Humble Bee wrote:Would it be a good idea to have them made out of stone? Like square pillars of granite say 10-15 cm high? And stick on some self adhesive rubber feet...
It depends on what the stands are going to be standing on!
In the perfect world, the best idea is to hold the monitor speakers rigidly in space so that the driver chassis and cabinet can't move at all. That's generally the format for large soffit-mounted speakers, and large stand-mounted speakers -- assuming the floor is solid. This requires a lot of mass and very rigid structures.
But if the mounting surface is lightweight and potentially resonant (like a table or shelf) , it's usually a better idea to provide a damped suspension of some kind, so that the speaker is held in a reasonably stable way, and any vibrations are isolated from the mounting surface.
This is where foams and cunning sorbothane-type designs like the Isoacoustics mounts come into play... and the Isoacoustics are extremely good provided you match the speaker weight to the stand correctly.
So, in your case, granite slabs would have quite a lot of mass so could provide a stable un-moving base if they are themselves placed on a very solid surface, and the Genelecs have isolating feet anyway to minimise the passage of vibrations... so it could work well... but if the surface the granite sits on is a lightweight shelf I'd probably just go with something like the Isoacoustics mounts.