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In Reply to: RE: My only point was that there are two sources of skating force posted by Lew on April 22, 2015 at 13:14:50
My only point was that there are two sources of skating force Even if the pivoted tonearm had no headshell offset angle, there would still be skating force, in other words.I'm trying to understand your point on this. Your statement is correct, however. All fixed-point pivoted arms will experience skating force, regardless of design.
And IMO the headshell offset angle is added to the mix so as to achieve two points of tangency to the groove across the surface of the LP, when you combine that with overhang.
Yes, the overhang and offset angle are for reducing tracking angle error. Together they are really just one thing: The mathematically optimal cartridge position for a fixed arm. This position defines the nature of the skating force because it defines the stylus arc and the direction of record drag at every point along it.
I don't see the 2nd source.
Pivoted tonearms with underhang (like the crazy RS Labs RS-A1 and that new one with the floating bearing) can achieve only one point of tangency on the playing surface, but at that point, there would be no skating force, because all the friction force vectors line up and point back to the pivot, as in your clock analogy. And there is no use for headshell offset angle on these types.
But cartridge/groove tangency alone does not cancel skating forces unless the cartridge is mounted in a line with the pivot (as with an LT arm or short scratch arm). So the null points of an offset arm are still experiencing drag that's out of alignment with the pivot.
EDIT: Let me add that I realize skating force is not consistent across a side due to the arc, and maybe that's what you're saying. The 'drag angle' (I'll call it) shifts in the same way the tracking error does so it'll always be a moving target.
Edits: 04/22/15 04/22/15Follow Ups:
Bry, I am indeed saying that tonearms like the RS-A1 (and that new one with the floating bearing) that are to be mounted with the stylus under-hanging the spindle (not reaching the spindle) and in which there is zero headshell offset angle will achieve tangency to the groove at one point on the arc of the stylus across the playing surface of the LP. And at that one point of tangency, there will be NO skating force. At that instant in time, the RS-A1 is exactly like a linear tracker. Of course, one instant before and after that magic moment, there is skating force.
Straight arms aligned with underhang have no offset. Skating force is reduced to very small levels, so much so that anti-skate is not needed. At least that is the claim and it makes sense.
With the absence of offset and anti-skating, torsional affects from the arm on the cantilever are greatly eliminated. "They" say, elimination of these torsional affects provides better sound quality than increased alignment error.
neo
BIRD LIVES
I stand by what I wrote above your post. Yes, the designer of the RS-A1 does claim to have done away with the "inside force", but in fact there still would be an inside force or skating force at all points on the arc of the stylus tip where the cantilever is not tangent to the groove. At that one moment in time when tangency is achieved, there is no skating force, I agree. If there is a flaw in my logic, I welcome correction.The RS-A1, in particular, does have itshead shell mounted on a unipivot, which allows free movement in the lateral plane and in theory the headshell itself may choose its own offset as it traverses the groove, thus maintaining tangency at least some of the time, but in actuality the signal wires between the cartridge and the arm body impede free movement around that pivot point. Thus I have doubts that it self-corrects for inside force.
EDIT. Upon further thought I realize I was wrong in this last paragraph. If the headshell does passively pivot to hold tangency, then the fact of its pivoting creates a headshell offset angle and thus generates an inside force. No free lunch.
I own an RS-A1, and it punches way above its weight with an MC (low compliance) cartridge, for sure. I have yet to try it with a high compliance cartridge for fear of damaging the cartridge suspension; there's too many ways to screw up while mounting the cartridge and cue-ing it.
Edits: 04/24/15
> I don't see the 2nd source.
The second source of skating force is dynamic in nature and caused by the the modulation level of the recorded signal. A modulated groove produces more drag on the stylus than an unmodulated groove. Consequently, there is a constant skating force proportional to the sine of the angle of the groove tangent at the stylus and there is additional dynamic skating force applied by the modulation level of the groove. Antiskating mechanisms counteract only the constant aspect of skating force but not the dynamic portion.
Best regards,
John Elison
I left the dynamic part out because my main point was to show how the geometry of the arm makes skating force a fact of life and not so much to determine what that force actually is. But yeah, the cartridge generates electrical energy from mechanical energy and that involves an increased load in the form of drag.
IF so little a/s is needed (less than 1/2 of the indication on the a/s devices....and is not accurate anyway being a variable depending on the loudness of the signal, where the stylus is (beginning, middle, or anywhere in between), etc...then using none is as appropriate as using it at all.
All the skating forces will fall within a range which is greater than 0. Even if you set the anti-skate to only cancel the lowest point of drag on an LP side, you're still better off than having none at all. Finding a value close to the average will be best for your stylus life.
Here is a vector diagram of skating force:
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