ADAAG Manual

Infrared Systems

These systems use invisible (infrared) light beams to carry information from a transmitter connected to a public address system or microphone to special portable receivers worn by the listener. The receiver is connected by wire to any of a variety of couplers or directly to a hearing aid equipped with direct audio input. A receiver and a coupler must be supplied to each listener, including those using hearing aids.

Infrared light, like visible light, does not penetrate most construction materials but can reflect off many materials and is broad beamed. An uninterrupted line of sight is required between the transmitter and the receiver. The configuration of rooms and architectural elements such as columns or decorative pillars are important factors in selecting and designing an infrared system. The overall strength of the incident light on the receiver will determine whether or not a usable signal can be received. Emitters must be installed high up on the walls and more emitters may be added and located as necessary to insure proper signal strength. Since the signal is overpowered by the sun, infrared systems may not be suitable in some outdoor areas that are unshaded, uncovered, or exposed to much sunlight. Incandescent and fluorescent lighting can also produce interference. One reported problem, not well documented, is possible interference from other devices using signals, such as audiovisual controllers for slide or VCR presentations.

An infrared system is the only wireless system that provides confidential transmission since the signal cannot go through non-transparent materials. There is no spillover to nearby systems and all transmitters and receivers in a facility can be tuned alike, an important consideration where multiple systems are provided in a facility. A person can walk from room to room, as in a conference, and not need a new receiver, or need to adjust a receiver for each room. Multiple channel systems are available and can be used to support descriptive video for people who are blind or simultaneous translation in multiple languages. Two channels are typically available by modulating the wavelength. (ALSs broadcast an infrared signal at a wavelength of 950 nm.) Infrared systems are reported to have somewhat better frequency response than FM systems.