Large Area Assistive Listening Systems: Review and Recommendations

2.2.1 General Description

There are two types of FM listening systems. One is a personal system, designed to be used by an individual on a one-to-one basis (Yuzon l994). The other, the type that concerns us in this paper, is meant to service one or more listeners in such large-area listening venues as auditoriums, classrooms, all types of theaters, and houses of worship (Ross l994). Both types are basically FM radios where the audio signal is "broadcast" to listeners wearing FM receivers tuned to the transmitting frequency. ALS can be a "standalone" device, or be integrated into an existing Public Address (PA) system (Compton l991). Of the three types of ALS described in this document, FM radio systems appear the easiest to install; generally, all that is required is a patch cord between an output from the PA amplifier ("line-out" or other audio output) and the input to the FM transmitter. Transmitters range in complexity from simple devices that include only basic interconnection and transmission capacities, to sophisticated devices that are capable of accepting a range of inputs from different sources and that incorporate many signal processing options (such as high frequency pre-emphasis, various compression options, etc.). Examples of commercially available large-area FM systems are displayed in figures 5, 6, 7, and 8.