Sound intensity is more objective.
Work Step by Step
The intensity of a sound is a quantitatively defined value that can be measured by acoustical instruments. Loudness is related, but is a physiological sensation, and is more subjective than sound intensity. Some sounds appear to be "louder" because we are more sensitive to their frequencies, even though the waves might have the same intensity as others. The perceived loudness can even vary from person to person. This is discussed on page 394.