subwoofer 19 by 18 room

Try a sub from Genesis Advanced Technologies. The G928 is awesome. Price is a little high but well worth it. If you are on a budget, try a Z Sub from BG. Best sub I have heard under $1200. Fills the room, without a boomy box feel. It has 2 10" drivers, fast enough for music, and powerful enough for good movie watching.

thanks for all the insights

I talked to a friend who does home theatre and he says the JL Audio has been a dream sub to put in a system

looks like I'm leaning that way

two F110's or 1 F113?

everything I demo is too loud, rolled wrong and it sounds like a booming box

probably need some eq in my near square room

I may even have Jim Salk build me something

ASC sub-trap,dont leave home with out it,its that good.

I cannot agree more with Bob Reynolds on setting up the sub.

Apart from that, bass traps behind the speakers at the corners would substantially improve bass definition. I have read from a few posts that they don't help in some rooms but once I took out the bass traps from the corners of my room, the definition was lost and bass got considerably loose. That was the point when I figured out I cannot live without those traps.

Yes! What Bob Reynolds is infering here is correct! You simply don't know what all the variables you were dealing with
are, and their impact (no pun). Single 3 biggest issues for sub performance is location, location, location--then setup, level matching, phase with speakers/seating, and EQ'ing!!!
In your still relatively smallish room, I suggest passing on the Arcam (which lacks severely needed EQ and DSP room correction features! Any relative potential great sound quality will be mostly voided by the likely bombastic room mode problems you'll likely have, as well as other acoustic issues. That's my perspective. Infact, in all these smaller acoustic spaces, that's one of my main issues! That being that even the best potential audio equipment is necessitated by needing EFFECTIVE room correction or EQ'ing! Most high end gear doesn't include much here(yet). I'd like to see more, because it's a HUGE ISSUE! Food for thought here.
Yes, the Arcam is an otherwise good sounding piece, on it's own. But then what about the extremely difficult acoustic issues you'll be faced with? That's the dilema, IMO.
As for Subwoofers, and your original post, if you have to go with one sub (not knowing sub placement and setup), I might suggest you won't go wrong with the Paradigm Servo 15--especially for the money!! You'll spend more on a sub, and not get more really. Overall impact, extension, lack of distortion, tightness, relative accuracy, quality, etc.
That's my blind suggestion.(unless you don't end up with a system EQ, then look into others like Velodyne, with Parametric EQ feature) And I've sold/used a lot of subs over the years, and don't think you'll beat this, overall.