Bad Vibes! Page 6
What began---with the likes of Tiptoes and Sorbothane pucks---as a cottage industry within a cottage industry has evolved into a bewildering array of products, all promising to enhance the resolution of our cherished systems. Most of these devices do result in a noticeable change in the sound of one's system, often for the better. However, the prospective buyer must understand that the changes wrought by some of these vibration-control products are primarily a function of tuning. In other words, they merely shift the frequency and level of offending resonances around in the system, hopefully achieving a more pleasing balance.
Like many of you, I use cones and spikes for coupling certain components---with good results. However, a basic understanding of how to use cones within the mechanism of rigid coupling will not only help to get the most out of them, but will contrast their tuning benefit with the overall increase in resolution resulting from more elaborate methods of equipment support (for example, exceptional pneumatic isolation systems). As I related earlier, my experience is that the subjective improvement resulting from effective pneumatic isolation is clearly different in kind, not just in degree, from that afforded by resonance tuning, and can be quite dramatic, particularly when used with source components---or, better yet, the whole system. Confusing the tuning of system resonances with an across-the-board enhancement of resolution can be a trap that leads the unwary down the slippery slope of tonal manipulation.
Making The Connection: Of Modes & Nodes
Rigid cones actually create a frequency-selective coupling between any two or more structures, acting somewhat like random low- and high-pass filters. Which frequencies are de-coupled vs which are coupled between two specific objects will depend primarily on the modal patterns of the two connected surfaces and the placement of the cones relative to each. In other words, their beneficial effect will generally not be uniform over a broad frequency range, or be equally translatable to a wide variety of components in different environments. If we map out the composite modal shapes of a given platform, we will find areas of very large relative motion, and
points of minimal movement known as "nodes"---actually, these are points of zero displacement. Try visualizing a long ruler, on edge, moving like a sinewave. Now imagine a straight line cutting through the center of the sinewave and representing the ruler at rest. Even when the ruler is flexed, certain points will remain at rest along the center line; these are the nodes. The points of maximum excursion represent peaks of the bending modes. Expand this view to a three-dimensional platform and the complexity of vibrational forces becomes clearer (see "The Rigid Body Concept," fig.3).
The pointed tips of a cone will tend to enhance the mechanical interface between the cone and the structure it touches. If, through empirical experimentation, the tips of each of the applied cones are located at minimum nodes on a supporting platform, a reduction in the amount of added system resonance would result. This improved mechanical interface due to the tip's contact with a narrow point on a platform (at least on one end) provides the primary benefit of cones over standard solid equipment feet (which are usually broad on both ends). On the other hand, the broad, flat end of the cone will generally have a poorer mechanical interface with the bottom of a component or platform to which it is coupled---more like that of the stock feet.
In the case of an audio component with its irregular distribution of modal shapes, it's likely that the contact area of the cone's flat end will overlap areas that vary in degree of motion. You'll probably be better off with cones or spikes that are relatively narrow on both ends. Regardless, if either end of the cone is placed at a point of maximum modal displacement on its connecting surface, not only will all of the original floor vibration couple to the platform, but those frequencies which are related to the resonant modes of the platform---and stand, component, etc.---will be amplified. Also, additional resonances will likely be generated and added to the mix, leading to probable changes to the system's tonal balance, and---well, you get the picture. Cones can be a mixed bag.
The ideal scenario of rigid coupling is predicated on our ability to perfectly align the minimum nodes on a concrete floor with those on our damped, rigid platform. The chances of this happening in reality are about as likely as folding the continent in half and having the Rocky Mountains fit perfectly with the Adirondacks. The much larger concrete floor will have its own varied resonant modes, but since the platform's size is so small compared to that of the floor, the floor is "seen" by the platform, via cones, as a more or less rigid body. Note that, with respect to a suspended wooden floor, the mutual excitation of resonant modes between the stand, platform, and floor can be much more complex and unpredictable. On wooden floors, try locating your equipment near structural support beams or other weight-bearing regions. If possible, also use house jacks to shore up the areas of the floor directly under and around your equipment rack and speakers.