A folded horn is NOT the same as a transmission line, and they are not a type of one or the other, they are very separate and distinct technologies.
First off, Bose does not know what high-end IS... Their (sh*te)Wave Radio (TM) is not a true transmission line, it is a quasi-transmission line. It's woofer is in a box - a SMALL box for its parameters, with a HUGE port attatched to the back of it, then they EQ the HELL out of it... for "low frequency reproduction". Yeah, it is CLSE to what I am about to describe, but since I have never torn one apart to examine it, I can't say much more than that to the construction of one. I have to rely on word of mouth from my Harman engineer friend (who HAS torn one apart, but cannot reveal the trade secrets discovered).
A transmission line behaves very similarly to a vented enclosure in the fact that the back wave is used for re-inforcement of the front wave, but instead of 90 degrees out of phase like a vented box, the wave is 360 degrees out of phase, and there is no box, the driver attaches DIRECTLY to the resonant pipe. The benefits to this method include - better transient response, smaller enclosure for deeper resonance, smoother frequency response and impedance curve - allowing better damping from your amplifier, NO, and I mean NO port noise. They do NOT offer significantly enhanced output, except at resonance.
How do I know about transmission lines? I had two Infinity Pro 12's in a TL in my 86 Civic HB about 10 years ago. It was 9 cubic feet, damped with sand, it weighed over 400 pounds, and was tuned for 22Hz. Actually the DESIGN was for 22Hz, but it ended up landing closer to 18Hz - certainly a desireable, if not completely USEABLE error! I still have two 18" transmission lines tuned for 12Hz in my living room. They are as big as refrigerators, and take four guys to move them, and have 32 FEET of line in them!
The TL is a MUCH easier design than a vented cabinet, though more difficult to construct - the science comes with the stuffing, if you decide on a stuffed line. Here is the basic math:
Terminus = 25% of Sd_of_woofer
Opening of line = 50% of Sd_of_woofer
Length = wavelength_of_driver_Fs / 4
Driver = ideally a Qts of .4 or lower
These are the basic rules to an unstuffed line, and if you ever decide to buid one, I am sure you will not be disappointed.
A stuffed line follows the basic same rules, but the line is MUCH shorter, by at least 50%. The stuffing slows the speed of the sound through the line, making it appear much longer thus allowing a shorter line with the same resonant frequency as a long line.
A folded horn, (which is just a horn, folded...) on the other hand, offers EXTREME output, with absolute minimal movement of the driver cone. It is a buried driver, meaning, you never see the driver cone. The horn is attatched to the front of the driver, the driver is acoustically suspended in a saled box at the end of the horn, and the mouth of the horn is often times MANY TIMES the size of the driver Sd. Horns are NEVER stuffed, and are always physically HUGE, and get larger the lower down you go... i.e. a bass horn is dozens of times larger than a mid horn, which is many times larger than a highs horn. You will never see a low frequency bass horn in the car, there is simply not space for it. A properly designed horn can be an awesome experience, my favorites being from a company called Moondog Audio. For you who call yourselves TRUE audiophiles, listen to them sometime... here's a link to read some about them: http://www.fsaudioweb.com/listen/moondog.html For those of you that THOUGHT you liked horns as/when/if you listened to Avantguarde Horns, "you ain't never HEARD GOOD HORNS" - AvantGuarde horns SUCK next to the Moondogs... But I digress...
Anyway, there is a quick little primer on horns (folded or not) vs. the Transmission Line Loudspeaker.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."