NCB (Balanced Noise Criteria)

Balanced Noise Criteria (NCB) is a background noise rating method defined in ANSI S12.2 that evaluates both the noise level and its spectral balance. NCB extends the frequency range to include 16 Hz and 31.5 Hz octave bands and introduces a speech interference level (SIL) component and a rumble balance criterion. The rating consists of an NCB number (determined by the highest NCB curve exceeded at any frequency from 16 Hz to 8000 Hz) plus optional quality indicators. The SIL criterion identifies when noise levels may interfere with speech communication. The low-frequency balance criterion checks for excessive rumble by comparing low-frequency levels to the mid-frequency average. NCB provides more comprehensive evaluation than NC or PNC and is the noise criteria method standardized by ANSI. It is recommended for general building noise assessment and is particularly useful when both speech interference and low-frequency comfort need to be addressed.