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The standard unit of loudness level, ranging upwards from zero for the faintest audible sound. The loudness in phons of a sound is defined as the intensity level in units of decibel sound pressure level (dB SPL) of a comparison pure tone of 1,000 hertz that is judged by the listener to be equally loud. Thus if the comparison tone is 20-dB SPL, then the loudness of any tone of another frequency that is judged to be equally loud is defined to be 20 phons; if the comparison tone is 40-dB SPL, then any tone judged equally loud is 40 phons, and so on. See also equal-loudness contour. [From Greek phone sound or voice]

Subjects: Psychology.

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