Assistive listening devices (ALDs) are portable systems that help individuals with hearing loss communicate more effectively. Unlike hearing aids, which amplify sounds, ALDs work by separating speech from background noise. This allows the person with the hearing impairment to hear more clearly. Some ALDs are used in conjunction with hearing aids, while others work as standalone devices. ALDs are useful in a number of situations, primarily those involving distance, poor acoustics and noisy backgrounds.
Types of Assistive Listening Devices
There are several different types of ALDs available, for both large facilities and personal use. Some focus on amplifying speech, while others utilize computer programs to convert text to speech. Some of the different types include:
- FM Systems. FM systems rely on radio signals to transmit amplified sounds directly to the user. They consist of a microphone, transmitter and receiver, and are used in a variety of public places such as classrooms, restaurants, movie theaters and churches. The microphone is worn by the person speaking (or placed near the sound source) and the signal is broadcast from the transmitter to the receiver, which is tuned to a specific frequency.
- Personal Amplifiers. Personal amplifiers are essentially small FM systems used in smaller, more intimate settings where radio signals are less effective; they are often used when watching television, traveling by car, or outdoors. The microphone is built directly into the unit, and is often directional, allowing the user to aim it in the direction of the sound source in order to pick up the signal most effectively.
- Infrared Systems. Infrared systems work on the same principle as FM systems, but use infrared light instead of radio waves to transmit sound. The transmitter converts sound signals into light and beams those to the receiver, which then translates the light signal back into sound. An advantage to infrared systems is the fact that their signal is unable to pass through walls as it does with FM systems, eliminating competing broadcasts that might hamper the listener and preventing confidential information from being disseminated. They are particularly useful in courtrooms and large cineplexes.
- Hearing Loops. Hearing loop, or induction loop, systems utilize electromagnetic energy to transmit sound directly to a hearing aid or cochlear implant. They consist of a sound source (public address systems are popular), an amplifier, a loop of wire and a receiver or telecoil (t-coil), a tiny wireless receiver built into many devices. When the listener is in close proximity to the loop, he or she will receive clear sound free of background noise. Hearing loops can be connected to all types of audio sources, and are often set up in public facilities such as airports, churches and lecture halls.
- Alerting Devices. Alerting devices hook up to telephones, alarm clocks, doorbells and other electronic devices. They alert the user through a loud sound or flashing light, making him or her aware of an incoming phone call, a visitor at the door, etc.