Doubling uncorrelated sound sources adds only 3 dB of loudness

Evidence

This equation will give the total SPL for N uncorrelated sources of equal level. For example, 10 sources will raise the SPL by 10 dB, since 10log(10) = 10. … So the summation of two uncorrelated sources increases the sound pressure level by 3 dB. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 295

Categorization

• CANDY: The fact that you need ten identical sound sources to double perceived pressure (+10dB) versus just two computer fans plus 3dB is a neat physical trivia about why more noise sources don’t feel proportionally louder.
• QUESTION: Worth chasing later: when do sound sources count as ‘uncorrelated’ versus correlated, and does that change how the 3 dB/doubling rule applies to things like chorus of crickets or a crowd?
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 295