Threshold sound power level

The human ear is sensitive to sound waves with frequencies in the range from a few hertz to almost 20 kHz. Auditory response is usually expressed in terms of the loudness level of a sound, which is a measure of the sound pressure. The reference level, which is given in the unit phon, is a pure tone of frequency 1000 Hz with sound pressure of 20 qPa (in cgs units, 2 -lO " dyn/cm ) loudness level is usually expressed in decibels (dB) relative to this reference level. If a normal observer perceives an arbitrary sound to be equally loud as this reference sound, the sound is said to have the loudness level of the reference. The sensitivity of the typical human ear ranges from about 0 dB, the threshold loudness level, to about 140 dB, the level at which pain sets in. The minimum detectable level thus represents a sound wave of pressure 20 jiPa and intensity (power density) lO W/cm. ... 

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