is it really ok to place a driver upside down? wont it squish the surround?
except for the basket arms, it does look similar ... what's the TC12 closest to todays design? or was it used in the SVS Ultra?
In the Vandersteen Model 5A, which contains a downward facing sub, there is a small DC voltage applied to the sub driver, just enough to counteract the weight of the diapraghm so that it's actually 100% centered. If you're not doing this you'll get less X-max to work with.
Sounds like a good idea but I guess difficult for a DIY project.
The PB13-Ultra uses drivers from TC, but you cannot buy them, perhaps this is something along the lines of that driver....
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=293-618
Audiopulse is actually manufactured by TC Sounds.
Regards
Harald N