Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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Actually, spikes couple - they don't decouple.

Posted by David Aiken (A) on October 30, 2004 at 15:53:23

In Reply to: Re: Spikes for a (heavy?)rack posted by pkell44 on October 25, 2004 at 18:58:31:

Spikes and cones are not decoupling devices - they actually couple what is sitting on them to what is below them.

Having said that, it does make an audible difference which way the spike/cone is pointing so obviously they don't pass vibration in the same way in both directions. My experience is that less low frequency vibration is transmitted from the point end to the other end than is transmitted from the other end to the point. So they aren't perfect couplers (nothing is) and to the extent which they don't couple perfectly they could be said to decouple or isolate.

On the other hand, spring systems and constrained layer platforms isolate (or decouple). That means they stop vibration passing from one side to the other. Of course nothing isolates perfectly so these could be said to couple to some degree. In particular spring systems only start to isolate at frequencies above 1.4 times the resonant frequency of the spring system. Below that frequency they not only pass vibration but actually magnify it with maximum magnification occurring at the resonant frequency.

Both coupling and isolation have noticeable sonic effects and both are valid forms of vibration control with their own specific advantages and uses. Still, the fact that spikes and cones have an effect upon transmission of vibration between a component and a support, and transmit less vibration in one direction at some frequencies than they do at other frequencies does not make them an isolation or decoupling device.

And both coupling and isolation, used appropriately, can produce positive changes in the overall sound of a system. It isn't a matter of coupling being always bad and isolation being always good, a view that some people seem to hold religiously. In fact I think a combination of both, in conjunction with damping of components and shelf surfaces, produces the best results overall.

And while 3 point support is commonly recommended over 4 point support because 3 points is always stable, I have seen comments that 4 points are to be preferred because that avoids having 2 corners unsupported and free to flex. I've found that 4 point support is better under some components like my sub because the motion inherent in their operation can actually induce rocking on a 3 point support. I use 3 points successfully elsewhere so my take on this theory these days is that I'd start with 3 points, but I would also check to see whether 4 point support made an improvement.

Read Shannon Dickson's article "Bad Vibes" in the archives at Stereophile's web site for a good overview of the physics and techniques of coupling and isolation.

David Aiken

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