@deep_333 For example, a servo controlled driver will be forced to slam STOP quicker than some floppy/sloppy driver. It will result in the perception of FAST BASS! There may be other ways to do it as well. What is so hard about this to comprehend?
Oops, I didn't mean to criticize the ability of servo control rather the basic premise of the term subwoofer speed. I write poorly, my bad. "sloppy / floppy" that I'm going to use, thanks.
I replaced the Octavium with my first servo sub in the late 70's from Jonas Miller and Ken Kreisel at their Wilshire Blvd store. They had a stunning with and without demonstration setup there.
Now that I understood I was listening for I heard an even better presentation when I brought home Velodyne's ULD servo design and currently use two DD Plus. That David Hall, smart guy.
I believe the sub in my large Bag End ELF-M / S18E-D Bass rig has some control associated.