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Induction Loop Systems

What is an Induction Loop?

An induction loop allows users with a telecoil equipped hearing device (switched to the T or MT position) or anyone wearing an Induction Loop Receiver to listen inductively to sound transmitted through a magnetic field without the interference of background noise.
The telecoil is familiar to many as the method used by the telephone companies to make it easier for a hearing aid user to use a telephone. The telecoil in a hearing aid picks up the sound via the magnetic field generated by the diaphragm coil in the receiver of a telephone.
Induction loop systems have been installed in locations such as churches, public halls and auditoriums, schools, lecture halls, cinemas, service counter windows, drive-thru order and pick up windows, information kiosks, offices, airports, train stations, parks, tour and guide buses, automobiles, boats, riding academies, and homes. BO EDIN (UNIVOX) is one of the world's leading designers and manufacturers of commercial grade audio frequency induction loop systems. Their systems are used in installations throughout the world.

How do Induction Loops Work?

It is well known that when an alternating current is passed through a wire, a magnetic field is generated around the wire. If a second wire is brought within this magnetic field, a corresponding alternating current is created within the second wire. In technical language, a current is said to be "induced" in the second wire. Hence the term “induction”. This particular electromagnetic principle is the basis on which electrical motors, electrical generators and transformers operate.
An induction loop system "induces" hearing aid telecoils or an Induction Loop Receiver in the same way. An Induction Loop System consists of an amplifier and a loop. The amplifier is connected to a sound source such as a TV, a radio, a public address system or a dedicated microphone. It then amplifies this sound signal and sends it out, in the form of an alternating current, through the loop. The loop itself consists of insulated wire, one turn of which is placed around the perimeter of the room in a simple loop system. When the alternating current from the amplifier flows through the loop, a magnetic field is created within the room. The magnetic field "induces" the hearing aid telecoil or the Induction Loop Receiver.
If a hearing aid user switches to the T or MT position on their hearing aid or if an individual is wearing an Induction Loop Receiver, the telecoil in the hearing aid or Induction Loop Receiver picks up the fluctuations in the magnetic field and converts them into alternating currents once more. These are in turn amplified and converted by the hearing aid or the Induction Loop Receiver into sound. The magnetic field within the loop area is strong enough to allow the person with the hearing aid or Induction Loop Receiver to move around freely in the room and still receive the sound at a comfortable listening level.
While this principle is well known and appears straightforward, in practice only well designed constant current driven amplifiers coupled with correct loop design, can provide the pure, undistorted sound necessary to satisfy both the listeners and the regulators demands.

Advantages of an Induction Loop

In a noisy environment, or one in which reverberations and echoes are noticeable, we all find it difficult at times to hear and understand what is said. For a person with impaired hearing wearing a hearing aid, it can be almost impossible to hear and understand under such conditions. Induction Loop Systems offer the following advantages:
Hearing aids with a telecoil do not need a loop receiver / headset to receive the sound signal. This eliminates picking up and returning receivers / headsets and battery maintenance issues.
Induction Loop Systems can be used anyone without a telecoil equipped hearing aid by using an ILR2 receiver / headset or similar. The system is useful to both the hearing disabled and those with normal hearing.

Induction Loop Systems deliver sound directly to the hearing aid in pure, undistorted form. This optimizes the benefits of hearing aids that are customized for an individual's specific hearing loss. The signal provided by an induction loop system is not affected by the distance the listener is from the sound

source, or by any interfering background noises in the room. The can significantly improve the intelligibility of speech.
Using a telecoil is inconspicuous. There is no need to call attention to a disability. This translates into much greater acceptance by those with hearing disabilities. Induction Loop Systems are much more likely to be used than either IR or FM systems.
Telecoils eliminate hygienic concerns. This overcomes a normal reluctance to putting something in one's ear that has been used in someone else's ear.
Induction Loop Systems are the only workable option in transient situations. In settings such as ticket counters, drive-thru windows, airport gates, trains, subways, and information kiosks there is no practical way to pass out the receivers / headsets required for using FM or IR systems.
An Induction Loop System can be used without others in the area being disturbed by the sound level in a sheltered or residential environment.
Induction Loop Systems accept any analogue signal as input, i.e. microphones, audio, TV, mixer boards, doorbells, voice intercoms, telephone ringers and can transmit it throughout the entire looped area. Digital signal sources can be converted to an analogue signal source.
Induction Loop Systems are the most cost efficient assistive listening technology.
Induction Loop Systems operate on a universal frequency. This eliminates problems inherent in operating on multiple frequencies associated with FM systems.
Induction Loop Systems are not affected by light or line site issues. This permits use in areas that are brightly lit or in direct sunlight.
UNIVOX Induction Loop Systems can be configured in phased arrays and low spill over designs eliminating privacy concerns.

It is for these reasons that more attention is now being given to induction loop systems in churches, public halls and facilities, schools, theatres, cinemas, sheltered and residential accommodations, workplace settings, service counter windows and transient environments. As Social, welfare, and public health authorities become increasingly aware of the needs of the hearing disabled, and the Americans with Disabilities Acts mandates accommodating those hearing disabilities, the cost-efficient, flexible induction loop system stands out as the best assistive listening technology.
Types of Loops
Domestic loop system

The Domestic Loop System (DLS) series powers personal loop systems in the home environment.  It covers from the smallest TV room up to the size of a complete house.  By using a loop pad or neck loop any DLS system becomes flexible do-it yourself option to all FM and IR TV systems, thereby utilizing each users individually adjusted hearing instruments.

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Professional loop system PROFESSIONAL LOOP SYSTEMS:
The Professional Loop Systems (PLS) series offers powerful amplifiers for the professional setting- conference rooms, churches, cinemas and theatres.  For all conventional loop systems a PLS amplifier is the right choice.  Many different models, ranging from medium sized PLS-100 and PLS-300 to the larger PLS-70 and PLS-900, will handle virtually any area.
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Counter loop system

Complete Loop Systems for permanent installation in receptions, information desks, supermarket cashiers and ticket booths.  All systems include loop amplifier, loop pad and microphone.  Reliable and powerful amplifiers guarantee problem free use.  With a choice of adhessive (for glass shields) or goose neck microphone.

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Portable loop system

If there is a need to use the loop system in different locations from time to time, a portable loop case
(p-Loop) might be the best idea.  If there is no loop installed – simply take the loop with you. The portable loop can also be equipped with several wireless microphones and used with wireless speakers, thereby working as a complete sound system.

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Measurement and Certification

No loop system is finalized until it has been certified by the installer.   The following is important:

The system shall always be measured and certified according to IEC standard 60118-4. Professional measurement can only be performed by a true RMS Field Strength Metre.  With this professional measuring tool the demands for maximum background noise levels, magnetic field strength evenness, frequency response smoothness and required overall field strength can be assessed. THE INTERNATIONAL LOOP STANDARD – IEC 60118-4 The International standard for assessment of hearing loops, IEC 60118-4, is designed to ensure that loop systems all over the world are designed to reach a quality that sufficiently will assist hearing impaired people.  Any loop system has to be adjusted in such a way that the demands of the standards are met.  If the hearing loop complies with the standard, a certificate is completed and included in the technical documentation of the venue.


What is a Telecoil

A wonderful feature available on many hearing aids is called the "telecoil". It's also referred to as a "t-switch" or "t-coil".

It's nothing more than a tiny coil of wire around a core that will induce an electric current in the coil when it's in the presence of a changing magnetic field.
A telecoil, can therefore, be an alternate or supplemental input device for a hearing aid.
Normally, a hearing aid "listens" with its microphone, and then amplifies what it "hears".  But, with a telecoil used as the input source instead of (or in addition to) the microphone, the hearing aid can "hear" a magnetic signal which represents sound.
Originally, the telecoil was meant to "hear" the magnetic signal naturally generated in an older telephone, whose speaker was driven by powerful magnets. This allowed someone with a hearing aid to hear the telephone better, if they just turned on (or switched to) their telecoil as an input source for their hearing aid.
Now there are many more magnetic sources that can be "heard" by a telecoil equipped hearing aid.
Even though newer phones are not natural sources of a magnetic signal, most phones contain extra electronics to generate a magnetic signal and are thus "Hearing Aid Compatible" (HAC). What that means is that a hearing aid with a telecoil can "hear" the magnetic signal they put out.
You can also use a telecoil to hear the TV, telephones, in meetings, in noisy restaurants, or in a noisy car if you supply the magnetic signal using an Assistive Listening Device (ALD) coupled with a room loop, or a neckloop.

One major advantage of a using a telecoil is that you can turn off your normal hearing aid microphone, and thus, not hear all the noise that might be around you. You only hear the magnetic signal, which doesn't include all that noise, so you can hear it a lot better.
Telecoils are available on most Behind the Ear hearing aids and on some In the Ear hearing aids.
Telecoils can provide that extra help you need to hear in many otherwise impossible situations.

General Information

South African Hearing Institute's website flyer



Johannesburg Cochlear Implant Newsletter – Winter 2011 Edition
Southern (ENT) Sounds – July 2011 (Volume 1; Issue 2)
Cochlear Implant Unit:  Tygerberg Hospital – July 2011


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