Have any of you guys looked at the dynamics of AFM tips? Given, to very small degree 😀, this is the ultimate end of the stylus/cartridge modeling.
Well no, it has to be one or the other. Because, if the cantilever flexes there will be a series of resonances, and that happens to match observations well. It's all classic stuff, and there are posted equations and illustrations of it here on the thread.
So there's no place for a vinyl resonance if cantilever flex happens. And very good reasons why vinyl indentation can't happen, IMO.
So one foot in each camp isn't a valid position, IMO 😉
I don't buy the visual inspection line at all: it's impossible to deduce spectrum and level from programme material that way.
There's just a mistake: something has got lost along the way as to scale or units or something, IMO.
LD
Yep, if the cantilever flexes there will be a series of resonances. That will still occur if the vinyl flexes too - and the series of resonances is likely to become even more complicated, since we've added an extra spring to the system. The frequencies at which all these resonances will lie depends of the actual compliance of the cantilever and the vinyl. And the magnitude of each "peak" and which one will dominate depends on the moments of inertia of the system and on the damping of the cantilever and the vinyl respectively.
Starting with the static case (the stylus simply resting in the groove) the vinyl will deflect - squish a little. At the tracking pressures we're (hopefully) talking about (well under 5 grams), the deflection will be elastic and no permanent deformation will result. And when the vinyl moves relative to the stylus, deflection will continue to occur, much as when you run your finger along a foam cushion. And when the vinyl groove starts its lateral wiggle, the fluctuating dynamic deflections of the groove wall will be superimposed on the static deflection caused by the tracking pressure.
Now all that doesn't mean that the vinyl deflection is dominant in determining the first resonant frequency of the system - my personal hunch (in the absence of vinyl compliance data) is that it's cantilever flexure that determines the first resonant frequency.
And admitting the existence of vinyl deflection doesn't preclude discarding it from the model if the effects of its inertia, compliance and any associated damping are shown to be negligible.
Data is what I seek!
Thank you. All slow progress, but one step at a time. Some of the project backlog is 18 years behind schedule. Life has a habit of getting in the way!
Whilst looking for something else came across a couple of interesting links from an old VE post to some AES papers that 'may' have a data point on vinyl deflection.
AES E-Library: The Limiting Tracking Weight of Gramophone Pickups for Negligible Groove Damage by Barlow, D. A.
The Limiting Tracking Weight of Gramophone Pickups for Negligible Groove Damage
JAES Volume 6 Issue 4 pp. 216-219; October 1958
It has been observed that when spherical styli are dragged over flat vinyl surfaces, scratches are produced under loads considerably exceeding the elastic limit as calculated from theory. The author, in this paper, describes the results of his experiments which bear out his argument that under load the point of yield begins below the surface; and reaches the surface, producing visible tracks, only after the calculated yield load is exceeded. This critical value of load for styli of various radii has been measured and found to be equivalent to, for a 1-mil stylus, 0.64 gm. for a 90° record groove. No size or skin effect was found with the vinyl material tested.
Author: Barlow, D. A.
Affiliation: Aluminium Laboratories, Ltd., Banbury, Oxon., England
AES E-Library: Groove Deformation and Distortion in Recordings by Barlow, D. A.; Garside, G. R.
Groove Deformation and Distortion in Recordings
JAES Volume 26 Issue 7/8 pp. 498-510; August 1978
The elastic and plastic deformation of vinyl record compound under indenters of various profiles has been studied in large-scale tests. Curves of total depth of penetration versus load have been used to calculate the net distortion on record playback. In general, in the lower treble, net distortion is less, and in the upper treble, net distortion is greater than tracing distortion alone. This is important for attempts to reduce tracing distortion by inverse predistortion of the recorded signal. Nylon was also studied as a material with contrasting mechanical properties to vinyl. Further light has been shed on the nature of translation loss.
Authors: Barlow, D. A.; Garside, G. R.
"Role of Scanning Electron Microscope in Disc Recording." George Alexandrovich. AES Preprint 1274, 58th Convention.
Among other subjects we investigated was the method of playing records wet. By applying a thin film of water as the record was rotating and playing the groove with an ordinary stylus, it produced unexpected increase in vinyl deterioration in the area where the stylus was touching the groove. Our SEM pictures unveiled extraordinary ripping of the vinyl surface which I can explain only by the fact that the vinyl is not allowed to liquify momentarily under the pressure of a fast moving stylus because of the cooling action of water in the groove. This phenomenon, I believe, is identical to ice skating where one does not skate on ice but actually on a film of water which comes from the ice being momentarily melted under the pressure of the thin metal blade. If ice is too cold, one cannot skate. Evidence of the fact that vinyl melts can be found in pictures taken of record grooves played at different temperatures.
Also found where the whole vinyl melting idea went into print. Apparantly it's in the 'handbook for sound engineers' in a chapter written by G.Alexandrovich.
Any AES members able to have a scan of the above articles to see if there is any useful data in there?
Edit: looking for the Alexandrovich paper comes up with this http://www.aes.org/e-lib/browse.cfm?elib=1645 which is right name but different authors.
Here is the right paper http://www.aes.org/e-lib/browse.cfm?elib=3080
AES E-Library: The Limiting Tracking Weight of Gramophone Pickups for Negligible Groove Damage by Barlow, D. A.
The Limiting Tracking Weight of Gramophone Pickups for Negligible Groove Damage
JAES Volume 6 Issue 4 pp. 216-219; October 1958
It has been observed that when spherical styli are dragged over flat vinyl surfaces, scratches are produced under loads considerably exceeding the elastic limit as calculated from theory. The author, in this paper, describes the results of his experiments which bear out his argument that under load the point of yield begins below the surface; and reaches the surface, producing visible tracks, only after the calculated yield load is exceeded. This critical value of load for styli of various radii has been measured and found to be equivalent to, for a 1-mil stylus, 0.64 gm. for a 90° record groove. No size or skin effect was found with the vinyl material tested.
Author: Barlow, D. A.
Affiliation: Aluminium Laboratories, Ltd., Banbury, Oxon., England
AES E-Library: Groove Deformation and Distortion in Recordings by Barlow, D. A.; Garside, G. R.
Groove Deformation and Distortion in Recordings
JAES Volume 26 Issue 7/8 pp. 498-510; August 1978
The elastic and plastic deformation of vinyl record compound under indenters of various profiles has been studied in large-scale tests. Curves of total depth of penetration versus load have been used to calculate the net distortion on record playback. In general, in the lower treble, net distortion is less, and in the upper treble, net distortion is greater than tracing distortion alone. This is important for attempts to reduce tracing distortion by inverse predistortion of the recorded signal. Nylon was also studied as a material with contrasting mechanical properties to vinyl. Further light has been shed on the nature of translation loss.
Authors: Barlow, D. A.; Garside, G. R.
"Role of Scanning Electron Microscope in Disc Recording." George Alexandrovich. AES Preprint 1274, 58th Convention.
Among other subjects we investigated was the method of playing records wet. By applying a thin film of water as the record was rotating and playing the groove with an ordinary stylus, it produced unexpected increase in vinyl deterioration in the area where the stylus was touching the groove. Our SEM pictures unveiled extraordinary ripping of the vinyl surface which I can explain only by the fact that the vinyl is not allowed to liquify momentarily under the pressure of a fast moving stylus because of the cooling action of water in the groove. This phenomenon, I believe, is identical to ice skating where one does not skate on ice but actually on a film of water which comes from the ice being momentarily melted under the pressure of the thin metal blade. If ice is too cold, one cannot skate. Evidence of the fact that vinyl melts can be found in pictures taken of record grooves played at different temperatures.
Also found where the whole vinyl melting idea went into print. Apparantly it's in the 'handbook for sound engineers' in a chapter written by G.Alexandrovich.
Any AES members able to have a scan of the above articles to see if there is any useful data in there?
Edit: looking for the Alexandrovich paper comes up with this http://www.aes.org/e-lib/browse.cfm?elib=1645 which is right name but different authors.
Here is the right paper http://www.aes.org/e-lib/browse.cfm?elib=3080
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Agreed. However, apparently the resonant series is typically simple in practice, and follows Eigen values one might expect from cantilever vibration modes only. I posted a Happ/Shibata f response plot on this thread that shows this. This simplicity would not be expected if both vinyl spring and cantilever flex were present, IMO.
So far so good. Though deformation might be partly or residually permanent/temporary I suppose. IIRC this was characterised by Barlow in one of the papers Bill cited.
Well, that depends on how fast your finger/the vinyl moves. To scale, you finger would be moving at about 1000km/hr or 280m/S across the foam cushion !!! Then it's pretty obvious that the foam cushion can't deform, it would effectively be rigid, not least because of energy considerations (though you could set fire to your finger trying), and partly because there is no time for the foam to compress.
Energy wise, it would be like you had tried to indent the foam cushion at 250kHz with your finger: the mechanical impedance of the cushion spring would make the amplitude of any indentation negligible when applied at the same force as a very slow press. Plus, the loss modulus of the foam would add to the impedance, increasing rigidity further. The foam would be rigid.
And, I say it seems to me, vinyl playback must be like this.
IMO that can't happen, for the reasons above. Static deflection can only happen when vinyl is stationary or moving very slowly indeed.
Well, I think one can prove it reductio ad absurdum, by considering what would be true if the mechanical resonance at c 15-25kHz is due to vinyl compliance.
We can deduce a vinyl spring constant because we know effective tip mass from published figures, say 0.3mg, and we know resonant frequency. We also know static indentation, from either Hertz equation or various papers such as Bill cited.
We then have to compress, in sequence, 250000 separate such springs per second, with a contact time of a few µS per spring and a force of a few gf, to the depth of the static indentation.
If the impossible spring mechanics aren't convincing enough, one can add loss modulus of the material.........
LD
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I have found a couple of threads that missed the purge! currently trying to find where LD goes from thinking wet play doesn't cause dry issues to finding it does. Nov 2009 its still good 🙂. Also realised how much more reading up I need to do on things that just flew by me in the past. All good.
🙂 Yes IME it can cause serious dry playback surface noise, but not always, and I never got to the bottom of what might be the factors behind why. IIRC, at the time I was using wet playback to make profound improvement to surface noise on records which were already noisy. However, at some point, perhaps using test records, I realised that profound degradation for dry playback of records which were previously quiet is also possible.
At some point I noted the correlation between surface noise and stylus-groove friction, and, after a lot of theorising, I found an explanation of the effect, if not the cause, of both the improvement and the degradation that I find satisfying and probably correct IMO.
But the mechanism for changes that can happen at the groove surface during wet playback remains a mystery. As to the Alexandrovich paper you posted Bill, I think one needs to separate the facts, such as micrographs of groove changes, from the author's thesis as to mechanism of their cause. IMO the latter isn't very satisfying and contradicted by energy considerations. So explanation still remains an enigma I think.
Meantime, any permanent way of reducing stylus-groove friction remains an opportunity to improve surface noise, IMO and IME, and is also fairly uncharted water AFAIK.
LD
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I've got about another 30 pages on 3 threads to get through, but so far I have noted that
1. RCA (who also had SEM) disagreed with Alexandrovich
2. Alexandrovich used lacquers not test records
3. Challenging beliefs involves lots of upset people on forums 🙂
I'm still sifting wheat from chaff here. But you are right that I see cases of people jumping to conclusions as to why they have observed things.
Fascinating stuff. Shame I missed all this first time round. Ah well never too late 🙂
1. RCA (who also had SEM) disagreed with Alexandrovich
2. Alexandrovich used lacquers not test records
3. Challenging beliefs involves lots of upset people on forums 🙂
I'm still sifting wheat from chaff here. But you are right that I see cases of people jumping to conclusions as to why they have observed things.
Fascinating stuff. Shame I missed all this first time round. Ah well never too late 🙂
Thanks for digging up these ancient manuscripts from Dr. Don Barlow Bill. 🙂
The cure for this is of course known as the Scientific Method
- You try to fit a Hypothesis to FACTS.
- Dream up an 'independent' experiment whose results you predict from the Hypothesis.
- Depending on the results of the experiment, you might modify the Hypothesis or raise it the august level of Theory
- The Theory allows you to usefully predict the outcome of similar type situations.
- Of course further experiments may move outside the area of 'similar type situations' and you might modify the theory to explain these new results or simply define limits to where your theory applies.
FACTS
Beach bum reports Jurassic memories of Doc Barlow (who has forgotten more about vinyl playback than probably all da pseudo vinyl gurus on this forum combined) writing Engineering Memos threatening death penaly to those using his Test Record without following his Rules. One of these being allowing a rest between response sweeps else you'll get 2 different curves.
This may be with Doc Barlow's specially cut lacquers but might have also applied to CBS & B&K Test Records with V15-3
HYPOTHESIS
This would be explained by vinyl elastic & inelastic compliance/deformation .. a belief considered heretical by one pseudo vinyl guru here 😀
EXPERIMENT
As original data is from a dodgy beach bum, it would be wise to check it by simply doing 2 response sweeps on a test record one after another ... and then again after 24 hrs.
Other experiments suggest themselves eg playing at half speed.
I'm saddened that so far, no one, with the capability, has done this simple EXPERIMENT but seem to prefer hurling ancient scriptures and arcane incantations .. eg Bessel functions etc at those not of their sacred beliefs 😡
After all, most of us are not really interested if the resonances are due to cantilever resonances or vinyl compliance .. but we ARE interested if playing a record changes it in the short & long term. 🙂
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it was the scientific method that was getting people hot under the collar. They preferred beliefs.
I would love to help, just stay alive a few more years so I can actually get things working! Tonight its the wacky motor support bearing that's playing up. Wife will be grumpy in the morning with bits of turntable everywhere in the living room...
There is a problem with your hypothesis tho. Has anyone got evidence of the sweeps being different? A memo is not after all a proof of anything! Scott did post 2 consecutive sweeps a few pages back.
I would love to help, just stay alive a few more years so I can actually get things working! Tonight its the wacky motor support bearing that's playing up. Wife will be grumpy in the morning with bits of turntable everywhere in the living room...
There is a problem with your hypothesis tho. Has anyone got evidence of the sweeps being different? A memo is not after all a proof of anything! Scott did post 2 consecutive sweeps a few pages back.
I don't remember Scott posting this.
Its EXACTLY the EVIDENCE I'm after. I don't trust dodgy beach bum claims either 😱
I used to, and might still have somewhere.......
IIRC though, it covers static indentation and stress/strain......
LD
For sure........
If common understanding of vinyl playback is true then it stands scrutiny, and explanations make sense no matter how deeply one explores. However, one generally doesn't have to look too deeply to expose flaws and loose ends in all manner of common knowledge and lore. The upside is opportunity for improvement in playback quality I figure, and for me it already has provided that in spades.
Look on the bright side, even after half a century, apparently profound opportunities remain, and this forum is far far more skilled and tolerant than most, IME.
Indeed.....
And the idea that iconic papers might be flawed isn't too popular either......
Well, IMO you miss the point as to where proper understanding of cantilever mechanics/vinyl compliance might lead..........
Whereas, apparently you hold important a belief about tribology of vinyl grooves affecting dynamic elasticity that, AFAIK lacks evidence and is unexplained, and seek evidence for it in a test IMO unlikely to show the effect you're looking for........ which is your prerogative, of course.
LD
I ran out of time after unsticking the motor pillar to finish the historical trawl. The indentation question is interesting as the pressure from a stylus IS high enough to cause static indentation, but measuring dynamic effects would seem to be a little challenging.
One part that is intriguing me, at least having got the concept of spherical cows skimming at supersonic speeds across infinite rubber sheets out my head. In the simplistic models of contact pressure it's assumed to be constant, but of course in reality it cannot be as the diamond is being accelerated in various directions at up to many G and the cantiliever is oscillating around as mechanical systems are wont to do.
It would be comforting* to think that in fact the vinyl doesn't deform and the cantiliver behaves like an epee in this case, mainly because I cannot think how on earth you would measure this with any accuracy. You can see the carnage of a damaged groove afterwards, but in real time I am flummoxed.
*Not that I am sitting on the fence here but I'm lacking the baggage of having read all the articles on vinyl 'spring' in my youth so looking at all options.
One part that is intriguing me, at least having got the concept of spherical cows skimming at supersonic speeds across infinite rubber sheets out my head. In the simplistic models of contact pressure it's assumed to be constant, but of course in reality it cannot be as the diamond is being accelerated in various directions at up to many G and the cantiliever is oscillating around as mechanical systems are wont to do.
It would be comforting* to think that in fact the vinyl doesn't deform and the cantiliver behaves like an epee in this case, mainly because I cannot think how on earth you would measure this with any accuracy. You can see the carnage of a damaged groove afterwards, but in real time I am flummoxed.
*Not that I am sitting on the fence here but I'm lacking the baggage of having read all the articles on vinyl 'spring' in my youth so looking at all options.
You know you've getting close when you're thinking about spherical cows sliding at supersonic speeds across infinite stretched rubber sheets......but that's about right IMO. The rubber sheet has its own mass, is quite thick and is lossy. And the cows are white with black spots 😉
It shows up as tracing error, harmonic distortion. But yes, separating cantilever flex from vinyl compression I don't see how one can.........and hence, I suppose, the case of mistaken identity over the decades?
LD
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