Counter Weight Question

Counter Weight Question

Postby Johnny » Mon Jan 07, 2019 2:54 pm

Looking for some advice.

My counter weight is near the end of my tonearm stub and my dealer informs me that I will get better performance from a heavier counter weight that can be positioned closer to the pivot point. Is this good advice and something that I should pursue? I should add that I have no problem with balancing the cartridge with the current counter weight.
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Re: Counter Weight Question

Postby Packgrog » Mon Jan 07, 2019 6:09 pm

One issue with counterweight position is how it effects effective mass, which in turn changes compliance. If you're out near the end of the end stub, you might well be better off with a heavier weight. What's the mass of your current counterweight?
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Re: Counter Weight Question

Postby WntrMute » Mon Jan 07, 2019 7:04 pm

If you want to experiment, go the local tire shop and ask for a few ounces of stick-on tire weight. That's what worked well for me and It is still in place! Costs nothing or a few bucks in tip money.
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Re: Counter Weight Question

Postby Stringreen » Mon Jan 07, 2019 8:30 pm

The closer to the fulcrum the better. You don't want that counterweight to move around with any warp and affect the stylus.
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Re: Counter Weight Question

Postby Golear » Tue Jan 08, 2019 12:47 am

Interesting question.

I read this:
https://www.vinylengine.com/turntable_f ... hp?t=77151

The third post, by analogaudio, provides some math that was written by another user, ldg. Analogaudio concludes:

In itself, this is an interesting result. It shows the contribution to effective mass from each side of the tonearm, mostly it comes from the cartridge side. It shows what to vary if one seeks to increase/decrease effective mass, principally the mass of the cartridge side of the tonearm, Z. But some influence is also possible from a heavier counterweight, and in a non-intuitive direction perhaps (heavier = lower M because balancing distance r influences M as power of 2).

So there you have it. A heavier counterweight lowers the effective mass of the arm! I did not know that. (But not by much.)

Will you hear better sound? Harder to answer that question. There could be other factors that might come into play (which may, for example, have an impact on the cartridge's "trackability"). But if it sounds good now, I wouldn't worry about it. If you try it, do let us know what you discovered.
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Re: Counter Weight Question

Postby Brf » Tue Jan 08, 2019 9:20 am

The counter weight is used to balance the tonearm/cartridge to produce sufficient torque to achieve the desired tracking force. There are literally endless combinations of counter weight masses and distances from the pivot that will result in the desired tracking force.

In Johnny's example, he has a lighter counter weight extended farther away from the pivot that achieves Johnny’s desired tracking force. His Dealer suggests a heavier counter weight that will require a placement closer to the pivot to achieve the same desired tracking force.

The “universal” claim that a counter weight should be place as close to the pivot as possible to achieve optimal results is often quoted and is false and cannot be supported by physics.

Physics tells us that a lighter counter weight placed farther away from the pivot will result in a higher contribution to the moment of inertia compared to a heavier counter weight that is place closer to the pivot to achieve an identical tracking force i.e. a change in the arm’s effective mass.

As Packgrog alluded to in his post, the cartridge’s compliance must be matched to the arm’s effective mass for optimal performance. By changing the counter weight’s mass and location changes the arm’s effective mass. The universal claim that optimal result can only be achieved by a combination of a heavy counter weigh placed close to the pivot is incorrect, because it assumes that the cartridge’s optimal performance will always be at the arm’s least effective mass for said cartridge and tracking force combination.

In Johnny’s situation, the Dealer may be right that Johnny’s cartridge may benefit from less tonearm effective mass, but IMHO, I doubt that this will translate into any noticeable improvement due to the magnitude of the change in effective mass. Again, IMHO, if you can achieve the desired tracking force range with your current counter weight, don’t worry about changing it out.
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Re: Counter Weight Question

Postby tony22 » Tue Jan 08, 2019 9:33 am

Great post, Brent! And in general I agree. I only worry when (as has happened in one or two cases) the combination of cart and counterweight was such that the counterweight was literally at the end of the tonearm stub. That made me nervous! :shock: Fortunately I was using the counterweight that let me use those little add-on weights.
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Re: Counter Weight Question

Postby Golear » Tue Jan 08, 2019 12:49 pm

I'd still try out different counterweights. Different mass, shapes and materials. Upto... depleted uranium?

The math assumes idealized/simplified behavior. In the real world, there'll be vibration and the arm will flex. If a light counterweight is far from the pivot, more might be required of the tonearm. And may be there's a difference if the counterweight is at a node or anti-node (for a particular frequency - and this can also depend on the cartridge). It may also depend on the cartridge - some are quite heavy. And may be there's a Dual Pivot....

And may be there'll be no audible difference. The conclusions would be specific to a particular arm and a particular cartridge in a specific system, of course.
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Re: Counter Weight Question

Postby Brf » Tue Jan 08, 2019 3:16 pm

Some good points made.

Golear wrote:The math assumes idealized/simplified behavior. In the real world, there'll be vibration and the arm will flex .

Flex where? The end stub? This assumes inadequate rigidity. Any competent engineer would ensure adequate rigidity over the usable span as to avoid adverse flexing

Golear wrote: If a light counterweight is far from the pivot, more might be required of the tonearm.

100% correct, this is referred to as increasing the arm’s effective mass and should not be concluded as a negative. This could be of a benefit with lower compliance cartridges
Golear wrote: And may be there's a difference if the counterweight is at a node or anti-node (for a particular frequency - and this can also depend on the cartridge).

If you are referring to a resonance at a specific frequency, this would be attributed to a mismatch between the cartridge’s compliance and the tonearm’s effective mass. Assuming that the cartridge compliance is in a suitable range for the tonearm’s effective mass, changing the cw mass and position would have a negligible effect on the calculated resonance peek.

If you are implying that the cw provides tonearm damping, and changing the position and mass a fraction of an inch and will have a impact on sound, you will have to convince me as to the “why”.

Having said the above, changing the counter weight's mass and position may be of a benefit for the rare user who's at the extreme edge of their cartridges compliance and tonearm's effective mass compatibility. This is not the case in Johnny situation.

I would also like to add that on my 12-3DR tonearm I have the piggy back fine tuning VTA weight attached to the main counter weight. I have tried my tonearm with and without the piggy back weight and did not discern any difference i.e. varying the c/w mass and end stub location. Others may have different experiences, but I can only relay what my experience has been and try to rationale my findings with some theory.

I do however agree with Golear, if you have access to different c/w designs, mass, material etc. give it a try yourself or if you have a good relationship with your VPI dealer, maybe they will lend you a c/w to try out.
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Re: Counter Weight Question

Postby Johnny » Tue Jan 08, 2019 3:42 pm

Thanks everyone for their comments.

I took Wntrmute’s advice and purchased (actually, the Tire Store guy gave them to me for free) 2-10g self adhesive weights in which I applied them to my counterweight. This required me to move the counterweight closer to the pivot. I dialed in the exact same tracking force as before.

My conclusion – no sound difference, nada, nothing. Saved myself $100 and promptly went on Amazon and purchased $200 worth of vinyl.

Thanks for the education. Love this forum for straight answers.
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