Calculator Form
Formula Used
The calculator uses a spreading-loss model with optional atmospheric absorption:
L2 = L1 − k log10(r2 / r1) − α(r2 − r1)
For a point source, k = 20. For a line source, k = 10. L1 is the known level at the reference distance. L2 is the level at the target distance. α adds optional attenuation per distance unit.
When distance is the unknown and absorption is zero, the calculator uses a direct algebraic solution. When absorption is included, it uses a numerical bisection method because the distance term appears inside both a logarithm and a linear attenuation term.
How to Use This Calculator
- Select what you want to solve: target level, reference level, target distance, or reference distance.
- Choose the source model. Point sources decay faster than line sources.
- Enter the known sound pressure level values in decibels.
- Enter the known distances in one unit system only.
- Add atmospheric absorption if you want extra distance loss included.
- Set the decimal precision and click Calculate.
- Review the summary table, chart, and loss breakdown above the form.
- Export the calculation using CSV or PDF if needed.
Example Data Table
Sample values below assume a point source with 90 dB at 1 meter and zero absorption.
| Reference SPL (dB) | Reference Distance (m) | Target Distance (m) | Estimated SPL (dB) |
|---|---|---|---|
| 90.00 | 1.00 | 2.00 | 83.98 |
| 90.00 | 1.00 | 4.00 | 77.96 |
| 90.00 | 1.00 | 8.00 | 71.94 |
| 90.00 | 1.00 | 16.00 | 65.92 |
FAQs
1. What does this calculator measure?
It estimates how sound pressure level changes between two distances. It can also solve for an unknown level or distance using propagation loss equations.
2. When should I use the point source model?
Use the point source model for sources that radiate outward in three dimensions, such as speakers, machines, or outdoor equipment in open space.
3. When should I use the line source model?
Use the line source model for long sources where sound spreads more gradually, such as some traffic corridors or elongated industrial lines.
4. What is atmospheric absorption?
Atmospheric absorption adds extra loss per distance unit. It represents energy loss from air effects and can matter more over long paths.
5. Why does doubling distance reduce level?
In free-field point-source conditions, doubling distance spreads the same sound energy over a larger area. That causes a reduction of about 6 dB.
6. Can I use feet instead of meters?
Yes. Keep all distances in the same unit. If you enter absorption, it must also match the chosen distance unit.
7. Why does the calculator use a numerical method sometimes?
When absorption is included and distance is unknown, the variable appears in more than one term. A direct algebraic solution is no longer simple.
8. Are reflections and barriers included?
No. This calculator is for propagation loss estimation. Room reflections, ground effects, shielding, and complex environmental acoustics need separate models.