Strange Tonearm Tweak. Long

Ok, we have a couple of suppositions here, and I will try to address them as I see them.

First, it seems we all agree that the headshell/arm should position the cartridge directly centered over the groove, and should maintain that position as it plays the entire record.

Next, we all seem to agree that it is possible for the cartridge compliance to move the arm out of the ideal position, especially if the arm has insufficient lateral mass, or no fluid damping.

Now, our contentions are that with either increased lateral mass, or fluid damping, this problem can be mitigated/eliminated. But, both solutions introduce their own potential problems which need to be dealt with.

It initially seems as though the fluid damping creates less inhererent possiblity of problems, because it does not have a mass that could be set into motion, and thus go out of control. However, the problems introduced with the fluid damping system, as I see them, are these: The paddle must be set into some level of accellerated motion before it can begin to work, therefore it will allow some arm motion to occur before the unwanted movement becomes damped. If the arm does move before damping occurs, then it has to move back, and could be slowed by the damping during its return to the center. This creates a bell-shaped amplitude curve regarding its movement away from center and back to center. Granted, this will be a small amplitude, but it will be there none-the-less, due to the requirement for the arm to laterally accellerate to a certain speed before damping occurs. So therefore I conclude that fluid damping has static/low amplitude limitations, and works best in higher amplitude/ high acceleration conditions. And, in all cases, allows some unwanted movement to occur before coming into play, as it is a dynamic system.

Increased lateral mass has what appears to be more difficult inherent problems associated with its use in this application. This increased lateral mass can be accellerated out of control, if the mass is insufficient to perform its intended task. Momentum would take over and create mayhem. Return to center under these conditions would be out of the question, as the arm would be flying across the record surface. However, there is something here that works in favor of increased lateral mass. It is a static system that raises the "moment of inertia" to a point where the cartridge compliance cannot overcome the static moment of inertia. In this case, the cartridge is stabilized over the groove center, with no movement needed, or allowed, to work. So the stabilization, if sufficient, can be complete, with no lateral accelleration(movement)of the arm needed to bring the stabilizer into play.

So, what we have here, as I see it, are a dynamic control system, and a static control system. The dynamic system requires some movement of the arm to work, but then comes into play very aggressively to limit movement. The static system doesn't require any movement to work, and in fact cannot allow it, or it will spin out of control from momentum. Or at best, create a nasty "swinging door" effect, which we definitely don't want.

Now, my assessment of these systems, is that we really don't want to allow any deviation of the arm from the center of the groove, so that the stylus will do all the moving, not the arm. So, from an absolute performance point-of-view, the static system of increased lateral mass allows no deviation, assuming sufficient mass. But, if the mass is insufficient, or if some unforseen large accelleration enters the system that can overcome the static moment of inertia, it can have a major disruptive effect. The dynamic system, while allowing a small degree of deviation from the ideal, will control any large accelerations very well, and will never get out of control(except at the very low accelerations, which it does not control at all, due to the "damping threshold").

So, where do we want to go with this? Do we allow some movement, and then quickly stop it, or do we allow no motion, and possibly get out of control if a large force enters the system? Or is there another idea, or combination of ideas that would better resolve the problem without causing additional ones?

There are some other issues that enter into this discussion also, and they are, how are the other aspects of arm function affected by these mods? There is no question that the added mass system can cause a change in vibrational modes that may or may not be benign. The fluid damping does not have this characteristic. It has no potential problems in this area, and even may tend to damp some larger vibrational modes. It is less "cartridge dependant" for its correct operation. On the other hand, if the cartridge is selected with all the correct capabilities(low compliance), then the increased mass of the static system, may enhance the vibrational and resonant modes to not need any damping, or need less damping. And if lead is used, especially in the proper locations, damping may occur by the lead material itself. I believe that this is happening on my tonearm, with this mod. Another benefit that I believe I am getting from this is the reduction of bearing chatter, due to the increase of the static "chatter threshold" by placing the lead weights directly on the bearing axle. This greatly increases the mass of the axle, and is much less likely to chatter in the bearing, because it is too heavy for the vibrations to excite/move it in the bearing races. This does not come into play with a unipivot, obviously, since the unipivot has tons of PSI on the pivot tip already. But interestingly, the added mass(PSI) on the tip, is what causes the unipivot to be chatterless.

I could ramble on about this, but please give your comments on what I've said so far.

Very well broken down, Twl. I agree about the fundamental aims you suggest. Your analysis of the probable dynamic response limitation of a fluid damper reinforces the reasoning behind Mr. Townsend's implementation I was expounding on above.

But I must point out a flaw, or at least a simplification, in your characterization of mass-damping as a "static" system. Assuming negligable bearing friction (and this might not always necessarily be the case, but for now I will assume that a premium bearing's friction will fall below the level where it would play a larger role in dynamics), the horizontal mass of the tonearm does not entirely resist the arm's deflection by the cantilever, as you state, but conforms to the basic principle 'for every action, there is an equal and opposite reaction'. In other words, the motion of the stylus will produce deflection in the cartridge/tonearm which is inversely proportional increasing mass of the cart/arm (and also to increasing cart compliance), but this delfection will not = zero, just as in the fluid-damped example. (Had it = zero, you then would have been implying that there existed some 'mass threshold' for deflection, which your unmodified arm hadn't yet crossed, but that had been crossed once you added the extra mass. Of course, and again assuming bearing friction isn't mucking the system up at this point, this isn't the case; there is no 'mass threshold' - it is a continuum, and you have simply moved down the scale in the direction of less deflection.)

What the levels of allowed deflection would actually be in each example of these respective damping systems is unknown to me, and I would guess is likely to remain so. Obviously, in each case there are many variables to be played with that would affect the answer. To achieve an optimum balance of dynamical attributes for any given cart/arm combination, the fluid system allows for relatively easy adjustment via modification of the fluid level, so the mass-damped system should probably feature a method whereby the user can either change the amount of applied mass, or more likely adjust its distance from the pivot point, like a common counterweight adjuster, either by sliding or helical means. (Twl, did I just suggest a major price increase? :-)

The effect of the cantilever deflection in the reverse is a real thing. I've read about it and observed it. When you get your fluid damping devise (where are you getting it, by the way, so we may obtain our own), you may be able to observe it as well. I am blessed with near sightedness, and if I may pause to brag, I can count the seven strands or litz wire in cardas. To make it easier to observe, I get my mag-light and look head on at the cantilever, observing its revative movement with the cartridge. Then also I sometimes find a spot in the background and observe both the movement of the cartridge and the cantilever as it traverses the record. It is much easier to see with a record that is more off-center than usual, but it is rare that I find a record that I can't observe as being off-center. I have, and do, observe less movement of the cantilever when I damp the arm.
I'm going to jump around- first, yes the last sentence is speculation, I'll explain why later,
I am seeing two separete reasons/uses for damping fluid.
The one reason, is the centering of the cantilever in the coils. The other is the taming of unwanted frequencies.
On the first point on fluid, I am suggesting that the cartridge is a more accurate transducer with its cantilever centered in the coils.
On the second, There is both the issue of the speed at which the cantilever moves (which translates to unwanted bass information, the movement of the cantilever transmitting a bass frequency, which is the 'bell curve' stated above) and the control of the other frequencies higher in the audioband, the resonences.
Now I bounce again. You are correct in your statement of the tonearm being of mass according to the complience, as one reason tonearms are heavier than they used to be, and mass having other purposes. The current thinking in design is to keep the moment of inertia as low as possible in all planes, and at the same time, add as much mass as possible while keeping the moment of inertia low. Tonearm makers are also adding mass at their bases (no doubt allowable by better tables). This can be likened to the effects of a heavy platter being a better sink for resonences, as opposed to just better speed control. Or a heavy suspensionless table as opposed to one that seeks only to isolate.
The other trend, although not new, is the use of new lightweight materiels. The reason for this is not simply to make the arm lighter, but to make the arm stiffer by using more of these stiffer materiels. The stiffer the arm is, the more energy is channeled to these massive energy aborbing bases, and the more solid the headshell is at the cartridge as a result of all this.
Now I bounce back to the meat of our discussion. If we explore the use of damping for the second reasons I stated above, and we explore what is happening at the cantilever as far as movement (I like the bell curve analogy) we may be able to get better results by substituting mass for the reasons we use fluid in that area. The evidence I use to support this is that 1) arms have been getting a lot heavier, and that they seem to be attempting to put it where the moment of inertia would be lowest, 2) The graham arm has its weights slung out at an angle for stability and proper tracking of the cartridge offset angle, and may be enjoying the effects of greater horizontal mass as a side effect, 3) the reputation of linear trackers to have good soundstaging qualities, as they have a disproportionate horizontal mass to their vertical mass, perhaps an overlooked side effect in their quest for accurate transcription.
All of these arms use fluid, however, and in the case on the linear trackers, before it was made available on the E.T., the heavier armtube had a reputation for snapping cantilevers, for the first reason I stated above for the use of fluid. The wheaton also uses fluid, (a real heavywieght), slung out in what seems effective for tracking more than transferring resonences, and of coarse the immedia and graham both depend on it for proper operation.
Further evidence I suggest, and this is perhaps the most compelling, is that the rb-type arms are the lightest in this class, and that they have all benifitted from adding more weight from aftermarket counterweights, And in the deliberate attempt to add weight only in the horizontal plane, seems to have shown results disproportionate to simply adding more weight, and was added in what was stated in the beginning of the thread as perhaps an oversight to why the graham works so well. (the rega does not need counterwights for lateral stability the way the graham does).
I would correlate that fluid on a rega is a rarity and that it is also a lightweight.
So my thoughts now are, do we need to emply fluid on the rega to explore this to a higher limit, and also, if we choose to use more mass, if we would be better off not using fluid for certain applications. There may be trade offs as to how much we allow the cantilever to move in relation to the cartridge, wheather or not the cartridge/arm would work better being in a static position over the record, and reap the benifits of stability, at the expence of letting the cantilever out of center,(or evan if we could get dangerously close to causing damage).
What is particularly fascinating to me is that I have never heard of adding weight for the purpose of modifying the behavior at the cartridge end, but certain evidence shown here seems to support it. That is why, although I believe that to allow the arm to freely with the groove, as opposed to remaining static, is better, I am willing to question it.

Thanks, Zaikesman. I agree that with the low bearing friction, there may be some movement allowed with the mass system. I cannot say that absolutely no lateral movement is present over the groove. But I can definitely say that it is much reduced, because of the results of greater dynamics, crisper detail, and bass I got with it. I may not even have the best ratio, because I did not try a bunch of different weights. But by luck, I got a pretty good result on my first try.

I have thought of making the weight on a threaded shaft, so it could be adjusted for distance from the pivot. This would complicate the prototype, but production would be just as easy. You may have caused a price increase :^). It would certainly be more applicable to a wider range of cartridges with a system like that. But the spread would have to be equal on both sides, or you'll be changing the anti-skate force.

What type of arm are you using, Zaikesman? If you have a way to fix these weights onto your arm, I could send you a set for evaluation on your TT. I know that they easily go onto a Rega arm. I would like to get some feedback on this. I am already sending a set to Nrchy, who has a Rega RB900. And if Basement wants some to try out on his RB300, he can have some too. They don't cost much, I just get them at the fishing store. If you think you could somehow get them onto whatever type of arm you've got, just email me your address, and I'll send a set to you.

By the way, I think that there is a sort of "mass threshold". As an example, if I am lifting weights, and I keep increasing the weight, at some point I won't be able to lift it. The static moment of inertia will be too high for me to overcome. That is the "threshold" that I am looking for with this system. If the mass is higher than the cartridge can overcome with its suspension, then the theoretical infinite mass can be approximated. As long as the arm can still move freely to track the groove spiral. Since the spiral tracking occurs over a long arc, the low friction of the bearing should allow this to occur, but on the quick dynamic spikes of the groove info, this mass should be sufficient to virtually eliminate arm deflection, if the mass is calculated correctly. Do you agree with this hypothesis?

Basement, I wish my eyes were as good as yours. Now that I'm over 45, I can't see up close anymore.

About the off-center records, I don't really see this as a problem, because the mass increase is easily moved during the long arc of an off-center record. The shortest arc that it could have to navigate would be 180 degrees, because the hole is only off-center in one direction from the center. That means that the record will start to move one way for 180 degrees, and start moving back for 180 degrees. On the outside of the LP, if there was 1/8" off-center, the stylus would have to adjust only 1/8" over 19 inches of groove travel(the circumference of a record is about 38 inches). This could hardly be called a rapid movement. The low bearing friction could easily handle this. And 1/8" off-center is a hell of a lot. I personally would not even play a record that bad. None of my records are even close to that far off. I do have some warps though.

Adressing your statement about the "speed of the cantilever", the cantilever is designed to operate at the speeds and distances it will encounter in the RIAA curve that is encoded into the groove. These parameters are known and designed-for by the cartridge makers. I see no way that a well-designed cartridge will be caused to mis-track by the proper orientation of the arm over the groove. If you are saying that the damping or horizontal mass increase will cause the arm not to properly track the off-center record, I have already covered that topic. It can track the off-center record. If the record is so far off-center that a damped arm cannot track it, then that record is junk. I cannot consider items like that in my design. A high-performance Ferrari suspension is not made for going "off road". We have to assume at least a decent level of record quality. I will accept the loss of some defective records, in the pursuit of improving the sound of 99.9% of my collection. The slightly off-center records are not affected by this design.

On the next issue, I agree with all 3 of your points regarding increased mass on tonearms. The problem with cantilever breakage on ET arms is generally attributed to the TT not being level. With the low friction air bearing and the lack of anti-skate on linear arms, leveling is crucial on these arms. The other cause of breakage was the "Groove guard" ridge, that caused a rapid accelleration of the stylus into the lead-in groove, as it slid down the side of the "Groove guard" ridge. This is why many recommended the starting of play after the first groove into the first song, with these arms. Fluid damping reduced these hazards. These are cases of "runaway, out of control mass" as we talked about in the previous posts. On pivot arms, this is less problematic since there is usually higher bearing friction in these, as well as an anti-skating mechanism. However the "Groove guard" can be a pain in the ass, at times.

Continuing to address your points. The use of fluid damping in addition to horizontal mass increase is not out of the question. It may be a good combination for reasons previously stated. I have not tried it yet. I have already addressed that I don't think that there is any possibility of damaging the cantilever with any of these systems. We want the cantilever to move as much as needed to retrieve the info off the record, and no more. If the cantilever is stiff enough to not bend under these stresses(no cantilever should bend), then these methods of keeping the cartridge centered should only help matters. It is the mass of the arm moving away from groove-center that may damage the cantilever. None of these systems allow the cartridge to move off groove center, even on off-center records, as previously stated. The entire purpose of these mods is to keep the cartridge groove-centered in all circumstances. I really don't follow your point of saying that these mods will cause/allow the opposite of their intended purpose. They do not impede the long slow movement of the arm during tracing of the groove spiral, or even off-center records. They only stablize the cart/arm during quick movements of the stylus, particularly during dynamic bass activity. If you are seeing your cantilever moving sideways because of an off-center record, then your cartridge is too high compliance for your arm. Or your records are really bad. What kind of cartridge are you using? This may be the reason why you had dead sound when you increased the mass. If you have a med-high compliance cart, your arm may already have enough mass to provide stabilization. If you can see your cantilever moving off groove-center, then something is drastically wrong.

Regarding your last sentence, I am not promoting the idea of preventing the arm from moving with the groove spiral. I want it to move with the groove spiral. I just want the arm/cart to remain centered over the groove while it is moving with the groove spiral. This is the aim and purpose of my mod. Remaining centered with the groove, and still being able to move enough to trace the spiral, is not a mutually exclusive combination. It can do both, and do it quite well. And it does not carry with it any greater danger of breaking the cantilever.

I wanted to offer you some of my weights to put on your RB300, but now I'm not sure if your cartridge can handle them with the records you are playing. Tell us what cartridge you have. If I think you can benefit from these, you are welcome to them. I am a little concerned right now that you might be over-weighted as it is now.