Noise Criterion (NC), Noise Rating (NR)
Noise Criterion (NC), Noise Rating (NR) :
Units used in enginering to measure the acceptability of sound levels in enclosed spaces. The noise rating (NR) system was introduced by Kosten and van Os in 1962. Numerically, the NR rating is equal to the sound level indecibels at a frequency of 1000 hertz, but the rating requires lower levels at the more objectionable higher frequencies. The noise criterion (NC) system, introduced by Beranek in 1957, is similar, but it is designed more toward preserving speech communication, requiring lower levels of both high and low frequencies. It was updated in 1971, and the updated system is called PNC (prefered noise criterion)
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