Correction to my previous post. The moving system of the PowerDriver tweeter is that of the CS7.2 with a spherical dome and rubber surround. The newer SCS4 tweeter moving system was co developed with the CS3.7 / CS2.7. It has the catenary dome and silk surround. Also, I had mis-remembered the SCS4 tweeter breakup frequency. It is about 27kHz with very nicely controlled behavior.