What is the best subwoofer you have ever heard?

Custom built, 6' tall, 4' deep, 2.5' wide. Four 15" woofers in an isobaric arrangement. Double walled cabinet with the inner wall isolated from the outer wall, including panel deadoning components.

+/- 3db down to 18hz. Max SPL 120db.

If money is not an option I would purchase the bass engine from a pair of the Scaena loudspeakers, they are 3 stacked per side 18 inch woofers in a specially designed cabinet.

They go, low, low, low, fast and articulate with massive pressurization. Check out HP soundings review of the Scaeana's

There is no substitution for massive displacement of six 18 inch bass drivers and a few thousand watts of juice!

Well Matjet, I like subs that augment the main speakers and blend well. So for me it is the REL Britainia series. I have the B2. If you don't connect it off the main amp...then it will never blend and you will always be tweaking with it. I hate that, I never touch my REL its AWESOME.

I've had a Paradigm servo 15, good sub. M&K MX-350 MK2 in really cherry wood. Good sub but just didn't have the low level extension. I now have a SVS PB13 Ultra and at 2 notches on the volume and -15 on my pre output level it is dynamicly robust .i do want to compare it to two SVS SB13 Ultras as I would like a smoother response and two will give tighter, faster bass.

I have owned B&W, Aereal, Rel & JL Audio. I like JL Audio f113 best. They are very fast so I can use them for 2 channel as well as home theater. I still have 1 of my Rel's but I use it as a rear sub. It is a Stadium III.