Calculator
Plotly Graph
The chart shows predicted sound pressure level versus distance using the solved or entered sound power level.
Example Data Table
| Scenario | Model | Given | Distance | Q | Sources | Result |
|---|---|---|---|---|---|---|
| Ceiling speaker coverage | Free field | Lw = 96 dB | 2.00 m | 2.0 | 1 | Lp ≈ 82.00 dB |
| Small mechanical room | Room / mixed field | Lw = 92 dB each | 3.00 m | 2.0 | 2 | Lp ≈ 83.32 dB |
| Measured receiver estimate | Free field | Lp = 78 dB | 4.00 m | 1.0 | 1 | Lw ≈ 101.03 dB |
Formula Used
Lw = 10 log10(W / W0)where
W0 = 1 × 10^-12 W.
Lp = 20 log10(p / p0)where
p0 = 20 µPa.
Lp = Lw(total) + 10 log10(Q / (4πr²)) - αr
Lp = Lw(total) + 10 log10(Q / (4πr²) + 4 / R) - αr
L(total) = L(single) + 10 log10(N)
Variable meanings:
- Lw = sound power level of the source.
- Lp = sound pressure level at the receiver.
- Q = directivity factor.
- r = source-to-receiver distance in meters.
- R = room constant in square meters.
- α = atmospheric attenuation coefficient in dB per meter.
- N = number of identical independent sources.
How to Use This Calculator
- Choose whether you want to calculate sound pressure level or estimate sound power level.
- Select free-field mode for open spaces, or room mode when reflections matter.
- Enter the source level you know, either Lw or Lp.
- Add distance, directivity factor, and the number of identical sources.
- Enter room constant only when you use room mode.
- Use atmospheric attenuation when long paths or higher frequencies matter.
- Press the button to see results above the form.
- Use the CSV or PDF buttons to save a report.
Frequently Asked Questions
1. What is the difference between sound power level and sound pressure level?
Sound power level describes the source output. Sound pressure level describes what a receiver experiences at a location. Power belongs to the source. Pressure depends on distance, directivity, reflections, and losses.
2. Why does distance reduce sound pressure level?
In open space, sound energy spreads over a larger area as distance increases. That geometric spreading lowers pressure at the receiver. The calculator models this with the inverse-square distance term.
3. What does the directivity factor Q represent?
Q shows how strongly a source concentrates sound in one direction. Higher Q means more focused radiation and a higher pressure level in that direction compared with an omnidirectional source.
4. When should I use room mode?
Use room mode when reflections, reverberation, and enclosure effects are important. It adds the room term through the room constant, which can raise pressure levels compared with pure free-field conditions.
5. Why are multiple sources added with 10 log10(N)?
Independent sources add by energy, not by simple arithmetic level addition. The logarithmic term 10 log10(N) converts the increase in combined acoustic energy into decibels.
6. Can this calculator replace field measurements?
No. It is an engineering estimate tool. Real environments include barriers, frequency effects, reflections, background noise, and source spectra that may require detailed measurement or simulation.
7. What is the room constant R?
The room constant summarizes how much sound the room absorbs. Larger values indicate more effective absorption or a less reverberant response. Smaller values increase the reflected contribution.
8. Why does pressure use 20 log10 while power uses 10 log10?
Power is directly proportional to energy, so it uses 10 log10. Pressure is an amplitude quantity, and acoustic power is proportional to pressure squared, so pressure uses 20 log10.