OK, Muskrat, good point. I would try placing the cdp directly on the granite; I wouldn't decouple the granite from its support with vibras. I'd try the vibras under the cdp and compare to cdp direct (above).
Given its mass, the granite's resonance frequency should be quite low -- be aware however that it can store energy so, you'd probably want to decouple yr cdp fm the granite.
You must try various combinations (granite is heavy, I know).
