What is loudness of sound? What factors does it depend on?

Loudness is a physiological response of the ear to the intensity of sound.

The loudness of sound heard by a listener depends on the following factors:

1. Amplitude — Loudness is proportional to the square of the amplitude.
2. Distance from source — Loudness varies inversely as the square of the distance from the source.
3. Surface area of the vibrating body — Loudness depends on the surface area of the vibrating body.