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In Reply to: Do granite slabs work because they're granite, or because they're heavy? posted by MTZ on June 07, 2004 at 11:37:08:
Hi MTZ,In general, granite is not an appropriate vibration control matreial because it (and most other hard, rigid materials such as stone, Corian, glass, steel, etc.) ring when excited by vibration. In addition, many other materials (such as natural wood, wood cutting boards, plexiglass, acrylic, plastic, etc) are resonant and are also not the best choices for vibration control. When materials ring or are resonant they will impart those characteristics on the signal that is flowing through the component and aletr the sound (or the picture in a video system). The objectiove is to minimize or eliminate vibration and resonance so that we can faithfully play back the signal that is contained in the recording - not alter it by adding undue negative effects.
Some people will sometimes confuse the negative effects of the above materials. Granite will many times make the upper midrange and highs more prominant and some people may mistakenly describe the sonic result as "having more detail". This is a false presentation but that person may like the result because their system (or particular comoponents within their system) lack true transparency. In this case, two wrongs don't make a right because it would be MUCH more appropriate to assemble the components in the system to be innately transparent instead of adding a false effect of brightness that gives onlt the sense of more detail (but will actually be fatiguing over time).
Granite is massive but mass alone is not sufficient for proper vibration control. The mass must also be absorptive to be effective. Granite, and most other hard, rigid materials, do not dissipate vibration. The do transmit vibration and if they are coupled to the floor will allow flor-borne vibration to make its way into the component and compromise the signal.
Best Regards,
Barry Kohan
Follow Ups:
Hi All,I'd like to make clear that the hypothetical system I described was not meant as a criticism of anyone's particular system or any specific components.
A system can lack transparency as the result of a number of factors. It sometimes only takes one mismatched component or cable to send a high quality system in the wrong direction. Sometimes there are a number of causes that have to each be addressed. Likewise, room acoustics, AC quality, set up or misapplied tweaks and accessories can also have a negative impact.
My point is that it is best not to use vibration control (or any tweak for that matter) as a reciprocal tone control. If a system has weaknesses or excessiveness in particular areas we should root out the cause and cure it - not put a band aid over it.
Best Regards,
Barry Kohan
My understanding of the sandbox idea was that the sand dissipates the vibration and the mass of the granite/marble/rock is required such that new vibrations are minimal, due to the hefty weight of the material.In such a design the granite wouldn't be part of dissipating vibration but only part of preventing new vibration from creeping up to my turntable.
Right? Maybe I'm not understanding the design theory.
Hi MTZ,Thank you for your question.
I created the original Big Rock sand filled platform in 1985 and was issued a patent on the design in 1993. Virtually all versions of sand filled platforms that are discussed on audio forums are variations of my design. I do like to think that my long-term experience with the design has given me a few insights.
The interface between the component and the platform itself is critical. Even though the sand may provide some damping, the choice of material and the thickness of the material used between the component and the bed of sand will have a significant effect on overall performance. I have found that using a material that either naturally rings or is highly resonant will not provide the best performance. Granite (even when damped by the sand) will still be able to be excited above the minimum threshold desired. It will also store and transmit that unwanted energy into the component.
Best Regards,
Barry Kohan
So you would disagree with the accepted use of granite period? In your first post you said that stone, Corian, glass, steel, natural wood, wood cutting boards, plexiglass, acrylic, and plastic are all bad choices.I would ask what that leaves because I can't think of anything; if there were a material that has 0 resonance associated with it I think everyone would be using it for every audio application.
I suppose I'm not the first to ask this though so I'll run a search.
Material objects resonate. Their spectrum of "modes" (natural frequencies) depends on their shape and the stiffness of the materials from which they are made.All solid materials have a degree of stiffness. Think of this like a spring constant but in three dimensions instead of one. In general, the higher the stiffness, the higher the resonant spectrum modes will be in frequency, and the less motion will be associated with each mode. The force associated with the spring is proportional to displacement.
All materials also have some damping. Think of this like an automotive shock absorber, but again in three dimensions instead of one. Damping force is proportional to velocity.
By Newton's Second Law, F=M*A, there is also a force associated with acceleration. These three forces must be balanced, so one can write an equation that expresses the balance, and solve it for the motion.
The science behind resonance control is to select materials for stiffness and damping to a) get the job (ie, support a static load or transmit motion) done, and b) provide optimum damping. One can have too much as well as too little damping depending on the circumstances, so there is a best solution which requires effort to understand and fabricate. This is where vendors like Barry add value to your audio system, by providing the most economical solution that gives close to the optimum damping.
Some materials, like Plexiglas (acrylic plastic) and medium-density fiberboard, have more damping that others of similar weight and stiffness. However, it is very unlikely that simply making the required object out of these materials will result in an optimum damping solution.
Usually, the solution involves a composite, where another material such as Deflex (polyurethane), Dynamat Xtreme (butyl plus thin aluminum constraining layer) or a proprietary rubber compound such as Barry can obtain, with very low stiffness and very high damping, will be attached to a stiff, rigid material. Note that Dynamat Xtreme is easily available, but optimized by design for auto sheet metal. Unless your audio system is made from auto sheet metal, it will not provide an optimum solution to your rack and shelf damping requirements.
I'm not a dealer for Barry's products, but have met him and respect his engineering expertise.
I'm not a dealer for Barry's productsWell, according to the way you've registered you're not a dealer for any product. That clears things up because I was under the impression that you had a vested interest in Atma-Sphere and/or Glacier Audio.
I built my own clones of Atma-Sphere amps 8 years ago and have maintained contact with Ralph and Mark. I did help with the Glacier rooms at the 2004 CES and T.H.E. shows, but have no present business relationship with Glacier, Atma-Sphere, or any other manufacturer or dealer. I can't sell anything, but am happy to share my good experiences.
Hi MTZ,I have found very few situations where granite would the best material to choose for a particular application. You are correct when you state that all materials resonate. The key is to combine specific materials in a particular fashion to minimize the resonance and/or place the primary resonance point at a frequency that will do the least amount of harm.
Best,
Barry Kohan
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