a unit of subjective sound loudness. One sone is the loudness of a pure tone of frequency one kilo hertz and strength 40 decibels. A sound has loudness sones if a listener judges it to be times louder than a sound of 1 sone. The phon is another unit of sound loudness; a sound of loudness phons has loudness 2( - 40)/10 sones. The sone is often used in industrial engineering to express the perceived loudness of engines, fans, and other items of industrial equipment. The unit was introduced by S.S. Stevens and H. Davis in 1938. Its name is from the Latin word sonus, sound.