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The sound level of a source emitting at a sound level Ls (in dB) and recorded at a propagation distance r, Lr, can be written as:where the −20 log10(r) term corresponds to the spherical distribution of energy (also known as the inverse square law and yielding a 6 dB attenuation per distance doubling), K′ is a constant equal to −10 log10(4π) for spherical radiation and −10 log10(2π) for hemi-spherical radiation and Aa is the atmospheric absorption.
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