What effect does distance have on the propagation of sound?
The effect of distance on the propagation of sound depends on the nature of the sound source and the surrounding environment and climate. If the source is outdoors, and it is small compared with the distance to the measurement location, the sound energy will spread over an area which is proportional to the square of the distance. This “inverse square” relationship dictates that sound level will decrease by 6 dB for each doubling of distance. Noise sources such as a train or moving traffic will radiate noise in a cylindrical pattern so that the sound energy will spread over an area which is proportional to the distance. Thus, the sound level will decrease by 3 dB per doubling of distance. Of course, climatic conditions will have an effect on this.