Counterweight positioning observation

The bit about first class levers might point you in the right direction https://www.clear.rice.edu/elec201/Book/basic_mech.html#SECTION00932000000000000000

Hi Chris, it's more complicated than principle of moments with no friction and no resonances. With that model it wouldn't matter if we had a small counter weight a long way from the pivot. I think Tony is right and it does make a difference to tracking and the sound.

It may be the see-saw effect Tony described, perhaps it affects dampening of the arm resonances, or maybe how quickly the transient energy goes from the arm into the pivot/bearings and arm board.

It seems that 'synthetically' manipulating the counterweight position on a tonearm, whether by using a heavier one than nominal/needed or by adding washers, BluTack and whatnot yet maintaining the same VTF as before probably does affect the entire tonearm's center of gravity. Chris referred to reduced arm inertia which I thick is a factor here. There was a fascinating article over on Vinyl Engine over the last few months that discussed 'Some Thoughts On Turntable Design'. Among other things relating to physics and resonances it mentioned the arm's 'moment of inertia'. Directly correlating an arm's overall inertia to it's center of gravity while taking into account it's effective mass, length etc. is frankly beyond me though I wish I could understand it better.

I ask myself, would an arm's 'inertia' really change if it's tracking force and tonearm height (SRA) remained the same? As the record plays and the tonearm 'bobs' up and down to passages of music ever so slightly, the effective SRA may be constantly varying positive and negative from it's stationary angle forming an average of sorts. My guess is if the counterweight positioning is 'synthetically enhanced' to track better, all other things being equal, it's effective SRA average may be biased slightly more positive during loud passages and thus track better.

But in this scenario, it's hard for me to attribute a visual or sonically perceivable change in a tonearm's 'inertia', in and of itself, to be a cause of anything other than a near-immeasurable increase in tracking force. If all else remains the same, I reckon this tracking improvement is rather a symptom of the weight and balance displacement affecting resonances in the tonearm. Maybe I'm wrong and this counterweight positioning modification is indeed a better way of utilizing the available weight for tracking performance and unrelated to other factors (insert proverbial lick of Tootsie Pop here).

Still, I'm a classicist and tend to give the designer the benefit of the doubt on such matters, even if that designer happened to take a 'noncorrectionist' approach like Rega supposedly does according to the OP of that Vinyl Engine article. While I think it's a cool solution to certain tracking problems I'd probably only attempt it when needed due to fear of undue wear, suboptimal performance of other unknown factors etc. Unless my ears told me otherwise. It's good to be back.

Steven

I would add that in Andrews case, the arm in question is dynamically balanced rather than statically balanced (it uses a spring to apply VTF).

He also observed that the setup he settled on seemed to reduce what may have been ringing from the VTF spring, an issue on which others have commented in the past and one of the reasons the RB250 based arms have been more popular as a base for modifications, since they do not have this spring arrangement.