Nice! I've been curious about transmission lines for a while. Bob Brines uses a burly Fostex 8" single driver that supposedly goes strongly down to 30 hz using this alignment! He uses the Martin King design software and supposedly the final result performs way above the price point, which I'm pretty sure is under $1,000 usd.
The FTA-2000s use the Fostex F200A Alnico based drivers. The full set of speakers go for about $1500.
For what it counts, I own a pair, out of maybe 4 or 5 that he has handcrafted for sale. I think there will be others that are DIY.
The FTAs are speakers that leave other commercial speakers up to 5K or more in the dust, due to their flatness in sound. They are not peaky, midrangey, but fairly flat with a slamming low end that is rhythmicaly taut, fast and with plenty of it.
The only drawback I see with these speakers is that you will need WAF, because they are large, imposing. I call them the "trunks" but they are doing guard duties now, as a livingroom speaker.
The FTAs paired with opchip amps=speed, slamm, affordability and fun.
Bob Brines is a true artist who makes the cabinets, I think for his own passion. I doubt he makes any money out of the venture. I bought the DIY plans and let me tell you, they are not a walk in the park.
The funniest thing that happened to me is that someone came to listen to them last year in my older apartment and later, the person compared them with a pair of Wideband Tannoys that went for 12k. He liked the Tannoys better, but let me tell you, the FTA were not shabby for about 90% less.
