RC Curve

Room Criteria (RC) is a noise rating method developed by Blazier (1981) for ASHRAE that evaluates both the level and spectral quality of background noise in buildings. Unlike NC and NR, which simply rate the highest curve touched, RC characterizes the noise spectrum shape by comparing low-frequency, mid-frequency, and high-frequency regions. The RC rating consists of a numerical value (the arithmetic average of 500, 1000, and 2000 Hz levels) and a quality descriptor: (N) for neutral/acceptable balance, (R) for rumble (excessive low-frequency content), (H) for hiss (excessive high-frequency content), and (RV) for perceptible vibration. This spectral quality assessment makes RC superior for HVAC noise evaluation because it identifies the character of the noise, not just its magnitude. RC was updated to RC Mark II, which provides more detailed evaluation. ASHRAE recommends RC over NC for mechanical system design in their Applications Handbook.