What is sound intensity ?

This may be defined as the rate of sound energy transmitted in a
specified direction per unit area normal to the direction. With good
hearing the range is from about 0.000000000001 Watt per square metre
to about 1 Watt per square metre (12 orders of magnitude greater). The
sound intensity level is found from intensity I (W/m^2) by:

Sound Intensity Level = 10 x lg (I/1.0E-12) dB

Note: 1.0E-12 W/m^2 normally corresponds to a sound pressure of about
2.0E-5 Pascals which is used as the datum acoustic pressure in air.

Sound intensity meters are becoming increasingly popular for
determining the quantity and location of sound energy emission.