Perhaps I've 'executed' my granite slabs correctly. Here is a pic of a vibration readout from my phone while laying atop an empty 22"x22" granite shelf I use while being rapped with my brass hammer. As is clearly displayed, after the initial knock and rebound there is essentially no ringing between the hammer strikes other then that last one, where I struck quite hard. Just a bit of low level ring on that one. The strikes were about in the center of the piece and spaced about 2 sec between.
I also rapped the side-edge of the granite slab, but the initial spike was about 1/3 the height of these and, again, essentially no ringing.
Think you'll be good with granite.
Almost forgot to mention, the Allman Brothers' "Live at the Fillmore" was rocking & rolling on the TT on the shelf about 4" to the right of the one I was striking and there was zero noise feed back thru the system that I could hear.
