By Zencalcy Editorial TeamLast reviewed About us
Decibels cannot be added directly because they are logarithms. Two uncorrelated 80 dB sources produce 83 dB, not 160 dB, because their intensities add. This page combines two arbitrary levels or a number of equal sources and reports the result to one decimal place.
Combine uncorrelated sound levels and identical sources.
L = 10 log₁₀(10^(L₁/10) + 10^(L₂/10)) Equal sources: L = L₁ + 10 log₁₀(n)
This is an intensity sum. Correlated sources, such as two loudspeakers fed the same signal at a symmetrical point, can add with pressure instead and produce larger peaks.
| Symbol | Meaning |
|---|---|
| L | Combined level in dB. |
| L₁ | First source level. |
| L₂ | Second source level. |
| n | Number of identical sources. |
10 log₁₀(10⁸ + 10⁸) = 10 log₁₀(2 × 10⁸) = 83.0 dB. Four equal sources would give 86.0 dB, and ten would give 90.0 dB.
Continue with the Doppler Effect Calculator, Sound Distance Attenuation Calculator, or the Mach Number Calculator — or browse more acoustics and sound tools and all physics calculators.
Decibels are logarithmic. Adding two equal levels doubles the intensity, which is a 3 dB increase, not a doubling of the dB number.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026