The American Speech and Hearing Association (ASHA) outlines several situations that can create listening challenges for people who are Deaf or hard of hearing, including too much distance between the listener and the sound source, competing noise in the environment, and poor room acoustics.
Assistive listening systems by-pass these acoustical conditions and deliver sound directly to listeners, enabling many people to participate more fully in programs and meetings. Assistive listening systems can be used alone or can be connected to a public address system, television, or other sound source.
There are three main types of assistive listening systems commonly used in public spaces:
Induction-loop systems: A hearing loop system includes a sound source, such as a microphone which may be connected to a public address system, an amplifier, a thin loop of wire that encircles a room or area (sometimes installed underneath carpeting), and a receiver used by an individual.
The system produces an electromagnetic field around the loop to distribute the sound signal. Individual receivers, which are either built into or connected to headphones or earphones (often, miniature earphones called “earbuds”) can pick up the signal.
Individuals who have personal hearing aids or cochlear implants equipped with telecoils can pick up the signal directly from the loop; they do not need separate individual receivers. Telecoils, also called t-coils, are tiny wireless receivers built into many hearing aids and cochlear implants (cochlear implants are surgically implanted electronic devices that stimulate the auditory nerve to send signals to the brain).
To pick up the signal from a loop system, a listener must be wearing the receiver (or have a telecoil on a personal hearing aid turned on) and be within or near the loop.
FM systems: FM systems use radio signals to transmit sound. A transmitter is equipped with or connected to a microphone or public address system, and listeners use individual receivers equipped with earphones or headphones.
Individuals with telecoil-equipped hearing aids or cochlear implants can connect a miniature loop to the FM receiver. The miniature loop is placed around the neck (these miniature loops are called “neckloops”). These individuals can then pick up the signal through their hearing aids or implants, and don’t need earphones or headphones.
FM systems may be purchased with multiple channels so that different meeting rooms can use different channels at the same time. These systems can transmit signals up to 300 feet and may be used indoors or outdoors. They can be used for large meetings, small groups or even one-on-one conversations.
Infrared systems: These systems use infrared light to transmit sound. A transmitter converts sound into light waves, which are picked up by individual receivers built into or connected to earphones or headphones. As with FM systems, people whose hearing aids or cochlear implants have a telecoil may pick up the signal from a neckloop. Infrared signals cannot pass through walls, so infrared systems are a good choice where confidentiality is a concern, but they cannot be used in environments with too much competing infrared light (such as outdoors).
Find more information on assistive listening systems from the National Institute on Deafness and Other Communication Disorders (NIDCD) and the Hearing Loss Association of America.