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Listen to This!

9/6/2005

By Will Craig

Those ubiquitous white cords that snake up to the ears of returning students this fall should remind us of the effects and necessary remedies of prolonged exposure to high volume sound. While OSHA rates permissible noise exposure for 8 hours as high as 90 dB, many experts favor an 85 dB cap on long-term noise. And, let’s face it, nobody plays their music at what audiologists view as a safe level. No wonder a recent Newsweek article (May 2005) cited a study that estimates as many as 5.2 million students in the United States have hearing damage from prolonged exposure to loud sounds.

The Americans with Disabilities Act (ADA) requires lecture halls and other rooms “where audible communications are integral to the use of the space” with fixed seating that seat 50 or more _OR_ have an audio amplification system be equipped with a permanently installed assistive listening system. Such a system may utilize infra-red, induction loop, or radio frequency broadcasts, but the number of receivers must equal or exceed four percent (4%) of the total seats, with a minimum of two (2).

Several of my recent experiences with assistive listening systems may be instructive:

Have somebody else try it before you buy it.

Demonstrations of assisted listening equipment frequently consist of putting earphones on people with normal hearing (usually the people involved in making an acquisition decision) and playing music and spoken word content to them through a wireless system. Aside from technical glitches, I’ve never heard much difference between different manufacturer’s systems--sure, there are small differences in the amount of background noise, or in frequency response--but even with back-to-back listening through different systems, they’re hard to differentiate.

I recently conducted an evaluation of assistive listening systems in conjunction with the State of Minnesota Department of Human Services’ Deaf and Hard of Hearing Division. We invited several leading assistive listening manufacturers to bring their best products, and had evaluators on-hand with a broad range of hearing losses, from mild to profound. Not only could the evaluators discern important differences between the systems, they found that one particular manufacturer’s equipment, which sounds great to listeners with normal hearing, was completely unacceptable due to lack of available gain/volume. Just because it sounds fine to the person in the purchasing office d'esn’t mean it will work for students (or faculty) with hearing loss.

Density makes a difference.

On a recent project, we were specifying a large number of systems for proximate rooms (a common situation in campus buildings with large numbers of classrooms and lecture halls). The users requested FM-based assistive listening systems, with neck loop option for T-coil users and headphones for everyone else. Most standard FM assistive listening systems have 10 wide-band channels. When there are more than 10 rooms in close proximity and cross-over interference is possible, FM system users must move to narrow-band receivers (many standard transmitters can broadcast wideband or narrowband). The construction and composition of the walls, as well as any need for privacy, can also drive whether FM (wideband or narrowband) is an appropriate solution. This requires up-front planning and careful specifying to ensure that the units delivered will be compatible with each other and that users in nearby rooms are not adversely affected.

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