Loudness measure is a term used to describe the measurement of sound intensity. The three most common units used to measure loudness are Sone, Decibel, and Phon. Sone is a unit of loudness that is based on the subjective perception of sound. Decibel is a unit of measurement for sound intensity, which is based on a logarithmic scale. Phon is a unit of loudness that is based on the average human's hearing threshold.