Single‐Number Criteria for Room Noise

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.