JL Audio F113 or F112 For Dynaudio Confidence 5

Trance, I have two F113's with Tyler Acoustic D3's which integrated very easily in my big room. One sub was still good but adding the second was the ticket. Two F112's dialed in for your room size would be all you need. Both the F113 and F112 are extremely musical and fast. Start and stop on a dime. Once they are dialed into your liking you won't even know they are there. I would do two F112's before one F113 if that is even an option. Also, hearing or feeling a difference between these two subs is going to really depend on what is going on in the room. You are moving air inside that cube so one is going to sound a little different than the other. At 80hz you may not be able to tell but anything below 40hz you more than likely will feel the difference. You can control the response of the room easier with two subs as well and it won't affect the neighbors anymore than with one unless you want to.

Trance, Forgot to mention that the JL's like any other good sub can shake your walls if want them to. For movies it is fun but the JL's are built more for music. They are extremely tight when you get them right and create an uncanny black background.

Trance, your room size is very good. I could live with that and make the room sing easier. Harder to control a bigger room. Ceiling height makes a big difference from what I have experienced. I like that mine are 10'. Drop JL a note on your cubic foot area and see what they recommend.
Rel just came out with a new top line sub that is built with a solid enclosure and a beefed up frame along with a new 12" carbon fiber driver. They must have built this to try and contend with the Velodyne DD18 ( very good ) and the F113. Both the Velo and JL have there strengths when comparing. Demoing these two subs with a dedicated drum test track is like being in front of the drums. I found the F113 to be stellar in this area. Very fast and controlled is what I hear.