What is the accepted audio wisdom and its basis? With my common sense, I think if the cartridge can be isolated from the arm then problem of resonance can be avoided.
There are many methods of damping or isolating tonearm from plinth, but I don't know about any other method of isolating catridge from tonearm.
Older SME arms for example use tiny rubber grommets between the wood screws used to secure the arm base to the plinth. The rubber grommets are placed between baseplate and plinth, threaded through the wood screws. This provides some amount of damping BUT the wood screw that passes from the base plate into the plinth below is still a short circuit and vibration still passes through. It's not an isolation. It only dampens somewhat.
Another unique dampening mechanism is the one used in Townshend Rock. The headshell is given an extension and this extension has a paddle attached to it. This paddle swims in a silicon oil. The container that contains the silicon oil can be swung into position, or away from the top of the spinning record. This damps the extraneous vibration closest to the cartridge. Supposed to work very well.
Others use similar silicon oil near the pivot. For example, KABUSA sells after-market damping devices for Technics SL 1200 arms.
But the above examples are damping of one form or another.
Others use a pod separate from the main plinth for mounting the tonearm so that the vibration from motor to plinth does not directly affect the tonearm. But the plinth and pod, though separate structures, are usually mounted on the same support platform. So the isolation is partial, as in theory some of the vibration would still pass through the support structure to the pod, but it would have been very substantially attenuated. But it's not a cakewalk to maintain correct mounting distance for a separate pod. And there is also the question of stability of the pod itself, besides having to build plinth and pod as independent entities.
Heavy mass plinths are another popular damping mechanism, especially effective with high torque idler drive TTs.
The isolator I cloned is made of three layers - one sheet of steel with a screw threaded through it to attach it to the headshell. One layer of the isolating material is glued onto the surface from which side the screw head is threaded in. Appropriate sized holes are cut at the position of the screw head. One more layer of isolation material is then glued to the first layer. No cutouts done on this later. Third layer is isolation material again, with appropriate holes cut out for screw heads. This is finally glued to the lower steel plate. This plate attaches to cartridge through two screws threaded through it. I have filed down the thickness of the screw heads so that screw heads doesn't protrude and touch the other steel plate. There is no metallic circuit (the screw attaching the headshell does not physically touch the other plate or screws that connects to the cartridge) to pass on the vibration in either direction. The assumption here is that the isolation material is good enough to dissipate all unwanted vibrations without passing it on to the other coupled structure. At least that's the theory
We know how cones drain vibrations from cabinets and speakers. Well, people have extended the concept to headshell-cartridge interface. They use a spacer with tiny cones inserted on one surface of the spacer. It needs capability to machine tiny parts. Use three grubs screws on each surface and sharpen the tip of the grub screws to a conical point. That's it! Non-cone surface goes to cartridge top and coned surface goes to headshell. Of course the assumption here is that headshell's bottom surface is flat to be able to mount it properly. Supposed to improve the sound in much the same way a cone under a speaker does.
There are many ideas - ranging from the seemingly foolhardy, or dubious to outright brilliant. How much benefit they actually bring about, considering the cost, time, and difficulty involved - that's the thin line separating wisdom/experience from knowledge/information and general audiophilia (progression usually being in the reverse order). Personally, I believe many small and cheap or free tweaks can bring about substantial improvements in the sound. I have been experimenting a lot with a couple of friends (Hi, fellow loonies
) on sand and heatlon foam damping on top and below gears. We've come to some conclusions and it has definitely helped sharpen my sound further. We need to experiment further with their setups. And it has been a dirt (literally! pun intended) cheap exercise
