Sound intensity level

Sound intensity level or acoustic intensity level is a logarithmic measure of the sound intensity in comparison to the reference level of 0 dB (decibels).

The measure of a ratio of two sound intensities is

L_\mathrm{J}=10\, \log_{10}\left(\frac{J_1}{J_0}\right)\ \mathrm{dB} \, $$

where J1 and J0 are the intensities.

The sound intensity level is given the letter "LJ" and is measured in "dB". dB is dimensionless.

If J0 is the standard reference sound intensity, where

J_0 = 10^{-12} \, \frac{\mathrm{W}}{\mathrm{m}^2} \, $$

(W = watt), then instead of "dB" we use "dB SIL". (SIL = sound intensity level).