The Phon Scale: Measuring the Human Perception of Loudness The is a psychoacoustic unit of measure used to quantify the perceived loudness of sounds. Unlike the decibel (dB) scale, which measures the physical intensity or sound pressure level (SPL) of a sound wave, the phon scale accounts for the human ear's non-linear sensitivity to different frequencies. Core Concept and Definition
Here is a detailed write-up on the phon scale. phon scale