A good tonearm will not have any sound of it's own. It will limit discrepancies so as to minimize distortion into inaudibility.
In dealing with the imperfect world of records. A tonearm must be designed in a certain way and have specific features to function at the state of the art. The SAT tonearm does not qualify. it is nothing more than a substitute for a "mighty sword" (Randy Newman). A tonearm should have no sound of it's own.
Given the problems with tangential arms, which theoretically would be best, a pivoted offset arm is still the staple of tonearm design. It should have ridged bearings of the lowest friction without any play. It should have a ridged, non resonant wand with a fixed head shell and continuous wiring clips to phono stage termination. Short arms are superior because of their lower inertia and superior tracking abilities.
The arm should have neutral balance as opposed to stable balance. This is easy to see. You should be able to draw a straight line through the center of mass of the counter balance weight through the vertical bearing on through the center of mass of the cartridge and head shell. This usually means that the counter balance will be dropped. If you adjust the counterweight so the arm floats horizontally a neutral balance arm will stay at whatever elevation you place it. A stable balance arm will oscillate until it finds horizontal again. A neutral balance arm maintains the same tracking force regardless of elevation. A stable balance arm decreases tracking force with elevation.
An anti skate mechanism is mandatory of the lowest friction possible. Magnetic mechanisms are best.
Appropriate mechanisms must be present to adjust the orientation of the cartridge in all planes. Once locked they should be perfectly rigid. This disqualifies most VTA towers. People who insist on them need to find themselves a good hobby like cooking or basket weaving.
From an aesthetic view tonearm cables should exit beneath the tonearm board. They interfere less with suspensions and dust covers this way aside from looking much better. People who need to show off their wires need a sports car they can polish. A proper system should have all of it's cabling hidden as best as possible. This business with fat cables and fancy sheaths is again for men with undersized mighty swords.
The Schroder CB is an example of such an arm.
