Sound Decibel (dB) Distance Dropoff Calculator
Calculate acoustic sound pressure level (dB SPL) dropoff over distance using the inverse square law for point sources, line arrays, and room acoustics.
Source & Distance Parameters
Acoustic Physics & Safety Analysis
Sound Level Reference Benchmarks
About this tool
How to use it
- Select a quick noise preset (lawnmower, concert PA, highway traffic, generator) or enter your reference sound pressure level in dB SPL.
- Enter the reference measurement distance (e.g. 1 meter) and your target observer distance in meters or feet.
- Select the acoustic source geometry (spherical point source vs cylindrical line array) and boundary directivity (free space, half space on ground, quarter space corner).
- Inspect the calculated target sound level in dB SPL, psychoacoustic perceived loudness ratio, acoustic energy retention percentage, and OSHA/NIOSH exposure threshold.
Why it matters
Sound intensity does not decay linearly over distance. Because the decibel scale is logarithmic, human hearing perceives every 10 dB reduction as roughly half as loud, while acoustic power drops according to the inverse square law (6 dB per doubling of distance for point sources). This tool models exact spherical dispersion, room boundary loading, and atmospheric air absorption to accurately evaluate noise exposure and audio coverage.
When to use it
Use this calculator when designing live event sound reinforcement arrays, conducting environmental noise impact surveys for industrial generators and HVAC units, checking municipal noise ordinance property boundary limits, or verifying occupational hearing safety compliance.
Good to know
Calculations assume an unobstructed line of sight. Solid acoustic barriers, foliage, terrain topography, and strong wind gradients can introduce additional attenuation not modeled in free-field equations.
Common questions
How does sound drop off with distance?
In an open free field (point source), sound pressure level decreases by 6.02 dB for every doubling of distance from the source under the inverse square law. For line sources like busy multilane freeways or concert line arrays, sound drops by only 3.01 dB per doubling of distance.
What is the 10 dB rule of thumb in human hearing?
While a 6 dB drop represents a 50% decrease in physical acoustic sound pressure, the human ear and brain interpret acoustic changes logarithmically. Psychoacoustically, it requires approximately a 10 dB change for a sound to be perceived as twice or half as loud.
How do walls and ground surfaces affect sound levels?
Placing a sound source against reflective boundaries concentrates acoustic energy into a smaller radiating solid angle. Placing a speaker on the ground (half space, Q=2) boosts low frequencies by +3 dB, against a wall (+6 dB), and in a room corner (+9 dB).
At what distance is a 100 dB noise safe without hearing protection?
In a free field, a 100 dB point source drops to 80 dB (well below the NIOSH 85 dB 8-hour continuous exposure limit) at approximately 10 meters (33 feet) from the source.
Does humidity and temperature affect sound dropoff over long distances?
Yes. While geometric dispersion accounts for most sound dropoff, atmospheric air absorption causes additional high-frequency attenuation, typically between 3 dB and 10 dB per kilometer depending on humidity, temperature, and audio frequency.