SPL with Atmospheric Absorption (ANSI S1.26)
Far-field SPL with per-octave-band atmospheric absorption (alpha dB/m) per ANSI S1.26-2014 (R2019). Octave breakdown 125 Hz to 8 kHz; companion to the v1 spl-distance tile (inverse-square only).
Formula and source
SPL_far = SPL_ref - 20*log10(d_far/d_ref) - alpha(f, T, RH, P)*d_far. Per-octave alpha (dB/m) from the ANSI S1.26 relaxation-frequency formula: alpha = 8.686 * f^2 * { 1.84e-11 * (p_r/p_a) * sqrt(T/T_0) + (T/T_0)^-2.5 * [ 0.01275 * exp(-2239.1/T) / (frO + f^2/frO) + 0.1068 * exp(-3352/T) / (frN + f^2/frN) ] }.
ANSI S1.26-2014 (R2019) Method for Calculation of the Absorption of Sound by the Atmosphere. Inverse-square law from classical acoustics.
Audience
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