Vibration control is a concern and yes everything sounds different. Glass, tile and stone all can be used but they ring and will impart hardness and glare. Wood is better and the sound you get will depend on the type of wood, thickness, and construction (laminated, slab, etc).
There's no reason not to put them directly on the floor. But if you do want something that works really good without spending much Nobsound springs are only about $30 a set of four and are phenomenal value. Way more improvement than you would expect for so little money.
Much better, but also much more expensive, Townshend Pods are springs that are much more carefully engineered than Nobsound and deliver a whole lot better sound. Much more extended, dynamic, and true to tone and timber of the instruments.
There's no reason not to put them directly on the floor. But if you do want something that works really good without spending much Nobsound springs are only about $30 a set of four and are phenomenal value. Way more improvement than you would expect for so little money.
Much better, but also much more expensive, Townshend Pods are springs that are much more carefully engineered than Nobsound and deliver a whole lot better sound. Much more extended, dynamic, and true to tone and timber of the instruments.