After reading half of the earlier thread on linear vs. pivoted arms (and being annoyed by the reiteration of wrong and mixed up technical arguments) I want to chime in with some notes.
- "stress" on the cantilever (by linear arms): If you want no deflection of the cantilever, there will be no signal. Most radical practical approach: Use a tiny carbon string glued to a straw, with a very low compliance cartridge that is light, like a beginning of 80's Coral. Or use an Infinity Black Widow arm. Obviously this want give ou much bass below 50Hz.
Otherwise you *choose* deflection along what you find "optimal". Deflection means that the arm moves not in-phase with the cartridge. This is not a bug but *the feature* that produces a signal from the cartridge. The most (and optimally "linear") LF output of a cartridge comes from a perfectly flat, centered LP ( :-) and an arm of infinite mass.
Between these poles, the optimization takes place.
- What is optimal? If we end up tracking the excentricity of the record because of infinite mass and imperfect LPs, it's obviously not optimal - this *real* stress on the cartridge does not produce a musical output of the cartridge, it's just subsonic junk, no master tape has useful musical information below 1Hz. On the other hand we don't want to compromise the tracking of LF musical signals by too low mass, and this extends to phase in the bass too, ie. we need a certain excess LF extension below actual musical notes and subsonic room noise and cues. I assume that there is musical information, mono, on tapes right down to (below) 10Hz. Musically seen, we should keep away from (and stay lower than) 10 Hz. This is not orthodox - but consequent and well thought through. The optimal cut-off/ resonance frequency leads IMO to frequencies in equal interval distance from 0.55 (LP) / 0.75 (EP) Hz and these 10 Hz. This results in an optimal *horizontal* resonance frequency around 2-3Hz (=SQR(0.55 * 10).
- Actually with a useful tool (sadly missing at that time) we could adapt any LP for optimally correct centering, and almost no 0.55Hz wobble, which fucks up music "even" on radial arms BTW.
- Vertical warps have a considerably higher frequency, just watch the cartridge from the side... It's usually double the frequency or more, up to 5-7 Hz. These signals should be filtered out by low enough vertical mass / resonance frequency. Doing the same calculation as before, we should know the LF cut-off of *vertical* signals: These are the out-of-phase signals in the bass. Any useful LP must try to keep at least the amplitude of these signals extremely low, because cartridges have an extremely hard time to track such signals. Usually the out-of-phase signal is high pass filtered below 100 Hz, and below 20Hz there isn't anything useful to be reproduced in a normal room anyway, as it's off-phase, will be cancelled, messes up cartridge tracking and consumes amplifier power with no purpose.
So we end up practically (in the safety zone IMO) with "between 7 and 20Hz", ie. ca. 12Hz *vertically*, preferably even higher. And maybe in this case a bit damping could be desirable.
- The "stress on the cantilever" is mostly dependent on horizontal resonance frequency, which is linked to horizontal mass & compliance . And bearing friction (practically non existing in an air bearing) and wire stiffness.
- It's interesting that one of the very best radial tonearms, the Moerch DP-8 "mimics" properties of a well set up air bearing arm: Very high horizontal mass with average vertical mass. :-) :-) :-)
- Problems of linear arms:
Wire stiffness - no lever advantage here. Wrong setup, changing lateral setup with VTA. In my ET 2.5 this is a problem. The thing that suffers most is... the bass. Very audible differences here with careful setup!
Subchassis movement: A subchassis (if desirable at all :-) should swing in the rotational plane quite lower than 2Hz... I don't know of any, and it would be problematic too. Wit the usual air-bearing arms (placed tangentially) the subchassis movement will be tracked by the cartridge, as will be any lateral acceleration of a turntable (seen from cartridge into the arm).
A linear arm has much less sensitivity to this, because the lateral forces cancel to a major degree, dynamically. But instead of forces on the cartridge you get forces on the bearing. These are audible too.
- Problems of radial arms: The cantilever pulls off-line of the tonearm axis, creating a skating force. This varies with musical signal, the tracked place on the record (radius), and surface properties which change more than we might expect. These *dynamic* skating forces constantly energize the horizontal resonance of cartridge/arm and modulate the musical signal. And the amount is dependent on the magnitude of the offset angle, giving a considerable advantage (here) with longer arms - or other more unorthodox approaches, like the Thales arms or similar.
BTW the same happens in the vertical plane with a "correct" vertical bearing placed exactly at the height of the LP tracking plane...
- In the end a well set up linear arm (not complicated, but still not often attained) has potentially a more stable tracking of LF musical signals.
- It's a complex trade-off! Setup is very important, and careful listening too. And better not based on wrong or semi-wrong theories, as much "expert" bandwidth as they take.
- Thanks Mepearson!
PS: I *like* to listen to music on a well set up vinyl rig... And yes, the proof is in the listening.
