Deep, musical, in-wall subwoofer

I'm looking to build a musical subwoofer with true 20HZ extension as part of a new home theater system I'm building into my wall in the basement.

I have room for an enormous enclosure (14'x4'x3') and I have space for one or more drivers of nearly any size.

So--where do I start on a project like this? Is this a DIY? If not, who would you trust to build a custom built-in subwoofer system that can make deep bass and still be musical?
There are a number of reputable vendors that make great in wall systems and subs. I don't recall if they go down to 20HZ but try Wisdom and Paradigm and Triad to begin with. There are some other companies that I've come across that I can try to reference and post. I have an Atlantic Technology in wall sub in my secondary system. The only caution I will tell you from experience is that some in wall subs have certain requirements for sheetrock. I used 3/4" sheet rock and soundboard. So my actual wall thickness is 1" plus. You then need to match wall thickness with the mounting. And finally, you may or may not need insulation in the cavity. And finally, finally it's going to be hard to predict room resonances so I highly recommend room correction for the sub.
Why limit yourself? This [url=]one[/url] will do 10 hz. Definitely a DIY job but what the hay?
I'm less interested in pre-built in-wall speakers--I'd rather find a custom speaker builder who could take advantage of the unique and large space that I have.

If I could find someone who'd be willing to build a box similar to the Wisdom S90i, but oriented horizontally, that would be ideal.

Maybe I'm hoping for a bit too much? I see custom car enclosures all the time made out of MDF, seems like it wouldn't be too hard to do the same thing in my entertainment center...
You might try

Great products, helpful people.