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Historical
ANSI/ASA S1.8-1989 (R2011)
Reference Quantities for Acoustical Levels
This Standard provides certain reference quantities to be used for acoustical levels. Reference quantities are stated in the International System of Units (S1). The unit of most acoustical levels is the decibel. Acoustical levels are equal to ten (or twenty) times the common (base-10) logarithm of an appropriate nondimensional ratio of a variable quantity (in the numerator) to a reference quantity of the same kind (in the denominator). The multiplier ten is used when the numerator is a power or power-like quantity (such as the time-average of the square of a time-varying sound pressure or vibration acceleration) or an energy-like quantity (such as sound exposure). The multiplier twenty is used when the numerator is the root-mean-square of a field quantity or an instantaneous quantity, such as a peak or maximum sound pressure.
Acoustical Society of America [asa]