vibration and resonance

I too would like to know what you built in order to provide advice.
For Schipo, what are the dimensions between the legs of the lack tables? Could they be stacked? Maybe place a piece of granite on top? Might try these myself. At the cost there's little to lose.

I built a rack from slate and threaded rods. My rack is very heavy but will wobble if the nuts aren't tight. I really crank them to make it rigid.