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A subjective unit of loudness, as perceived by a person with normal hearing, equal to the loudness of a pure tone having a frequency of 1,000 hertz at 40 decibels.
(General Physics) a subjective unit of loudness equal to that experienced by a normal person hearing a 1 kHz tone at 40 dB
[C20: from Latin sonus a sound]
an acoustic unit for measuring loudness, judged equal to the loudness of a 40-decibel, 1-kilohertz reference sound.
[1945–50; < Latin sonus sound1]