Independent partitions sum their attenuation in decibels

Evidence

The solution is to have two or more partitions that are independent of each other. If the two partitions are truly independent, the total attenuation, or effective sound isolation, is the product of the attenuations of individual partitions, that is, the dB attenuation is the sum of the dB attenuations of the individual partitions. In practice, the partitions are not independent, although the isolation is improved dramatically, but not as much as would be predicted by simply summing the dB attenuations. Coincidence resonances also reduce the effectiveness of a partition, and it is important to ensure that the two partitions have different resonances. This is most easily assured by having them made with either a different thickness or a different material. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2119

Categorization

• DEFINE: Defines effective sound isolation operationally as the sum of individual dB attenuations, and explains why real-world coupling breaks the ideal.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2119
• XREF: connects to: Decibel increases map powers of ten to logarithms; Independent partitions sum dB attenuations but real ones underperform this; Sound level multiplications become decibel additions in reflections (+2 more)

Broader Connections

• Uncorrelated sound waves sum by power, not by amplitude. #expands (0.95) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 244
• Sound level multiplications become decibel additions in reflections #expands (0.90)