Alexey Korf post at Lencoheaven about tonearms
- Thread starter adnick
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JP
7480 74111110101115
The bands. They're in the same vein as the axial flexure bearings.
I'll only add that the B&K paper goes a little further in examining resonance-induced tracking issues, avoiding obvious mismatches seems to still make a lot of sense.
I'm acquainted with the paper - actually had it recommended by Alex Korf himself a couple of years ago. I'm honestly - not critically - curious, which part of it are you referring to?
See pages 10-11, "Variations in tracing force."
It's a fantastic paper - recommended for anybody who hasn't already studied it. But I fail to see how the cited part would go beyond what I think is Korf's point.
What he is saying isn't that these resonances do not exist or don't matter, only that their actual level and frequencies do not follow from the "standard" calculations. Once you have a setup able to provoke them badly enough, you will get exactly what the B&K paper shows. Most effectively by combining a low compliance cart with a low mass arm. Or do I miss something in my reading of the paper?
What he is saying isn't that these resonances do not exist or don't matter, only that their actual level and frequencies do not follow from the "standard" calculations. Once you have a setup able to provoke them badly enough, you will get exactly what the B&K paper shows. Most effectively by combining a low compliance cart with a low mass arm. Or do I miss something in my reading of the paper?
Well B&K didn't seem to struggle with the formula, they in fact seemed to prove the math experimentally. The trouble (as some pointed-out above) is that the values we're provided by manufacturers these days are often wrong.
Read the last page of the B&K paper and it seems pretty obvious that B&K and Korf came to the opposite conclusions about what matters.
I may be wrong, but I can't see the good folks of B&K actually using the formula, only citing it in the introductory background. What I see is them making excellent measurements of actual combinations of carts and arms. Not testing how they would fit any calculations, or citing any specs, since that wasn't the topic of the paper.
Not really, but he doesn't put as much emphasis on the exact frequency as on the spectral distribution of the subsonics. He has an interesting "Compliance/Effective Mass Calculator" with explanations here: http://korfaudio.com/calculator
JP
7480 74111110101115
The B&K paper is an app note presented at a convention - not peer reviewed and not published as such. It's cursory data with a lot of hand-waving over the most interesting bits. I don't happen to have any records with .2mm radial slits in them that I listen to, so that data isn't all that useful to me, especially in consideration that most of it lacks vertical scales. Instead we get 'obviously this is audible'. I don't think it was ever intended to be an epitome on the concepts raised, rather just background to support the papers conclusion.
A lot of Alexi's thoughts are interesting, but again, too much hand-waving. I wish there were more rigor in his experiments and a lot more transparency. For the topic of resonance, the latter series of four posts on matching were rather interesting: http://korfaudio.com/blog68. However this leaves us with two conflicting sets of experimental data derived via two rather different methods.
A lot of Alexi's thoughts are interesting, but again, too much hand-waving. I wish there were more rigor in his experiments and a lot more transparency. For the topic of resonance, the latter series of four posts on matching were rather interesting: http://korfaudio.com/blog68. However this leaves us with two conflicting sets of experimental data derived via two rather different methods.
I just need to point out that the analysis in the B&K paper is fundamentally flawed. The conclusion was that a low mass arm with damping was better than two other medium mass arms without damping. Unless the conditions for testing are the same (ie all damped or all undamped) you cannot draw a conclusion about where the resonance frequency should lie.
A cynical take on the paper would be seeing it as an advertisement for what can be done with their kit on turntables. Still an interesting paper, and sadly one of the very few on the topic in the public domain.
My entire point here has been that the Korf stuff would deserve further research. There hasn't been much of progress in the field for some time now.
I think that one of the problems with the paper today is that it is written long before current ideas on tonearm design. They are discussing damping or non-damping of vibrations, not transmitting them out of the arm. I don't think that part would affect the resonance frequency stuff though, but possibly the amplitude of the resonances.
JP
7480 74111110101115
That's not cynical, it's the way of things.
Agree there's more work to do here before conclusions can be drawn. Both 'papers' are rather shallow.
I wouldn't expect there to be any, since it isn't the type of research paper that was even meant to generate such work. I guess a few AK:ers have access to the AES archive where one might find that kind of papers, but I don't know if any of them are on this thread.
Most of actual research done on this is not at all in the public domain, but was done inhouse by makers of turntables and their accessories, often using the methods and equipment advertised in the paper.
Still, the gist of the paper should still be valid, if taken for what it was meant to be.
What exactly is it meant to be?
A white paper from the leading manufacturer of audio measuring equipment, showcasing what can currently be achieved with their most sophisticated equipment. Target audience is the top notch of engineers in that field having access to, or considered possible buyers of, such equipment. This marketing aspect is why this study now is in public domain, probably as opposed to more specific research papers from the same conference.
This scenario means that the substance of the paper must be good enough to make an impression on the specific audience, without being too specific on design aspects of the objects of the study. The emphasis is on the methods of measurement and the results from them, and how they can be applied to the design of turntables.
What it is not, is a paper on the calculation of resonance frequencies from combinations of cartridges and tonearms, since it doesn't contain any of those. It contains the standard formula for harmonic oscillators, taken as a given in the background for the actual subject, the top notch measurements. And since the paper is from 1977, some new ideas may have turned up along the way.
This scenario means that the substance of the paper must be good enough to make an impression on the specific audience, without being too specific on design aspects of the objects of the study. The emphasis is on the methods of measurement and the results from them, and how they can be applied to the design of turntables.
What it is not, is a paper on the calculation of resonance frequencies from combinations of cartridges and tonearms, since it doesn't contain any of those. It contains the standard formula for harmonic oscillators, taken as a given in the background for the actual subject, the top notch measurements. And since the paper is from 1977, some new ideas may have turned up along the way.