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What are Assistive Listening Devices (ALDs)?
Assistive Listening Devices
(ALDs) are amplification instruments that are designed to be helpful in
specific, but not all listening situations. For instance, there are ALDs that
amplify the TV, the telephone, that amplify in theaters, in places of worship,
and that amplify public speakers. Hearing aids, which also amplify sound, are
instruments that can be used in all listening situations. But because a hearing
aid is an all-purpose instrument, it may not be as successful in each and every
specific application.
How do ALDs differ from hearing aids?
The construction of an ALD is
different from a hearing aid in one important aspect. All of the components of
a hearing aid, the microphone, the amplifier, and the loudspeaker are located
within the body of the instrument that is placed on the user's ear. Therefore,
the microphone of a hearing aid picks up both signal and noise. In contrast,
the microphone of an ALD is separated from the body of the instrument and is
placed at the sound source so that it picks up the desired signal and reduces
the interference of background noise. This is the biggest advantage of
ALDs.
How do ALDs transmit from source to receiver?
The method that is used to send
the signal from microphone (transmitter) to receiver is the most important
factor that distinguishes the various types of ALDs. There are four primary
methods that are used.
- Hard Wired:
A thin cable from
the receiver attaches the microphone. This type of ALD is useful for one-to-one
conversation such as while traveling in a car.
- FM:
The signal is transmitted by an FM radio signal. An FM system is often used in classrooms for
the hearing impaired or in auditory trainers for hearing impaired children.
- Infrared:
The signal is transmitted by an infrared light signal, similar to the remote control on TVs
or VCRs. An infrared system is often used in the home to amplify the TV or in
movies, theaters, or public speaking situations. The infrared system requires a
clear line-of-sight from the transmitter to the receiver.
- Loop:
The transmitter is attached to a loop of wire that is placed at the perimeter of the room. The
loop of wire generates an electromagnetic field that is picked up by the
receiver. This system is also used in classes for the hearing impaired or while
watching TV at home.
When should you consider using an ALD?
An ALD should be considered
when you have difficulty in a specific, but not all situations. For instance,
if you like the TV louder than your family, an infrared, FM, or loop system
would allow you to solve this problem. A microphone is placed in front of the
TV loudspeaker (attached with Velcro) and is connected to the transmitter. Your
family would adjust the loudness of the TV to their comfort; you would adjust
the loudness of your receiver to your comfort. In this way, the specific
problem of TV viewing is solved. If you have difficulty in a number of
different situations, you should consider a hearing aid instead of an ALD. You
also may use an ALD with your hearing aid to enhance the performance of the
hearing aid.
Website links for Assistive Listening Devices
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