A unit to describe the comparative LOUDNESS between two (or more) sounds. One sone has been arbitrarily fixed at 40 PHONs at any frequency, i.e. at any point along the 40 phon curve on the graph.

Since laboratory testing has shown that a difference of ten phons is sufficient to produce the impression that a sound is twice as loud, two sones are 50 phons. Four sones are twice as loud again, viz. 60 phons (see scale). A chart such as that shown here can be used for general conversion from phons (or DECIBELs) to sones for PURE TONEs.

For loudness summation of complex tones see LOUDNESS and Appendix F. See also: EQUAL LOUDNESS CONTOURS. Compare: MEL, PERCEIVED NOISE LEVEL, VOLUME.

Equal loudness contours for pure tones and normal threshold of hearing for persons aged 18-25 years, using free-field hearing (from ISO recommendation R226).