Very interested in building a transmission line enclosure as a DIY project. But I'm wondering would you get good results from using reference speakers in a 2.1 design where another external subwoofer is used?
There is long history of Transmission line speakers.
Are transmission line enclosures only good for subwoofers?
No, They excel at bass but most are full range speakers.
I have a nice pair of DCM Timewindows, one of the first TL speakers. They do provide great bass, (That is probably the genesis of the design, to get great bass) as well as crazy good imaging, sound stage.
I'm wondering would you get good results from using reference speakers in a 2.1 design where another external subwoofer is used?
Sure you can use them in a 2.1 set up but weather or not you get good results is dependent on many variables and your knowledge of sound-waves. You could set your sub-woofer crossover to carry the frequencies below what your TL speakers cut out at. If you build some you may find the bass they provide is enough for music, (because presumably you will engineer them to your preferred specs.) Movies/TV soundtracks may benefit from the lower sub-woofer.
Interesting read on a DIY build.