At this point I am of the opinion that transmission line speakers, like any ported speaker, are often not tuned quite right. With transmission lines, in my experience, the results of improper tuning tend to be even more of a "one-note" bass than a sightly mis-tuned conventional bass reflex cabinet.
Also, in the case of conventional ported boxes the port tends to be somewhere near the driver associated, where with TLs the vent is either very close or, more often, far from the driver. I think when it is far, then room integration becomes in some cases almost impossibly complex as a result.
In the case of the Fried Model Hs the box was 4 ft long with a single bend. This made the line about 8' long with the open end adjacent to the driver. It worked so well I copied it in what was to be the last set of speakers I made (and which I still have).
These used a KEF B110 and a T27 (ouch) in a slim TL with the vent at the top back. It was intended to be wide bandwidth but low power handling - aimed at apartment dwellers who couldn't and didn't want to play loud. Also it was designed for positioning on either side of an armchair to function as near fields, or headphones for those times when no one else in the house particularly wanted to hear what you were playing. I never measured them, but there was surprising low bass extension. In fact they really shocked a few people who didn't expect 35 Hz from 4".
You have to realize, this was 1978!
