Limited vibration attenuation provided by composite cones that possess a degree of damping may provide some latitude with respect to their placement…
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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.
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…
Fundamentals of Isolating Suspensions
In Sidebar 1, I explained, graphically, how the resonant frequencies of a solid structure relate to its modal activity when stimulated by vibrations. It is apparent that, regardless of which method of rigid coupling, damping, or a combination thereof is used to minimize the negative impact of vibration on a platform, stand, or component, the best one can achieve through these means alone is a reduction in amplitude approximating the ideal rigid body line.
In Sidebar 1, I explained, graphically, how the resonant frequencies of a solid structure relate to its modal activity when stimulated by vibrations. It is apparent that, regardless of which method of rigid coupling, damping, or a combination thereof is used to minimize the negative impact of vibration on a platform, stand, or component, the best one can achieve through these means alone is a reduction in amplitude approximating the ideal rigid body line.
To further reduce the impact of vibration, we must isolate any rigid structure from outside…
On a number of occasions we have commented on the effects of an amplifier's output impedance on a system's performance. A high output impedance—such as is found in many tube amplifiers—will interact with the loudspeaker's impedance in a way which directly affects the combination's frequency response. The Cary CAD-805, for example, has a lower output impedance than most tube amplifiers, and should be less prone to such interaction. Some months back—before the CAD-805 arrived—I investigated this phenomenon in conjunction with measurements for a forthcoming review of the Melos 400 monoblock…
A letter in response appeared in April 1994 (Vol.17 No.4):
Thomas J. Norton's "Questions of Impedance Interaction" in January (p.109) showed that a ghostly echo of a loudspeaker's impedance modulus can be imposed on its frequency response by virtue of an amplifier's source impedance acting as the top limb of a potential divider. Mr. Norton illustrated the effect with some specific graphics, but the data can be usefully generalized by means of a simple rule arising from the ohmic arithmetic.
Assuming a worst-case situation of very large impedance undulations, with, for instance,…
Although Kentucky loudspeaker manufacturer Thiel has produced some standmounted models for home-theater use, all of their serious music speakers have been floorstanders. Enter the PCS: even though styled to match every Thiel speaker since the groundbreaking CS5 of 1989, the 19"-high PCS sits on a stand, not the floor.
All the PCS's drive-units are made in-house by Thiel, and the heart of the speaker is the coaxial tweeter-midrange unit, similar to that used in the Thiel CS2.3. As Brian Damkroger discussed this unit at length in his January 1999 review of the '2.3 , I will refer you to…