100hz and below OB servo plates with 12" HE drivers.
100-300hz Mid Bass Columns with correction and direct driver coupling.
300hz and UP NB Small Planar/Ribbon columns, valve driven.
To tell the truth, one of the BEST systems I've ever heard was a stand mount speaker AND Servo subs.. The ROOM was still 50% of that great combo though.. 16 x 20 x 9. It had a built in gear rack (LOW) into the front wall. It was tube driven monitors and GRs OB servos.
http://pointillistic.com/vmps-audio/626R.htm.
TRY to find a pair.. They are like gold when they are set up right..
First time I ever saw and understood the reason for bearding a stand mount speaker.. GR OB servos and super fast planar/ribbons..
Time to feed the chickens..
Regards