Measuring Pickups 1967 Article... comments?

[dlaloum]

Hi Folks,

just reading through the 1967 measuring pickups article that was recently added to the library....

I thought I would open a topic for the more geeky participants to discuss.

One thing that struck me was that in discussing resonance, it was called stylus/groove resonance ... so there is an assumption as to what the resonance is.

Later articles tend to talk about cantilever resonance (which is the assumption I have made in my measurements...).

The stylus/groove resonance is measured as part of measuring the stylus mass... but, if in fact it is not a stylus/groove resonance, but in fact a cantilever resonance, does that in fact invalidate the measurement method?

Are there problems with this paper, are there methods and assumptions that supersede the measurements described, or is it still spot on? (Physics certainly has not changed - but some assumptions underlying some of the measurements may have since been shown to be faulty...)

bye for now
David

[Ldg]

Are there problems with this paper, are there methods and assumptions that supersede the measurements described, or is it still spot on?

I like this article, and think the author has amongst the better grips of what is going on I've read.

Along with a vast body of published papers, the author assigns the top resonance to groove indentation spring and effective tip mass. If this is true, your method for optimising loading isn't too good, DL. Because much would then depend upon specific vinyl composition, and spring properties of the test discs you use.

Amongst supporters with published papers endorsing the vinyl indentation link to top resonance are big names, like Mr Shibata, for example. This is what you have to overcome to safely ignore groove-mass interaction. There are complete models, and on the face of it, it's well explored.

I'm in a firm minority here in not accepting that groove indentation happens during play. Rather that cantilever flexes. Actually, they're very hard to tell apart. The key difference, IMO, is that energy would be left behind by indentation. But conserved in cantilever flex. And when I do the sums, there's not enough energy by way of drag to support indentation.

There are published, peer reviewed, complete models for the top-resonance. Based on indentation. Which describe the whole thing very well. On the other hand, I personally have a model not based on indentation, but just cantilever flex, which describes the whole thing well too.

But, you can't really stand with a foot in both camps. There is only one resonance, so both indentation and cantilever flex can't both occur. For your purposes, DL, it matters to know which it is.

AFAIK, mine is the only analysis that describes a cantilever only answer. I might just be wrong, of course !

I'm sure I've posted this before to you, DL, in the context of it not being safe to assume the top resonance is due to cantilever flex. Personally, I can see a sound reason why indentation might not happen, but can't see a reason cantilever flex wouldn't. So I prefer cantilever flex.

However, if you decide to be anti-indentation, and support the minority cantilever flex camp, a whole raft of stylus profile preconcepts have to go too. Such as fine line contact areas.......and you have to say that a whole raft of published literature is wrong. But, I don't accept indentation happens during play, that is my opinion, FWIW. And I don't see contradictions. Everything is tidier.

HTH !

[Ldg]

One further point, the term 'cantilever resonance' as crops up in some latter marketing blurb and articles, is used simply as a term to describe the top mechanical resonance. That is, it does not describe a mechanism per se. AFAIK, the term simply derives from the cantilever being implicated either way. Whether by mass or by flex, it is the cantilever which moves. And whether groove spring and indentation is also involved is academic for many purposes. But it would seem to matter for your assumptions, DL.

[dlaloum]

There are other models of cantilever behaviour (eg: the electron microscopy papers I linked to some months back) - which discuss cantilever resonance ..

At the time I was searching for more information on phase behaviour of the cantilever resonance... these papers discussed cantilever resonance and its phase behaviour.

So...
1) Cantilever resonance does happen and is documented in various environments (in the case of that paper - electron microscopy)
2) Why would knowledgeable, scientifically trained minds not assume or identify cantilever resonance?
3) How would one measure/differentiate between needle/groove resonance and cantilever resonance? (at a reasonable level of significance...)

Yes I do recall your mentioning the alternative theory - but your approached seemed internally consistent, matched what I was measuring and seeing, and agreed with other materials I was digging up around the web....

I guess I am revisiting this, having read again elsewhere about Shibata's contention regarding the top resonance and then this, particularly detailed and well written article.

A recording medium where variations in the composition of the medium itself causes changes in the frequency, phase and separation of the resulting recording would be a very frustrating thing to pin down!!!!

Any reproduction would therefore become an approximation... ( to a greater degree than most people think! )

[Ldg]

No, you've got that all around your ears again, DL. The idea that cantilever self-resonance accounts for the 'top resonance' is the alternative theory ! And that is my proposition, which you apparently subscribe to. Stick to the plot, read the script !

You're just being misled by the term 'cantilever resonance', which is widely taken to mean the 'top resonance'. But doesn't actually describe a mechanism, in common usage.

I don't recall reading any paper, linked by you or not, which associates the top resonance with cantilever flex. Or denies the existance of indentation, and groove spring-mass resonance. AFAIK, that is my original proposition. One article (electron microscopy) you mention expounds beam theory (which supports my position) but does not apply it to phono cartridges. The other (Ortofon phase marketing article) is silent on the nature of the mechanical resonance (and is generally nonsense anyway).

And, I don't recall you ever pointing out any 'internal inconsistancy' in my postings on this topic. You'll have to remind me.......

So, DL, I reckon you're in with me and the minority on this one, or you have to acknowledge some serious flaws in the assumptions for electrical loading optimisation you use. Hey, if I'm wrong, you're wrong too !

But, if you are to credibly oppose the whole raft of published work that contradicts your position, DL, you have to be able to point out what's wrong with it. But I really doubt you have the skills to do this, or to form a sensible opinion about the whole issue. Frankly.

Suggest try starting by knocking over the following papers which oppose your position :

"An Experimental Study of Groove Deformation in Phonograph Records", James White, Harvard 1974

"Groove Deformation and Distortion in Records" D.A. Barlow et al 1973

"Technical Requirements and Analysis of Phono Cartridges for Proper Playback of CD-4 Discrete Four Channel Records", N. Shibata et al, 1974

[bauzace50]

Hi,

just caught a glimpse of this long article. Quite impressive, and congratulations to you folks who can navigate its density. I feel that good technical knowledge of cartridge performance is absolutely necessary for handling some conundrums that crop up here.

A good educated ear and basic user's knowledge are sufficient to sort out one's preferences, but it takes better tools and understanding to scratch deeper.

That's a great article,
bauzace50

[Ldg]

Yes, b_50. Actually, one can't get very far exploring these things without having to resolve whether the top resonance is due to groove indentation spring or cantilever self flex.

It really is a crux, a great divide in a whole host of follow on theoretical matters and operating principles. And pivotal in understanding the core of tracking and tracing mechanics, the root of better decisions about configuration, setup and buying decisions.

There is only one top resonance. And if one prefers cantilever flex as an explanation, there's a whole body of established, accepted research to overcome. It's quite iconoclastic, and a minority position. I can argue it.

But I'm not at all convinced that DL hasn't just got caught up in my slipstream here. There's a whole host of consequences, and cantilever flex poses contradictions as to opinions on a whole host of other matters. But without cantilever flex, the electrical loading optimisation method DL uses looks holed beneath the waterline. So let's hope I'm right !

Interesting, and controversial then. If you're into operating principles !

[dlaloum]

Heh ... I don't claim to be a physicist... and yes I am at least partially if not wholly caught up in your enthusiastic slipstream...

I need to do more reading to get my mind around the concepts, and the ramifications of the alternatives....

[missan]

FWIW, a couple of things that puzzles me re vinyl resonance/needle mass.
Even at a very high frequency the possible indentation is not instant, the needle is transported along the vinyl surface.
Isn´t the movement of the vinyl in the elastic area very much depending on the vinyl´s intrinsic damping, which would seem to be high? It would then prevent a resonance?
The resonance cannot happen at a low frequency, say 10-15KHz it would then scrape the grooves from information? Just thoughts.
missan

[davidsrsb]

Fig 3. on the 3rd page (page 583 in original). The Shure M44 mechanical? impedance is doing something strange at 5-10 kHz, where MMs often suffer droop

[Ldg]

FWIW, a couple of things that puzzles me re vinyl resonance/needle mass.
Even at a very high frequency the possible indentation is not instant, the needle is transported along the vinyl surface.
Isn´t the movement of the vinyl in the elastic area very much depending on the vinyl´s intrinsic damping, which would seem to be high? It would then prevent a resonance?
The resonance cannot happen at a low frequency, say 10-15KHz it would then scrape the grooves from information? Just thoughts.
missan

Hi missan. Yes, it's exactly contradictions as you point out above which have no answer in the indentation/mass model. I agree, measured Q of the top resonance is too high for vinyl compression, for the reason you post.

And yes, indentation would take time to happen, and time to relax. Not only is there not enough time available, but energy available is insufficient to make it happen quickly enough. Furthermore, energy would be left behind the stylus in compressed vinyl, so drag on the stylus would be far far larger than is actually measured.

These are awkward contradictions to explain in the indentation spring/mass model. There's no contradiction if indentation is negligible. As in the cantilever self flex model.

It's far more likely the stylus surfs the moving groove wall surface with negligible indentation, IMO.

[Ldg]

Fig 3. on the 3rd page (page 583 in original). The Shure M44 mechanical? impedance is doing something strange at 5-10 kHz, where MMs often suffer droop

Hi davidsrsb. The author defines mechanical impedance as tracking force required per 5cm/s stylus velocity, which illustrates nicely the role mechanical impedance (and so cart compliance) play in defining trackability at various frequencies.

Mechanical impedance typically varies significantly with frequency, by an order of magnitude. Here's published mech impedance plots for the Shure V15II and Denon DL103 courtesy of Yosh's excellent site, from JVC measurements IIRC :




This seems a more typical characteristic shape. In the Walton paper ref davidsrsb's comment, this shape is generally seen, except for the Shure M44 case. It made me think it was likely to be an anomaly in that paper.

The general shape is tempting to try to fit with the mid-droop. But there are contradictions to this, not least the scale. There's an order of magnitude difference in mech impedance here. But that does not necessarily make any difference to physical cantilever movement, just the amount of force needed to make it happen.

So I don't see a link, I think it's more likely a happy coincidence in the shape. And IMO, the mid-droop is more likely an artifact of combined mechanical and electromagnetic responses, as per the Yamamoto and JVC models Yosh posted previously.

[davidsrsb]

Ok, so the mechanical impedance is corrected for the RIAA curve.
This leads to the possibility that there is effectively a shunt impedance from the cantilever mounting, body etc. This would have effect on the output with frequency and cause the droop.
I was looking at HiFi World November 2001 with measurements of some budget cartridges.
AT 120E - no droop but early resonance, peaking at +4dB at 10kHz
Goldring 1006 - fairly flat
Goldring Elektra - early droop, 6dB down at 20kHz
Ortofon Super OM10 fairly flat

[Ldg]

Hi davidsrsb. Those mechanical impedance plots are based on physical stylus velocity. As such RIAA shouldn't come into it, i reckon. Except to note that a 'flat' recorded frequency response doesn't equate to 'flat' velocities, of course, because of RIAA.

Just because more or less force is needed to move the cantilever doesn't mean it doesn't move in exactly the same way. It just changes the amount of VTF required to hold the stylus down and prevent mistracking, versus stylus velocity.

Actually, VTF needed is at a minimum at frequencies associated with the mid-dip. That is, stylus is easiest to move, needs lowest force. I really think it's just coincidence. And any additional external non-ideal impedances must always be additive too, ie making it harder to move. It's all the wrong way round to be associated with mid-dip. If the mid-dip had a purely mechanical cause, the armature would have to move less, to make the dip. I suppose it's plausible that the cantilever flexes, but why with that profile versus frequency ?

I don't see it !