Anti skate and tonearm damping query

Axel,

Try your experiment using a pivoting arm having zero offset angle (like a transcription arm). Provided the cantilever is aimed correctly (i.e., directly at the pivot point of the tonearm), skating force will be zero. This will be true regardless of overhang.

Skating force is generated when we mount a cartridge at an angle in the headshell such that the cantilever is NOT aimed at the tonearm pivot (in a word, offset). Overhang has nothing to do with it.

Using that transcription tonearm (which has zero offset by design) you could still create an inward skating force by mounting a cartridge at an inward angle, just as on a regular tonearm that has built in offset. You could even create an OUTWARD skating force by mounting the cartridge at an outward angle. Again, you could do either of these regardless of overhang.

Dear Doug, lets not mistake the torque tension force (which is indeed a result off the offset angle at the headshell) or the J-/S-shaped form (featured on tonearms with detachable headshell) common on most pivot-tonearms (and seldom addressed....).
As many (not all) a tonearms do not feature any lateral balance device at all to counterbalance the torque tension of its armpipe, these all too often do indeed produce a movement on a plain record.
I have performed the test you suggested several times.
With my 12"+ tonearm and a cartridge with Q4-capable stylus the tonearm (... with correct applied lateral counter-balance and on a dead level TT) sits still (no inward move) at the 2 zero error points of the tangential curve.
Am I missing parameters?
Pure luck ?
Coincidence ?
Correct model ?
Whatever......
Fact is - as a selected handful (precisely...) of the bavarian routed A'goners do know very well - that sibilant distortion, inner groove distortion or "wandering images" are non-existent on the front-ends set-up by me.
And no - these aren't all FR-tonearms, but do include DaVinci, Kuzma 4P, Graham, SAEC, Micro MAX, Triplanar (to name the better of the pivot-designs).
9" to 12" which - by the way, Axel - can not really be distinguished in groups by their overhang.

And yes - exactly - what would we prefer?
A "simple" (but precisely designed and engineered - all too often forgotten as we are so accustomed to it - german car or a "complex" (....complex ? where ?) british one (and - oh, sorry - is there still any major british car brand NOT owned today (and improved in terms of reliability and performance by its new owner) by either BMW, Audi or VW .... Jaguar is owned by Ford isn't it?).....?

And yes, I know that the japanese cars are even more reliable - fact is that I still prefer 2-3 japanese born tonearms (which by the way did address the issue of torque tension producing lateral movement...) above any german designed tonearm.

>>10-12-09: Stringreen
10-12-09: Stringreen
Dougdeacon...you're correct, but anti-skate decreases with velocity<<

Wrong again stringbean.

Mark Kelly has it right.

As does Nsgarch.

Of course my idea is wrong.
But that is always the case.
After we have agreed upon that and set it aside, maybe someone is willing - or not..... no problem (at least not mine) - to visualize what is actually happening aside from dogmas, simplified models, laws (which aren't what they used to be either) and small hills which became mountains (ever seen the nice movie with Hugh Grant who climbed up the first and came down the later?).
With all those clear models around, I really wonder why there still are so many complaints and discussions about inner groove distortion, off-angle cantilevers, wandering images and sibilants which pierce the ear.
With all those great anti-skating devices around.
Strange.

Axelwahl

You are assuming attitude is important but it isn’t.

Consider the frame of reference of the tonearm with its pivot point as the origin and the arm lying along the y axis. The stylus frictional reaction force vector runs directly from the stylus tip in the direction of groove motion. The restraining force vector runs directly from the stylus tip to the tonearm pivot. The sum of these two vectors is the net force on the stylus.

The angle between the groove tangent and the x axis is the true offset angle. The stylus reaction force vector can be resolved into x and y components equal to its magnitude multiplied by the cosine and sine of this angle respectively. Since the x translational degree of freedom is constrained, the sum of forces in the x direction must be zero so the restraining force must be equal to the x component of the stylus reaction force vector.

For the y translational degree of freedom also to be constrained (eg the stylus not skip out of the groove) there must be a force which balances the y component, this force is either supplied by a reaction force on the groove wall or by antiskate.

IFF the force is supplied by reaction against the groove wall then the fact that that reaction force is not purely in the Y direction creates complexities but we can assume that the arm has been designed by someone who knew what he was doing so it has antiskate therefore we can ignore this: designing a pivoted arm with no antiskate is prima facie evidence of incompetence. The antiskate can be applied as a torque to the arm pivot or a force to a point somewhere on the arm, it’s all the same as long as the vectors resolve.

The argument from attitude rests on a falsehood which is that the stylus frictional reaction force somehow depends on the attitude of the stylus to the groove wall. A misalignment of say 10 degrees would result in a displacement betwen contact patches of about 25 microns for an elliptical stylus 7mil across, for a spherical sylus there would be no displacement at all since the contact areas between a sphere and a plane are always normal to the radius of the sphere.

This torque arm would result in a torque of about 0,5 uNm at 20 mN VTF where the actual skating torque is around 1mNmm, a difference of 2000 to one.

The issue which I’d like to resolve is that of the influence of stylus shape. Amonton’s law for rigid bodies breaks down if one body is much softer than the other, which is definitely the case with vinyl and diamond. The breakdown takes the form of a pressure dependent coefficient of friction; the coefficient decreases with increasing pressure – this seems counterintuitive but think about a car tyre: wider tyre, lower pressure, better grip. Since elliptical styli have greater contact pressure than spherical, the friction will be less for them and this was reflected in many tonearms having separate scales for elliptical and spherical styli “back in the day”. Check the owners manual for the Torens TD160 mk2 for an example. Since a line contact has, by design, a larger contact area the skating force should increase not decrease as our befuddled friend supposed.

Mark Kelly