Best Subwoofer avaible?

Anyone can purchase a sub,but the spoils go to the DIY guy who assembles his reference and calls it his own.Adire Audio's Tumult,Adcom GFA 555mkII (bridged mono of course ),Behringer parametric, Marchand Audio Bassis.In a 2.5cu. ft. sealed box it rocks and rolls.Good luck.

I'll tell you this much from years of experience, and that's that any of the top rated more accurate audiophile subs out there, properly setup, calibrated, possitioned, integrated, balanced with the seats and rest of the sytem, etc, will sound immensly better than even the most expensive highly touted sub(s) which isn't set up correctly!
There are many many good candidates, as long as the bass output is enough for the room/system it's used with!(e.g., enough bass for the set up). Most of the "A rated" subs', and even "B" for either music(if that's your use) or HT(if subs in that category apply).
I'm sure many people will associate woofers from companies like Rel, Bag End, Entec, or whatever other music sub comes to mind for audiophile playback. But I can easily think of subs like Revel B-15, M&K MX5000, Paradigm Servo 15, Infinity MTS woofers, maybe Velodyne HGS18, Thiel's woofer, Genesis's THX woofer's,
Wilson's way too expensive woofer, Wise Profounder's woofer, Earthquake's Supernova 15, etc, etc, and many others, that would be sonically superb in most any HT/music system when set up/calibrated properly!
I'm in favor of thinking that, at least for music, all things considered, with a good sub with a good high "Q factor"(e.g., tight well damped woofer), set up correctly, you should be able to get some sonically superb results from many of the offerings out there! I think there's not just "one sub" to be had is all I'm saying

Nothing or, at least, large numbers of smaller drivers, will move the air or couple with the room like a large driver (think as a minimum 18" or larger). Many years ago I heard a Levinson HQD system with the 24" Hartley subs. Boy could those drivers move air with impact. I later used Entec L40F's (4 10" woofers per side with equalzation and servos). Faster and cleaner than the Hartleys but unable to move the same amount of air. Have you ever considered the cost of the drivers used by most manufactrers of subs; not a pretty picture. Check out the drivers used by Velodyne for instance, then price a single 24 " Hartley. Likewise consider the weight and bracin of the cabinets.