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Published as a letter to the editor in the July 1996
Canadian Acoustical Association Journal

Providing Speech Intelligibility
in Public Spaces

by Barry McKinnon


There is more than a little irony in the National Building Code's mandating the requirement for disability access for the hearing impaired, when there is no similar requirement for the disability challenged (people with normal hearing) to be provided with intelligible speech in a space intended for public assembly or occupation. As part of our daily routine of business, we evaluate room acoustics of public assembly spaces that have excessive reverberation time or background noise, and do not provide acceptable speech communication under the conditions of use outlined by the owner. More often than not, the recommendations for acoustical treatment are deemed to add too much to the cost of construction and are pared down or eliminated. Architects seem to believe that acoustical treatment is just another room finish, and half as much is an acceptable compromise, if you can't afford the whole thing (after all, they couldn't get all the marble tile they wanted). Instead of being treated like stringent requirements of structure, HVAC or lighting, the criterion for speech communication is treated like some superfluous byproduct of the use of the room. (A library is the only place it may not be all that important.)

Similar situations exist in speech reinforcement or public address system design. We regularly review system designs from electrical engineers that have been produced without due consideration for the acoustical environment they will operate in. Sometimes these system designs are provided by equipment manufacturers or contractors, and the design professional is assuming a liability for a design that they do not understand. We recently reviewed a system design that would produce a %ALCONS of 40% at all listening positions (guesswork is not design!).

The real irony is that the parameters for speech intelligibility are quite well documented and understood. It is possible to objectively measure and classify %ALCONS, STI, MTF for unaided and amplified speech. The effects of signal to noise ratio, of excess reverberation, late reflections etc., are understood by the acoustics community as well as the knowledgable sound system designers. It is possible to design for speech intelligibility from the drawing stage of a project.

Maybe it is time to force this issue back into the view of architects and engineers by having a minimum speech intelligibility performance standard established in the National Building Code. This standard could be as simple as a requirement to provide a minimum of 10%ALCONS (or STI 0.52) for unaided speech, and for all sound systems, in spaces designated for use as public assembly or occupancy, and for spaces where life safety may be dependent on a voice warning system. Let's face it, most life safety systems are also designed without any consideration for the acoustical environment, they are merely designed to meet code (i.e. "be loud enough"). In situations where the public address or paging system may serve some life safety or evacuation announcement function, speech intelligibility is a life safety issue. The existence of a regulation would require proper acoustical design of public spaces, and would certainly require some design responsibility for the sound systems destined for these spaces. Every time the acoustical environment or speech reinforcement system is compromised, and does not meet the owner's requirement, the facility design is as much a failure as if it were too dark, or too small, or had too little fresh air. If the owner needs functional acoustics and a functional sound system to fulfill their needs, then the design team does them a disservice in not providing it. It's ludicrous that many projects now under construction would only provide intelligible speech for people using a listening assistance system.

Contrary to popular belief, this shouldn't increase real building costs, because every project where the room acoustics or sound system are substandard as a result of shortcuts in the initial construction, will have to be upgraded or fixed later. There's never money to do it right, but there's always money to do it twice.

If adding a building code regulation is the only way to make owners, architects and other design professionals pay attention to the importance of these issues, then let's establish a regulation. Let's at least find out how big this dragon is so we can set about slaying it.

The Canadian Acoustical Association meeting in Calgary, Alberta, Canada on October 11, 1996 from 8:45AM-12:00 Noon is the date set for the roundtable discussion on this issue. A group of consultants, contractors and construction industry regulators will be brought together to discuss the implications of this issue, and to determine if there is enough likelihood of success to pursue further discussions on the issue. There is a possibility that a new standards committee will be formed. (See the followup discussion), and the Systems Contractor News article on Life Safety System Safety.

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