I built his DTQWT-12. One that Troels himself never built, he just extrapolated from the shorty version. It did some things very nicely, like good sensitivity, easy load, nice midrange, VERY musical for long listening. Other things not as well, the concept that the mid and bass horns mix and support each other is dubious, imo, and the results favor my prejudice: bass transient response was poor in the big horn though he claimed it was "dry and fast" bass or something that implied it would be better than it was - to each his own. The midrange driver had "cone cry" distortion that ruined the tone enough to prevent serious classical listening. That's the main reason why I sold it. But there is a new version of his midrange driver now, so I'd be open to building it again, the shorty version that he actually built and tuned, hoping that's where the fast dry bass actually lives.
I'd love to build one of his more advanced "hifi" speaker designs like Jenzens or ATS. I might just do that.
The quality of the Jantzen kits was mostly good and the discount parts price from Poland is good. Troels is available and very helpful by email. Somebody once remarked on this forum that Jantzen coils use lower quality copper windings. I can't verify that, but I think mine sounded OK. The Jantzen caps and their copper/silver/teflon hookup wire in the kit was excellent. The kit included those shitty Dayton chinese cast zinc speaker binding posts. Troels appears to use them in his own builds, that baffles me. The sound really suffers using them, I don't see how his speakers could possibly sound as good as he claims using such poor quality connectors.