Phon

phon [fän]

(acoustics)

A unit of loudness level; the loudness level, in phons, of a sound is numerically equal to the sound pressure level, in decibels, of a 1000-hertz reference tone which is judged by listeners to be equally loud to the sound under evaluation.

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loudness level

Of a sound, the sound-pressure level of an equally loud 1,000-Hz pure tone, expressed in units called phons.

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Phon 

the unit of loudness level. Since sounds of differing intensity—that is, of differing sound pressure—may have the same loudness at different frequencies, the loudness of a sound is evaluated by comparing it with the loudness of a pure reference tone, usually a tone with a frequency of 1,000 hertz (Hz). One phon is the difference between the loudness levels of two sounds of a given frequency whose intensities, or sound levels, at a frequency of 1,000 Hz differ by 1 decibel (dB). For pure tones with a frequency of 1,000 Hz, a difference of 1 phon in loudness level is equal to a difference of 1 dB in sound level.