Strange Tonearm Tweak. Long

Basement please clarify your points, we need to know more accurately what you mean, so we can discuss intelligently with you.

About your question about the fluid damping with the Rega arms. I don't know if anyone is doing that. The Townshend Rock TT's use an unusual fluid trough that swings across the record, and damps the arm at the headshell end, all the way across the record. When you put on a LP, you have to then swing this long curved trough across the LP, and when you put the tonearm onto the record, the paddle in the headshell dips into the silicone in the long trough. Totally unique. No-one else does it this way, that I've heard of.

While you are on the web, go to the Dynavector site, and look at their description of the 505 and 507 tonearms. They have a very good technical presentation on lateral mass increases. Also, go to some unipivot sites, and read what they say about the silicone damping. Maybe we can combine these two, and get something rolling.

I think you had your weights on shafts that were too flexible. The paper clips are too thin to stabilize the weight that is hanging almost 2" out there. They allow the weight to vibrate, and cancel out some information. I did not experience anything like that in my modifications.

Keep in mind I am still trying to grasp a lot of this myself. I'm still wondering about the benifits/consequences of the differences/simularities. Zaikeman makes some really good points in that last post. Keep in mind here that the most commonly used fluid for damping, silicone, is newtonian, that is, it resist faster movements disproportionally to slower movements. Ideally, slow movements get no resistance, fast movements get great resistance.
Ideally, we tune this to follow that slow moving warp or eccentricy with no resistance, but resist movement faster than that.
Now picture a high complience cartridge on a heavy arm. The arm stays put, the cantilever follows the record.
Now picture a low complience cart on a really lightweight arm. The arm can follow it anywhere, but it is not a good enough 'base', if you will, to allow the cart to do its job. potentailly, the cartridge just throws it around, and it can't transmit the information.
Now, if the arm has some resistance, and the cantilever flexes, but the cantilever also is stiff enough to pull the arm, the arm goes in motion after the initial deflection to follow the cantilever. As the arm chases the cantilever, and the cantilever then is pushed the opposite way, the arm and the cantilever are both moving in opposite directions, and we get movment in the cantilever that is greater than the initial deflection. In this way, we get cantilever deflection that is greater than if the arm was not allowed to move at all.
In the above post, the statement that fluid resist movement constantly as opposed to mass resisting movement initially is a good explaination of how we use fluid to tame these unwanted cantilever deflections. But that is just one reason for fluid.
Fluid is also used to tame the arm of movement that does not allow the arm to transmit information, movement or vibrations that would allow information to be lost at the cantilever, (that is why townsend put the trough at the headshell, but I believe that it might have been a failure).
In my experiment with the immedia and the pennies, it is highly faulted, for those reasons you mentioned and others. the weights were literally just flopping front to back, and this would most problably cause some bad stuff. The purpose was to try to demonstrate to myself the possibility of substituting mass for damping fluid, as well as add mass to the horizontal plane. If in fact I did hear what I thought I was hearing, that is a wider feild and better separation between instrument, despite the degragations, that is something. I might not be able to go too far with the immedia though as it is already a heavy arm. The added mass may be too much. Also, what I was hearing might be side effects of the degragation.
Zaikesman, please ring in with some of the arms you used with fluid damping, I can see some good info here that may help us, as you seem to have a pretty good handle on this damping of fluid.
I'm going to follow up on some of that stuff and see if I can see what's happening. For now, I contend the following possibilities; Mass is highly desireable, and better than fluid for the taming of unwanted frequencies, (notice that arms have gotten a lot heavier), and that mass might be better placed than the current understanding of it's use, or that it may have more use than one. (or my understanding needs to catch up).

I will respond to some of your points if I can, Basement. First off, I myself have no direct experience with using fluid damping (yet - I expect to before very long), so all of my information comes from what I have gathered on the subject from various sources, and a lot of my assumptions in the above posts also stem from nothing more formal than just my own common good sense and scientific/mechanical aptitude/intuition (which, believe me, is merely a little better than average, and not the result of extensive education or training). In short, I am no expert.

Your supposition about out-of-phase movement of the cantilever relative to the cartridge body/tonearm, and its causing of positive amplitude errors, is interesting. But do you know for a fact that it is true? I would liken this view of the situation to pumping a swingset for increased altitude, or the cracking of a whip. The other view would be that of trying to push a tackling dummy on a muddy field and having your feet travel the other direction instead - it would result in less motion of the dummy. We could call the first example the "whip-crack" model of relative motion as it affects signal amplitude, and the second example the "traction" model.

The traction model seems fairly straightforward - any unintended deflection of the arm causes a signal undershoot. The whip-crack model would be a good deal more complex. When attempting to push the tackling dummy in the mud, your result will be similar no matter when you engage in pushing. But when cracking a whip or pumping a swing, timing is everything. Get the frequency wrong, and you'll get negative acceleration, not positive. So presumably, the whip-crack model would often show a similar result to the traction model, and only sometimes result in signal overshoot, depending on the conditions of groove frequency, velocity, and amplitude. I do not know which, if either (or even both, under differing dynamic circumstances), of these possibilities is valid.

As far as the Townsend damper design goes (something this thread has enlightened me to), I would surmise the reason he moved the damper out the arm's radius close to the cartridge is because that is where the arm's motion will be greatest in amplitude and velocity, relative to the same damper installed closer to the pivot point as is common. This is very ingenious, as it both increases the effectiveness of the fluid's damping properties, and simultaneously eliminates the cartridge's leverage advantage vs. the normal arrangement, while also ridding the cartridge/damper interface of several inches of potentially resonant and flexible intervening armtube length. It does sound ungainly as hell though (and scary to boot - who wants all that viscous fluid above the record surface?)

I'm not sure I understand the reasoning for the conclusion you draw in your last sentence, since you don't seem to have provided an explanation of why you feel this to be the case (mass being superior to fluid). I would comment regarding your observation about the increase in average arm mass, that this has to be taken in the context of average cartridge compliance - these two parameters evolve hand-in-hand as they must, but it is the compliance issue that leads the dance. My own feeling, as it has developed over the course of this thread, and for reasons I explained in my previous posts, is that a theoretically ideal system would probably be infinitely low in mass in both planes, and hence inertia-less in all directions, and entirely resistively damped, whether by fluid or some equivalent. Of course such is not possible, but it does tend to point away from increased-mass solutions - not that they won't be effective in some ways as well, and maybe even just as good for practical purposes, though I am somewhat skeptical of this right now.

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? :-)