A-Weighting Explained — Why dBA Matters
A-weighting is a frequency correction curve per IEC 61672-1 that approximates human hearing sensitivity at moderate levels. It strongly attenuates below 500 Hz and above 6 kHz, making dBA correlate better with perceived loudness and hearing damage risk than unweighted measurements.
Origin
Based on the inverse 40-phon equal loudness contour per ISO 226:2003. Represents perception at moderate levels. Despite being an approximation, decades of research confirm dBA correlates with hearing damage risk across all exposure levels.
The Curve
IEC 61672-1 clause 5.4.6: -26.2 dB at 63 Hz, -16.1 at 125 Hz, -8.6 at 250 Hz, -3.2 at 500 Hz, 0 at 1 kHz, +1.2 at 2 kHz, +1.0 at 4 kHz, -1.1 at 8 kHz. Steep low-frequency roll-off reflects reduced hearing sensitivity to bass.
A vs C vs Z
C-weighting is much flatter (-3 dB at 63 Hz), used for peak measurements. The C-A difference indicates low-frequency content. Z-weighting has no correction, measuring true physical pressure for research.
When to Use dBA
Occupational noise (OSHA requires dBA), environmental (ISO 1996 uses LAeq), building acoustics background noise, general complaints. Nearly all regulations specify A-weighted metrics.
Limitations
Underestimates low-frequency impact from HVAC, traffic, machinery. At high SPL, hearing becomes more linear. For dominant bass, use C-weighting or octave-band analysis instead of dBA alone.
Try It Now
Measure dBA, dBC, and dBZ with the SPL meter