My research brought me to the same conclusion. There are differences between various TL but in general they are the same as BLH. That isn't to say a Voigt pipe is the same as a MLTP is the same as a BLH but I think the basic principles are the same. A front loaded horn is more efficient but it only works for an octave or two so can't be used for a single driver. At least that's what I thought. Then one guy (who will remain anonymous here) tried to tell me a backloaded horn can be as efficient as a frontloaded horn so I wanted to get some opinions here. Looks to me like his opinion is not shared by anyone else. As much as I like my speakers, they do what they do and it is unrealistic to expect them to be as loud as say a compression horn with the same 1 watt input. No problem, I'm after quality not quantity.