided, they must be positioned outside the loops. The distance between the loop and the dynamic microphone should be at least half the diameter of the loop.
Using a condenser or electret microphone usually produces better results with respect to interference or acoustic feedback. A microphone with a high-quality, insulated connection cord also generally reduces magnetic feedback.
Reduce the area of the loop! The connection wire to the loop must be firmly twisted or closely parallel.
Make a test installation. Always test the loop system to make sure that it is powerful enough, that the overspill does not cause any problems, etc.
Adjust the height of the loop (1.2 to 2.0 m) to provide for the greatest possible range with the smallest amount of overspill.
Conducting materials, such as reinforced concrete, can increase or decrease the area covered by the loop. The magnetic field strength is often increased outside the loop, while it is decreased inside. This fact considerably increases the risk of acoustic feedback. In a new building, you should try to install an LOS system. The LOS system makes it more difficult for the current to connect with large metal objects.
Pay particular attention to metal frames. Do not fasten the loop to structural elements made of metal or to similar objects.
|Reception, counter:||LA-90 |
|TV rooms, nursing homes, living rooms:||LA-240 |
|Conference rooms, theatres:||PROLOOP C |
|Very large induction loop systems:||PROLOOP DCCplus |
|Systems with little overspill:||Systeme mit geringem Overspill:||PROLOOP DCCplus |
|Portable induction loop system:||loop system kit |
This table serves only as general orientation for selecting the amplifier. Please take advantage of our consulting services before you make your purchase.
Standard induction loop systems produce a magnetic field that usually exceeds the »core service area«. This »overspill«, which travels horizontally and vertically, might still be audible three to four loop widths away. This limits the use of this technology.
Low-overspill systems (LOS) considerably reduce »overspill«. They use special loop patterns to reduce the signal strength outside the loop. For these patterns, two loops have to be operated out of phase with each other to achieve an equal distribution of the desired signal without creating any undesirable signal-free areas.
An LOS system consists of two induction loop amplifiers that are operated out of phase. This configuration prevents overspill and makes it possible to operate several induction loop systems in adjacent rooms without having their signals interfere with each other:
Each individually optimal customisation and configuration depends on the conditions prevailing in the area of application, in other words, on the room floor plans and the sizes of the coverage areas, the number of internal loops and the demands made on low overspill.
Determining the corresponding values for the »customised« low-overspill layout and the optimal level adjustments in each case is based on a complex method of calculation and installation. That’s why we strongly recommend that you take advantage of the services offered by HUMANTECHNIK. We provide competent support to architects, technicians and installers in planning LOS installations.
The overspill (Crosstalk) of standard induction loop systems works in a horizontal and vertical direction. The resulting »eavesdropping effect« is often still measurable over distances of up to three induction loop widths.
Low-overspill systems (LOS), that are competently customized and configured reduce overspill considerably to allow the operation of induction loop systems in directly adjacent rooms.