Calculator Inputs
Plotly Graph
The graph shows predicted sound level versus distance using your current settings.
Example Data Table
| Scenario | Reference Level (dB) | Reference Distance (m) | Target Distance (m) | Sources | Q | Barrier Loss (dB) | Air Absorption | Predicted Level (dB) |
|---|---|---|---|---|---|---|---|---|
| Generator Yard | 102.00 | 1.00 | 10.00 | 1 | 2 | 3.00 | 0.010 | 81.92 |
| HVAC Plant | 94.00 | 1.50 | 12.00 | 2 | 1 | 2.00 | 0.015 | 76.79 |
| Pump Room | 88.00 | 1.00 | 6.00 | 3 | 4 | 5.00 | 0.008 | 78.19 |
| Fan Discharge | 99.00 | 2.00 | 20.00 | 1 | 8 | 4.00 | 0.012 | 83.81 |
Formula Used
General prediction formula
L2 = L1 + 10 log10(N) + 10 log10(Q) - 20 log10(r2/r1) - B - α(r2 - r1)
- L1 = reference sound level in dB.
- L2 = predicted sound level in dB.
- N = number of identical sound sources.
- Q = directivity factor.
- r1 = reference distance.
- r2 = target distance.
- B = barrier or shielding loss in dB.
- α = air absorption loss per unit distance.
The calculator uses inverse distance spreading for pressure level change. It also applies optional source count gain, directional gain, barrier loss, and air absorption.
How to Use This Calculator
- Select the calculation mode.
- Choose meters or feet.
- Enter the known reference sound level.
- Enter the reference measurement distance.
- Add a target distance or target level.
- Set source count and directivity factor.
- Enter barrier loss and air absorption if needed.
- Press Calculate to view the result and graph.
- Use CSV or PDF buttons to export the output.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates how sound level changes with distance. It can predict level at a target point, solve for a required distance, or compare two distances under the same source conditions.
2. Why does sound level drop with distance?
In open space, sound energy spreads outward. That spreading lowers sound pressure level as distance increases. The calculator uses a free field inverse distance relationship for this effect.
3. What does the directivity factor mean?
Directivity factor describes how concentrated the sound radiation is. Higher values represent more directional emission, which increases level in the preferred direction compared with an omnidirectional source.
4. Why add source count gain?
Multiple similar sound sources raise the combined level. The increase is logarithmic, not linear. Doubling identical sources adds about 3 dB under ideal combining conditions.
5. When should I use barrier loss?
Use barrier loss when shielding, enclosures, walls, berms, or acoustic panels reduce sound before it reaches the receiver. Enter the estimated insertion loss in decibels.
6. What is air absorption?
Air absorption is extra attenuation caused by atmospheric propagation. It depends on humidity, temperature, and frequency. This calculator treats it as a simple user supplied loss per unit distance.
7. Can this replace a full acoustic study?
No. It is useful for screening and planning. Complex sites may need octave band analysis, ground effects, reflections, meteorology, and professional measurement methods.
8. Which unit should I choose?
Choose the same unit used for all distances and the air absorption rate. Keep the data consistent across reference distance, target distance, and any interpreted site measurements.