Two subwoofers in smallish HT room?

Hi Soundprogression - thanks for the note. This particular Vandersteen subwoofer (V2W) is made specifically for HT applications. It does not have an external crossover like the Vandersteen 2Wq subs most audiophiles are familiar with. It's a line-level input only sub, and uses the processor's crossover, so in that respect it is just like any other HT sub on the market. My processor has two identical LFE outs, so adding a second line-level sub is a piece of cake from that standpoint.

My local dealer suggested I try the route you put forward in your first paragraph. I have been pleased with the bass of the Vandersteen, but not with its output. He thinks I ought to try a single Velodyne DD15 in the room before considering adding a second Vandersteen HT sub (or dual subs from other brands). He says the combination of higher output capability and the EQ functions of the Velodyne would probably make it an easy fit. It would also not create additional space constraints.

The only problem is that adding a second Vandersteen would cost approx $1300, whereas the Velodyne lists for like $4000. :-( I'd be able to sell my existing Vandersteen very quickly, but the Velodyne is still a big chunk of change.

That's good news. I saw Richard Vandersteen at CES and I failed to look up the newer sub. I mostly looked at his speakers.

What you could do in a pinch is stack Vandersteen subs. You get significantly more output with another sub (not double but say 3-5dB. 3dB officially but it depends on how they react in the room). That's often enough to satisfy people. Kevin Voecks used to do that at shows to make sure he had enough output to satisfy a crowd.

I think you still need to look at the room behavior to find out if your dealing with a big frequency hole next to a big peak to make sure that your not fighting another battle. Adding another sub in the smae location won't help you then. If you have some time and want to learn the subject, especially about multiple subs, try Dr. Floyd Toole's white papers on the subject, http://www.harman.com/wp/index.jsp?articleId=1003.

I use a small and free tone generator named NCHTONE, http://www.world-voices.com/software/nchtone.html, from of the headphone out of my laptop to my system when I don't wnat to setup my complete testing system. With that and a Radio Shack meter you can make a graph of your system's behavior and pretty much KNOW and not believe you know what the problem is.

Not knowing the power and capabilities of your sub, I will say that placing the sub in the corner is giving you some sonic challenges. However, it is boosting the bass output of the sub in the room. So, there's tradeoffs. You would get better quality bass if you put the sub where it is getting "flatter" response. This often means out in the room more, maybe nearer the front speakers. However, you may then have to try to overdrive the sub to make up for the lack of bass output.
A solution would, yes, be to add more sub(s), to add efficiency. Then, you simply will have to spend time finding good locations for both subs, and get phase right, etc.
If you find a good spot for one sub, where you're getting reasonablly flat bass response, you can then put another sub elsewhere in the room possibly. I would ONLY DO THAT, if I needed to counter a bass mode problem where the first sub is at. If, say, there's a peak from the first sub at a frequency, I'd try to place the second sub were it was in "the null" at that frequency, and vice versa. This would help smooth out bass mode problems, and provide smoother bass. HOWEVER, if you find a place where you're getting very flat response from the first sub, then I'd try placing the other sub right next to or on top of the second! That makes things easier, and you'll note have to worry about comb filtering phase problems, because all effected frequencies are longer than the distance between drivers.
In your case, sounds like, for best overall sound, you need, yes, another well placed sub possibly.
Still, spend time getting best sound from the first sub, then add another and experiment