Calculate the change in sound level between two distances using ideal geometrical spreading.
Level at another distance
Select a source geometry and enter the reference and target positions.
Level at target distance
dB
Level change: —
FormulaΔL = 10n log10(r2 / r1) Lp,2 = Lp,1 − ΔL
Level over distance
The distance axis is logarithmic. Markers show the reference and target positions.
Geometrical spreading
For an ideal point source in a free field, sound energy spreads over a spherical surface. Sound pressure level therefore decreases by approximately 6 dB each time the distance doubles. An ideal line source spreads cylindrically and decreases by approximately 3 dB per doubling.
Worked example
A point source produces 80 dB at 1 m. At 10 m, ideal spherical spreading gives:
ΔL = 20 log10(10 / 1) = 20 dB Lp,2 = 80 − 20 = 60 dB