Rating of Noise with Respect to Speech Inferference
John C. Webster · The Journal of the Acoustical Society of America · 1969
Two simple noise-rating schemes are proposed—the three-band preferred frequency speech interference level (SIL) and A weighting (LA). The proposed SIL is the simple arithmetic average of decibel sound-pressure levels in the octaves centered at 500, 1000, and 2000 Hz. These simple noise rating schemes are interpreted in a nomograph relating distance between talker and listener and voice level. An additional interpretation over the older SIL, voice-level, and distance table is the inclusion of the voice level expected to be used in specific calculated noise levels (the Lombard voice-level reflex). Relationships between A weighting and the new SIL, the old SIL (based on average levels in the octaves ranging from 600 to 4800 Hz), and other noise rating schemes will be listed. Limitations of applicability to quasisteady-state noises within spectrum slopes of −12 and +9 dB/oct, etc., will be noted. Some of the background experimental results and validation studies specifying suggested criterion levels will be discussed briefly.