When Does A Tonearm Have Medium Effective Mass Etc

[flavio81]

Aha!! Coming soon... The "crackly record" tonearm optimization!!

Very interesting. So what we have is basically a "click" or "pulse" track. I guess it would be even better if the grooves are non-modulated.

Sorry flavio, I scratched your record..........scratched your record........scratched your record..........scratched your record....scr

Indeed, it works ! Here's a screenshot of a single recorded click, and the consequent settle time :



The ratio of any two successive amplitude peaks is entirely defined by the damping ratio.

This is a historic moment in vinyl playback. You saw it first here, in vinylengine.

Ok ld, i'm just waiting for your new calculator, the one that calculates cartridge damping ratio by doing click analysis!!!

Although if i understood correctly; i'd just divide peak B / peak A and that would be the damping ratio... ?

Yeah!!

[Ldg]

.....Although if i understood correctly; i'd just divide peak B / peak A and that would be the damping ratio... ?

Yeah!!

Oh yeah ! Thanks flavio81, missan. The maths is a bit more convoluted than that. Basically, points A, B, C, D sit on an exponential line. Since you know it is exponential, if you know any two points, you know the curve. And the curve is defined entirely by the damping ratio. It is a standard, called 'logarithmic decrement'

But wait............it gets better.

You can use this method to tell if you have good or bad type arm bearing friction. Or how good/bad overall. Good type is friction that arises say through viscous bearing drag, or elastic loss. Bad type is stiction that arises through bearing contact force, not proportional to velocity.

Basically pure stiction (bad) produces a straight line between points A, B, C, D. Whereas drag friction (good) produces an exponential curve through A, B, C, D.

So, once the calculator is out, by comparing damping ratios between A&B, B&C, C&D, the closer the damping ratios obtained the more good friction. By eye, closer to a straight line is bad.

[WAPFU]

The graphs show a damped oscillation - brings back memories now of control systems settling after an input. Return to normal as quickly as possible - wow that got the grey cells thinking. Cheers LD for getting me to think and use that old grey matter again.

[Ldg]

Hi WAPFU. Yes, that damped oscillation plays a key role in lf cart/arm matching and stability. It explains the enigma of your original post questions. A method for measuring combined cartridge and tonearm damping is now posted on the cartridge forum, in the cartridge and tonearm damping sticky thread.

HTH !

[flavio81]

My new Lenco L75 tonearm damper. Took me just 1hr to make.

[Ldg]

Good stuff, flavio81. Presumably the damper is on the cartridge side of the tonearm. The CW side mod is seperate, as I think you posted seperately. Simple and should get it done, enough to try out !

[BigE]

Very inspired work.

Please continue ld! You have my full attention.

It appears that the problem of cartridge/arm matching reduces to finding an optimum damping ratio at an acceptable resonant frequency.

So what is the optimum damping ratio?

[Ldg]

Thanks, BigE.

It appears that the problem of cartridge/arm matching reduces to finding an optimum damping ratio at an acceptable resonant frequency.

Well put, BigE.

So what is the optimum damping ratio?

Here's my 2p worth :

Much depends whether the arm supports external damping. If no explicit damping, then perhaps above 0.25 is very good, above 0.2 is good, less than 0.15 is poor, less than 0.10 is very poor. If the arm supports damping, then aiming for a figure near 0.3 seems the mark. Should expect opinion to evolve as discussion and experience develops.

The same question is being discussed on the cartridge and tonearm damping sticky. It's probably better to address these things on the damping sticky in the cartridge forum, i think.

Thx again, BigE.

[Aerobat]

Has anyone checked the distance CW using the ld EMC resonance calculator? On my turntables, the CW distance in the spreadsheet is always about 1cm more than the actual CW distance as measured on the TT. Just curious.

[Ldg]

Hi Aerobat. Thanks for the feedback. I just did a quick check on two TTs (one with a 6g arm, one with a 24g arm), and both were within a few mm as best one can estimate where the centre of mass of the CW is.

Curious though. What measurements do you have, and I'll do a quick manual check ?

[Aerobat]

Hi,

Here are the numbers:

Pioneer PL-L1000 with AT155LC, OEM headshell
9.2
9.5
19
102
7
1.2
CW=4.57

Mitsu LT-30 with Grace F9E, OEM headshell
8.1
5.1
17.5
98
13
1.2
CW=4.47

On both tables, the CW distance measures to the back edge of the counterweight.

This isn't meant to be a critisicm - your tools are great and I appreciate all the work that went into them! I'm just wondering if I'm doing something wrong, or perhaps a formula needs to be tweaked.

[Ldg]

Thanks Aerobat. I found a bug in the calculator, where a detachable headshell of course has a shorter length once the headshell is removed. So when one weighs the armtube, the length that is associated is a bit shorter than when there is a fixed headshell, if this makes sense.

Anyways, it's fixed now, same link .

Testing with your figures and a couple of my own TTs with detachable headshells indeed yields slightly longer CW-pivot lengths, better matching reality.

So thanks for the feedback, Aerobat. It's only by spotting such things that improvements happen, so such things are welcome. And Tonearm Effective Mass predictions for arms with detachable headshells are a bit better for it ! The effect is not major, but well worth fixing.

Thx again !

[bastlnut]

yup,

there is always a bug.
this is why so the called science approach is not really serious.
it blows up in the scientists face and all he has to say is.....
ooops, back to the drawing board.
never even a 'sorry'

even months later you get only a oops, i found the mistake and have now fixed it...
that is only until it comes to the next time that a mistake is discovered.
we just get the same lame ass apology that really isn't one.
its science right?
HA HA

regards,
bas

[Ldg]

Hey, that's the nature of progress. The effect is relatively minor, but well worth fixing. And I appreciate Aerobat's input to that, same as everyone who provides feedback.

You are, of course, trolling again, Bas.