Tonearm vertical motion - good thing or bad thing?

ack

VIP/Donor & WBF Founding Member
May 6, 2010
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This is a fork from another thread, where I wrote

it strikes me that we continue to make huge leaps with new arm designs... and a thought crossed my mind: why did my magnetic arm stabilization make such a huge improvement, especially in macro dynamics? I did place the magnets in such a way as to actually push down the armwand a bit, and then it occurred to me: the cutting head is immobile in the vertical plane, so is vertical arm motion a good thing or a bad thing? How can it possibly be a good thing???? At that point I began to appreciate SME arms even more, considering their spring-loaded thingy some of them have - I believe the idea is the same??? Or is it... you guys tell me. But currently, I am not liking vertical arm motion one bit, and I am beginning to suspect the better designs impede that motion.

What are your thoughts on arm vertical motion? I am beginning to really like 'impeding' designs, those that barely follow warps, but otherwise impede micro-motions in the vertical plane beyond what mass inertia does by itself.
 
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PeterA

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Dec 6, 2011
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This is a fork from another thread, where I wrote



What are your thoughts on arm vertical motion? I am beginning to really like 'impeding' designs, those that barely follow warps, but otherwise impede micro-motions in the vertical plane beyond what mass inertia does by itself.

Interesting topic, Ack. In your system thread you mentioned the dynamic VTF design of some SME arms. What are some of the other examples of "impeding" designs, and what do you think are their advantages? I seem to remember another discussion about dynamic VTF and the effect on an arm that has a neutral balance. It had something to do with the center of gravity or mass of the arm in relation to the pivot point or plane of the arm bearing.

I am curious about some popular or well regarded arm designs like the SAT and SME 3012R which do not have this feature. Can you describe what you think is the sonic effect of dynamic VTF? On my SME, I hear a more controlled, stable, smooth, and natural sound. However, in the case of my SME V-12 arm, using dynamic VTF (applying tracking force by rotating a dial which adjusts a silicone damped spring to apply vertical tracking force), means that the counterweight is further back and away from the pivot point of the arm bearing, so inertia is higher. This higher inertia alters the effective mass of the arm and may be a better match for the compliance of my cartridge which may be the reason it sounds better. There are so many variables involved, that it is hard to isolate the effect of each. It is a complex system. This may be similar to the effect of the silicone dampening trough on the horizontal movement of the arm. This increases the inertia of the arm with regard to horizontal movements. How can we separate the effect of changing the resonant frequency of the arm/cartridge match through damping from the effect of altering the inertia of the arm?

I think the idea behind the dynamic VTF of my SME V-12 is that the tracking force stays more constant during the cartridge's movement over warps. But I seem to also notice an improvement over flat records and I don't understand why this would be the case unless the effect I'm hearing is really the different effective mass of the arm because the inertia is greater.
 

JackD201

WBF Founding Member
Apr 20, 2010
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I think you are both right. I think we need some pre-loading or damping just like in vehicle suspensions so we don't get runaway oscillations which is obviously a bad thing. The question is how much is just right? Too much I imagine would stress the suspension of the cartridge itself and the sound is compressed, too little and we get wow and flutter-like pitch variations as the stylus attempts to ride the warp vomit comet as inertia has it bucking at all sorts of "Gs". Of course there's the other side to the vertical movement problem.....keep the records flat :)

Personally I went with my VPI (Clamp and Ring) and later the TechDAS (VHD) precisely for their flattening features. Even just visually as the cart just glides across the surface, I just know the cart must be working under more ideal conditions given what microscopic motions create the output from the coils and magnets.
 

PeterA

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Dec 6, 2011
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Ack, Don't you use the outer ring and spindle clamp on your VPI? I would imagine that your records are pretty flat. What do you think is going on when you apply the non static downward force on your arm? You probably described in
your system thread how the sound of your table changed when you added those tiny stablizing magnets to your unipivot arm, but could you do so briefly again here?
 

ack

VIP/Donor & WBF Founding Member
May 6, 2010
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Boston, MA
Peter, I cannot answer some of the question with confidence. However, I can tell you a few things: a) I picked the VPI table partly because of the ring availability, which few other tables offer; b) I picked the arm because I knew I could improve it; c) I had ideas - eventually implemented as shown in my system thread - on how to deal with floor-born vibrations (granite, Isodamp, Stillpoints, etc); d) cost was a factor.

The magnetic stabilization consists of two stacked ring magnets at the base of the arm, of different radii, plus two opposing magnets under the armwand, set slightly behind the centerline connecting the two stabilizing "ears" of the armwand, in order to affect a slight increase in VTF which obviously ended up me having to move the counterweight a little further back to compensate, and thus increase horizontal inertia. But the real benefit, I think, is in impeding vertical micro-motions, due to the strength of the neodymium magnets - see dedicated thread on this. All of these things were done on purpose, but with unknown results, until I began listening. The increase in macro-dynamics, as you heard, was shocking; there were other improvements in imaging, but we won't discuss in here.

If I remember correctly, dynamics are printed on the LP as increased groove depth, therefore, I feel impeding vertical arm motion is critical, however that is achieved. And I think this is why I hear this sudden increase in dynamics, and everything else. BTW, I posted my mods on the VPI forums back then as well - no response from VPI; I suspect they are bound by the various magnetic-stabilization patents that folks like Graham, Schroeder et al own. I feel VPI arms are way behind their tables in sophistication.
 

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