Sone

The sone scale, developed by S.S. Stevens in 1936, provides a ratio scale of loudness — meaning that 2 sones is perceptually twice as loud as 1 sone, 4 sones is four times as loud, and so on. This ratio property makes sones far more intuitive for expressing loudness comparisons than decibels, where the relationship between numbers and perceived loudness is non-linear and frequency-dependent.

The conversion between phons and sones follows a power law. Above 40 phons (1 sone), each 10-phon increase doubles the loudness: 50 phons = 2 sones, 60 phons = 4 sones, 70 phons = 8 sones. Below 40 phons, the relationship steepens — small decreases in level produce disproportionately large decreases in perceived loudness, reflecting the ear's rapidly falling sensitivity near the threshold of hearing.

The sone scale is widely used in engineering contexts where loudness comparisons matter: HVAC noise specifications, product noise ratings, and environmental noise assessment. A computer fan rated at 2 sones is perceived as twice as loud as one rated at 1 sone — a much more useful comparison than knowing their dBA ratings differ by approximately 10 dB.

In SonaVyx workflows, sone values help contextualize measurements for non-technical stakeholders. While the SPL meter displays dBA values (standard for regulations and standards), understanding the sone relationship helps explain measurement results. When the treatment calculator predicts a 6 dB reduction in noise, translating this to "roughly 1.5× quieter" (via sones) communicates the impact more intuitively. The noise dose calculator deals with dBA-based regulatory limits, but sone-based thinking helps prioritize which noise sources to address first for maximum perceived benefit.