Originally Posted by Jan3
I agree on what you wrote here. I have the disadvantage of having an L shaped room with one corner being actually a large cirkel, and different ceiling height, which makes it unpredictable.
After reading the Harman paper on multiple subs I think not to go beyond 4. Spending extra time playing around with different locations, time delay in minidsp might give the best outcome I think.
IMO the best bang for the buck happens with 2 subs, which are already no walk in the park when it comes to timing them. My mains, for instance, each employ a pair of 8's in the bass bins (which yes, are already timed to each other), so with 2 subs I'm already trying to get 6 cones to move in unison around the crossover point.
4 subs, as long as they are equidistant from the MLP CAN be an advantage, but it all depends on your room. If they're all at different distances, good luck with that...you'll be neck deep in test tones for a while, with no real guaranty it will sound better than just a well placed pair of subs. It really all depends on your room and positioning within it, but each sub you add makes the timing complexity go through the roof, and you'll STILL have room modes to deal with, regardless of how much smoother it may present at first blush.
I really wish these AVR/pre pro manufacturers would include timing for 4 subs in their correction software. The best one I've used for dual subs is Pioneer's MCACC, with Audyssey XT32 a little less accurate. I currently use Anthem's ARC which does not include sub timing at all...it must be done manually before sweeps are run. In Anthem's defense, their EQ corrections are very good, and the timing omission is due to their unique approach of having a PC do the calculations, thereby making the wireless latency unknown and not practical for phasing.
Nowadays, the hot ticket with these processors is how many more holes you can put in your ceiling, with almost complete disregard of the bottom end of your system (where the most correction is needed) potentially sounding like an elephant fart. Sure, they EQ a summed sub channel, but timing is where the real magic happens. Let's hope they get with it soon.