Calculator
Example data table
This example assumes 90 dB at 1 meter and no air absorption.
| Distance (m) | Estimated level (dB) | Drop from 1 meter (dB) |
|---|---|---|
| 1 | 90.00 | 0.00 |
| 2 | 83.98 | -6.02 |
| 4 | 77.96 | -12.04 |
| 8 | 71.94 | -18.06 |
| 16 | 65.92 | -24.08 |
About sound level and distance
Why this calculator matters
Sound level changes fast when distance changes. A short move away from a source can lower the measured level by several decibels. This calculator helps you estimate that change from a known reference point. It also works the other way around. You can enter a target level and solve for the distance that produces it. That makes the tool useful for physics study, speaker placement, lab planning, room checks, and basic exposure reviews.
What the calculator measures
The core model uses sound level in decibels and distance in meters. It applies inverse square spreading for a point-like source in free space. That is the standard first estimate in introductory acoustics. An optional air absorption term adds extra loss over longer paths. The results include target level, solved distance, geometric spreading loss, absorption loss, intensity ratio, and pressure ratio. A modeled distance table and graph turn one reference reading into a wider acoustic picture.
Where this helps in practice
Use this page when checking how far a listener should stand from a source, when comparing two listening points, or when building clean worked examples for classes and reports. It is also useful for stage planning, public address layouts, loudspeaker demonstrations, microphone discussions, and simple environmental noise screening. Export tools help you save the summary and the modeled table. That keeps the workflow practical for homework, internal notes, and repeat calculations.
Limits of the model
This calculator gives a clear first estimate, not a full room simulation. Real sound fields include reflections, barriers, source directivity, ground effects, humidity, and weather. Indoor spaces can raise or lower the true value compared with a free-field estimate. Near-field behavior can also differ from the ideal point-source assumption. Even so, the model is transparent, fast, and easy to audit. That is why it remains a strong starting point for many physics and acoustics tasks.
Formula used
Point source spreading: L2 = L1 − 20 log10(r2 / r1)
With optional air absorption: L2 = L1 − 20 log10(r2 / r1) − α(r2 − r1)
Intensity ratio: I2 / I1 = 10(L2 − L1) / 10
Pressure ratio: p2 / p1 = 10(L2 − L1) / 20
Distance from target level: the page solves the absorption form numerically with bisection, because the distance appears in both a logarithmic term and a linear term.
How to use this calculator
- Choose a calculation mode.
- Enter the known reference sound level.
- Enter the reference distance in meters.
- Enter a target distance or a target sound level.
- Add an air absorption value if you need it.
- Set the graph range and point count.
- Optionally enter a comma-separated list of modeled distances.
- Press Calculate to show the result above the form.
- Review the graph, modeled table, and summary metrics.
- Use the CSV or PDF buttons to export the result.
FAQs
1. What does this calculator estimate?
It estimates how sound level changes with distance from a known reference point. It can also solve the required distance for a chosen target level and compare two listening positions.
2. Why does sound level usually fall with distance?
As sound spreads outward, the same acoustic energy covers a larger area. For a point source in free space, that spreading creates the familiar inverse square relationship.
3. Does doubling distance always reduce level by 6 dB?
It is close to 6.02 dB for an ideal point source in free-field conditions. Real rooms, reflections, and source direction can change the actual drop.
4. What is the air absorption field for?
It adds extra loss per meter. This is a simple way to represent energy reduction from propagation through air, especially over longer paths.
5. Can I use this for indoor rooms?
You can use it as a first estimate. Indoor reflections and room modes can shift the real measured value, so results should be checked with measurements when accuracy matters.
6. Why does the tool show intensity and pressure ratios?
Those ratios connect decibel change to physical scale factors. They help explain whether a level drop came from a small or very large change in acoustic intensity or pressure amplitude.
7. What units should I enter?
Enter sound level in decibels and distance in meters. The optional absorption value is in decibels per meter, so keep those units consistent.
8. When should I trust measured data more than this model?
Use measured data when the source is directional, the room is reflective, barriers exist, weather matters, or safety decisions depend on high confidence.