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Related to loudness level: equal loudness contour
loudness level[′lau̇d·nəs ‚lev·əl]
The level of a sound, in phons, equal to the sound pressure level in decibels, relative to 0.0002 microbar, of a pure 1000-hertz tone that is judged to be equally loud by listeners.
Of a sound, the sound-pressure level of an equally loud 1,000-Hz pure tone, expressed in units called phons.