Why does the loudness of a sound note vary with the distance from the source of the sound?

The loudness of a sound note varies with the distance from the source of sound due to the phenomenon of sound wave dispersion. 

When sound waves travel through a medium, they spread out and become more spread out as they move away from the source. This spreading out of sound waves reduces their intensity or amplitude, leading to a decrease in loudness as the distance from the source increases.