(Acoust) A unit of loudness level equal to the sound pressure in decibels of a 1000-Hz reference tone judged by listeners to be equally loud. Note: The basic unit of loudness is the sone. Sones and phons are related as follows: 1, 2, 4, 8, 16..... sones are equal, respectively, to 40, 50, 60, 70, 80, . . . phons