Large Area Assistive Listening Systems: Review and Recommendations

1. INTRODUCTION

Assistive listening systems (ALS) are designed to improve communication access for people with hearing loss. Signals generated by a loudspeaker or talker must often traverse a less than optimal acoustical space before being received by a listener. Though such acoustical conditions may be acceptable for people with normal hearing, this is not necessarily true for those with hearing loss. Because of the acoustical environment these people must expend a great deal of energy, with concomitant feelings of frustration and anger, in order to comprehend less than their basic auditory capabilities would otherwise have permitted.

This is a point worth emphasizing: an acoustical environment acceptable for normal hearing individuals may not be so for those with hearing impairments. Hearing impaired people frequently exhibit an inordinate sensitivity to noise and reverberation (Ross 1992; Nabalek 1994). Because of the hearing loss, they have already lost much of the linguistic and acoustical redundancy ordinarily present in speech signals. In a sense, they are already holding on to speech comprehension by their finger tips; add a bit more noise and reverberation into the equation, and their understanding of speech may go from barely adequate to complete incomprehension. Assistive listening systems (ALS) help by bypassing the acoustical space between the sound source and the listener. They do this by utilizing electromagnetic, radio, or light waves to transmit the signal from the source (either a loudspeaker or a person talking) directly to the listener. In this way, the deleterious effects of noise and reverberation upon speech perception is eliminated or minimized.

Assistive listening systems are not a new development. Over 90 years ago, some Churches in Denmark were using wired systems that led from a microphone on the pulpit to earphones located at designated seats within the sanctuary. Fifty years ago almost all the Churches in the same country were using induction loop (IL) systems (Hermansen 1979). Twenty years ago in this country, one manufacturer reported that in the previous five years over 2000 AM radio ALS had been installed in various public places (Williams, personal correspondence). While for a number of technical and convenience reasons neither hard wire or AM radio systems are used very much nowadays, it is nevertheless instructive to note that the need and advantages of some kind of ALS has been apparent for many years (Ross 1982). This was recognized almost 20 years ago by the Architectural and Transportation Barriers Compliance Board (the "Access" board) in their ruling that effective January 6th l981 all federally funded facilities must include listening systems in assembly areas to assist no fewer than two persons with hearing loss. Although we do not know how effectively this ruling was implemented in fact, it does testify to a long-standing national intent to improve "communication access" to persons with hearing loss, comparable to that provided for person's with physical handicaps (Federal Register, Volume 42, Number 6, May 4th, 1977).

It is apparent, however, that the recent resurgence of interest in ALS date from the passage of the Americans With Disability Act in 1990. Among the many provisions that can affect people with hearing loss, the law requires that any business (auditoriums, theaters, movie houses, etc.) with 50 or more fixed seats in an assembly area must make assistive listening devices available for at least 4% of the seating capacity. (Note: The law does not apply to houses of worship) Nothing in the law designates the type of ALS that should be provided in the different venues in which they can be used or the nature and adequacy of the receiving devices. Nor were installation or performance standards, at either the transmission or the receiving end, included in the implementing regulations. In taking advantage of the law, hard of hearing people often find themselves victims of uncertainty: On the one hand, when "everything" works well, the ALS will substantially improve communication access. Instead of feel ing frustrated, angry and isolated by a poor listening experience, hard of hearing people instead can relax, enjoy the performance, and continue their engagement in social/cultural activities. But, on the other hand, Murphy's law ("whatever can go wrong, will") describes too many real-life experiences. But even when things go right, hard of hearing people often report an underlying uncertainty, based on their own or other’s prior experiences, that "something" will indeed occur to interfere with the realization of the full benefit of an ALS.

It was because of the persistent reports of problems by consumers that the Rehabilitation Engineering Research Center (RERC) of the Lexington Center received a grant to investigate and recommend ALS performance standards to the Access Board. As a consumer-driven project, the first step was to convene a consumer focus group, in which hard of hearing people discussed the problems they encountered with ALS and to elicit their perspective on how the situation could be improved. Later a second focus group was convened, this one composed of the representatives from manufacturers, installers, and large-scale users of such systems (theaters and movie houses). Finally, a third meeting was held, attended by participants of both the previous groups, plus representatives from the National Systems Contractors Association (NSCA).

In this report, we will (1) provide an overview of assistive listening systems, incorporating and summarizing the observations and suggestions made by the participants in all three meetings, (2) present the consensus recommendations regarding logistical, signage, receiver and coupling issues, (3) comment on the installation-related issues, (4) report the research study that was conducted by the RERC and, in conclusion, (5) present the recommended electroacoustic performance standards arrived at through both the research project and modifications suggested by focus group members.