Noise Attenuation with Distance Calculator
Sound level drop-off from a fan or equipment as distance increases.
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ⓘ Live results
Results
- Sound level at new distance
- 65 dBA
- Reduction
- 20 dB
- Distance ratio
- 10
Quick answer
For a point source in free field, sound pressure level drops about 6 dB for each doubling of distance.
L2 = L1 - 20 x log10(d2/d1)
How to use the Noise Attenuation with Distance Calculator
- 1Measure or take the sound level at a known reference distance from the fan.
- 2Enter the new distance you want to estimate.
- 3Read the estimated sound level, based on the 6 dB per doubling of distance rule for a point source.
Worked example
Using the values the calculator loads with:
Inputs
- Sound level at reference distance85 dBA
- Reference distance3 ft
- New distance30 ft
Results
- Sound level at new distance65 dBA
- Reduction20 dB
- Distance ratio10
Frequently asked questions
Does this apply indoors?
Free-field spreading loss is reduced indoors by reflections; expect less attenuation than calculated in reverberant spaces.
What about line sources like long ducts?
Line sources attenuate roughly 3 dB per doubling of distance instead of 6 dB.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.