Power and Intensity Levels

Decibels are often used as absolute measurements.

There is an implied fixed reference (e.g. the threshold of audibility).

Sound power level of a source:

    dB$$,$$

where $W_0 = 10^{-12}$    W.

Sound intensity level at a distance from the source

    dB$$,$$

where $I_0 = 10^{-12}$    W/m$^2$.