An observer’s auditory impression of the strength of a Loudness: The subjective judgement of intensity of a sound by humans. Loudness depends upon the sound pressure and frequency of the stimulus. Over much of the frequency range it takes about a threefold increase in sound pressure (a tenfold increase in acoustical energy, or, 10 dB) to produce a doubling of loudness. The unit is the Sone. The Zwicker method of calculation of stationary loudness is described in ISO 532 B and DIN 45631.
