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In the Forum: Audio Discussions
In the Thread: Mastodont DIY Rack: Wall Mount?

Post Subject: Sand contextPosted by N-set on: 12/1/2013

Paul, I can olny speak within my context and with no audio tests, only knuckling.
I use pure silca sand in 3 granulations (2 of them fine unfortunately), mixed with steel shots.

Of course the sand is there to quench the steel ringing. But while achieving this very nicely
(I hear zero ringing, only deep, bell-like "thunk") it adds something: lowers the construction
resonances and makes them less damped (the effect of the added mass). In my case I clearly feel
gelly-like subsonic vibrations, lasting >1s !!! Now everything depends on the context how the support is used.
For electroncs I'd not care much with <5Hz.
But I have the air springs resting on the columns with ~3-5Hz fres. The frame with its own ULF vibrations in that range instead of
providing a solid support for the springs adds them additional very hard work. You see what I mean? I'd prefer to have frame resonances
somewhere higher, 10-15Hz region where the speings start to work efficiently.

Perlite: yes, it's very light. I have it now in the upper table holding the springs. When knuckled at some points
it does have a faint ringing in the 2-3kHz region, barely audible also through the slate (!),
so the perlite is not so effective but I needed some additional kilos to be saved here.
In the horizontal braces I have a third material: perlite ore. This is unexpanded perlite, denser than the expanded one but
lighter than the sand (1.1g/cm3 vs ~1.6g/cm3). It seems to work nicely where it is: the initial knuckle tone is higher but lasts shorter (feels dumber
vs organic with the sand), there is some LF vibration but not so pronouced and I do not feel much of a subsonic one.
I'm thinking of buying a simple guitar piezo and looking at the resonances instead of shooting in the darkness.

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