It makes no difference what so ever. Put Conrad’s condition aside. Here are the reasons why I think the string test is useless for judging if a pivot arm skates or not.
1, The friction between stylus and groove causes skating. But in the string test, the pivot arm suspends in the air. It means the friction is ZERO. In other words, the friction is NOT included in the test. If you don’t include the basic factor, how can you study skating?
2, Let’s assume that you pull the string, the arm doesn’t move sideways. By your definition, the arm doesn’t skate. In fact, all the arms skate except on the Thales circle no matter how the arm reacts in the string test. So, the string test can’t tell us if a pivot arm skates or not.
3, You were saying to reframe it in reference to the tangent to groove force vector. How? In the string test, the arm suspends in the air. There’s no relation to the groove. Once you pull the string, how do you know that the arm is tangent to the groove? The arm doesn’t even touch the groove.
1, The friction between stylus and groove causes skating. But in the string test, the pivot arm suspends in the air. It means the friction is ZERO. In other words, the friction is NOT included in the test. If you don’t include the basic factor, how can you study skating?
2, Let’s assume that you pull the string, the arm doesn’t move sideways. By your definition, the arm doesn’t skate. In fact, all the arms skate except on the Thales circle no matter how the arm reacts in the string test. So, the string test can’t tell us if a pivot arm skates or not.
3, You were saying to reframe it in reference to the tangent to groove force vector. How? In the string test, the arm suspends in the air. There’s no relation to the groove. Once you pull the string, how do you know that the arm is tangent to the groove? The arm doesn’t even touch the groove.
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A tangential tracking pivoting tonearm #14
I did some simulations of the variation of the moment (torque about the horizontal pivot) of the magnetic antiskate force for various strut angles.
The strut is located 20 cm from the stylus end and is 10 cm in length (the first diagram is not to scale with these values).
The angles with the tonearm rear direction are 2π/3, 3π/4, 5π/6, 7π/8, π radians or 120, 135, 150, 157.5, 180 degrees.
The last case has the magnets coinciding on the tonearm tube, as a test of the mathematical model. On two grounds this should provide zero antiskating torque which it does. The two superimposed anti-phase magnets should have cancelling magnetic fields as well as the magnets are in line with the tonearm horizontal pivot, hence produce zero moment. The downwards vertical order of plots on the diagram follows the increasing values of the strut angle.
The plots show that the antiskate decreases in magnitude as the strut angle with the tonearm rear increases. That is, with increased distance between the antiskate magnets and the fixed magnet at the pivot. Unfortunately if the angle of the strut decreases below aproximately 2π/3, the antiskate force across the disc groove is not monotonic, and so will not be able to follow the stylus skating moment profile with any accuracy. Hints of the turning point are beginning to appear in the 120 plot.
These are preliminary investigations, to investigate whether the trends are realistic for providing a reasonable degree of frictionless antiskate. There remains a whole lot of optimisation to find a combination of parameters that provide a more linear antiskate profile that matches closely the stylus skating force.
I did some simulations of the variation of the moment (torque about the horizontal pivot) of the magnetic antiskate force for various strut angles.
The strut is located 20 cm from the stylus end and is 10 cm in length (the first diagram is not to scale with these values).
The angles with the tonearm rear direction are 2π/3, 3π/4, 5π/6, 7π/8, π radians or 120, 135, 150, 157.5, 180 degrees.
The last case has the magnets coinciding on the tonearm tube, as a test of the mathematical model. On two grounds this should provide zero antiskating torque which it does. The two superimposed anti-phase magnets should have cancelling magnetic fields as well as the magnets are in line with the tonearm horizontal pivot, hence produce zero moment. The downwards vertical order of plots on the diagram follows the increasing values of the strut angle.
The plots show that the antiskate decreases in magnitude as the strut angle with the tonearm rear increases. That is, with increased distance between the antiskate magnets and the fixed magnet at the pivot. Unfortunately if the angle of the strut decreases below aproximately 2π/3, the antiskate force across the disc groove is not monotonic, and so will not be able to follow the stylus skating moment profile with any accuracy. Hints of the turning point are beginning to appear in the 120 plot.
These are preliminary investigations, to investigate whether the trends are realistic for providing a reasonable degree of frictionless antiskate. There remains a whole lot of optimisation to find a combination of parameters that provide a more linear antiskate profile that matches closely the stylus skating force.
Attachments
Hi Ralf.
Will any of the passive tangential trackers claim zero sidethrust? Maybe with perfect sidethrust compensation? The Shroeder LT, Thiele, etc? I would just like to recognise it if/when I encounter it.
Regards
Bon
First, Kogen (1967) got it right, based on maths from the 20's IIRC.
Many contemporary commentators incorrectly use the headshell/stylus offset instead of the correct tangent to groove force vector.
That reason is probably that it is a close enough approximation and visually discernible in practical, pivoting, offset tonearms.
The "pull" in the string test is the simulation of groove friction, you are correct, if you pull at zero force nothing will happen
Let me include some drawings deduced from your video on skating.
This shows the 3 positions in your demonstration.
I've added the tangent to groove force vector for each stylus tip position.
If you used Kogen's formula to calculate the skate force at the inner and outer position, using the effective length vector and tangent to groove force vector angle instead of the stylus offset, it correlates perfectly with your results in the video.
The zero skate condition on the middle position also correlates because it has a zero product property, the tangent to groove force vector and effective length vector are collinear.
It is a thought experiment, imagine you are pulling a string, collinear with the tangent to groove force vector. It will behave correctly, there is a tangency error, because the drag force is not collinear to the effective length.
To make it easier for you, perhaps imagine the arm stationary on an unmodulated surface that is not rotating. Similar to your demonstration, but the motive force has been changed from rotation to string pull.
If you pulled on the string, that is always collinear with the tangent to groove force vector, it will still react in the same way as your demonstration, as well as all other tonearm geometries.
Isn’t the string test completely based on offset? So is Conrad’s condition. If the arm has offset, you pull the string and the arm will move sideways. Therefore, the arm skates. If the arm doesn’t have offset, you pull the string and the arm won’t move sideways. Therefore, the arm doesn’t skate. Both string test and Conrad’s condition are saying the same thing from different angles. Both should not be the standard for judging wether a arm skates or not.
It seems that all your comments enforced my views against the string test.
newbie post.
I think offset angle and groove friction combined results in skating. In string test the pulled string represents friction.
regards
addition : this friction pull is so high Once while playing record on some old cartridge when I lowered it on first song the stylus yanked off from the cartridge and came loose. (Probably not related but wanted to share)
I think offset angle and groove friction combined results in skating. In string test the pulled string represents friction.
regards
addition : this friction pull is so high Once while playing record on some old cartridge when I lowered it on first song the stylus yanked off from the cartridge and came loose. (Probably not related but wanted to share)
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Not any more.
I cannot make it any clearer for you.
The string is the tangent groove force vector, offset has nothing to do with it.
But we all know a conventional pivot tonearm without offset headshell a la some DJ turntable cannot be tangential tracking through out the record. The idea of the string test is a simple thought process to verify any multi-linkage articlated tonearm claimed to be tangential tracking has skating force or not.
The Thales Simplicity tonearm has built-in magnetic anti-skating at its split counterweights so it's obvious they signaled their tonearm can skate. But other arms are more ambiguous so the string test comes in handy. The Reed 5A touted its tangential accuracy but with no mention of skating force and does not appear to have any built-in anti-skating device. My guess is that it does skate, albeit smaller than typical pivot arm.
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Hi Jonathan.
I would appreciate any comments you can make on the prospects for my magnetic antiskating device. I hope my assumption of an inverse 4th power law for bar magnet fields is appropriate, and also the way the force vectors resolve orthogonally to the tonearm. I intend to use multiple neodymium button magnets.
BTW since you are based in Japan, is the ORSONIC FORCE CHECKER SG-1E a useful device, and is it still available? It might settle some of the debates about sidethrust.
Regards
Bon
Your String test v2 is completely undoable in reality. If you say it is doable, I would like to see how you are able to do the string test v2. Therefore, you can't get any meaningful conclusions from an undoable test at all. I quote what you said:" It is a thought experiment." If it is just a thought, I won't say anything. Please don't call it a test.
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This is precisely what I think string test is useless. If you perform the string test on a DJ tonearm, you will get the conclusion that a DJ tonearm will NOT stake. (Ok. someone may say it is string test VERSION 1). The truth is that a DJ tonearm does skate outside of Thales circle. If DJ tonearm has overhang, it surly skates. No tests are needed. The string test can't get correct results for a simple straight arm without offset. Don't even mention an arm with multi-linkage articulated arm.
If you said string test is just a thought process, that is fine with me although this thought is not correct. In the meantime, I just saw people kept asking if someone did the string test or not.
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A straight DJ tonearm never claimed to be tangential tracking! It can be tangent at only one null point. Again, the idea is that any so called tangential tracking arm with multiple linkages will exhibit skating force by merely pulling the string in line with the vector and is not taut. That is, (a) it's not a parallel tracker, (b) it's not servo, (c) it does not have a perfect antiskating device, (d) it does not have a magical armwand that can change effective length at a fixed pivot point. You keep referring to the Thales circle but the segments are not equal length and a straight DJ tonearm has only one fixed legth and one fixed pivot point. I don't know what else to say.
Sorry, Bon. I apologize for the distraction of your thread. I will refrain from this topic again.
Sorry, Bon. I apologize for the distraction of your thread. I will refrain from this topic again.
I was not talking about DJ tonearm to tangential tracking at all. All I talked about was that the string test can't be used for the skating test. This is it. I kept referring to the Thales circle because it is possible for a pivot arm not skating on the Thales circle. In the outside area of the Thales circle, ALL pivot arms skate. I don't care what kind of pivot arm is.
super10018,
Please do build a "Birch two-pivot arm," but please build a good one so we can see what you come up with and so you get to enjoy the performance this design is capable of.
It will skate.
I argued strenuously with diyray about that, but lost. What has never been determined as far as I know is what proportion the various pivot points and stylus drag/side force all contribute. Maybe Bon's mathematical approach will shed light on this.
The base can be built with adjustments to counter the skating.
Please do build a "Birch two-pivot arm," but please build a good one so we can see what you come up with and so you get to enjoy the performance this design is capable of.
It will skate.
I argued strenuously with diyray about that, but lost. What has never been determined as far as I know is what proportion the various pivot points and stylus drag/side force all contribute. Maybe Bon's mathematical approach will shed light on this.
The base can be built with adjustments to counter the skating.
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A tangential tracking pivoting tonearm #15
The diagram below shows how the magnetic antiskate is supposed to work.
The two magnetic dipoles (bar magnets) are fixed to the struts in anti-phase.
The bar magnet at the origin is free to rotate aligned with the tonearm but fixed in lateral position.
It would be fixed to the lower non-sliding bearing component that allows horizontal rotation. (In a conventional tonearm it would be attached to the bearing yoke)
Shown is the effect of the outer magnet. The repulsive force has a component (red arrow) along the strut direction.
The moment (counterclockwise torque) about the bearing pivot is determined by the perpendicular distance to the origin.
At the strut connection with the tonearm, there will be a force component in the direction of the tonearm in the elongation direction.
Now the other magnet will have the mirror image vector diagram. The composite counterclockwise torque will double and the force components along the tonearm direction will cancel.
The diagram below shows how the magnetic antiskate is supposed to work.
The two magnetic dipoles (bar magnets) are fixed to the struts in anti-phase.
The bar magnet at the origin is free to rotate aligned with the tonearm but fixed in lateral position.
It would be fixed to the lower non-sliding bearing component that allows horizontal rotation. (In a conventional tonearm it would be attached to the bearing yoke)
Shown is the effect of the outer magnet. The repulsive force has a component (red arrow) along the strut direction.
The moment (counterclockwise torque) about the bearing pivot is determined by the perpendicular distance to the origin.
At the strut connection with the tonearm, there will be a force component in the direction of the tonearm in the elongation direction.
Now the other magnet will have the mirror image vector diagram. The composite counterclockwise torque will double and the force components along the tonearm direction will cancel.
