My common sense tells me that a speaker cabinet being "pushed" in the opposite direction by the excursion of a driver isn't a big deal - a tiny loss of amplitude. But when a speaker that is wobbly or mounted on an insufficiently stiff support recovers its "neutral" position following this push, that's probably when a mess is created, since that recovery motion is independent of and out of phase with driver motion. Roller bearings might be good under speakers if they keep the small, reactive motion of the cabinet in time with the driver motion. And, a speaker cabinet that is free to move as a unit on bearings in reaction to driver motion may not be prone to flex and resonate as much as a cabinet that is being held in place by just one of its surfaces. Also, spiking a cabinet to the floor means the behavior of the floor has a chance to affect the sound of the loudspeaker, another factor that bearing supports may alleviate. I don't have any first-hand experience with bearing supports, but I speculate on some possible advantages just to illustrate why simple, general rules (always spike to the floor, always mass load, etc.), though appealing, may not offer the best guidance for any particular situation.
Cones vs. factory spikes?
Has anyone done any A-B testing for various speaker cones? Currently, my KEF REF 4s (120 lbs each, ported base) have the factory spikes. Before spending big bucks on Orchard Bay cones (used on Talon Khorus and recommended by my dealer) or Black Diamond Racing (why is their web site is abysmal?), I would like to know what others have used on the bottom of their speakers and if they make an "audible" differnce. Rest of system (for 2 channel) is: Aranov tubemonos, firstline pre, Sony SCD-1 (on order).