What defines a good tonearm

So much misinformation here.

A properly designed unpivot arm does not rock due to stylus tracking simply because the design has the stylus aligned with the pivot point; there is no torsional leverage and the only degrees of freedom from the stylus are the planes in the vertical and horizontal, which is what ANY arm has to have. There is no torsional "rocking" due to stylus motion in the two planes of a stereo recording going and what little of very low frequency may be provided from record warps and non-centered hole are effectively damped and remian unheard.

This is a very intelligent, reasoned discussion. It seems we all agree on certain major points as regards the advantages and disadvantages of unipivot designs vs fixed bearing designs. And I like that Hiho mentioned the issue of azimuth adjustment (AA) when it takes place upstream from the headshell (cannot avoid also altering both VTA and the angle in space between cantilever and LP surface). But that would be the same for both basic types of pivoted tonearm. As far as I know, the only "modern" tonearm that permits AA at the headshell itself is the Reed, when ordered with the optional AA headshell. I hope you unipivot guys will agree also that it is the cartridge that needs to follow the groove and that Ralph is quite correct to say that if the tonearm per se were to respond to the groove undulations, there would be no music. What lies in between those two extremes is probably what actually happens with most unipivots. Still, I have to explain the ethereal quality of the Talea that I heard locally. It made me want one. Obviously, the Talea "works". In thinking about what I heard from it, I came to the tentative conclusion that in part I was responding to highly euphonic "imperfections" that I have heard before with unipivots in my own system. I think this is what Mike was trying to get at; there is a certain sense of freedom (still not a perfect word for it) associated with unipivots that is very beguiling. And that's perfectly OK in my book.

+++++ " And what's wrong with that? " ++++

nothing, evryone is free on his choices.

regards and enjoy the music,
Raul.

Dear Lewm: +++++ " Still, I have to explain the ethereal quality of the Talea that I heard locally. ............. the Talea "works". In thinking about what I heard from it, I came to the tentative conclusion that in part I was responding to highly euphonic "imperfections" that I have heard before with unipivots in my own system. " +++++

at least a " sight " on the unipivots. Halcro, got it?

As I agree and posted: nothing wrong with that, our each one choice.

Regards and enjoy the music,
Raul.

Dear Stevecham, You wrote, "A properly designed unpivot arm does not rock due to stylus tracking simply because the design has the stylus aligned with the pivot point". I completely agree with you, but who said that in the first place? I did not see such a claim being made here, but I may not have read all the posts. However, I cannot agree with all that you go on to claim; it seems to me that the interplay between skating and anti-skating forces, which can be neither perfect nor constant as the tonearm traverses the surface of an LP, could cause variations in azimuth as a unipivot moves. This cannot happen with a fixed bearing design. Granted, all the best unipivots use one or another of several strategies to mitigate this issue.

With a WT tonearm, which you may or may not liken to a unipivot, I have personally seen that azimuth changes dramatically over the surface of an LP. WT likes to say their tonearm has no bearing; that's the problem, IMO.