Thought about it at one point .. instead, bought the Yorkville Unity system. The Unity sub is a nice horn loaded 15" .. one of the most musical subs I've heard. Just couldn't keep dragging 118# in and out of my SUV.
Yeah...I think you just reaffirmed my reasoning as to why I never bothered to purchase an 18 before. I also prefer to keep every piece of gear I have under 50 lbs...While the 69 lb Carvin, or 70 lb Alto TS218S isn't that bad...I'm likely not going to like lifting it and out of my Traverse...
...It looks like I'm going with 2 new 12 inch Subs this Spring. I'd order them now and put them on CC, but I have 1 wedding next Saturday, and nothing else on my calendar until March 11th....and that one I can just use my TS215s on with no sub. The gig I have on April 8th is going to be a fundraiser for over 300 in a fairly wide ballroom so that will likely be my first gig with the new Subs I get.
In my opinion...and I had a double 10" Yorkville subwoofer, the 18" would be my choice. Granted the double ten's would probably be louder, but the 18" would give you the robust resonance. However, weight would by my main consideration. The Yorkville LS801P is 137 lbs. and 1500 Watts 18".
I would like to hear DJ Freddy's recommended sub FWIW.