SPL and Inverse Square Law

L2 = L1 - 20 log10(d2/d1) with free-field / hemispherical / indoor mode adjustment.

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Formula and source

L2 = L1 − 20 × log10(d2 / d1). Free-field (−6 dB per doubling of distance), hemispherical (ground-coupled), or indoor (less attenuation due to reflection).

Classical acoustics (inverse-square law); ISO 9613-2 (Acoustics - Attenuation of sound during propagation outdoors) by name.

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