Abstract:

Since 1955, the NC curves have been used with considerable success to specify and rate room sound quality. Although newer rating schemes have appeared, and in several areas supplanted the NC curves, many practitioners still use and prefer the old scheme. The newer RC and NC-B rating techniques exhibit one aspect which makes them both problematic in practical use. They both attempt to include in one rating number a further ``quality'' factor of the sound. While it is simple to establish the goal that room noise should meet a specific RC (or NC or NC-B) value, with a specific curve shape (neither ``rumbly'' or ``hissy''), it may be more difficult to evaluate whether a space meets the criteria. If the goal is to provide a background sound level of RC-40, or NC-B 40, does a room which is RC-35R meet the criteria, or fail it? Is an NC-B 30R better or worse than an NC-B 40? These questions are faced by the practitioner on a regular basis, and is one of the factors which makes the NC scheme more acceptable. When the room noise is ``rumbly'' or ``hissy,'' or when it is modulated or cyclic, or contains pure tones, a statement can be made to indicate this. The practitioner must first be able to specify the measurable physical quantities without ambiguity. Where there are sound quality factors present, they may indicate that an otherwise acceptable spectrum is unacceptable. Detailed background material is included along with examples, including those from the literature. [See NOISE-CON Proceedings for full paper.]