Positive summation always for dual subs

[nwickliff@gmail.com]

Do you always want positive summation with dual subs and then EQ afterward or do you sometimes use the second sub to even out the response at the cost of SPL?  

[SME]

With just two subs, you almost always want positive summation in the listening area.  With 3 or more subs, assuming you have enough headroom to spare, it may or may not be useful to run some of the subs out of phase from the others, at least for some frequencies.  For example, the double-bass array involves configuring the rear subs using delay and phase inversion to cancel out what would be the rear-wall reflection.  That is definitely not positive summation---by design!

My own system is configured so that the mid-bass modules behind my sofa interfere somewhat with the sound from the (main) front subs in order to diminish the "power alley" effect which causes hotter bass in the middle seat than the outer seats.  I'm not really sure if it was worth it.  The result may be rather hypersensitive to small changes in level, placement, and the surrounding room environment.  There's also a larger question of whether pressure response is solely responsible for bass perception and if flat and/or smooth pressure response at a particular seat is the best indicator of how good the bass will sound at that seat.