Regards, Dlaloum: TA = ToneArm. Vibration analysis is such a complicated branch of physics there may be a few professionals who can understand all of it, you can be assured I'm not one. Perhaps not a "black art" but it is a subject prone to generalizations. Building on your comments and Henry's most recent post, permit me a few?
My rudimentary understanding is that a vibration, emitted from a source point, “propagates” and follows the path of least resistance, somewhat like the ring of waves seen when a rock is tossed into a puddle. When these vibrations meet a border between two surfaces, they split, part reflected back and the rest continuing along the second body. How much goes where depends on the acoustical impedance of these materials.
Resonances are characterized by selection of materials, geometry or various devices attached to this body. These resonances may be reflected, amplified and reflected again until the source of the excitation ceases. Mass, materials, wether hollow or solid, holes, stress, associated materials this body is in contact with, texture or coating of the surface (skin effect) and physical configuration (straight/curve/taper/length) all have a consequence in frequency, amplitude, or transient behaviors. From my layman's perspective (read poorly supported opinion), if I intentionally selected a questionable design it would incorporate a removable headshell, and I did.
All this is so very complicated some simplifications are, for me, a neccessity. There are three means of address or correction available in my limited tool kit: Vibrations can be damped, reduced, or tuned. Selection of headshell material and mass are means of addressing these concerns, the choice of wether to retain the o-ring at the coupling is another. Cartridge isolation is also an influence long recognized. I'm reminded of the dimpled triangular alu. plate Grado offered as an option in the late '70's. There are some who are now exploring hard-points between the cartridge and headshell, "tip-toes" for your cart.
Although some of the above statements are probably accurate, I hope you'll correct me where wrong. None the less, a trial and error approach still seems sensible. Was it Voltaire who said, IIRC, "Best" is the enemy of "Better"?
Peace,