Two JL F212s verses two Velodyne 18 plus?

Go with JL F212s and save money for room treatments and bass traps.Think about ease of setup and integration using a spectrum analyzer to match it to the rest of your system.

I must say I really like the improvement when I went from two
Dd-15's to 2 F-113's,BUT:
three weeks ago I home auditioned a Velodyne 1812.
The Velodyne totally took over the JL's.
The midbass punch is just incredible and I was shocked how she
left the rest of the music alone.
It's so good that I sold my other Jl's(113's) and will buy one more 1812.
Down side she's heavy and pricey 6500.But she's the best bottomend I have ever auditioned to date.
My dealer even gave me a lifetime warranty,gotta like that.

Exactly what is your sonic goal? Home theater with massive bass effect impact, music only with seamless low frequency integration, or both?

If you have the room and don't mind a large enclosure the ultimate and possibly most economical is a 400w ServoDrive bin which could easily be powered by a modest pro amp such as a fan less Crest or QSC, EQ'd using the Velodyne SMS.

I rented the small 2-18 for an outdoor gig, brought it home for a day and used my DD 18 for the EQ HT signal. Nothing on the consumer market even comes close to the low frequency energy the ServoDrive has on tap.

Mitchell has been around the block and I couldn't agree more. IMO, regardless of what brands you check out the Velodyne EQ, whether in the stand alone SMS or in their powered systems, is the easiest and possibly the best consumer method to EQ and integrate low frequency into a listening room.

I've replaced my single DD 18 with two DD 12+ in my two channel system with dramatic results. Velodyne has done their homework on the + series but I'm very biased.

Both, I utilize as home theater and listening room. One of my dilemas presently is finding a place to audition these subs.