A-Weighting

A-weighting is a frequency-dependent filter applied to sound measurements to approximate the human ear’s sensitivity, which is less responsive to very low and very high frequencies. Defined in IEC 61672-1, the A-weighting curve attenuates frequencies below 500 Hz and above 6 kHz, roughly matching the equal-loudness contour at 40 phons. Results are expressed as dB(A) or dBA. A-weighting is the default frequency weighting in nearly all building regulations, including BS 8233, DIN 4109, and ANSI S12.60. It is used for background noise assessments, environmental noise limits, and occupational exposure standards. While convenient as a single number, A-weighting can underestimate low-frequency noise impacts in buildings with HVAC or traffic noise sources.