Phon
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- Phon is also the name of a town in Thailand.
Fig. 1: The Fletcher-Munson equal loudness level contours for pure tones.
The phon is a unit of perceived loudness level LN for pure tones[1]. The purpose of the phon scale is to compensate for the effect of frequency on the perceived loudness of tones[2]. By definition, 1 phon is equal to 1 dBSPL at a frequency of 1 kHz[3]. The Fletcher-Munson curves are a way of mapping the dBSPL of a pure tone to the perceived loudness level in phons.
The phon model can be extended with a time-varying transient model which accounts for "turn-on" (initial transient) and long-term, listener fatigue effects. This time-varying behavior is the result of psychological and physiological audio processing.