Inverse Square Law

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For a free field every doubling of the distance from the noise source, the sound pressure levels - L_p, will be reduced by 6 decibels. The inverse square law can be expressed as in the diagram below.

L_p2 - L_p1 = 10 log (R₂ / R₁)²

            =  20 log (R₂ / R₁)

where

L_p1 = sound pressure level at location 1 (dB)

L_p2 = sound pressure level at location 2 (dB)

R₁ = distance from source to location 1 (ft, m)

R₂ = distance from source to location 2 (ft, m)

A "free field" is defined as a flat surface without obstructions.

Example - Shot of a Rifle and Decibel Level

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