Alexey Korf post at Lencoheaven about tonearms

[tothmes]

So to me the Korf calculator is pretty meaningless. I don't think it calculates the natural frequency of a resonance correctly (so the frequency where the amplitude is highest) and I don't think it shows the relation between peak amplitude at the natural frequency in relation to lower and higher frequencies.
To make such a calculator work, cartridge manufacturers would have to publish Q factor or damping factor data, like how speaker chassis manufacturers do.

I'm certainly not the one to question what you are saying - this seems pretty convincing. But just to sort things out:

Do you mean that Korf is wrong in questioning the "standard" formula used for calculations of resonance frequencies, or in his application of this in his new calculations? I take it that what you ask for isn't going back to the old way, but instead asking for a refinement of the new calculations (which of course would require information from the makers of cartridges that we will never get)?

 

[mr_petit]

Yes he's wrong in questioning the standard formula. Hooke's law still applies today. It's a physics law for a reason.
If Korf's calculator calculates a different natural frequency (eigenfrequency) of the resulting resonance, which it looks like in my example, then it's not correct.

But the standard formula only says something about the frequency of the resonance. It say's nothing about the damping of the suspension of a cartridge, or how big the excursions of the arm are at that resonance (amplitude).
But Korf's calculator doesn't either. It just makes an assumption. First of all it assumes that all cartridges have the same damping properties of their suspension, which is certainly not true, and secondly, I think it also doesn't display an excursiongraph that is anywhere near what is usually taking place. His graph shows an increase in excursion of about 10-20% where I think in reality this is much more. So the Q factor he's using is imho way way to low (or, the damping factor he uses is way too high; Q is basically inverse proportional to damping). So the profile of the excursion graph should be way more spikier.
So as Korf's calculator seems to not do any of these things right, I don't see the point of it. Not an accurate representation of the resonance frequency, nor an accurate representation of the excursion or excursion profile.
To make a calculator that accurately shows excursion indeed you need data that cartridge manufacturers don't supply.
Ripblade compared it to speakerdesign. But you can't design a cabinet when you only have MMS (analog to effective mass of the arm+cart) and CMS (analog to compliance).

With using the 'standard formula', so Hooke's law, you just get the eigenfrequency of the resonance. With that, it's important to take care in what meaning you give to that.
But that's better than giving false representations in my book. To me it seems that Korf mainly tries to be different instead of being accurate or 'right'.
And I also think it's strange (or sloppy) that he didn't figure out that the HFNRR test record has that fubar vertical resonance track...

 

[gusten]

The damping factor for the cartridge must in reality be much higher IMHO. Also one has to factor in a tonearm damping to be able to do the calculations, which isn´t easy. We certainly can´t do this if only using eff mass and compliance.

 

[mr_petit]

The damping factor for the cartridge must in reality be much higher IMHO.

You probably mean Q factor?
These systems are imho per definition underdamped, so the Q factor is per definition higher than 0,5, and I suspect it to be really high (so very little damping/damping factor)
Q factor to damping ratio

(zeta) relation: Q=1/(2

)

I expect there to be also very little tonearm damping at 10hz, unless there is a silicone fluid damper, or an electromagnetic damper, or eddy current damper.

 

[cgallery]

When that paper was written in 1977 the only high-mass/low compliance crowd would had been a dozen or so of graybeards banging on about their neolithic Garrards and 3012's on their way to the terminal ward. By then, the scientifically based future was still low mass / high compliance. Isn't history of technology fun?

Back in the late 70's/early 80's when I was looking at the Infinity Black Widow arm to pair with an ADC cartridge I already owned, Milwaukee and Chicago dealers were still selling plenty of Denon and Ortofon mid and higher mass arms and moving coil cartridges.

 

[JP]

Nope just pointing-out that you needlessly picked the extreme (18Hz), whereas 15Hz+ would be quite easily achieved with a low mass arm and medium compliance cartridge.

Sure, with an allocation of 6g for the cartridge and fixtures, you can throw a 12-13CU cartridge on a Black Widow and hit 15Hz. Do we consider 3g EM common for low mass arms?

This is what you'd stated that I disagreed with: "Their conclusion that that damped low mass arms + high compliance cartridges outperform." On a 1g EM arm with a 5g cartridge/fixtures you can just hit 15Hz with a 20CU cartridge. Hair splitting and contrived scenarios aside, in any practical sense it's a low mass/low compliance game.

Regardless, I'm still befuddled about the 15-18Hz prescription/contradiction out of nowhere.

And yet "that's not to say in general that info it contains is incorrect.".

Never said it was. My criticism is the use of a marketing document as an authoritative source on a subject simply because the subject was mentioned and the document was authored by an authority. There's a logical fallacy named after that. Makes no difference if the information happens to be correct or not.

 

[cgallery]

Sure, with an allocation of 6g for the cartridge and fixtures, you can throw a 12-13CU cartridge on a Black Widow and hit 15Hz. Do we consider 3g EM common for low mass arms?

This is what you'd stated that I disagreed with: "Their conclusion that that damped low mass arms + high compliance cartridges outperform." On a 1g EM arm with a 5g cartridge/fixtures you can just hit 15Hz with a 20CU cartridge. Hair splitting and contrived scenarios aside, in any practical sense it's a low mass/low compliance game.

Regardless, I'm still befuddled about the 15-18Hz prescription/contradiction out of nowhere.

I did correct and indicate medium compliance.

The fact remains though that the arm and cartridge providing the highest combined resonance (about 15Hz) outperformed the same cartridge on higher mass arms, throughout their testing.

It looks like they hit approx. 15Hz, 11Hz, and 8Hz for these tests, and 15Hz was clearly superior.

Never said it was. My criticism is the use of a marketing document as an authoritative source on a subject simply because the subject was mentioned and the document was authored by an authority. There's a logical fallacy named after that. Makes no difference if the information happens to be correct or not.

Well if we're going to start discussing logical fallacies, we should probably start with the ad hominem attacks questioning B&K's motives for producing the document in the first place, rather than discussing the actual substance of the paper.

 

[adnick]

Does Korf actually, or directly challenge Hooks Law?

Do the traditional calculators completely or accurately represent Hooks Law?

Furthermore, if he’s “wrong” then why does his calculator work whatever % of application (appears to work more often than not).

There ‘s obviously issues with calculators, are these issues (In Vitro vs In Vivo), a misapplication Hooks Law.

Neither side of the argument answers the question:

Why do some cartridge/tonearm combo’s work well that are presented as extremely mismatched by calculators?

Korf’s research and applications also fails to answer the question but it comes closer in some respects, doesn’t it?

Overall it’s a mistake to completely discount these calculators, conversely it’s also a mistake to completely trust them.


VR
Andy

 

[tnsilver]

we should probably start with the ad hominem attacks questioning B&K's motives for producing the document in the first place, rather than discussing the actual substance of the paper

With all due respect, that's not ad hominem attacks. That's clearly a challenge on the appeal to authority (ipse dixit) and it's 100% legit. I don't find offense in JP's posts. Quite the contrary, it's well deserved criticism.

 

[cgallery]

With all due respect, that's not ad hominem attacks. That's clearly a challenge on the appeal to authority (ipse dixit) and it's 100% legit. I don't find offense in JP's posts. Quite the contrary, it's well deserved criticism.

For example, post #73: "Boy, while I'm trying to figure out how to make the right trade-offs to get as close to this impossible goal as I can, it'd sure be nice if there were some test kit that could help me out all these pieces together."

Pretty obvious appeal to motive. https://en.wikipedia.org/wiki/Ad_hominem

Not offensive but certainly not constructive.

If there is a problem in the document fine, let's hear about it. Stick to the document.

 

[tnsilver]

Sarcastic in a way perhaps (and I mean healthy), but the point is definitely clear (it's a good point too IMO). Why is it so inconceivable that B&K have had commercial interests?

 

[JP]

Full-on tongue-in-cheek, absolutely, but not divisive.

 

[cgallery]

Sarcastic in a way perhaps (and I mean healthy), but the point is definitely clear (it's a good point too IMO). Why is it so inconceivable that B&K have had commercial interests?

It isn't, are you suggesting they fabricated data or misrepresented their findings?

 

[tnsilver]

No, but science is a process and what they present as 'data' or 'findings' in that context isn't considered 'data' or 'findings' in the scientific circles. It's like those toothpaste commercials presented by an authoritative dentist. In real life that dentist can be a true authority... He's not winning any medical prizes for that commercial.

 

[tothmes]

It isn't, are you suggesting they fabricated data or misrepresented their findings?

I think what we all are trying to tell you is that noting the commercial interests of B&K behind this paper doesn't necessarily imply anything malicious from their side, or that the findings in it would be tainted in any way. Only that the intention of the paper was for it to be used as a technical instruction for how their latest gear could be used for turntable design, showcasing some real-world measurements. The results and interpretations from them were, and still are interesting, but they never were intended as any sort of last word on turntable design. It is a good paper, well worth reading, but not what you seem to want it to be.

Poul Ladegaard seems to have moved on to become at least a local Danish audio authority, but even the tangential tonearm he designed later is something else than what this paper is about, although he of course did his calculations and measurements for it.

 

[cgallery]

No, but science is a process and what they present as 'data' or 'findings' in that context isn't considered 'data' or 'findings' in the scientific circles. It's like those toothpaste commercials presented by an authoritative dentist. In real life that dentist can be a true authority...

Most of the discussions here seem quite informal, I didn't realize I was at the National Academy of Sciences.

 

[cgallery]

I think what we all are trying to tell you is that noting the commercial interests of B&K behind this paper doesn't necessarily imply anything malicious from their side, or that the findings in it would be tainted in any way. Only that the intention of the paper was for it to be used as a technical instruction for how their latest gear could be used for turntable design, showcasing some real-world measurements. The results and interpretations from them were, and still are interesting, but they never were intended as any sort of last word on turntable design. It is a good paper, well worth reading, but not what you seem to want it to be.

Poul Ladegaard seems to have moved on to become at least a local Danish audio authority, but even the tangential tonearm he designed later is something else than what this paper is about, although he of course did his calculations and measurements for it.

I don't expect the paper to be a last word on anything, but it does present some very compelling ideas and enough details to easily duplicate the work.

I can understand how people with mid- and high-mass arms would want to pretend it doesn't exist, though.

 

[JP]

Lol.

 

[ctjetta]

yawn

 

[adnick]

I don't expect the paper to be a last word on anything, but it does present some very compelling ideas and enough details to easily duplicate the work.

I can understand how people with mid- and high-mass arms would want to pretend it doesn't exist, though.

Maybe I’ve missed your point, why do you think it was written?



Believe there’s many here with a wide range of tonearms, on one end of the spectrum I’ve got a Denon DA401, and a Grace 707, at the other end a several 10-12” arms, and Karmadon Gray 108 clone…



VR
Andy