Assistive Listening Devices are amplification systems designed specifically to help people hear better in a variety of difficult listening situations. ALDs can be used with a personal hearing aid or by themselves to help overcome background noises and distance from the sound source. The basic function of an ALD is to improve the "signal to noise ratio" for the listener. This means that desired sounds (signals are amplified, and undesirable sounds (noise) are minimized.

ALDs are used in many listening situations. They can be used to enhance sound in large public facilities or in group situations. They can be used to improve enjoyment of the TV, stereo or conversations. Choosing an ALD is based on the listening situation and personal listening needs. The several types of ALDs include: Personal Amplified Systems, Infrared Systems, FM Systems and Loop Systems.

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Personal Amplified Systems

Personal amplified systems are designed to be very portable and can be used anywhere, indoors or outdoors. They are great for one-on-one conversations and TV listening. They are particularly helpful when in a car and it is difficult to face the person who is speaking. The units are pocket-sized and can be used with your choice of earphones, headphones, neckloops. or telecoil couplers. Some personal amplified systems have the option of modules that can he used in other listening environments. The basic unit is used as a personal amplifier. With added modules, you can use the units as receivers for FM, infrared or loop transmissions.

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Infrared Systems

Infrared systems transmit sounds by invisible light beams. To be effective, the receiver must he within direct line of sight of the light beam from the transmitter. There is added security in an infrared system because sound can not "spill over" to other rooms. (Many multiplex theater facilities are equipped with infrared systems for this reason). These systems cannot be used outside because of interference from sunlight. Bright, incandescent light may also cause interference.

Infrared systems are perfect for TV listening and small group meetings. Relatively easy to set-up, the transmitters connect directly to TV, audio output jacks or can be used with a microphone. Receivers come in lavalier or headset styles.

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FM Systems

FM systems transmit sound via radio waves (generally on 72-76 MHz frequencies. The speaker wears a compact transmitter and microphone, while the listener uses a portable receiver with headphone or earphone. (Those with hearing aids equipped with a telecoil can use a telecoil coupler). They are ideal for classroom or meeting use and work well both indoors and outdoors. If multiple FM systems are used near each other, separate broadcast frequencies should be used. FM signals are not limited to line of sight and can penetrate walls and ceilings.

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Loop Systems

Based on a principle of electronics called electro-magnetics, these systems are easily used by those having hearing aids equipped with a telecoil circuit. The technology consists of a loop wire which is placed around a listening area. A special amplifier and microphone are used by the primary speaker. Speech signals are amplified and circulated through the loop wire. Those wearing telecoil-equipped hearing aids can pick up the resulting energy field and have it amplified by the telecoil. Those who don't have telecoil-equipped hearing aids can use special receivers with earphones to pick up the magnetic signal. They are easy to install and can be used in classrooms, small meeting rooms, and automobiles.

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