Sound intensity is a measure of the energy of a sound wave and is a quantitative term that refers to a specific physical measurement: the energy carried by a wave through an area per unit of time. The intensity varies as the square of the wave's amplitude. Thus, the greater the difference between the regions of compression and rarefraction of the sound wave, the higher is its intensity. intensity is closely related to the more subjective word loudness, which refers to how the sound is perceived by us. For example, a sound that seems loud and out of place in a quiet room may be almost unnoticeable when it's heard on a busy street corner, even though it has the same intensity. So that is the difference between sound intensity and loudness.