Formula used
Ltotal = 10 log10(Σ 10Lᵢ/10)
Ltotal = Lsingle + 10 log10(N)
Lremaining = 10 log10(10Ltotal/10 − 10Lknown/10)
L₂ = L₁ − 20 log10(r₂/r₁)
How to use
- Select the calculation mode matching your measurement task.
- Choose a compatible decibel weighting label.
- Enter source levels and optional correction values.
- Apply distance models only when geometry supports them.
- Disable sources that should not affect results.
- Select precision and automatic download preferences.
- Calculate, review contributions, then export your findings.
Example data
| Example | Inputs | Expected result | Purpose |
|---|---|---|---|
| Equal sources | 80, 80 dB | About 83.01 dB | Shows the three-decibel increase |
| Different machines | 85, 82, 78 dB | About 87.35 dB | Combines unequal sources |
| Ten sources | Ten sources at 70 dB | 80 dB | Uses identical-source mode |
| Background removal | 84 total, 78 background | About 82.74 dB | Estimates source-only noise |
| Distance change | 90 dB at 1 m, then 2 m | About 83.98 dB | Applies point-source spreading |
Difference-based quick reference
| Source difference | Add to louder source |
|---|---|
| 0 dB | 3.0 dB |
| 1 dB | 2.5 dB |
| 2 dB | 2.1 dB |
| 3 dB | 1.8 dB |
| 5 dB | 1.2 dB |
| 10 dB | 0.4 dB |
| 15 dB | 0.1 dB |
| 20 dB | Nearly zero |
Important interpretation guidance
- Decibel values represent logarithmic energy relationships.
- Direct arithmetic addition produces incorrect combined levels.
- Two equal independent sources add approximately three decibels.
- Ten equal independent sources add exactly ten decibels.
- Distance formulas assume unobstructed idealised sound propagation.
- Reflections, barriers, absorption, and coherence change real measurements.
- Different weighting networks should not be combined directly.
- Background correction becomes unreliable when differences remain small.
Frequently asked questions
How are two decibel levels added?
Convert both levels into linear energy values. Add those energies before applying the logarithm. This method preserves the physical meaning of measured sound.
Why cannot decibels be added directly?
Decibels use a logarithmic scale rather than linear units. Arithmetic addition exaggerates combined sound energy. Logarithmic addition produces physically meaningful combined sound level results.
What happens with two equal sources?
Two equal independent sources double the total energy. Doubled energy adds about three decibels. The combined result becomes roughly three decibels higher overall.
How much louder are ten identical sources?
Ten equal sources multiply sound energy by ten. This creates a ten-decibel level increase. Perceived loudness changes depend on frequency and listener conditions.
Does a source ten decibels lower matter?
Its energy equals one tenth of the louder source. The total usually rises about four tenths. Therefore, quieter sources may contribute little to final levels.
Can dBA and dBC values be combined?
They use different frequency weighting networks. Direct combination can misrepresent actual sound energy. Convert measurements consistently before performing combined noise calculations safely.
How is background noise removed?
Convert measured and background levels into energy. Subtract background energy from measured energy. Then convert the remaining energy back into decibels carefully.
Can this calculator subtract noise levels?
Yes, it subtracts energy rather than decibel numbers. The total must exceed the known source. Invalid relationships cannot produce a physical remaining sound level.
How does distance affect sound level?
Free-field point sources decrease with distance squared. Doubling distance reduces level about six decibels. Real environments may change this ideal spreading behaviour significantly.
What assumptions does the formula use?
Sources should remain independent and effectively incoherent. Measurements should share compatible weighting and reference conditions. Reflections and barriers may require professional acoustic modelling instead.
Is a three-decibel increase twice as loud?
Three decibels represents approximately doubled sound energy. Perceived loudness does not double identically. Human hearing responses vary across frequency, duration, and context.