Table A2. Summary of Types of Assistive Listening Devices and Systems

1. FM BROADCAST: (40 frequencies available on narrow band transmission systems. Ten frequencies available on wideband transmission systems.)

Transmitters: FM base station or personal transmitter broadcasts signal to listening area.

Receiver: Pocket size with: a) earphone(s), or b) headset, or c) induction neck-loop or silhouette coil coupling to personal hearing aid equipped with telecoil, or d) direct audio input (DAI) to personal hearing aid.

Advantages: Highly portable when used with body-worn, personal transmitter. Easy to install. May be used separately or integrated with existing PA-systems. Multiple frequencies allow for use by different groups within same area (e.g., multi-language translation).

Disadvantages: Signal spill-over to adjacent rooms or listening areas (can prevent interference by using different transmission frequencies for each room/listening area). Choose infrared if privacy is essential. Receivers required for everyone. Requires administration and maintenance of receivers. Susceptible to electrical interference when used with induction neck-loop or silhouette (Provision of DAI audio shoes and cords is impractical for public applications). Some systems more susceptible to radio wave interference and signal drift than others.

Typical Applications: Service counters, Outdoor guided tours, Tour busses, Meeting rooms, Conference rooms,, Auditoriums, Classrooms Courtrooms, Churches and Temples, Theaters Museums, Theme parks, Arenas,, Sport stadiums Retirement or nursing homes, Hospitals

2. INFRARED LIGHT

Transmitter: Amplifier drives emitter panel(s) covering listening area.

Receivers: Under-chin or Pendant type receiver with: a) headset, or b) earphone(s), or c) induction neck-loop or silhouette coil coupling to personal hearing aid equipped with telecoil, or d) direct audio input (DAI) to personal hearing aid.

Advantages: Unlike induction or FM transmission, IR transmission does not travel through walls or other solid surfaces. Insures confidentiality. Infrared receivers compatible with most infrared emitters. May be used separately or integrated with existing PA-systems. Can be used for multi-language translation (must use special multi-frequency receivers).

Disadvantages: Receivers required for everyone. Requires administration and maintenance of receivers. Ineffective in direct sunlight. Careful installation required to insure entire listening area will receive IR signal. Susceptible to electrical interference when used with induction neckloop or silhouette (Provision of DAI audio shoes and cords is impractical for public applications). Lifetime of emitters varies with company. Historical buildings may pose installation problems.

Typical Applications: Indoor service counters, Meetings requiring confidentiality, Meeting rooms, Conference rooms, Auditoriums, Classrooms, Courtrooms, Churches and Temples, Theaters, Museums, Arenas (indoors only), Sport stadiums (indoors only), Retirement or nursing homes, Hospitals

3. CONVENTIONAL INDUCTION LOOP

Transmitter: Amplifier drives an induction loop that surrounds listening area.

Receivers: a) Personal hearing aid with telecoil. b) Pocket size induction receiver with earphone or head-set. c) Self-contained wand. d) Telecoil inside plastic chassis which looks like a BTE, ITE, or canal hearing aid.

Advantages: Requires little, or no administration of receivers, if most people have telecoil-equipped hearing aids. Induction receivers must be used where hearing aids in use are not equipped with telecoils. Induction receivers are compatible with all loop systems. Unobtrusive with telecoil hearing aid. May be used separately or integrated with existing PA-systems. Portable systems are available for use with small groups of listeners. These portable systems can be stored in a carrying case and set up temporarily, as needed

Disadvantages: Signal spill-over to adjacent rooms. Susceptible to electrical interference. Limited portability unless areas are pre-looped or small, portable system is used (see advantages). Requires installation of loop wire. Installation may be difficult in pre-existing buildings. Skilled installation essential in historical buildings (and may not be permitted at all). If listener does not have telecoil-equipped hearing aid then requires administration and maintenance of receivers.

Typical Applications: Service counters, Ports of transportation, Public transportation vehicles, Tour busses, Meeting rooms, Conference rooms, Auditoriums, Classrooms, Courtrooms, Churches and Temples, Theaters, Museums, Theme parks, Arenas, Sport stadiums, Retirement or nursing homes, Hospitals

4. 3-D LOOP SYSTEM

Transmitter: Amplifier drives a 3-D mat that is placed under the carpet of the listening area.

Receivers: a) Personal hearing aid with telecoil. b) Pocket size induction receiver with earphone or head-set. c) Self-contained wand. d) Telecoil inside plastic chassis which looks like a BTE, ITE, or canal hearing aid.

Advantages: Requires little, or no administration of receivers, provided most people have telecoil-equipped hearing aids. Induction receivers are compatible with all loops systems. May be used separately or integrated with existing PA-systems. Three-dimensional reception of loop signal regardless of telecoil position. Reduced signal spillover allows adjacent rooms to be looped without signal interference. 3-D loop mats must be separated by 6 feet to avoid signal spillover.

Disadvantages: Limited portability (areas may be pre-3-D Loop matted to facilitate portability). Requires installation of 3-D Loop mats. Installation may be difficult in pre-existing buildings. Skilled installation essential in historical buildings (and may not be permitted at all). If listener does not have telecoil-equipped hearing aid then requires administration and maintenance of receivers. Susceptible to electrical interference.

Typical Applications: Service counters, Ports of Transportation, Meeting rooms, Conference rooms, Auditoriums, Classrooms, Courtrooms, Museums, Theme Parks, Retirement or nursing homes, Meetings requiring confidentiality, Hospitals.

This information is derived from a chart published by Centrum Sound, Cupertino, California as modified by Cynthia L. Compton, Assistive Devices Center, Department of Audiology and Speech-Language Pathology, Gallaudet University, Washington, DC