Fine Tunes #32

As an audio journalist "servicing" the High End (ouch!), I surf the Web waves to see what's going on on the various audio newsgroups and bulletin boards. Sometimes the Net resembles the Concorde going down, the crash video'd by a passing French motorist: Ashen faces pressed against car windows driving slowly by to check out the carnage.

But occasionally the Net can be fodder for "Fine Tunes," and the issue of whether or not placing cone footers under an audio component has any audible effect is hotly debated in Tweakdom. Some feel that cones create some sort of diode effect, passing energy more effectively one way than the other and thus changing the sound based on their orientation (point up or point down). Someone calling him/herself "JDK" put up a fascinating post on the Audio Asylum Tweaks Forum regarding footer cones and a theory about how they function:

"Depending on which direction the cones are pointed and the type of material that they're used on, the results will vary. In my experience, using cones facing point-up into components will typically result in a much looser, undamped bass response with poorer soundstaging. My comment is based on having some type of solid shelf or platform as a foundation. Flipping the cones so that they point down results in a much tighter, well-defined bass with a much more coherent soundstage. In terms of mechanical resonances, the parts that mate with the most cross-sectional area will be the most rigidly coupled. Those that have the least contact area will have the least coupling. There's greater coupling (more surface area contact) between the flat side of the cone and the component than between the tip of the cone and the shelf. This dictates an uneven exchange of energy taking place.

"Since the resonance of a large rack would be typically much lower in frequency than the much smaller and lighter component itself, the smaller cross-sectional area at the very point of the cone (when facing down) would not allow the longer, lower-frequency wavelength of the rack to travel back up into the component. The components' higher-frequency resonance (due to less mass) and shorter wavelength would be less hindered by the smaller contact area of the point, allowing a greater amount of energy to be 'drained' from it into the rack.

"I always assumed that I was allowing the 'rack resonance' to 'focus' at the components, with the points facing up concentrating the energy into the chassis. That's why I had muddier bass with less detail and definition. Having the energy concentrated away from the component and into the shelf always gave me the best results.

"Think of three very short vertical arrows pointing face down into a flat wood base. The arrows are spread out in an equilateral triangle and linked at their tops by horizontal braces. The arrows are all relatively stable, due to the mass loading of the braces and having two other points of contact at opposing ends of the triangle to help keep them balanced. If one arrow moves, they all move, because they're coupled together via the horizontal braces. This is equivalent to the component's chassis resting on three cones pointing down into a shelf on a rack.

"If you strike the base, the arrows might tremble or shake slightly. Due to their limited contact area at the tip and only being mass-loaded by their bracing, not much of the energy would pass into the arrows. Because each arrow moves at the same rate as the other two in the triangle and all are mass-loaded relatively equally, they would counterbalance each other and remain relatively stable. Most of the energy would be spread out and absorbed by the larger mass of the base.

"Now, if you apply the same amount of energy to the 'back' of the arrows as was applied to striking the base, it would make them penetrate or more rigidly 'couple' with the wood. [That seems to make sense to me.—JS] All the energy that was applied to the tops of the arrows is now 'concentrated' (instead of isolated) at the tips so that it now 'transfers' into the base. Unlike our shelf, which retains most of the energy and isn't able to pass it back up through the arrows because of their isolated points of contact, the arrows have the opposite effect and transfer the energy that was applied to them down into the base.

"The 'arrow' shape of the cones does 'double duty' to our benefit. The cones or 'arrows' in effect isolate the component from rack or floorborne excitation, yet 'couple' the majority of component or airborne resonance or vibration back into the rack. Seems pretty simple overall. Do companies sell 'isolation cones' and 'isolation feet' or 'coupling cones' and 'coupling feet'? Just wondering..."

I think JDK made the point, but another poster, "Sean," demurred:

"Obviously, mass comes into play in the situation. You're using the cones/points to alter the resonance point/amount of energy transfer between 'connected' or 'adjoining' materials. Depending on which way you have the point facing will be the difference between increasing or decreasing the coupling between the devices in question. The problem with minimizing contact points is that they're now physically less stable and far more susceptible to airborne vibrations or resonances. To help reduce these, one could 'mass-load' the component.

"Reducing one problem without addressing the others that you've now left yourself open for is not a step forward, but a lateral move. This is the very reason that many 'tweaks' show some benefits but are outweighed by their detractions. The full effect is not effectively dealt with or fully thought through."

Something to think about, tweakers. What's been your experience? Let me know...

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