Sound Intensity
The time-averaged rate of sound energy flow per unit area perpendicular to the direction of propagation.
Governing formula
I = P / A = p_rms² / (ρ v)
SI unit
W/m²
In depth
For a point source radiating uniformly in 3D, sound intensity follows the inverse-square law ($I ∠1/r^2$).
Examples in the real world
Whispering at 1 meter having an intensity of ~$10^{-10} W/m^2$, compared to a jet engine at 30 meters having ~$100 W/m^2$.