Phon

A subjective unit of apparent loudness. A phon is defined as the sound pressure level of a pure sine wave tone that sounds equal in loudness to some other sound(s) in question. Because of the ear’s complicated response versus frequency characteristics (see Fletcher Munson Curves) you can’t accurately relate the perceived loudness of sounds directly to their sound pressure level as read on a sound level meter. The phon allows us to relate this perceived loudness of sound to objective measurements of that loudness.