I don't know much about subs but I know both are very good subs. I would be using the sub for mostly home theatre as I prefer to use just my floorstanders in 2 channel. My fronts are Gallo Ref 3.1's. My room is 15x12x7 so it's fairly small and I don't have many options as to where I can place the sub which is why I'd be looking at a smaller one. Another option is to just buy the Gallo S.A. amplifier for the second coil of the Gallo Ref 3.1 's which goes down to 22Hz. Is adding a sub overkill in such a small room? Any thoughts would be appreciated. Thanks in advance.

Anyone have thoughts on these 2 subs? Or I could go with a couple of Rel R205's instead for about the same price?

There is no doubt in my mind that for home theater purposes, the Rel B3 is going to be the best performer of the choices you have mentioned. I'd choose that over the DD-10 or the pair of R205's.

I am looking for a high performance small sub as well, but am waiting on the jl audo f110 before making a decision. After a few delays, it is supposed to be released in June this year. You may want to add the f110 onto your list as well.

There is no doubt in my mind that for home theater purposes, the Rel B3 is going to be the best performer of the choices you have mentioned. I'd choose that over the DD-10 or the pair of R205's.

What makes it better than the Velodyne DD-10 for home theatre purposes, can you elaborate?

What makes it better than the Velodyne DD-10 for home theatre purposes, can you elaborate?

The DD-10 is a very small sub designed to have a flat, extended frequency response, but it does this at the expense of the ability to produce deeper bass at any significant volume. It cannot produce deep bass loud enough to do a good job with movie soundtracks that call for that. Things go real well up to about 90db or so and then severe compression begins to take place.

Here is a test result of a DD-10. Although this is with older SMS-1 software, it can give you a pretty good idea of what I'm talking about.
http://www.avtalk.co.uk/forum/index.php?t=msg&th=22961&start=0&rid=0&SQ=0

Pay close attention to how limited the output capability is in the 20 to 30 hz range.

The Rel B3 is a much larger ported sub which because of it's size and the fact it is ported, should be able to produce more output in that same 20 to 30hz range. Of course you had only asked about a few particular subs. There are many other subs out there that can easily outdo The Rel in that same deep bass area.

The DD-10 does have fairly limited absolute output capability but the depth of its bass is very well extended. Your room is indeed small (1260 cu. ft). Even though the DD-10 can't really beat out larger subs, you may actually find it adequate for your room. It tends to start to compress above 90dB but with the natural room gain, you might not really need more output. So it really depends on what you are expecting out of it. Thanks to the parametric EQ, the sub can be tweaked for good sound especially in a small room