ToolsSound, propagation & hearing
SPL vs. distance
Predict how sound pressure, intensity and level drop as you move away from a point source.
dB SPL
m
m
- Level at new distance
- 74dB SPL
- Change
- -20dB
- Sound pressure factor (1/r)
- 0.1×
- Sound intensity factor (1/r²)
- 0.01×
How it works
In free field, a point source loses 6.02 dB every time the distance doubles (the inverse-square law). Indoors, reflections and reverberation make the real drop smaller beyond the critical distance.
Formulas
- L₂ = L₁ − 20 · log₁₀(d₂ / d₁)
- p ∝ 1 / r (inverse distance law)
- I ∝ 1 / r² (inverse square law)
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