Subwoofer Question

I have 5 subs actually - two Rythmik F25s, two SVS SB 13 Ultras, and one HSU Mid Bass Module (MBM-12).  The MBM-12 is only engaged for home theater.  I use the subs for both 2 channel and home theater, but primarily for two channel listening.  The Rythmiks can play low and also play higher into the bass region so they are good for both.  I originally bought them primarily for home theater, but as I started learning more about the distributed bass / swarm systems, I thought why not try them?  It made a huge difference in my two channel listening experience.  Enrico and Brian at Rythmik are pretty easy to reach and very helpful.  Give them a shout.  My personal belief is that you're going to get more bang for your buck buying internet direct.  There's a lot of dealer mark up on those Rel subs.

puppyt, don't make life more complicated than it has to be. Just buy another 210 and a good crossover like the JL Audio Or dbx Drive Rack units. Put the subs in the corners like you planned and I think once you get things set up you will be very happy with the results. You can always add more subs in the future but would wager that you will not feel the need. 
I personally use 4 subwoofers but I'm forced to to get an equivalent radiation pattern to my satellites which are 8 foot tall ESLs (line source).
People with point source speakers which is the vast majority, can do just fine with two subwoofers in the typical residential setting. One subwoofer is never satisfactory. Those who think it is will change their mind when they hear and feel what two does. 

     Virtually anyone with fairly extensive experience utilizing more than 1 sub in their room and system, will agree that 2 subs perform twice as well as a single sub and 4 subs perform about twice as well as a pair of subs.       Yes, this is my opinion based on my experience of using initially a single sub, then a pair and currently 4 subs in my system and room.  But the theory that in-room bass performance improves as more subs are added to the room has been scientifically and independently proven, and with results documented and summarized in White Papers that are accessible online, by several acoustic experts including Dr. Earl Geddes, Dr. Floyd Toole and Todd Welti of Harman International.  You can google these names, read all about their findings and decide for yourself if you'd like.
     Of course, none of this negates the fact that the benefits of multiple subs begins to be clearly perceived with the utilization of 2 subs in any given room, especially if very good bass performance is only required at a single designated listening position in the room.  A minimum of 3 subs are required for very good bass performance to be perceived throughout an entire room.
     It's technically possible to attain somewhat decent bass at a single designated listening position with one sub. But this designated seated position needs to avoid being placed in a specific room position that avoids all bass modes in the room, which cause bass peaks, dips and even nulls. 
     Utilizing the 'sub crawl method' (google it) is a very useful tool to avoid this for both single and dual sub systems but, since it's fairly well known that dual subs in a room sounds so obviously and vastly superior to a single sub, very few individuals still use only a single sub in their systems anymore.  I believe 4425 just may be the very last human on earth with 1 sub.  Where's he been for the last 25 years? 

Tim

Virtually anyone with fairly extensive experience utilizing more than 1 sub in their room and system, will agree that 2 subs perform twice as well as a single sub and 4 subs perform about twice as well as a pair of subs.  

LOL. This one's a classic. Most of the time I avoid your drivel so you probably said this before multiple times and I missed it. Just had to call you out on it this time. LOL.

What drivel? He’s right. Call him out on what? You haven’t said anything! Talk about drivel!

Everyone here should be praising Tim. The DBA concept he’s explaining is not an easy one to understand. It flies in the face of all our accepted wisdom about timing and matching and symmetry. There’s no marketing angle because the advantages of using lots of subs overwhelms any one sub however good it may be. Its a hard sell not because it doesn’t work, but because it works so well its hard to believe how well it works!

The only thing DBA has going for it is that it does in fact actually work. Nothing else really does. Not really. For sure not anywhere near as good. Its physics: you put one sub in a room, you get one set of lumpy bass modes. The more subs you put in the room the more and the smaller and therefore the smoother the modes. Its not drivel. Its science. You should try it some time.