Calculator Inputs
Example Data Table
| Scenario | Reference Level | Reference Distance | Target Distance | Source Model | Air Absorption | Predicted Level |
|---|---|---|---|---|---|---|
| Portable generator | 88 dB | 10 m | 40 m | Point source | 0.20 dB / 100 m | 75.94 dB |
| Roadway edge | 82 dB | 15 m | 60 m | Line source | 0.10 dB / 100 m | 75.96 dB |
| Outdoor fan bank | 95 dB | 5 m | 30 m | Point source | 0.35 dB / 100 m | 79.36 dB |
Formula Used
Here, L1 is the known sound level at the reference distance r1, and L2 is the predicted sound level at target distance r2. The symbol α represents atmospheric absorption loss per unit distance, while Ladd represents any extra fixed loss such as shielding, foliage loss, or conservative design margin.
Point sources spread spherically and typically drop about 6 dB for each doubling of distance. Line sources spread cylindrically and typically drop about 3 dB for each doubling of distance.
How to Use This Calculator
- Select the calculation mode that matches your task.
- Choose point source for isolated equipment or line source for extended sources.
- Enter the known reference sound level and its measurement distance.
- Enter a target distance or a desired target level, depending on mode.
- Add air absorption and extra loss if your scenario needs them.
- Set graph limits to visualize how sound changes across distance.
- Press Calculate to show the result above the form.
- Use the CSV or PDF buttons to save the summary.
FAQs
1. What does outdoor sound attenuation mean?
Outdoor sound attenuation is the reduction in sound level as noise travels away from its source. Distance spreading causes the main drop, while air absorption and local shielding can add further loss.
2. When should I use the point source option?
Use the point source option for equipment that behaves like one localized emitter, such as a generator, a fan, or a loudspeaker cluster viewed from far enough away.
3. When should I use the line source option?
Use the line source option for long, extended sources such as highways, conveyor runs, or lengthy process lines where cylindrical spreading is a better practical approximation.
4. Why does sound not always drop exactly 6 dB per doubling?
Real outdoor conditions include reflections, terrain, wind, humidity, absorption, and source directivity. These factors can make the observed drop differ from the ideal inverse square expectation.
5. What should I enter for air absorption?
Enter a practical attenuation estimate in dB per 100 meters or feet. Higher frequencies usually absorb more strongly than lower frequencies, especially over long outdoor paths.
6. What is additional fixed loss used for?
Additional fixed loss lets you include barriers, vegetation, façade shielding, or a conservative design margin without changing the geometric spreading calculation itself.
7. Can this calculator find the distance needed to meet a target level?
Yes. Choose the distance-finding mode, enter the desired sound level, and the calculator estimates the receiver distance required under your selected assumptions.
8. Is this calculator suitable for regulatory noise studies?
It works well for screening, early planning, and quick comparisons. Formal compliance studies may require octave-band data, meteorology, terrain modeling, and site-specific standards.