shep,
I've been a fan of transmission line design for 35 years starting with I. M. (Bud) Fried's stuff. I love the fast/deep bass with clear midrange.
If you're interested in transmission line designs, recommend you visit:
http://brinesacoustics.com/Bob there does a good job explaining the concepts, with no need for humblehifi's old school trial and error approach. And he offers plans or flats for DIYers as well as fully custom built/veneered finished speakers at very competitive prices (that's how I got the original FTA-2000's built for me).
Personally I prefer a tapered design, if nothing else to reflect backwaves (that can muddy the midrange) away from the driver.