The lightning rod analogy is very inappropriate. The whole assertion, implied here so often, that the earth beneath our feet serves as a universal "ground" for all mechanical vibration the way it serves as a ground for electrical charge, is seductive but without basis. Common experience tells us it's not so. We've all felt the ground acting as a source of vibration.
A related but separate idea that is very suspect is that we know how to design mechanical systems that transfer vibrational energy in one direction but not the other. Again, analogizing electrical systems with mechanical systems would suggest that this should be true, but the analogies themselves are fallacious.
Another thing: Thinking of isolation (or absorption) and coupling as opposites that can be achieved in any practical application is appealing and makes for great audiophile arguments, but it's really of little use in seeking the right kind of vibration control in your system. I'd suggest that every effective vibration control approach relies on both coupling and isolation/absorption.
The basic idea is to use coupling to make your audio component just a piece of a larger mechanical system that can deal with the vibrations to which your component is subjected. The larger system should have the characteristic of absorbing vibrations that are harmful to the propagation of the audio signal and releasing that energy (it has to go somewhere) in a way that is not harmful to the audio signal. Thus, the system has to have a sink for harmful vibrations, and the parts of the system have to be coupled together in order for that sink to be of any benefit against vibrations generated by or reaching the component.
We might place magazines or a specially designed, heavy block on top of a component, using gravity to do the coupling that effectively changes the component's cabinet so as not to resonate at harmful frequencies. We might put the component on gel footers. Gravity couples the component to the compliant footers, which absorb detrimental vibrations and dissipate the absorbed energy as heat. We might put the component on a Neuance, BDR or some other shelf with appropriate energy dissipation properties. Again, gravity acting on the mass of the component does the coupling. We may seek to use cones or weights to increase the coupling of the component to the shelf, but then we have to be careful about the vibrational qualities of those items that we've introduced into the system. We might couple our components to a heavy, sand-filled rack or rack with suspension system, depending on the rack itself to serve the absorption and isolation functions.
As an extreme, we could mass load and clamp our component to a rack whose legs are sunk into a concrete piling buried deep into the ground, in an attempt to make our vibration control system really huge and use the earth itself as the sink. If we chose our materials right, this should have benefits -- certainly floor-borne vibrations would be eliminated -- but I don't know how much of a problem ground-borne vibrations would be. I would bet that you would experience a net gain, but anyway, that is getting a little impractical.
I really am unconvinced that any commercial equipment rack relies on the principal of coupling the component to the ground for its success. Such a rack would be way too specialized. It might work on a concrete pad, for example, but, as Fiddler has said, how could this rack be effective for audiophiles that had their systems on any floor but the ground floor or basement?
In Audiogon discussions, we've come to associate Sistrum equipment with the claim of "draining vibrations to the ground". But Robert of Starsound has posted that, by design, Sistrum racks vibrate like crazy, and he described the shelves of the racks as "rattle traps". To me, this sounds like a rack that derives it's effectiveness from materials and design that allow the rack to dissipate absorbed energy at frequencies too high to significantly affect the propagation of the audio signal. This is a strategy that is used by makers of rigid, lightweight equipment.
I'm not a person with any special technical expertise, but I do try to understand things in a practical, hype-free way. Please feel free to comment on my analysis.
My real point is that enjoying high fidelity sound really is a more complicated task than can be accomplished by following dogmas like "only use coupling" and "only use isolation". Coupling vs. isolation is a false dichotomy. I've done some but not a huge amount of experimentation with vibration control. I know it makes a significant difference, but I hope anyone just starting out will not be intimidated from experimenting with different approaches, including -- horrors! -- mixing so-called coupling devices with so-called absorption devices. As is the case with many other aspects of hifi discussed on this site, simple, universal formulas about hifi make for good debates and marketing pitches, but relying on them to build your system is a fool's errand.
A related but separate idea that is very suspect is that we know how to design mechanical systems that transfer vibrational energy in one direction but not the other. Again, analogizing electrical systems with mechanical systems would suggest that this should be true, but the analogies themselves are fallacious.
Another thing: Thinking of isolation (or absorption) and coupling as opposites that can be achieved in any practical application is appealing and makes for great audiophile arguments, but it's really of little use in seeking the right kind of vibration control in your system. I'd suggest that every effective vibration control approach relies on both coupling and isolation/absorption.
The basic idea is to use coupling to make your audio component just a piece of a larger mechanical system that can deal with the vibrations to which your component is subjected. The larger system should have the characteristic of absorbing vibrations that are harmful to the propagation of the audio signal and releasing that energy (it has to go somewhere) in a way that is not harmful to the audio signal. Thus, the system has to have a sink for harmful vibrations, and the parts of the system have to be coupled together in order for that sink to be of any benefit against vibrations generated by or reaching the component.
We might place magazines or a specially designed, heavy block on top of a component, using gravity to do the coupling that effectively changes the component's cabinet so as not to resonate at harmful frequencies. We might put the component on gel footers. Gravity couples the component to the compliant footers, which absorb detrimental vibrations and dissipate the absorbed energy as heat. We might put the component on a Neuance, BDR or some other shelf with appropriate energy dissipation properties. Again, gravity acting on the mass of the component does the coupling. We may seek to use cones or weights to increase the coupling of the component to the shelf, but then we have to be careful about the vibrational qualities of those items that we've introduced into the system. We might couple our components to a heavy, sand-filled rack or rack with suspension system, depending on the rack itself to serve the absorption and isolation functions.
As an extreme, we could mass load and clamp our component to a rack whose legs are sunk into a concrete piling buried deep into the ground, in an attempt to make our vibration control system really huge and use the earth itself as the sink. If we chose our materials right, this should have benefits -- certainly floor-borne vibrations would be eliminated -- but I don't know how much of a problem ground-borne vibrations would be. I would bet that you would experience a net gain, but anyway, that is getting a little impractical.
I really am unconvinced that any commercial equipment rack relies on the principal of coupling the component to the ground for its success. Such a rack would be way too specialized. It might work on a concrete pad, for example, but, as Fiddler has said, how could this rack be effective for audiophiles that had their systems on any floor but the ground floor or basement?
In Audiogon discussions, we've come to associate Sistrum equipment with the claim of "draining vibrations to the ground". But Robert of Starsound has posted that, by design, Sistrum racks vibrate like crazy, and he described the shelves of the racks as "rattle traps". To me, this sounds like a rack that derives it's effectiveness from materials and design that allow the rack to dissipate absorbed energy at frequencies too high to significantly affect the propagation of the audio signal. This is a strategy that is used by makers of rigid, lightweight equipment.
I'm not a person with any special technical expertise, but I do try to understand things in a practical, hype-free way. Please feel free to comment on my analysis.
My real point is that enjoying high fidelity sound really is a more complicated task than can be accomplished by following dogmas like "only use coupling" and "only use isolation". Coupling vs. isolation is a false dichotomy. I've done some but not a huge amount of experimentation with vibration control. I know it makes a significant difference, but I hope anyone just starting out will not be intimidated from experimenting with different approaches, including -- horrors! -- mixing so-called coupling devices with so-called absorption devices. As is the case with many other aspects of hifi discussed on this site, simple, universal formulas about hifi make for good debates and marketing pitches, but relying on them to build your system is a fool's errand.