What is a "transmission line" speaker?


Maybe I'm a dummy, but I don't know what differentiates a transmission line speaker from any other type of cone drive speaker. Please explain.
jphilips
A "transmission line" speaker has a labyrinth at the rear of the driver(s), usually to augment bass response.
The labyrinth increases the distance that the backward firing woofer soundwaves must travel to exit the port of the speaker. So it's like a bass reflex speaker with a very long (in distance traveled) port.
A good example of an actual transmission line speaker was those designed by Irving "Bud" M. Fried. See if he has a url and some more info on this design method.