What is the best subwoofer you have ever heard?

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.

By far and away Servo-Drive Tech7's.

For powered in home use nothing comes close to the Velodyne 1812. I heard a pair supporting a pair of Avalon Sentinels. Sounds like sever overkill but the presentation was sedately stunning.

For HT you could save a great deal by using any formidable sub without EQ/room correction since the HT processor would be handling those duties.

I had a REL Studio III, JL Audio 113, and a Velodyne DD-18, in the house for a side by side comparison a few years ago. The JL and the Velodyne were clear standouts.