How distance changes noise
For an ideal point source in free field, doubling distance drops level by about 6 dB:
L₂ = L₁ − 20 × log₁₀(r₂ ÷ r₁)
Sound Distance Calculator
Noise · inverse square
Estimate SPL at a new distance: L₂ = L₁ − 20 log₁₀(r₂/r₁).
Formula: L₂ = L₁ − 20 × log₁₀(r₂ ÷ r₁)
Frequently asked questions
Indoors?
Rooms and barriers break the free-field assumption — use this outdoors or as a rough lower bound.
Line sources?
Long roads/conveyors often fall nearer 3 dB per distance doubling — not this tool.
Near field?
Very close to large machines the rule fails — measure instead.
Hearing protection?
Still required when TWA or peaks demand it — distance alone is not a control.
