Decibel sound levels cannot be added directly because they are logarithmic

Evidence

Note that the combined sound level is only about 2 dB more than the louder of the two sounds and not 69 dB greater, which is the result that would be obtained if the SPLs were added directly in decibels. — David Howard, Jamie Angus, coustics and Psychoacoustics, 278

Categorization

Category: Definitional Content

• DEFINE: Clarifies the critical rule that decibel SPL values sum in the pressure domain, not the decibel domain themselves — a foundational misstep for anyone new to acoustics.

Related

• Decibel sound levels cannot be added directly because sound powers combine, not levels (similarity 0.90)
• Decibels cannot be summed directly because they are logarithmic power ratios (similarity 0.89)
• Decibel values must be converted to ratios before they can be added (similarity 0.87)
• Decibel increases map powers of ten to logarithms (similarity 0.84)
• Adding equal sound intensities yields a 3 dB total increment (similarity 0.83)
• Logarithmic hearing means equal decibel steps need larger absolute pressure differences (similarity 0.81)
• Adding sound levels differs depending on whether sources are correlated or not. (similarity 0.81)
• Adding sound intensities of equal level yields only a three-decibel increase (similarity 0.81)
• Sound level multiplications become decibel additions in reflections (similarity 0.80)
• Correlated sound sources combine by direct pressure addition (similarity 0.79)

Broader Connections

• Adding equal sound intensities yields a 3 dB total increment #exemplifies (0.92) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1329
• Combination tones become audible only above roughly 70 dB primary level #expands (0.72) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1542