Regards, all: I'm quite impressed by the depth of experience reflected in the comments above. Except that Gibson fellow. He's a hack and prone to gross exaggeration.
Viridian suggests that the removal of the tonearm from the plinth tends to remove plinth based excitations from the tonearm.
Atmasphere proposes precise coupling of the platter bearings and tonearm base, LewM seems to agree.
Richardkrebs writes: "A skeletal design makes this goal more difficult to achieve since we are introducing the support structure, shelf, platform, into the equation. It effectively becomes the plinth. Related to this is the minimization of joints and material changes in the platter-arm loop."
Ct0517 (hi, Chris) shares this experience "An exercise of Function over Form for me. The tonearm attached to the POD is a leading example of this.
If for some reason one "hears" a mismatch in resonances, the ET2 (tonearm) provides resonances tuning capability."
Halcro: "I simply use my ears and listen to actual examples BEFORE I blindly theorise." Henry implements a tweaked wall mounted shelf and considers it a plinth. There has not yet been proof offered of unwanted movement in the spindle/pivot dimension but neither should one deny the possibility.
These things are known for certain:
The greater the mass, the lower the vibrational frequency. Beams (tonearms) with a lesser mass vibrate at a higher frequency.
Vibration takes place when a system oscillates under the action of disturbance. A system will vibrate at one or more of its natural frequencies as determined by its mass and stiffness distribution.
Friction, viscous damping and mass acting as a vibrational sink influence the decay and amplitude of vibration. Damping has very little effect on eigen frequency of a system but is of some importance in limiting the amplitude of resonance.
These resonances are influenced by the different boundary conditions of a tonearm.
Our concerns are complicated if a tonearm is viewed as a semi-fixed beam with a "lumped" mass (cartridge) at the end. Boundary (reflected) resonances are observed at edges, shoulders and at the junctions of differing materials. Boundary resonances have been measured at levels greater than the original disturbance.
We are now confronted by Young's modulus, the Eigen frequency of the system, the mass of the tonearm and the interaction of boundary resonances, all of which are capable of interacting and consequently generating additional resonances.
Voltaire wrote "Best is the enemy of better". As observed in the past, not all roads lead to Rome but many will. Neither is there a single avenue to the great city.
It would seem the first choice is that of tonearm, the remainder is a matter of tweaking for best outcome.
As Henry said, much more directly, "I simply use my ears and listen to actual examples BEFORE I blindly theorize."
Peace,
