Generalized Speech Interference Noise Contours

Abstract

Based on an extensive literature review of the effects of noise on speech intelligibility, a series of noise rating curves are developed. These Speech Interference (SI) contours are intended to bridge the gap between (1) Noise Criteria (NC) and Alternate Noise Criteria (NCA) curves used to rate the suitability of offices, and (2) a Speech Interference (SI) noise rating curve that predicts the effects of higher level noises on speech intelligibility. The highest SI contour (SI-80) has a minimum at an octave level of 80 dB at 800 cps and is steeply sloped both above and below 800 cps. The lower level SI contours have minima at increasingly higher frequencies and have steep slopes for frequencies below the minima but gradually level off at the frequencies above the minima.