Noise Isolation Class

Noise Isolation Class (NIC) is a single-number field rating of the overall airborne sound isolation between two enclosed rooms, including all transmission paths (direct and flanking). Defined in ASTM E413 and measured per ASTM E336, NIC is the field counterpart of STC but without any normalization for receiving room absorption or the partition area. The NIC rating is determined by the same reference contour fitting procedure as STC, applied to measured noise reduction (NR = L1 − L2) values across third-octave bands from 125 Hz to 4000 Hz. Because NIC includes all paths and no corrections, it represents what occupants actually experience. NIC values are typically 5–15 dB lower than the separating wall’s laboratory STC rating due to flanking, penetrations, and workmanship issues. NIC is useful for diagnosing noise complaints and verifying as-built performance but is less suitable for specification because it depends on room size and furnishing.