Model sound levels outdoors across open space. Switch point or line source spreading instantly here. Add air absorption, then export results for reports easily.
For outdoor propagation in an ideal free field, sound pressure level decreases with distance mainly due to geometric spreading. The calculator uses:
Predicted level is: L2 = L1 − ΔL − ΔLair − ΔLextra. The distance solver finds r2 that matches a target L2.
Practical note: Real outdoor sound is affected by wind, temperature gradients, terrain, reflections, and directivity. Use extra attenuation to approximate these site-specific factors.
Example assumes point-source spreading, no atmospheric absorption, and no extra loss. Reference level is 90 dB at 1 m.
| Reference Level (dB) | Reference Distance | Target Distance | Predicted Level (dB) | Total Attenuation (dB) |
|---|---|---|---|---|
| 90 | 1 m | 10 m | 70.00 | 20.00 |
| 90 | 1 m | 50 m | 56.02 | 33.98 |
| 90 | 1 m | 100 m | 50.00 | 40.00 |
| 90 | 1 m | 250 m | 42.04 | 47.96 |
This calculator estimates outdoor sound level change caused by distance in an ideal free-field path. It assumes energy spreads geometrically from the source and converts that spreading into decibels. Use it for first-pass planning, comparisons, and sensitivity checks before detailed site modeling.
In open space, doubling distance typically reduces level by about 6 dB for a point source. For example, 90 dB at 1 m becomes about 84 dB at 2 m, 78 dB at 4 m, and 72 dB at 8 m. These steps come directly from the logarithmic relationship between distance ratios and decibels.
A compact source such as a loudspeaker is often approximated as a point source, using 20·log10(r2/r1). Long sources like a busy roadway can behave closer to a line source over some ranges, using 10·log10(r2/r1). The line model predicts slower drop with distance, which can matter for community-noise studies.
Air absorbs sound energy, especially at higher frequencies and over long paths. When enabled, the calculator adds an absorption term α·(r2−r1). A small value such as 0.0005 dB/m produces 0.5 dB loss per kilometer, while 0.005 dB/m produces 5 dB per kilometer.
Real outdoor propagation is influenced by barriers, ground effects, vegetation, and shielding. Rather than forcing complex inputs, the “extra attenuation” field lets you add a lumped loss. Examples include 3–10 dB for partial shielding or modest barriers, and larger values for strong line-of-sight blockage.
Typical use cases include siting generators, HVAC equipment, outdoor events, and construction activity. You can estimate whether a 55 dB guideline is met at a property line, compare two receiver distances, or determine a setback distance. Exporting CSV or PDF supports documentation in reports and compliance notes.
Suppose a source measures 88 dB at 5 m and you want the level at 80 m. With point-source spreading, the geometric loss is 20·log10(80/5)=24.08 dB, giving 63.92 dB before other losses. If you add 4 dB extra attenuation and α=0.001 dB/m over 75 m, total added loss is 4.08 dB, yielding about 59.84 dB.
Treat results as an engineering estimate, not a guaranteed field measurement. Source directivity, reflections, wind, temperature gradients, and terrain can shift levels by several decibels. When decisions are sensitive, validate with on-site measurements or a full propagation model, then use this tool for quick scenario testing.
It is a good rule for point-source spreading in a free field. Real sites can differ due to reflections, shielding, wind, and terrain, so the drop may be smaller or larger.
Use it when the source is long compared with your distances, such as traffic on a roadway segment. Over short ranges a line source may fit, but at larger distances it can transition toward point-like behavior.
α depends strongly on frequency, temperature, and humidity. For broad estimates, values around 0.0001 to 0.005 dB/m are common. Use smaller values for low-frequency noise and shorter paths.
Not explicitly. Use the extra attenuation field to approximate ground effects, foliage, or shielding. If you need octave-band ground interaction, use specialized outdoor propagation standards or software.
Yes. Choose “Find distance for a target level,” enter the reference level and distance, then the target level. The solver returns the distance that meets the target, including optional absorption and extra losses.
Field levels can be lower due to shielding, ground interference, or atmospheric conditions. Add extra attenuation to represent these effects, and ensure the spreading model matches the source geometry.
Enter the same weighting for all inputs and comparisons. If your reference measurement is dBA, keep targets and limits in dBA. The distance math works the same; only the spectral weighting differs.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.