One example of this misconception, frequently applied in audio, is the use of massive slabs of granite or marble alone. Many audiophiles expect that…
search
Removing the many sources of vibration is impractical, so we must next isolate our rigid structure from floor- and stand-borne vibrations. The concept is simple, but practical attempts to address these two separate aspects of vibration control are often mixed together in the mistaken assumption that, since the physics of vibration in rigid bodies and suspensions share several traits, similar criteria should be followed for the design of each.
Platform Construction
Very few structural materials deal efficiently with the requirements of both rigidity and damping. Some materials address one aspect while degrading the other. Therefore, better performance is usually obtained by a composite approach to platform or shelf construction. Mass can be a desirable quality in a material used for equipment supports as long as it contributes to dynamic rigidity. But excess mass that does not aid the cause of stiffness may actually be detrimental, as it can cause a reduction in the platform's resonant frequency, requiring extra damping…
Very few structural materials deal efficiently with the requirements of both rigidity and damping. Some materials address one aspect while degrading the other. Therefore, better performance is usually obtained by a composite approach to platform or shelf construction. Mass can be a desirable quality in a material used for equipment supports as long as it contributes to dynamic rigidity. But excess mass that does not aid the cause of stiffness may actually be detrimental, as it can cause a reduction in the platform's resonant frequency, requiring extra damping…
This may be an appealing concept, but it just doesn't work that way. Certain ambitious advertising campaigns for these devices make it sound as if all the bad vibes will be sucked out of your audio gear as if by a hose containing a one-way check valve (often made of exotic materials and special shapes), while simultaneously preventing any floor or rack vibrations from coupling to the component via the cones. This idea is misleading at best, even though rigid coupling can play a critical role as an adjunct to an overall vibration-reduction plan incorporating isolation and damping. But before…
For those fortunate enough to have concrete floors, the modal waves are spread out, and the peaks of the waves are far apart compared to those in the platform or stand. From the point of view of the platform, it would be similar to driving over a broad speed bump. You'll notice it as a gentle rolling, but nothing like hitting a sharp, narrow bump. In other words, most vibrations transmitted to the floor, from whatever source, will couple directly through the cones without much amplification of the modal activity from the floor. In any event, there isn't a whole lot we can do about floor…
Since most chassis have anything but uniform resonant signatures, the problems encountered in connecting a platform to the floor are compounded further when spiking a component to the top of the platform mounted on a stand. It's virtually certain that the irregular modal profiles of most component's thin enclosures will not only encourage significant amplification of related external frequencies, but the creation of new resonances as well.
Limited vibration attenuation provided by composite cones that possess a degree of damping may provide some latitude with respect to their placement…
This may all seem like a minor issue of semantics, but it's important to understand the distinction in order to prevent conceptual errors when deciding how best to deal with a particular vibration problem. Complete damping of a non-transducing component would imply the absence of any offending resonances to tune. This type of electronic component should act as an inert conduit for the signal; any resonances added to that signal via, say, an amplifier chassis, are, by definition, distortion---no matter how sonically pleasing.
Suspension Basics
The concept of a successful suspension is…
Elastomer Supports
A rudimentary version of the traditional damped suspension is formed when elastomer materials such as Navcom or Sorbothane are used to support a heavy preamp or amplifier, either directly or with an intervening platform. These elastomer pucks can be quite effective at isolating moderate amplitudes of vibration ranging from the upper bass and above, and will generally have a fairly predictable performance throughout this range of frequencies when used with a wide range of gear. Also, a broad band of vibrations generated within the component is partially damped by these…
A rudimentary version of the traditional damped suspension is formed when elastomer materials such as Navcom or Sorbothane are used to support a heavy preamp or amplifier, either directly or with an intervening platform. These elastomer pucks can be quite effective at isolating moderate amplitudes of vibration ranging from the upper bass and above, and will generally have a fairly predictable performance throughout this range of frequencies when used with a wide range of gear. Also, a broad band of vibrations generated within the component is partially damped by these…
Though some of these reactive spring-based systems have resonant frequencies that low, I feel that they simply are not as efficient as a good pneumatic system, and the stability of some is questionable. When properly implemented, air-based isolators attenuate much lower amplitudes of very-low-frequency vibrations than even the best spring designs (with the exception of the new NSM system offered by Newport, which is a little too expensive for home audio in its present configuration).
Take Andy Payor's Rockport Cappella and Sirius II turntables, for example. Each of these 'tables contain a…
Further Reading
Interested readers can reference the following for further information:
Interested readers can reference the following for further information:
Fundamentals of Noise and Vibration Analysis for Engineers, M.P. Norton, Cambridge University Press, 1989, reprint 1994 (highly recommended).
Mechanical Vibrations, 4th edition, J.P. Den Hartog, Dover Press.
Shock and Vibration, 3rd Edition, Cyril S. Harris, 1988, McGraw-Hill Books.
Newport Corporation's 1995 Catalog, Chapter 16, "Vibration Control," 791 Deere Ave, Irvine, CA 92714, Tel: (800) 222-6440.
Acknowledgment
I'd like to thank Newport Corp. for the kind…
The Rigid Body Concept
The performance of a table-top or platform is a function of the rigidity of the structure and the effectiveness of any applied damping. Each solid object will have many resonant frequencies and associated bending modes. The lower the dominant resonant frequency, the higher the modal displacement. Generally, the first several frequencies/modes are the most significant, and largely define the vibration performance of a given platform. By using materials for constructing audio platforms that are very stiff, the dominant resonances can be shifted to a higher frequency…
The performance of a table-top or platform is a function of the rigidity of the structure and the effectiveness of any applied damping. Each solid object will have many resonant frequencies and associated bending modes. The lower the dominant resonant frequency, the higher the modal displacement. Generally, the first several frequencies/modes are the most significant, and largely define the vibration performance of a given platform. By using materials for constructing audio platforms that are very stiff, the dominant resonances can be shifted to a higher frequency…