Intensity and Pressure

Intensity is the power per unit area,

   Intensity$$= \frac{\mbox{Power}}{A},$$

expressed in Watts/square meter (W/m$^2$).

Sound intensity is

• a measure of the power in a sound that actually contacts an area (e.g. eardrum);
• a quantity influenced by environment surroundings/surfaces and interference from other sources;

Intensity is related to pressure squared:

$$I = p^2/(\rho c),$$

where $\rho$ is the density of air (kg/m$^3$), and $c$ is the speed of sound (m/s).