didn't Tom say something about the length of the wire to the drivers form the xo being significant to the design?
I don’t recall that. He monitors the Thiel Owner’s thread if you want to ask him. I *do* remember he is a fan of short speaker cables. I haven’t told him my cables are 2 m!
Tom *is* concerned with heat management because of possible drift as resistors get hot. An outboard solution allows for this heat to be directly vented to the room. One iteration of my build had the resistors in stainless clips, mounted on aluminum bars. This really worked well for heat dissipation. I ran the speakers overnight, then at SPLs I use for rock recordings for one hour. Even a 30 ohm resistor was barely warmer than my skin. The bars, however, introduced a subtle sonic anomaly and I preferred the SQ without the bars. I did not run the same heat test after I removed the bars. That said, I don’t have experience regarding SQ degradation resulting from hot resistors.
As for vibration control, I also lack experience in if/how cabinet/XO vibrations degrade SQ. My build has the boards mounted with rubber feet against the cabinet and between the boards and screw heads.
I think it’s instructional to note how very few speakers have outboard XOs, even $$$ designs. The only outboard design I’ve heard (might be the only one I can even think of) is the Avalon Ascent. This was a fantastic sounding speaker and remains one of my “best ever”. But I heard it >25 years ago so I don’t know how it compares to newer uber designs such as Vandersteen 7, TAD Ref One, etc.
Regardless, I am over-the-moon happy with the SQ of my in-cabinet build.