I am considering a Velodyne DD-18...

Possibly another reason to have 2 subs is that its much easier to dial in a truly flat frequency response in room when you have two to smooth out nulls and gaps. For a multi channel room where you have multiple listening positions, you should also attempt to average out the flattest fr not just for the sweet spot but also the other listeners positions. This is much more doable with 2 subs than just the one Also would like to add that I know of an individual who just sold their DD18's and are moving to the dd15's for better integration with their main speakers for the above reasons, and financial considerations are not a factor. When you look at the specs for both the DD15 and DD18, they both use the same sized magnet motor, both 24 lbs. With the same sized motor, I'd rather have a smaller driver with the same size magnet controling it than a larger, anyday. Now, if the magnet were larger for the DD18 then it may be more of a horserace. I do believe also that there is something to trying not to jump up too large in size with the subwwoofer from your the size drivers in your mains. My experience with the B&W 801Nautilus which in my previous listening room the bass just never integrated well with the rest of the speaker. IMO it was just too large a driver when compared to the mid. The 802N was a better integrated speaker IMO.

Magnet size in a sealed enclosure should actually be smaller. But the 15 is a great sub on doubt.

Thanks, everyone, for your responses. The dd-15 appears to have the edge. Velodyne's website suggests that either is acceptable. Anyone have anopinion on their respective musicality? I should have mentioned at the beginning that the application is strictly two channel music.

Well, I've found the DD-15 sounds clean and powerful in my 2CH set-up with Merlin VSM-MXs and a BAT VK75SE. If the DD creates excessive floor resonance, try elevating it on an Aurelex foam platform. If you have good electronics, you'll prefer using the DD in LPF (bass augementation) mode, rather than HPF xover back to the main speakers.

Thanks, Dgarretson. In my current setup I run the B output from my Lamm LL2 out to a Sunfire Superjunior sub. The A output goes through an Art Audio Jota and from there out to Joseph 25Rm SigII speakers. The speakers claim +-2Db down to 32Hz but I measure a roll off much greater than that from about 40Hz and below. The Superjunior flattens that out down to 30Hz but can't keep it up in the sub-30 range and that's where I hope I can buld up some response.

Is placement in a corner/next to a wall critical?