Sone

A sone is a unit of subjective loudness used in psychoacoustics to convey how loud a sound is perceived, rather than its physical intensity. The concept was introduced by S. S. Stevens and colleagues in the 1930s as part of a family of scales for sensory attributes. The primary idea is to provide a direct, linear-like scale of perceived loudness: a sound described as twice as loud in sones is judged by listeners to be about twice as loud, all else being equal.

Definition and scale. One sone is defined as the perceived loudness of a 1 kHz pure tone presented at 40 dB above the listener’s auditory threshold under standard listening conditions. In practice, the sone scale maps to physical sound pressure level in a non-linear way and depends on frequency, bandwidth, and individual hearing characteristics. For a 1 kHz tone, an approximate relationship is N ≈ 2^((L_p − 40)/10), where N is the loudness in sones and L_p is the sound pressure level in decibels. This yields intuitive values: around 50 dB SPL gives about 2 sones, around 60 dB SPL about 4 sones, and so on. Across frequencies, the exact mapping uses empirically derived equal-loudness contours.

Usage and context. The sone is mainly used in psychoacoustic research and in certain areas of audio engineering and hearing science to describe perceived loudness of sounds or signals. It is part of a broader framework that includes phons (loudness level) and equal-loudness curves, which capture how loudness perception varies with frequency and level. The sone is a convenient, intuitive way to discuss loudness but remains a subjective, non-SI unit that can vary with listener and conditions.