Speech Communications as Limited by Ambient Noise

Abstract

Speech-intelligibility scores as a function of noise level are studied for face-to-face, sound-powered-phone, and amplified-speech- (earphone and loudspeaker) communication conditions. The speech-interference level (SIL) for octaves of noise centered at 500, 1000, and 2000 cps (0.5/1/2) is used as the measure of noise level. By using this noise measure, much of the work in this field can be brought together and interpreted. It is noted that “noisy” and “very noisy” spaces are associated with SIL's such that “shouting” or “very loud” voice levels (or 95-dB speech levels) are required for conversations at 1.5 or 3 ft, and this is the region where telephone conversations are judged to be “difficult” or “unsatisfactory.” All of these adverse noise conditions occur at the region where ear protection will aid intelligibility and at the boundary where ear protection should be used to protect against hearing losses. Where people must converse or communicate via some interior communication device (0.5/1/2), SIL's above 70 dB should be avoided. At levels greater than 90 dB (0.5/1/2) SIL, the wearing of hearing protection should be mandatory and every noiseproofing technique (except a noise shield for the microphone) should be employed. At levels above 100 dB SIL, every noiseproofing technique should be employed.