Indoor Noise Criteria

The SIL is mainly used to evaluate the effect of noise on speech in situations outdoors or indoors where the environment is not too reverberant. The A‐weighted SPL can be used as a guide for the acceptability of noise in indoor situations, but it gives no indication about which part of the frequency spectrum is of concern. A number of families of noise‐weighting curves have been devised to evaluate the acceptability of noise in indoor situations. These include noise criterion (NC) curves, noise rating (NR) curves, room criterion (RC) curves, and balanced noise criterion (NCB) curves. The curves have resulted from the need to either specify acceptable noise levels in buildings or determine the acceptability of noise in existing building spaces. A major concern has been to determine the acceptability of air‐conditioning noise. Beranek and coworkers [21–24] have been major contributors to the development of the NC and NCB noise criterion curves. Beranek and coworkers [21–24] and Blazier [25] were mainly responsible for the development of the RC room criterion curves. NR curves were devised by Kosten and van Os [26] and are similar to the NC curves. They have been standardized and adopted by the ISO. These noise‐weighting curves are now reviewed briefly.