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In Reply to: simple, affordable relatively speaking, pro isolation posted by tonemaniac on March 20, 2007 at 11:02:13:
Perhaps this is what you were hinting at regrading resonance graphs below?The web site claims these will 'absorb' frequencies down to x, but they don't bother to state what the level of attenuation is. This is pretty useless info if you ask me (I do realize you didn't!).
From the information offered, there is absolutely no way to determine even the potential effectiveness of such a device.
Your post does make for some interesting discussion, though. Among other things, it's quite obvious that many people still believe for some reason that placing their gear on something as rigid as granite can somehow contribute towards isolation. Rigid materials do not isolate, regardless of how heavy they are; in fact, they do just the opposite: they couple. Coupling is a necessary part of any vertical vibration management scheme, but if you believe rigid materials isolate, you're not managing vibration, you're just hacking.
This isn't to say placing granite under components won't change the sound of the component, and sometimes for the better, but this should not be confused with reducing the total amount of vibration traveling into or out of the component - you've only changed the nature of the component's environment relative to vibration.
Follow Ups:
I'd love to find a good retail source for superior grade industrial quality steel springs... the original oldie but goldie of vibration management.. a little math imagination suggest that you could stack a series of slabs and springs with their resonant frequencies in prime number series... (so no harmonic of one will resonate with a harmonic of the other).. would need a very low profile spring shape in order not to become ridiculously unstable, but once you've locked in your values there's never any bladder to adjust or electronics to fiddle with... just get the numbers right the first time
....instead of the usual air/rubber (or other compliant material) that many people mistake for a true air spring. Ture air springs employ only rigid materials to constrain the air, and since these materials tend to not be pourous, you don't have to constantly adjust them.The fact that we're talking about microscopic displacement, however, is probably why so many people have success with semi-rigid materials such as you'd find in constrained layer platforms.
-Pete
I'm investigating the use of dense gasses, either xenon or sulfur hexafluoride (a stable, nonreactive gas used for "blanketing" of reactive materials) as the inflating material... these are both about 5x times the density of air... although that isn't as exotic as it sounds, a scuba diver at 2 atm. or 64 feet below surface is inhaling compressed air of that density... I think this can be injected into these pods I see advertised in exercise catalogs, small inflatable disks... although a bicycle inner tube may work just fine, one of the physical parameters of gas that is interesting is *elasticity*... these differ considerably... it is probable that Xe and SF6 are not the same springiness, although closely related densities... and because they are larger atomic radius, they won't leak out nearly as quickly as air components will...
...with an innertube suspension.The vertical resonant frequency of an innertube suspension is actually much higher than most people realize. I'd offer some numbers, but this is very difficult to measure. Most people put a component on a tube, jiggle it, and then count the oscillations. This is not, however, a measure of the vertical resonant frequency.
The problem is that you cannot easily confine the motion of such a suspension to only the vertical. When a component is bobbing upon a tube, it is not linear vertical motion - it is actually a combination of pitch and roll (although the resonant frequency for *these* motions is usually quite low).
If you were to set up some vertical sliders or something so you could confine the motion to only the vertical, I'm confident you'd find the resonant frequency to be much higher than desireable (likely well into the audible region). You can get clever and try to mitigate this by putting feet between the component and tube, so that portions of the tube can expand as the portions under the feet compress, but I found it to not be worth the trouble. I got much better overall results and less hassle from a combination of constrained-layer platforms and roller bearings, with the rollers between the component and platform.
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