Unipivot tone arms

@helomech  Re: "Some unipivot tonearms (VPI for example) are poorly designed because they are inherently unstable, thus the tracking force is in a constant state of fluctuation as the tonearm traverses the record." 

Uhhh, no. They are no more unstable vertically, the axis of tracking force, than any other tonearm. There is no mechanism that accounts for what you describe, varying the vertical force simply from the arm moving laterally across the disc

As for the 'wobble', no one has ever been able to quantitatively measure any impact of the unipivot bearing during playback. It only makes inexperienced users uneasy during cuing. 

Finally, a unipivot bearing, by design, is incapable of rattling, chattering, or moving forward and back during playback. 

That's it X, Y, and Z axes. There is no 'inherent instability' in a unipivot arm during playback. 

What you describe sounds more like a cartridge compliance/arm mass issue which I'll affect any improperly paired arm and cartridge. The classic example being a low compliance MC mounted in a low-mass tonearm. We knew this 50 years ago when people tried mounting an Ortofon or Supex MC in a Grace 707 or Infinity Black Widow tonearm. Those bad matchups yielded a very high arm resonance frequency that wouldn't track well and lacked bass. The reverse was an ADC XLM or Sonus Blue (both very high compliance carts) in a Technics or Denon medium-high mass arm. The too-low resonant frequency was extremely susceptible to footsteps, and often the cantilever suspensions just failed from trying to push around a high mass arm. 

If you want an arm whose tracking force is unimpacted by warps and such, then get an arm with spring loaded rather than gravitational VTF, like a Rega 330. 

@helomech First, you need to quantify the amount by which VTF varies over any vertical displacement (warp), say 5mm. That would be a seriously warped record.

Next you need to assess any impact that has on the cartridges tracking ability. And the map those, if any, to changes in SQ that can be attributed to those variations in tracking force, and not the warp itself. 

Finally, you need to assess any variation in VTF as a function of arm length, as well as changes in Stylus Rake Angle (SRA). 

Let's throw in one last variable, F=MA. To function at all, the stylus and associated motor, MC, MM, or MI, must move relative to the cartridge body and arm. Ideally the arm mass would be infinite, and the resistance to movement vertically or laterally should be zero. Obviously mutually exclusive requirements. Instead, we are left with a mass (the arm) suspended by a compliant spring (the cantilever, stylus, and it's suspension) that results in a resonant system that has been objectively determined to be optimal around 9-10Hz. This enables the relative motion and generation of the electrical signal, while not being excited by the lower warp frequencies. Get that too low and even a small warp can throw the stylus out of the groove. Too high and 'the tail wags the dog', the system is too stiff and the sylus/cantilever pushes the tonearm, wiping out the bass. A dancing bear, to be sure - the miracle being mechanical not that it dances well, but that it dances at all.

With that data, you can begin a conversation on this dynamic system. Until then, the model is incomplete, and the discussion theoretical at best.