Experience with stacked subwoofers?

We have stacked pairs running in stereo of REL S812, Carbon Specials, and 212/SX.   In each instance space constraints caused us to stack.   When properly placed and dialed-in, stacked subs are terrific --  albeit I only have stacking experience with REL.   And with REL's direct-to-amp wiring, I won't be using any other manufacturer's subs any time soon.   Had other manufactures subs before REL, but there's no context.  For not huge $$, Carbon Special has to be one of the best sounding subs out there, at any price point.   (Note, I have not heard the Nos. 31 or 32).    

@emergingsoul    Sorry to pile on, but your take on subs is 15 years behind the times.   Speakers in our main system are Tannoy Kingdom Royal, which include a 15-inch sub driver.   Addition of a pair of Carbon Specials brought new dimension to the entire music spectrum.   IMHO, no system, none, is complete without a pair of top quality subs.  It's not just about the bass.  Its about the entire presentation, from top to bottom.  

Given the new S series I am keenly watching the second hand prices of the S/510s to maybe build up a 6 pack of my own.

@dwette - do you have the full setup in place yet? Whats the verdict?

@guysellingstuff Sadly, not yet. I'm still waiting on my third pair the dealer has out for repair. It turns out the company that makes the amp packs for the S/510 went out of business and/or stopped making them. REL has to do component level repairs now and have been backordered on parts. I keep hearing "any time now," but REL hasn't delivered yet. My wife and I are frustrated with it. We are anxious to get it all completed and dialed in.

The only other thing that remains for now is delivery of my 2nd HRS EXR rack. I don't expect that to be delivered before later this month.

@guysellingstuff I finally got my third pair of REL S/510. I installed them this afternoon, and started with some setting guidance recommended by my dealer's installer. I have a new HRS equipment rack coming within a couple weeks, so they will tune the six-pack when they deliver the rack. In the meantime I'm enjoying it so far.

It's interesting to see this, as it uses old "column speaker" tech to reduce vertical dispersion and increase horizontal dispersion.   You can see old Grateful Dead shows where they were using this technique to shorten throw and increase horizontal dispersion.  

The other technique is to line them up on the floor horizontally, an array, as this will reduce horizontal dispersion and focus bass more in the central area of the room.  Try it.