Bill, I am no expert,but there seems to be a number of people who prefer the sound of transmission lines, dipoles and infinite baffle bass. I think the common demoninator in these three variations is the prevention of the speaker's rear wave reflecting back through the speaker cone. That is what prompted me to try filling my Stage 4Pi's with polyfill(together with Vance Dickason's commment that do so would result in a cleaner midrange,along with some loss in efficiency and higher F3-see Loudspeaker Cookbook)as I mentioned in response one of your earlier posts. For bass only purposes I would think transmission lines would be practically limited to relative small drivers and would consequently give up a lot of dynamic range. Larry