Nice builds Boom!
If it's "your undertanding", then you're probably more correct than I. I've not attempted a TL, but have a few forum buddies that have done some. Most that I've seen (that I can recollect) have had an increasing cavity size from the driver chamber to the terminus. But there again, it's not like I've been "keeping score" or anything, just casually browsing the picks. If they were'nt friends, I probably wouldn't have even been reading the threads, you know.
A local forum dude brought over a very small pair of TL's equiped with 4" Lowthers (IIRC) for the sole purpose of showing me how much bass can be had from such small drivers. His source was an off the shelf unmodded CDP and a 5wpc Almarro A205A tube amp. Purely amazing man.... He played a LF tone that blew me away. Got me thinking about the capabilities of a couple purpose build monster sized 15" TL's for HT LFE's.
YEA BABY!!
Regarding Martin, I've chatted with him about OB before. That dude is waaaay over my head. Helluva nice guy, but he's so smart, when he sneezes he looses more information about acoustics than I even know! I've checked out his site but my eyes start glazing over by the time I'm halfway down the page. I may be a bit bold in saying this, but he might just be the "Nikola Tesla" of audio.
Bob