Combine many decibel sources into one total value. See stepwise sums and dominant contributor instantly. Designed for labs, rooms, traffic, and machinery surveys safely.
Decibels are logarithmic. To add sound levels, convert each level to a linear power ratio, add those powers, then convert back to decibels.
The result assumes independent, uncorrelated sources measured in the same reference conditions. For coherent signals, phase relationships can change the combined level.
These examples show why decibel addition is not simple arithmetic.
| Case | Input Levels (dB) | Combined Level (dB) | Practical note |
|---|---|---|---|
| 1 | 60, 60 | 63.01 | Doubling equal sources adds about 3 dB. |
| 2 | 70, 60 | 70.41 | A 10 dB gap makes the louder source dominate. |
| 3 | 72, 68, 65 | 74.35 | Several smaller sources still raise the total. |
| 4 | 85, 85, 85, 85 | 91.02 | Four equal sources add about 6 dB. |
A decibel value is a logarithm of acoustic power or intensity. Adding 70 dB and 70 dB as numbers would ignore the underlying energy. In practice, two equal, independent sources raise the combined level by about 3 dB, not 70 dB.
Each entered level L is converted to a linear power ratio using 10^(L/10), summed across sources, and then converted back with 10·log10(Σ10^(L/10)). This matches how sound energies combine for uncorrelated sources.
Doubling acoustic power is +3 dB. Increasing power by a factor of ten is +10 dB. For N equal sources, the increase over one source is 10·log10(N) dB (for example, four equal sources add about 6 dB).
Ensure all inputs represent the same weighting and time response (such as dB(A) fast, or Leq over the same duration). Mixing different settings can make the combined result misleading even if the math is correct.
If you measured a source on top of background, you should remove background before adding multiple sources. Subtraction is not linear either: convert levels to power, subtract the background power, then convert back, ensuring the result stays positive.
When readings are taken at different distances from sources, normalize them first. In free‑field conditions, doubling distance reduces level by roughly 6 dB (inverse‑square behavior), while reflections can reduce this drop indoors.
Energy addition is appropriate for multiple independent noise sources (fans, traffic lanes, machines) where phases are uncorrelated. It is not intended for coherent tones with fixed phase relationships, where interference can cause larger peaks or cancellations.
Used carefully, decibel addition supports engineering estimates, compliance checks, and noise control planning. It also helps explain why small sources can still raise a total.
As context, typical outdoor ambient levels can range from about 35–50 dB in quiet residential areas, 60–70 dB near busy streets, and 80–90 dB near heavy traffic or industrial equipment. If you combine multiple similar contributors, the total increases slowly because the scale is logarithmic. Many workplace programs treat sustained exposure near 85 dB as a trigger level, and each +3 dB roughly doubles acoustic power. This calculator lets you test “what‑if” scenarios quickly and document the combined level for reports.
The calculator returns that same level, because there is nothing to combine. Decibel addition is only meaningful when at least two independent sources contribute.
Two equal, uncorrelated sources double the acoustic power. A power doubling corresponds to 10·log10(2) ≈ 3.01 dB, which is why the increase is modest.
Avoid mixing them. dB(A) includes frequency weighting, while unweighted dB does not. Combine only levels that share the same weighting and measurement settings.
Not reliably. Coherent signals can interfere constructively or destructively, changing results beyond energy addition. The tool is best for typical environmental or machine noise sources.
Use as many rows as needed. The math scales well because it sums linear power terms. Very large lists are still fine, but keep inputs consistent and realistic.
Measure background separately, convert both levels to power, subtract background power from the combined measurement, then convert back to dB. If the source is near background, uncertainty increases.
A 10 dB rise is a tenfold increase in acoustic power. Human perception is nonlinear, but many listeners experience about a “doubling” of loudness for roughly a 10 dB increase.