PNC (Preferred Noise Criteria)

Preferred Noise Criteria (PNC) curves were developed as an improved alternative to NC curves, extending the frequency range to include 31.5 Hz and tightening the limits at low frequencies. Published by Beranek, Blazier, and Figwer in 1971, PNC curves address the limitations of the original NC system, which allowed excessive low-frequency noise. PNC is rated the same way as NC: the highest curve touched by the measured octave-band spectrum defines the PNC rating. PNC curves are slightly more restrictive than NC curves at low frequencies (63–250 Hz) and slightly more lenient at high frequencies (4000–8000 Hz). While PNC provided a useful improvement, it was eventually superseded by the RC and NCB methods, which provide spectral quality assessment in addition to level rating. PNC is still referenced in some older specifications and acoustic design guides but is rarely used in new projects. For current practice, RC Mark II or NCB are recommended alternatives.