Loved IMF speakers (which became TDL). Wilmslow audio do a TDF transmission line kit I've often toyed with.
@Salty seadog has a pair of TDL's...I hate him too....
My old speakers were home made transmission lines based on Kef b110 bass (maybe 6-7" diameter) and Isophon tweeters, the latter replaced with Kef T27 after one of the Isophons blew and they'd ceased making them (maybe ceased trading even) I'd wanted to build the Doctor Bailey (inventor of TL) design in wireless word using the bigger Kef B139 as base drivers but couldn't afford them 40+ years ago, but could in more modern and prosperous times, so found the Wireless World article on the interweb and got a pair of the big Kef woofers off fleabay intending to re-use my drivers from the smaller units I'd built
Here's a picture of Bailey's design
Before going ahead I realised I could buy a pair of secondhand Kef reference speakers for not that much more than the drive units were worth so got these for £550 or whatever and they are truly awsome. Apparently £3k+ new and stated by some pundits as "the best speakers Kef have ever made" though I dare say now surpassed by their £12k modern models
Sold off all the bits and it wasn't all that far off the price I paid for the fully built Kefs, particularly since I'd have needed to buy wood and other materials too.
Here is one of my kef 105. The middle mid-range has a concentric tweeter built in, and Inside the big hole at the bottom are two big bass units joined by a rod - I think it's the same idea as the Linn Isobarik, though can't quite remember the theory - but something to do with dissipating the rearward sound from the driver which would otherwise cancel out the sound from the front.