In order to determine an estimate of a sound pressure level at a distance the Inverse Square Law can be used. In terms of the propagation and attenuation of sound, the inverse square law is a principle in physics whereby a point source emits a sound wave uniformly in all directions (essentially spherically), where the intensity of the sound wave energy at any given point away from the source is diminished as a function of the total surface area of the sphere coincident with that point.
To determine the sound attenuation over a distance using the inverse square law, an idealisation needs to be made in which there are no reflective surfaces or barriers between the source and the location at which the sound level is being determined.
According to the inverse square law, it can be shown that for each doubling of distance from a point source, the sound pressure level decreases by approximately 6 dB. Examples of points sources could include valves, small pumps and motors.
Calculate the sound attenuation using either metric or imperial units of distance (i.e. metres or feet).