Yes yay for logs! But again I have to disagree.
To address your first comment, I was simply correcting where you state that power and volume are interchangeable which thy are not ie below:
Originally Posted by sc00by4life
10 * log10 (2) = 3.01 dB, where 2 is the double in power (volume).
I found a good reference talking about the interference of two wave sources which is exactly what we are dealing with (constructive interference of two acoustic wave sources to produce a louder sound.
Equations 4 and 5 are important, and assuming the waveform produced by both pairs of tones are the same (same amplitude and phase) you can see all delta phi's are zero and for the perfect exactly constuctive interference you get double the amplitude (related directly to spl) and quadruple
the power equaling a dB increase of 6dB.
Can't we just be friends??
Edit: and doubling the sources in this case is equal to two sources emitting the same amplitude/phase/power acoustic waves and how they constructively interfere to create a louder sound is what we are interested in