"Mechanical Crossovers"
The mid/tweet in the Theil 2.4 is described as "coincident / coaxial", and the crossover is mechanical.
As are the biflex Altec drivers.
Interesting. Flame on if this is old news.....
http://thielaudio.com/THIEL_Site05/P...icoildiag.html
http://www.lansingheritage.org/image...420a/page1.jpg