Single-Number Criteria for Room Noise

Abstract

Subjective noise ratings by executive office personnel, reported at the time that the NC curves were introduced [L. L. Beranek, J. Acoust. Soc. Am. 28, 833–852 (1956)], have been correlated with various physical measures derived from the 17 noise spectra originally published. The rank-order correlation coefficients (in parentheses) for the respective physical measures are: A-sound level (0.96), B-sound level (0.96), NC level (0.95), NCA level (0.95), N level per ISO proposal (0.96), speech-interference level (0.86), speech-interference level based on the three octave-band levels from 300 to 2400 cps (0.91), calculated loudness level (0.96), perceived-noise level (0.96), 40-noy-weighted sound level (0.95). With only one exception each, loudness level and perceived-noise level for the 17 airbase office noises are 13±1 dB greater than the A-sound level. Some type noise spectra of various shapes are provided, along with an auxiliary table, to facilitate estimation of the several physical measures simply by curve-matching. Since subjective ratings of office noise appear to be correlated with the A-sound level as well or better than with other commonly known noise ratings, and since the A-sound level can be measured readily with widely available meters, it is recommended as a replacement for the NC level in single-number specifications for office noise.