RC Mark II

RC Mark II is an updated version of the Room Criteria method published by Blazier (1997) and recommended by ASHRAE for evaluating HVAC-related background noise in occupied spaces. It refines the original RC method by extending the evaluation range down to 16 Hz and adding a more detailed assessment of low-frequency rumble and vibration potential. The rating includes a numerical level (average of 500, 1000, and 2000 Hz bands) plus quality indicators for spectral imbalance and vibration risk. Spectral assessment identifies departures from a neutral slope as rumble (R), hiss (H), or both (RH). The vibration criterion flags when low-frequency levels (16–63 Hz) are high enough to cause perceptible vibration in lightweight building structures. RC Mark II is the most comprehensive single-method evaluation for mechanical noise and is recommended in the ASHRAE Applications Handbook. However, its complexity means that simpler NC or NR criteria remain more commonly specified in practice.