Is sound "additive"?

Actually this question is virtually impossible to answer with the information at hand. The sound coming out of your speakers can not be represented by a simple scalar value. It is not as simple as saying the output is 89db. The sound is however, a complex quantity where the sound possesses magnitude and phase. If the speakers, cables, electronics etc. were all exactly the same, it is theoretically possible they would all be in phase with each other and add perfectly. But because we live in an imperfect world where the signal paths would not be the same, some of the sound pressures could theoretically cancel each other out if they were 180 degrees out of phase which is exactly what noise cancellation scientists are working on right now.

As much as I enjoyed your posts, I am glad that I asked something that did not have a simple answer. I was not asking for a particular reason -- just because the quandry arose in my mind. I have no experiment planned.

liguy, there is no theoretical reason why a properly set-up 2-channel subwoofer system would not be in phase - unless one subs' speaker leads were hooked up backwards from the other - just like w/a pair of regular full-range speakers, being driven by a stereo amp. of course, you could also have your subs out-of-phase from your monitors, if the subs' leads were reversed relative to the monitors', but this mix-up is also possible w/a single sub. in fact, assuming proper connections, there's actually a chance of signal-cancellation when using only *one* sub, w/the two-channel signal summed to mono. in this set-up, there's the possibility of left/right-channel signal cancellation...

regards, doug s.

btw, the proper reason to use two subs in a system instead of one, is *not* to increase the spl of the bass - this wood only make the sound too bass-heavy in relation to your monitors. as said before, a second sub allows the *same* spl's w/reduced distortion, as well as improving imaging/soundstaging.

doug s.

Sedond, agreed! I was only pointing out that the answer to the question is not simple. In order for sound to be perfectly additive they must be exactlt in phase. If they are a degree or 2 different the sum will be different. I made no attempt to relate this to a subwoofer.