N802 + Velodyne DD-18???

I'm planning to buy Velo DD-18 or DD-15. Did anyone try this combo? Is DD-18 worth 1k$ over DD-15???
IMHO, if you need a sub with N802s, either you're not using the right amp or you're using the N802s in an application where you would be better suited to use other speakers with a sub.

Again, just my opinion. I could be wrong. My wife often tells me so.
How big is your room?
Everyone needs a sub. I have the DD-15 and it's great.
The 802's only go down solid into the 30hz range.. a subwoofer is an excellent addition, plus this lets you put the 802's where they sound best and the sub where it sounds best! I used to own an F1800XR Velodyne 18" sub and went down to a DD15 and was disappointed (it hit harder but but didn't work as well with music)..... I would definitely spring for the DD18 unless you think later you could go for a Dual DD15 sub setup which really helps out the acoustics.

Otherwise a JL Fathom F13 works quite amazing... compared to both DD15 and DD18, except the room correction is better on the Velodyne.

Oh yeah drop a 25lb bag of #7 lead shot onto of the velodyne and be prepared to be amazed. Isolating the sub on Aurio Pro's, Sistrum stands, or Auralex sub isolator will also enhance your experience.
Use the room sizer applet on Velodyne's web site. They'll tell you which sub to get.
I had the same quandary with my 805’s and whether to get the DD12 or DD15. It all boils down to room size. As it turned out the DD12 was more than sufficient for a 16 x 25 room with 12’ cathedral ceilings.
My room is 15x21ft and my sweet spot is 11ft from speakers which are 9ft apart and 3ft from front wall. I have some bad modes on listening position (-10dB@50Hz / -4dB@80Hz) and other frequencies are pretty flat down to 25Hz. Yes, I tried move speakers around as well with N801D. Reverberation time is good within whole bas range (1.2sec) and I experiment with some absorbers. Still I think I need Velodyne!
I use a JL f113 with my 802Ds and, while it really does nice things when required, it is very rarely required.

It is extremely unlikely that a sub would do anything to improve a dip at 50hz. A Rives Parc or a digital corecction system would be more likely to achieve the result you are looking for. Very few rooms are flat in the low frequencies. Just look at the in-room graphs in some of the S-Phile tests and see what I mean. So you could quit obsessing and listen around/through the aberations.
I just tried to correct some nulls in the bass (40/50hz)as heard in the listening position by using a sub and a parametric equalizer to supplement mains operating full range (down to 28hz). It didn't flatten (raise) those nulls appreciably, either electronically or by woofer placement without shaking the walls! I may have been sitting in a null but the walls must have been in a node. Compared with results that worked a little bit (less than a 3db change in the nulls) I preferred an amp with a better bass response. FWIW.
Thanks guys, but I also tried different amps, Behringer digital EQ and Copland room correlator. This equipment improves amplitude, but in same time you have problems with distortion, handling, not to mention converters who are responsible for all others things... My point is: I don’t think that anything will fill 10dB dip, but can contribute. I tried with lower class subs and I had better results if you compare with other mentioned experiments. Finally, N802 need some extra energy below 30Hz. At least in my room!
Srdan01, My room is about the same volume as yours and a DD-15 does fine for me just filling in below 30Hz. However be cautious, as current Vel 2.2 software only allows crossover at 40Hz and above. Unless you can get Velodyne to FPT you the older 2.1 software, you will have excessive overlap between the sub's LPF and a full-range main speaker. Using the sub's EQ to fill in null points much above the crossover point is usually a bad idea.

Any Vel DD can be improved with a few internal mods to the plate amp & wiring.
I actually planning to build new box for DD-18. Goal is to look like hi-fi stand (invisible) with down-firing base driver, like Rel.
I am using 802d's and an HGS 15. THe Velodyne seemlessly covers the lower bass that the 802's cannot reach. I concur that weight on top is a great idea. I use a Bright Star Big Rock/Little Rock sandwich.
Srdan upgraded his speakers to Jamo R909