The Rehabilitation Engineering Research Center at the Lexington School for the Deaf was charged with recommending performance standards for Assistive Listening Systems (ALS) to the Architectural and Transportation Barriers Compliance Board (the “Access” board). Included in this charge was the preparation of a “State of the Art” paper that would describe the current status and major issues presented by ALS. The recommended standards were to be based not only on the results of a study investigating listening performance under various acoustical conditions, but also to include other factors that affect the real-life use of these systems. In addition to the research study, three focus groups were conducted composed of consumers, and representatives from manufacturers, installers, movie and theater chains, and the national sound contractor’s association. A detailed description of the entire project can be found in the accompanying paper; in this “executive summary”, we will focus only on our final recommendations.
Electroacoustic Performance Standards: Recommendations
That the speech signal meet or exceed a Speech Transmission Index (STI) of .84, measured at the earphones. (The STI is, in effect, a measure of reverberation and noise upon the integrity of the speech source; numbers lower than 1.0 reflect degrees of degradation of the originating signal).
That the system produce a signal-to-noise (S/N) ratio of at least 18 dB measured at the earphones.
That the receiver be capable of delivering a signal of at least 110 dB SPL and no greater than 118 dB SPL measured at the earphone output. Volume controls should be included with a range of at least 50 dB.
That the peak clipping levels not exceed 18 dB down from the peak level of the signal.
Logistical Considerations: Recommendations
Newspaper and other media advertisements should include information that the venue provides an ALS.
Recorded telephone information should include a comment that the venue provides an ALS.
Within each venue, there should be clear and visible signs that an ALS is available and exactly where the receivers can be obtained.
At each venue, information regarding the frequency of the FM and IR (sub-carrier) transmissions should be clearly posted for those consumers who bring their own receivers.
The same individual in the same physical location should be responsible for both the checking in and checking out of the receivers
This individual should be trained to operate, troubleshoot, and maintain the receivers. See report for a full listing of this person’s responsibilities.
Receivers and Couplers: Recommendations
The output jack of all ALD receivers should accommodate a 1/8” (3.5mm) stereo plug using a TRS (tip, ring, sleeve) configuration, with the sleeve always carrying the ground. In mono systems the signal should be carried on the tip; in stereo systems, on the tip and the ring. This will permit the use of stereo earphones, direct audio input (DAI) cables, neckloops, cochlear implant patch cords, and silhouette inductors.
Discrete and highly visible and easy to use controls should be included in receivers that have the capacity to detect multiple channels or be capable of other electroacoustic modifications (e.g. volume and tone controls).
Single-channel receivers that contain only a minimum of external controls should be available for use at locations catering to elderly people (e.g. nursing homes, senior centers).
Receivers should include “low battery” lights than signal limited remaining battery life.
Coupling options should include headphone, earbuds, and neckloops. We suggest that at least one neckloop be available for every four air conduction type receivers.
Headphones should fit comfortably over all types of in-the-ear hearing aids and permit users to couple either inductively or acoustically to receivers. Furthermore, the “bleed” should not exceed the ambient noise at seats adjacent to the user.
It would be desirable for the industry to develop a “universal receiver”, one that can be (1) tuned to any FM frequency used in ALS in the 72-75 MHz or the 216-217 MHz range, either wide or narrow band channels, (2) adjusted to detect any of the sub-carriers used with IR systems, and (3) include a telecoil for usage with IL systems. The rationale for this is to provide consumers with the option of purchasing a personal ALS receiver, one that could be used in any venue.
The adequacy of the installation and the competency of the installers were a recurring theme in all the focus groups. While the competencies required for selecting and installing the appropriate ALS will differ depending upon the specific type of venue, all require some minimum information if the appropriate system is to be selected and installed properly.
We recommend that the Access Board sponsor workshops to train or update the training of ALS installers.
Such training programs can be a joint effort of consumer organizations, professional groups, industry, and such agencies as the Lexington RERC.
Training materials should be prepared independent of but also as a component of these training programs. Such material can consist of printed and video material, all suitable for dissemination on the internet.