Ro7939, I've changed my mind about the x-polarity configuration that I once embraced, and now only recommend it for certain situations.
At RMAF last year, I started out with left front and right rear subs in one polarity, and the other two in opposite polarity. Someone came into the room and wanted to hear a cut with some really deep bass. He was disappointed when it was missing in action, and so was I. First chance I got, tried a song I was familiar with that had some really deep synth bass. It should have made the room shudder, but that didn't happen. Hmmmm.
After thinking about it a bit, I realized that at low enough frequencies the farthest room boundaries will be less than half a wavelength apart, so that in effect the four subs (two sucking and two blowing, so to speak) would all be working on the same fraction of a wavelength, and would cancel one another out. After going back to normal polarity for all subs, the room would indeed shudder when called for, but I didn't figure that out until the last day of the show. Dangit.
So in a room that size my inclination now is to only put one of the subs in reverse polarity, or maybe none of them, depending on which sounds best.
Anyway, the optimum may be using two of those rackmount subwoofer amps, with the phase control on one of them rotated to put it 90 degrees (rather than 180 degrees) out-of-phase with the other. This way at those ultralow frequencies, their outputs would not sum perfectly in-phase nor out-of-phase, thus approximating the semi-random phase summing in the middle and upper bass region.
Now if your room is big enough relative to the wavelengths you're trying to reproduce, that x-bass setup still works quite well.
Poll
