Hi Bricolo
IME experience granite is as bad as it gets. Most stones have a strong intrinsic sound due to resonance, high mass and parallel sides. The only exception i can think of is slate but it also requires attention. Some people absolutely love the strong resonating bass which granite imposes upon everything so it's pterry much a question of taste.
There is some truth in the claim that the best stand is shelfless as it deals well with air-borne vibrations but structural vibrations affect it as much as normal stands and you still need some way of isolating components.
Without criticising your design it appears to provide good coupling between shelves and supporting pillars but minimal isolation. In this case you need to individually isolate each component which works but is quite painful to achieve.
A simple, yet effective shelf design is a constrained layer sandwich, similar to Simposium. Central to this is polyethylene closed cell foam in the mid layer which behaves similarly to an air bladder. I use foam with 45kg/m3 which appears suitable for medium heavy loads. On both sides of the 15mm foam core i have layers of baltic birch/pvc and thin (1mm) alu. This platform provides very good isolation, comparable to an air bladder without the bladder annoyances. Combining materials with different density and resonances pretty much removes any audible signature. Even reducing the number of layers to three still provides most of the benefits.
To use a constrained layer platform with a stand of your design you have to make sure that the vertical pillars are only bolted to the bottom layer of the platform, otherwise you'll lose most of the isolation.
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My DIY Rack project
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