Two equal uncorrelated sound sources add only 3 decibels.

Evidence

On the other hand, if the sound waves are uncorrelated, then they do not add algebraically, like correlated waves; instead, we must add the powers of the individual waves together. As stated earlier, the power in a waveform is proportional to the square of the pressure levels, so in order to sum the powers of the waves, we must square the pressure amplitudes before adding them together. If we want the result as a pressure, then we must take the square root of the result. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 244 (#qualifies, via linked claim)

Categorization

• XREF: connects to: Adding equal sound intensities yields a 3 dB total increment; Decibel values must be converted to ratios before they can be added; Correlated sound sources sum to between zero and twice their individual amplitudes (+5 more)

Related

• Adding uncorrelated sound sources raises level as the square root of their number (similarity 0.95)
• Correlated sound sources add pressures while uncorrelated ones add energy (similarity 0.93)
• Correlated sound sources sum to between zero and twice their individual amplitudes (similarity 0.91)
• Uncorrelated sound waves sum by power, not by amplitude. (similarity 0.91)
• Correlated source summation swings from zero to twice amplitude by frequency (similarity 0.89)
• Correlated sound sources create spatial interference patterns that uncorrelated sources do not. (similarity 0.88)
• Correlated sound sources combine by direct pressure addition (similarity 0.87)
• Even identical instruments playing in unison produce uncorrelated waveforms. (similarity 0.87)
• Adding equal sound intensities yields a 3 dB total increment (similarity 0.86)
• Adding sound levels differs depending on whether sources are correlated or not. (similarity 0.86)
• Uncorrelated source totals ignore the relative phases of signals. (similarity 0.85)
• Two equal uncorrelated sources raise level less than two correlated ones. (similarity 0.84)
• Independent partitions sum their attenuation in decibels (similarity 0.84)
• Mutual resonance between sources boosts combined power beyond their sum (similarity 0.84)
• Interfering sound waves pass through each other because their energy flow is preserved (similarity 0.82)

Broader Connections

• Adding uncorrelated sound sources raises level as the square root of their number #expands (0.88)
• Correlated sound sources sum to between zero and twice their individual amplitudes #expands (0.85)
• Uncorrelated sound waves sum by power, not by amplitude. #qualifies (0.85) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 244
• Correlated sound sources add pressures while uncorrelated ones add energy #expands (0.82)
• Even identical instruments playing in unison produce uncorrelated waveforms. #exemplifies (0.78)
• Correlated sound sources create spatial interference patterns that uncorrelated sources do not. #expands (0.75)