Physical Measurements on Equally Speech-Interfering Navy Noises

Abstract

Noise measurements and recordings were made on board several ships. Speech interference level (SIL) calculations showed that the median noise levels were above SIL's recommended for habitable offices. Eleven diverse ship noises were edited out and added to two office noises and three laboratory thermal noises. The level of each of these 16 noises was adjusted so that loudspeaker-reproduced Rhyme words at a level of 78 dB at 1 m were reduced to 50 % word intelligibility. Various spectrum analyses (octave band and 20-cps band), physical measurements (C, B, A, DIN 3 sound-level meter weightings), calculations [SIL's and 6-octave weighted articulation index (AI)], and fittings (to noise-criteria-type curves) were done to find which method came closest to agreeing that the noises were equally speech-interfering. Averaging methods like the AI or the SIL gave the best agreement. The A or DIN 3 frequency-weighting networks were next best and the curve-fitting procedures and the B & C sound-level-weighting networks were the poorest.