Last updated October 5, 2026 · Report an error
Combines multiple independent decibel (dB SPL) sound-level readings using the standard logarithmic sound-level addition formula from acoustics: L_total = 10 x log10(sum of 10^(Li/10) for each source), since decibels are a logarithmic unit and do not add linearly. Pure acoustics/physics arithmetic. Standard permissible-exposure reference levels (e.g. OSHA's 90 dBA 8-hour time-weighted average, WHO's general environmental-noise guideline) are cited for context only — this tool does not perform an individual health-risk assessment. For general reference and educational purposes only.
How it works
Enter two to four sound-level readings in dB. The tool converts each to linear sound intensity, sums them, and converts back to a combined decibel level.
- Enter sound level 1 (dB).
- Enter sound level 2 (dB).
- Enter sound level 3 (dB) — optional.
- Enter sound level 4 (dB) — optional.
- Click Calculate to see your results.
Examples
Two sources at 70 dB each
Combined level = 10 x log10(10^7 + 10^7) = 10 x log10(2x10^7) ≈ 73 dB — not 140 dB, since decibels are logarithmic (doubling sound energy adds about 3 dB).
Who should use it
- Combining ambient noise readings.
- Acoustics/physics education.
Industry applications
- Occupational safety reference
- Acoustics/environmental noise education
Advantages
- Uses the correct standard acoustics formula.
- Includes permissible-exposure reference context.
Limitations
- Assumes sound sources are uncorrelated/independent.
- Not an individual hearing-risk assessment.
Common mistakes to avoid
- Adding decibel values arithmetically (e.g. assuming 70 dB + 70 dB = 140 dB) instead of using the logarithmic addition formula.
Best practices
- Use this to estimate combined ambient noise from multiple simultaneous sources (e.g. traffic plus construction) rather than summing dB readings directly.
Tips
- Because dB is logarithmic, halving the number of equally-loud noise sources reduces the combined level by only about 3 dB, not by half.