Tonearm effective mass

Excellent clarification by Quiddity, thanks. I should have included the proviso that the two c/w's be of the same shape.

With apologies to my friend Raul, this question is not as simple as you say. You're correct that changing to a heavier c/w would increase effective mass (moment of inertia) IF you mounted the heavier c/w the SAME distance from the pivot. But that would unbalance the cartridge, so this fact has no real world application.

For the *same* VTF...
with the *same* cartridge...
for two c/w's of the *same* shape but *different* masses...
the heavier c/w mounted closer to the pivot will result in a lower moment of inertia than the lighter c/w mounted farther from the pivot.

Hdm,
You left out a key factor. The heavier headshell will be mounted at (virtually) the same distance from the pivot as the lighter headshell. Therefore, its greater mass will increase the system moment of inertia, quite substantially given how much heavier it is.

Read Quiddity's excellent post. A headshell is mounted farther from the pivot than a c/w, so a change in mass at the headshell has a greater effect on moment of inertia than does the corresponding adjustment of c/w position. Adding mass at the headshell and adjusting the c/w to maintain the same downforce at the stylus increases moment of inertia (as Raul correctly stated above).

This will be true whether you use the existing c/w or go to a heavier one, although in the latter case the increase in moment of inertia will be less, due to the effect that was the original topic of this thread.

Doug: Yes you are right: my answer was to much plain. But what I was trying to say was that to really make a difference in the effective mass and due that the headshell is at the " farest " position from the tonearm pivot then here at the headshell is a good place to do it, that's all.

Many times I think the things and the explanation only I understand it like a whole, like in this time. I will try to be more precise.

regards and enjoy the music.
Raul.

Thanks again Doug (and Quiddity). I understand (now) that it's a given that the heavier headshell will have a much greater effect on increasing mass than messing with counterweights.

It was interesting to me that a lighter counterweight pushed out further from the pivot might have as much (or greater) effect in increasing or maintaining a given effective mass than a heavier counterweight balancing the same cartridge closer to the pivot point.

Following this, my next question is this: given that a lighter counterweight is capable of balancing out the same cartridge (but obviously further back from the pivot) that a more substantial counterweight can, would there be any sonic advantage to using the heavier countweight mounted closer to the pivot assuming the effective mass is approximately the same? Would there be a sonic advantage or improvement using the heavier counterweight closer to the pivot point?

Does anyone have any experience with this or any ideas as to whether one approach would be better from a sound perspective than the other?

Raul,

I agree that for practical purposes moment of inertia changes must be made at the headshell end. (Of course as you know, raising headshell mass can impair tracking performance over warps, there's no free lunch.)

Hdm,

The answer to your last question will be specific to the tonearm and cartridge. The difference in moment of inertia caused by changing counterweights (very small difference, as Raul points out) is unlikely to make as much sonic difference as the change in the system's INTERNAL resonance behavior.

I'm not talking about the change in resonance frequency of the spring-loaded cartridge/tonearm system that we've all seen the math for, and can demonstrate with the HFN record. Moment of inertia is of little sonic significance unless you make a BIG change. I'm talking about how the cart/arm reacts to stray energies in the audio band being fed from the cartridge into the tonearm. That will vary depending on the equipment.

The only way to know is to try, unless someone has tried the same combos before and can report.