Best Subwoofer avaible?

Someone's got a Krell Master Reference on eBay at the moment. You won't get much better than that...400lbs of bass

Look into a Revel B-15. Not only will it blend seamlessly with your mains, but it can make you loose your lunch with its deep bass. The best part is they cost around $2k and compete with subs costing four or five times that.

The best reasonably sized subwoofer in my experience is a sealed box design (3.5 cubic feet) based on the Adire Tumult 15" driver (www.adireaudio.com). In this configuration it is well damped (Q about 0.55) and has a typical in room F3 of just about 20 Hz. It has a very clean sound and can produce prodigious sound pressure levels when fed sufficient power. This is a DIY project (check out www.partsexpress.com for a good prefabricated enclosure and 1000 watt plate amp), but well worth the effort. I use two in my home theater and the results are astounding on both movies and music. Good luck!

I have a pair of the new powered 21" Cabasse A55 subwoofers on order for delivery in late march or early April. Based on what I heard at CES, I think they may be state of the art. They incorporate a woofer whose mass is about that of a typical 10" driver, a 1000 watt amp, a parametric equalizer, variable phase and cross over point and weigh 450# per side.

I too have tried REL subs (as well as many others)- and I could not get them integrated - in fact, they sounded the best when they were unplugged. If you ask Wilson Benesch about subwoofers, they will most likely tell you what they told me, "Subwoofers are evil". I didn't believe it at first but I do now. One of the many benefits to using Wilson Benesch speakers is how seamless they sound - adding a subwoofer seems to introduce nothing but problems.

If you go with a sub, make it a Velodyne HGS - 12" or smaller and try to find a home for it in-between your speakers or the midrange & soundstage will get too distorted. The volume will need to be set very low and the crossover must be set to the minimum (40Hz) or use an external crossover set between 33 and 37Hz depending on your room for better integration.