Some Effects of Spectral Content and Duration on Perceived Noise Level

Abstract

A number of experiments were conducted in which listeners equated a wide variety of sounds with respect to noisiness (equal acceptability) and loudness. The principal findings are as follows: (1) On the basis of data obtained from approximately 250 subjects, new equal-noisiness contours and tables for use in the calculation of perceived noise level were determined. (2) Over a range of durations from 112 to 12 sec, sounds were judged equally acceptable when the sound-pressure level was reduced by 412 dB for each doubling of duration. Variations in rise and decay times from 12 to 4 sec did not significantly influence the judgments. (3) Combining a pure tone of sufficient intensity with a band of filtered white noise caused subjects to judge the sound as noisier than the same band of noise at the same over-all sound-pressure level as the tone-plus-noise. On the other hand, the judged loudness of the band of noise, keeping over-all level constant, was not appreciably affected by the addition of the tone. (4) Calculated measures of perceived noise level (PNdB), loudness, and the readings on A, B, C, and “flat” scales on a sound-level meter were determined for a variety of “real” and artificial sounds of equal duration when these sounds were judged to be equally noisy or acceptable. Considering both absolute values and variability in the results, the order of merit, from best to worst, of the various measures for predicting the judgment data was as follows: PNdB, phons Stevens, phons Zwicker, “flat,” C, B, and A scale of a sound-level meter.