Assistive Listening Devices (ALDs) are amplification instruments that amplify sound to improve hearing in specific, but not all listening situations. They work by increasing the volume of desired sounds (such as the soundtrack of a movie or the voice of a tour guide) without increasing the loudness of background noises.
ALDs can help people with hearing loss get more out of specific listening situations, such as:
- Classroom instruction
- Communicating over the phone
- Hearing and understanding TV and movies
- Hearing and understanding speech in groups or large-area settings, such as churches and auditoriums
ALDs are different from hearing aids, which also amplify sound, but are designed for multipurpose use. ALDs may be used instead of or in combination with hearing aids, depending on the characteristics of particular listening environments.
Types of Assistive Listening Devices
There are many assistive listening devices available today, from sophisticated systems used in theaters and auditoriums to pocket-size personal models. Types of assistive listening systems include:
- FM Systems – FM systems use radio frequency to carry sound from a microphone-transmitter to a receiver. The receiver can be integrated with a hearing aid or amplified by use with earphones.
- Infrared Systems – Infrared systems are similar to the FM system, but use invisible infrared light waves to carry sound from the transmitter to the receiver. The receiver converts the infrared light waves back into sound, which then can be amplified.
- Loop Systems – Loop systems use a wire antenna “loop” that physically surrounds a given area. A transmitter circulates a signal through the loop wire creating a magnetic field. Hearing aid users when switched to “T” or telecoil will pick up the signal when they are within the “looped” area.