Geometric spreading

As the sound moves away from the source, the area that the sound energy covers becomes larger and thus sound intensity decreases. This is referred to as "geometric spreading," which is independent of frequency and plays a major role in sound propagation situations. Due to geometric spreading, the sound level is reduced by 6 dB and 3 dB for each doubling of distance from the point (e.g., fixed equipment) and line (e.g., road traffic) sources, respectively.

See inverse-square law.