johnnycamp5 Messages: 354 Registered: June 2015 Location: NJ
Grand Master
I think your guess of 60-80Hz is right on.
Last summer I did build a pair of angled, vertical towers (you can see their location by the darker pic).
They reside just outside of each left and right 4pi main (they are about 6'4" high).
I suppose they work as both flanking sub...and high flanking sub (or high distributed sub?).
In either case, it solved/eliminated my vertical null problem from sitting to standing.