I generally like the whole idea of double stacking. Whether it’s double stacking with cones and plates or double stacking with a combination of springs and roller bearings or even stacking springs or stacking roller bearings. But one thing to keep in mind is that when the resonant frequencies of the two layers are the same or even close the two layers will naturally interfere. So, the trick, my friends, is to pre-calculate Fr for the two layers to avoid interference. For a dual layer heavy masses and springs system, for example ensure the spring rate of the lower layer is much lower than the upper layer. My Nirvana dual layer isolation platform is based on just that concept, using very heavy masses and steel springs.
