Background Noise Measurement

Background noise measurement quantifies the ambient sound level in a room with all building services operating normally but without the intended activity (speech, music) taking place. Per BS 8233:2014 and ANSI S12.60-2010, background noise is measured in octave bands from 63 Hz to 8000 Hz and compared against criteria curves (NR, NC, RC). Measurements should cover a representative time period (typically 15–30 minutes) at multiple positions. The equivalent continuous A-weighted level (LAeq) is used for single-number comparison against regulatory limits. Common background noise sources include HVAC systems, traffic, and electrical hum. Excessive background noise degrades speech intelligibility and increases vocal effort (Lombard effect). Typical design targets are NR 25–30 for classrooms, NR 30–35 for offices, and NR 20–25 for concert halls. Measurement must use a calibrated Class 1 sound level meter per IEC 61672-1.