Sound Distance Attenuation
Calculate how sound level decreases with distance from a point source.
Results
Sound from a point source decreases by 6 dB every time the distance doubles - this is the inverse square law. At 10 times the distance, sound is 20 dB quieter. This calculator is used for noise barrier design, speaker placement, environmental noise assessment and determining safe distances from loud machinery.
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Frequently asked questions
dB = 90 - 20 × log10(10/1) = 90 - 20 = 70 dB. The sound drops 20 dB at 10× the reference distance. That is the difference between a food blender and normal conversation.
Sound intensity decreases with the square of distance. Double the distance = 1/4 intensity = -6 dB. Triple = 1/9 intensity = -9.5 dB. Each doubling reduces level by exactly 6 dB.
OSHA's 85 dB threshold requires a 35 dB reduction. Distance = 1 × 10^(35/20) = 56.2 meters. At 56 meters, the 120 dB siren drops to 85 dB.
Only partially. Indoors, reflections add 5-15 dB above the free-field prediction. The formula is accurate outdoors where there are no reflective surfaces nearby.
A concert PA at 110 dB at 1 meter is still 70 dB (moderate TV volume) at 100 meters. It drops below ambient noise (about 40 dB) at roughly 3,000 meters in calm conditions.