Phon

The phon is a unit of perceived loudness, which is a subjective measure of the strength (not intensity) of a sound. At a frequency of 1 kHz, 1 phon is defined to be equal to 1 dB of sound pressure level above the nominal threshold of hearing, the sound pressure level SPL of 20 µPa (micropascal) = 2 · 10^-5 Pascal (Pa). Our ears as sensors cannot convert sound intensities and powers, they can only use the sound pressure. At other frequencies, the phon departs from the decibel, but is related to it by a frequency weighting curve that reflects the frequency response of human hearing. The standard curve for human hearing is the A-weighted curve, but others are in use. The "unit" phon is dying away because it is is useless. It is replaced by the dBA, but will stay with us for a long time, because of so many written books and and teachers having not noticed that. See also: sone \n

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Phon is also the name of a town in Thailand.