Dual vs single sub

You want two. Most subs have to cover a range from low bass, which is 'locatable' by a listener, to very low bass which isn't  and the power needed to produce a given spl is only 1/4 as much with a pair than it is with one.

Best test is to play a CD of organ music with low notes with no sub, then with one, and finally with two - makes a big difference and moves you, the room walls and anything in between.

You need pretty decent quality subs to integrate well with hi fi audio. The best bang for the buck I could find was the  VTF-15H MK2 DualDrive 
http://www.hsuresearch.com/products/vtf-15hmk2Dual.html
110 lbs each, 600 watt on board amps and they look pretty decent, not like something that got drop kicked off the back of the band's bus.

@vt4c, a timely reminder. Nice, just before someone suggested 8 or 16 subs!

Stereo bass? Vinyl mixes bass to a single channel for practical reasons. Moreover, localization of low bass is a non issue as you can't really tell where its coming from, only the higher harmonics is a clue, AND most music only have one bass instrument.
More subs is for other reasons, but stereophony it is not.

While most of this is true, the comment about vinyl is not. We don't mix bass at all when mastering. That is a technique used to reduce the time and cost of mastering time but its not something cast in concrete.

The Ford Motor Company did a study some years ago, to determine what exactly was needed for really good bass. What they found is that below something like 80 Hz the bass on virtually all recordings is mono.

I just got my Swarm-based distributed bass array up and running last night and so I can now say from factual actual experience there is nothing else like it. If you want really good bass you will use FOUR subs distributed around the room. Period.
http://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/

Hello millercarbon,

     Congratulations on getting your custom 4-sub distributed bass array system built and operational!  Are you planning on posting some kind of more extensive review of your dba results? How about a new thread devoted to how to build and deploy a custom dba? 
     Using an Audio Kinesis Debra 4-sub dba myself for the past 4 yrs, I already knew your results would be spectacular but I think others really benefit by knowing how incredibly well this concept actually performs in virtually any room and with any pair of main speakers.
     If you're anything like me, you're going to find it hard to resist posting about the dba concept as the ideal bass system on the many threads consistently started by members looking for better bass response in their rooms and systems. 
    However, I completely understand if you'd rather just enjoy your newly improved system for a few weeks, months, years or decades.  The truth is that neither of us will ever need to buy another sub or bass system again. 
     I'm just still amazed the dba concept isn't more widely known and used, especially on a high-end audio site like Audiogon.  The fact that it's so difficult to overstate how well these dba systems actually perform, whether a complete $2,800 complete dba bass kit like my AK Debra or a custom dba system such as yours, I hope you agree we have an obligation to spread the word to our A'gon brethren and beyond.

Enjoy,
Tim