Equal-Loudness & Psychoacoustic Weighting
The human auditory system does not perceive all sound frequencies with equal sensitivity. In 1933, Fletcher and Munson demonstrated that human ears are significantly less sensitive to deep bass (below 500 Hz) and ultra-high treble (above 10 kHz) at moderate sound pressure levels, later standardized under ISO 226:2003 Equal-Loudness Contours ↗.
Comparison of Acoustic Weighting Curves
- A-Weighting (dBA): Mimics the human ear’s 40-phon equal loudness contour. It heavily attenuates low frequencies (-50 dB at 20 Hz) and peaks slightly around 2.5 kHz to 4 kHz (human speech resonance). Mandated by OSHA Standard 1910.95 ↗ and EPA for workplace and municipal environmental noise limits according to IEC 61672-1 ↗.
- C-Weighting (dBC): Mimics ear sensitivity at high sound levels (>100 dB SPL). Retains low-frequency energy from 31.5 Hz to 8 kHz. Used for measuring explosive sound, subwoofer punch, and venue concert peak SPL.
- Z-Weighting (dBZ): Zero-weighting. Pure flat electrical dBFS response from 10 Hz to 20,000 Hz without any psychoacoustic filtration.