Apologies for bad rapid phone pic of the part of the page in question, but I think I have worked out what they did, just not how. Reason for scan is easier to explain.
As only one groove is modulated, you can see all stylus movement is at 45 degrees, so if you were to put a teeny pencil on the stylus on the unmodulated side you would trace a sinusoid on that wall.
Now, the end result is an SEM scan. Impressive as I have used a 60s SEM and they were ornery beasts (especially when 30 years old). SEM needs a conductive surface to work, so I am wondering whether they worked out how to put something conductive on such that the stylus on the unmodulated side smeared the track into it. How and why it didn't ruin the tribology is beyond me but this matches what you see.
Could be wrong as it was 3AM when this came to me!
As only one groove is modulated, you can see all stylus movement is at 45 degrees, so if you were to put a teeny pencil on the stylus on the unmodulated side you would trace a sinusoid on that wall.
Now, the end result is an SEM scan. Impressive as I have used a 60s SEM and they were ornery beasts (especially when 30 years old). SEM needs a conductive surface to work, so I am wondering whether they worked out how to put something conductive on such that the stylus on the unmodulated side smeared the track into it. How and why it didn't ruin the tribology is beyond me but this matches what you see.
Could be wrong as it was 3AM when this came to me!
Attachments
Thanks, Bill. There's much content in the archive WW articles, I grew up reading that sort of thing in the 70's. I remember having to decide between the Beano and WW, such things are formative probably. I chose the Beano - only joking
This article describes J Walton's take on deformation, and if one reads it carefully I think he had a good grip and was aware of the elephant in the room of dynamic behaviour being different, and had a try at dealing with it.
..........However, we are not concerned with static indents on a gramophone record, but with gliding ones, and it was found that a considerable difference exists between the indent dimensions in the two cases.....
.....The following is an attempt to explain this in terms of a "surf board" action which causes the stylus to ride more on the surface of the medium upon reaching a certain critical speed below which there is a tendancy for the stylus to sink by a greater proportion.....
...this of course refers to the elastic region of deformation, and I have not so far been able to find a direct means of measuring this....
The article begins with Hertzian static indentation theory, which is accepted of course, then the author attempts to deal with the significant matter of a moving stylus-groove interface. The chosen way of doing this was to consider friction force as pushing the stylus upwards, then to apply the new balance of forces to the static indentation model......The following is an attempt to explain this in terms of a "surf board" action which causes the stylus to ride more on the surface of the medium upon reaching a certain critical speed below which there is a tendancy for the stylus to sink by a greater proportion.....
...this of course refers to the elastic region of deformation, and I have not so far been able to find a direct means of measuring this....
However, this approach overlooks that vinyl material has self-mass, and has viscoelastic and elastomeric properties that are far from ideal springs, and has time dependant material properties. This, IMO, is where the train leaves the tracks in terms of dynamic indentation calculations predicting real behaviour.
Lacking a means of measuring elastic deformation, the article measures plastic deformation versus VTF, verus stylus radius, and stylus-groove linear speed. Measurement is using blank vinyl and spherical stylus, and presumably inspecting permanent plastic deformation by microscopy after the test.
This means, by definition, that indentation tests used VTF and stylus radius radius conditions likely to cause plastic (permanent deformation), rather than conditions likely to be encountered in real playback today.
In any event, even if one takes at face value the article's prediction for magnitude of dynamic indentation for reasonable VTFs and stylus radius, eg figs 7 thru 9 in the article, indentation is less than about 25nm - consistent with what has been mooted on this thread - and which I consider to be close enough to zero as to endorse that no meaningful indentation happens in practice.
And to address Richard's point, which I take to be baiting, it's very obvious that cartridge designers back in the day were highly competent. If one reads this J Walton article carefully and critically, it acknowledges matters of uncertainty which in 1961 were still to be resolved, and doesn't contradict the modern thesis that dynamic groove indentation is negligible, for reasonable configurations.
I'm thinking that the SEM image on this thread showing the gouge and flattened modulations might have been for unreasonable conditions of plastic groove damage, whereas that showing polish and improvement after 250 plays was for reasonable conditions of elastic behaviour, and consequently very little indentation.... I'll post about Walton's wear/damage article separately.
LD
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Bill, here they are, resp. value for R23 and overall gain in steps of 3dB.
160k 37dB
48k 40dB
24k 43dB
14k 46dB
8k9 49dB
5k85 52dB
3k95 55dB
Hans
Agreed that the gouge picture was for a tip mass 3-5x higher than one gets today even on bonded tips. And it was probably a 'created' case to make his point that sub 1mg total effective mass (which is really a force calculation fudged back to effective mass to cause that force when resonating) and 3g tracking force are a safe upper limit for vinyl playback with a spherical tip. If my reading is right then that is a pleasing closing of that loop
I really doubt it has anything to do with tip-mass........Agreed that the gouge picture was for a tip mass 3-5x higher than one gets today even on bonded tips. And it was probably a 'created' case to make his point that sub 1mg total effective mass (which is really a force calculation fudged back to effective mass to cause that force when resonating) and 3g tracking force are a safe upper limit for vinyl playback with a spherical tip. If my reading is right then that is a pleasing closing of that loop
We know the test track was the 10kHz band on Decca SXL2057, which was one channel only modulated physically 5cm/s rms. For even a 3mg tip mass stylus, that works out as a lateral inertial force on the stylus of about 0.7g rms, coincident with 0.7g rms upforce, which is insignificant in the context of normal VTF here............and besides doesn't explain the continuous gouge pattern on the unmodulated wall.
I agree with you that, on the strength of J Walton's plastic deformation tests on blank vinyl with a spherical tip, about 3g was the observed limit for plastic damage. Yes, that seems to close a loop. But for those tests to be valid, the stylus would have to be truly spherical because the base of the stylus would have the contact point, whereas styli might not be produced with that in mind............? A rounded off conical, for example....... There's also a factor of sqrt(2) to apply to accommodate two support points in the V groove.
At least, I believe, we might have found the source of the stream.
I venture there might have been some mix-up between 3mg tip mass and 3g VTF in the labelling, handling or interpretation of the images ?? But even 3g VTF seems improbable to inflict such damage, which would be sure to show up in tests but doesn't, IME.
LD
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Definately tip mass, but I haven't waded through enough of his papers yet to get to the bottom of how he calculates this. I've found the section but need to confirm that he is consistent where he works out static force plus inertial acceleration to get beyond the plastic deformation limit. I've found the section, just need some time.
Just had another scan and the book is not consistent. In one section he calculates that the tracking force required for handling maximum expected modulation with a 2mgm tip mass is 7g then a few pages later he talks about the damage caused by that tip mass tracking a 2g, where it will clearly be mistracking. I need to look at the WW articles to see if he covers it in more depth.
Basically he is saying that tracking force needs to overcome Inertia in the stylus, the compliance and the frictional force required to move the tonearm. So far so good, but the source of the numbers is not shown. There are then some tables showing distortion for different tip masses at the same VTF vs frequency and modulation depth. In these at 8kHz and 5cm/s a 0.6mgm tip mass will be around 3.5% HD, a 2mgm tip mass 5% and a 3mgm tip mass is just shy of 20%. And he claims it is that 20% distortion that causes the stylus to 'plough its own groove'. or in other words mistracking damages things!
Or to put it another way, to get 3mgm to track you need such a high VTF that it's likely to damage things and if you track it too light it certainly will. But his argument is not presently particularly coherently.
Basically he is saying that tracking force needs to overcome Inertia in the stylus, the compliance and the frictional force required to move the tonearm. So far so good, but the source of the numbers is not shown. There are then some tables showing distortion for different tip masses at the same VTF vs frequency and modulation depth. In these at 8kHz and 5cm/s a 0.6mgm tip mass will be around 3.5% HD, a 2mgm tip mass 5% and a 3mgm tip mass is just shy of 20%. And he claims it is that 20% distortion that causes the stylus to 'plough its own groove'. or in other words mistracking damages things!
Or to put it another way, to get 3mgm to track you need such a high VTF that it's likely to damage things and if you track it too light it certainly will. But his argument is not presently particularly coherently.
Here's my 2p worth:
I wouldn't think of those parameters that way, Hiten. Partly because we generally don't even know what exactly is meant by some of them, nor can we agree about how the mechanics of playback work. If we can't even write down a self-consistent description of the mechanics involved that stands scrutiny, nor even a definition of the terms involved, it seems premature to think about ideal values, IMO.
LD
And mine:
Unless you have a Thales or Tangential setup, say very small geometrical errors, and unless you can keep your records really clean, then use a spherical tip. Spherical tip = hi-fi, elliptical one = hi-end. Choose needle type (with its optimum tracking force) according to your needs: If you are a DJ, you want higher force, if you play mostly LPs, lower one.
Finally set anti-skating properly, this is important. My player uses a weight for this and is such constructed, that when playback reaches inner grooves, angle between thread fix and weigth support is reduced from rite to diagonal, so anti-skating force is also reduced. It makes sense to me, because, tho skating also depends on modulation and ratio of modulation to groove speed, the static part of skating should rise with groove speed, and I rather be buddhistic about this: Do only, what is neccessary, so you will not make a mistake.
Thanks
Unless you have a Thales or Tangential setup, say very small geometrical errors, and unless you can keep your records really clean, then use a spherical tip. Spherical tip = hi-fi, elliptical one = hi-end. Choose needle type (with its optimum tracking force) according to your needs: If you are a DJ, you want higher force, if you play mostly LPs, lower one.
Finally set anti-skating properly, this is important. My player uses a weight for this and is such constructed, that when playback reaches inner grooves, angle between thread fix and weigth support is reduced from rite to diagonal, so anti-skating force is also reduced. It makes sense to me, because, tho skating also depends on modulation and ratio of modulation to groove speed, the static part of skating should rise with groove speed, and I rather be buddhistic about this: Do only, what is neccessary, so you will not make a mistake.
Thanks
Thanks, Bill. This article shows J Walton's thinking as of 1959 concerning the mechanical problem of isolating the massive generators of the time from inertia as seen by the stylus. Buried within it is a description that shows he considered tip mass to be related back to mechanical impedance and deduced from trackability, much along the lines of Yamamoto we discussed on this thread.
The author seemed to have in mind a target to achieve trackability without plastic damage for 15cm/s@10kHz peak. That is fierce, even for outer tracks and by modern standards, and represents accelerations/curvatures which probably were about as hot as ever cut IMO: about 960G acceleration, and 24um/8um curvature radius for outer/inner tracks would have been effectively untracable on inner grooves.
Stylus peak acceleration for a sine grooveshape is ω x peak velocity. So working with Walton's target requires trackable acceleration of about 9400 m/s2.
If tip mass were 3mg, the inertia to movement of stylus, F = ma gives a force of 0.028N (2.8gf).
So if a lateral sine 10kHz@15cm/s groove waveshape is tracked, force normal to either groove wall would be sqrt(2)[VTF + 2.8gf(sin(ωt))]
Since Walton considered that even momentary force above 3gf could permanently deform grooves, one might see why he considered 3mg tip mass, and/or VTF above 3g to be an issue for extreme limits of curvature.
I'm not saying Walton was right, just trying to understand the thinking............
The article also disclosed a figure for compliance of vinyl, perhaps the contemporary basis for industry deduction of tip mass from hf resonant f, 2.8 x 10-8 cm/dyne, presumably based on Hertzian static models which the author later acknowledged didn't apply dynamically. This works out about an order of magnitude stiffer than subsequent and modern cantilevers - consistent with other papers and models we discussed here. The elephant in the room, that a felxible cantilever can be self resonant, wasn't addressed, though the physics of how it can reduce impedance/inertia as seen by the stylus ('tip-mass') is all there. Just the associating link was never made, it seems...........
This article seems to mark the then leading edge of contemporary thinking in 1959, perhaps it became lore, right or wrong ? It certainly seems to have driven the progression toward lower VTFs and more flexible cantilevers. Very interesting.
Yes - I think it doesn't stand scrutiny, and I can't quite make those figures work, but a factor of sqrt(2) might cover it in terms of Walton's target. Tracking a 15cms/@10kHz grooveshape with a 3mg stylus would require about 3g VTF, and result in peak normal force of about 5.8gf, I think.
However, the SEMs we have are a much softer target: 5cm/s@10kHz on one channel only for the Decca SXL 2057.
I speculate that, considereing a 3mg 'tip-mass' stylus required 7g VTF to track, that is what was used for the test? Hence the gouge on the unmodulated wall, and damage to the modulated wall. For completely unforseen reasons, the association of high tip-mass needing high VTF was self-fulfilling in terms of causing permament damage due to high VTF ?? That would be consistent with the SEMs, IMO ?
LD
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I think you have it (a bit more alert now so I can type betterer). He calculated 1000g for the extreme peak modulation which is in the same spherical cow as your calculation. Now he changes to a 2mgm effective mass and calculates 5g VTF for mono and 6 for stereo. Then he says another 3g to overcome the 'damping' This then leads to the Walton spec for a pickup (as you say SOTA in 1960ish) should be
5cu compliance
less than 1mgm effective tip mass
'well damped'
3g VTF.
Still leaves a hole the test for the damage though and you might be right that he just didn't copy read properly. I guess you don't buy my theory of the unmodulated wall 'gouge' actually being a smearing of something conductive to give a stylus path recording? (don't blame you either ).
I have a suspicion that Decca considered a lot of Waltons work to be commercially sensitive so there are things that were not published and lots of too and fro as of course a big corp wants to have their cake (pay scientists little ) and eat it (stop them publishing stuff that gives them a market lead).
aside: going to be testing if you can form pvc conduit into damping troughs tonight if lil scrap actually sleeps
5cu compliance
less than 1mgm effective tip mass
'well damped'
3g VTF.
Still leaves a hole the test for the damage though and you might be right that he just didn't copy read properly. I guess you don't buy my theory of the unmodulated wall 'gouge' actually being a smearing of something conductive to give a stylus path recording? (don't blame you either
).I have a suspicion that Decca considered a lot of Waltons work to be commercially sensitive so there are things that were not published and lots of too and fro as of course a big corp wants to have their cake (pay scientists little ) and eat it (stop them publishing stuff that gives them a market lead).
aside: going to be testing if you can form pvc conduit into damping troughs tonight if lil scrap actually sleeps
Thanks LD.
My knowledge is weak in technical matters but....
There are softwares in which we can put physical properties of everything and simulate the outcome. Dont remember the name. From it we can short list few specifications and actually take measurement in real turntable system. Basically distortion/s, levels, channel balance etc. without damaging vinyls in the long run. Possible ?
Regards.
I guess you don't buy my theory of the unmodulated wall 'gouge' actually being a smearing of something conductive to give a stylus path recording? (don't blame you either
Wouldn't the SEM's be prepared after play?
I did say I had no idea 'how' they did it . I do need to write to Salford uni and see if they have any research archives on this as I am seriously intrigued as to what they did.
BTW looking at the DUAL CS-5000 user manual today, gives different antiskate settings for 'Dry play' and 'moist play'.
. I do need to write to Salford uni and see if they have any research archives on this as I am seriously intrigued as to what they did. BTW looking at the DUAL CS-5000 user manual today, gives different antiskate settings for 'Dry play' and 'moist play'.
