Ogden Clinic -
Audiology

Assistive Listening Devices (ALDs)

We offer a variety of ALDs. ALDs amplify specific sounds common to daily activities. They can be used alone or sometimes couples with a hearing aid. Whether a patient has difficulty hearing certain sounds in the home, talking on the telephone, talking with a friend, watching television or attending a meeting, an ALD may make the experience easier. ALDs include telephone amplifiers, vibrating alarm clocks, TV closed caption decoders, inexpensive personal hand held or body borne amplifiers, visual alarm systems, and TDDs (telephone devices for the deaf).

One of the major goals of signal processing schemes is to enhance the signal to noise ratio perceived by the listener. The use of aids with automatic low frequency reduction represent an attempt at this goal. Unfortunately, despite all the new technological advances, a basic problem remains for which wearable amplification falls woefully short. That problem relates to the physical distance between the microphone of the hearing aid and the source of the sound desired to be heard. Intensity (loudness) decreases as physical distance increases. Unfortunately most background noise surrounds the listener, so while the intensity of the speech decreases with distance, the intensity of the noise may not. This is one reason why hearing aids transmit sound so well if the speaker talks directly into the microphone, but at longer, more realistic distances reception diminishes. It would be ideal to have the sound produced at the source transferred directly to the listener without losing any intensity. It is usually impractical to ask the speaker to move closer to the listener's ear. One way of achieving this effect is with direct audio input, in which the speaker holds a microphone that is hard wired to the hearing aid itself near his mouth. Many hearing aid wearers are reluctant to ask the speaker to do this. An alternative approach is available through infrared transmission, FM transmission, or inductance loop transmission. These systems are currently used in many theaters, concert halls, houses of worship and households. One of the best uses is for television listening. The portable transmitter (usually smaller than most cable boxes) and microphone are located near the TV loudspeaker. The sound picked up by the microphone is then transmitted in the same intensity to a receiver worn by the listener. These devices can transmit with minimal distortion over a considerable distance (up to 50 feet). ALDs are becoming increasingly common in public places, due to the legislative enactment of the Americans with Disabilities Act.

Used with permision by the American Academy of Audiology.