I-AMP GPT 60-IV User Manual - page 4
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Excellence Through Engineering
Overview of Induction Loop Amplifiers
Induction loop systems transmit a signal to the hearing impaired person via baseband electromagnetic
waves. One of the greatest advantages of the induction loop system is the ability for the hearing aid to
receive the transmitted signal without the use of a separately supplied receiver headset. This is possible since
most hearing aids have an option to switch off the internal microphone and receive sound via an internal
telecoil pick-up. The telecoil pick-up was originally designed to pick-up electromagnetic radiation from a
telephone hand set speaker but this can also be used to receive signals from any magnetic source such as
generated by the induction loop system. Telecoils are now fitted to hearing aids specifically for induction
loop transmission systems.
“baseband”: sound is an air vibration or sound pressure wave. A baseband magnetic wave is created if the
sound pressure wave is directly proportional to the magnetic field created.
The pick-up area of a loop system is defined by a continuous loop of wire that encloses the area required. A
high level baseband audio signal is passed through the induction loop wire creating a magnetic field inside
the loop. Since the induction loop defines the pick-up area, the loop can be made to cover different sizes
and shapes, in both 2 and 3 dimensions.
Induction loop systems are susceptible to electromagnetic interference from sources such as high current
mains wiring, florescent lighting and dimming controllers which produce magnetic fields within the audio
spectrum.
Advantages and Disadvantages of induction loop systems:
Advantages
Does not require a specialised receiver to be supplied to each hearing impaired
person.
Listening area can be controlled by the layout of the induction loop.
System is not interrupted by physical obstacles in the pick-up area.
Disadvantages Susceptible to interference from mains wiring, florescent lighting and dimming
controllers.
Current required by the loop is dependent on the metallic structure surrounding the
pick-up area.
Some spill over outside the induction loop area.
Magnetic field strength can vary in the loop area in complex layouts.