Increasing distance from a source

A point source is one that radiates equally in all direction.

When it radiates into free space,

• the intensity decreases by $1/r^2$ (as the radius $r$ of a sphere increases, its surface area expands by ($4\pi r^2$), and
• the pressure decreases by $1/r$ (this follows from intensity being proportional to pressure squared),

where $r$ is the distance from the source.

In actual practice, sound sources wouldn't radiate so symmetrically as there would interference from other reflective objects.