Phon is a unit of the level of loudness of sound as perceived by a listener. The loudness level of a sound in phons is equal to the sound pressure level in decibels of another sound that has a frequency of 1,000 hertz (vibrations per second) and sounds equally loud to the listener. For example, any sound that seems as loud as a 60-decibel sound of 1,000 hertz has a loudness level of 60 phons. The loudness level of sound cannot be measured with a meter because it is based on the judgment of a listener. However, charts may be used to estimate loudness levels at different sound pressures and frequencies.
