Basement - Have to say that I too, either do not understand most of your post, or may even disagree with some of it, but my uncertainty about what you have said puts me on hold from commenting specifically. But I am picking up (sorry!) that you are wondering about possibly combining Twl's hoizontal mass increase with fluid damping.
Twl maintains the two perform basically the same function, so this would be unecessary. But this makes me rethink that proposition a little more, and whereas yesterday I was inclined to think the same thing, I now have another thought occurring:
As it regards initial resistance to horizontal arm deflection at the onset of a transient, I would say yes, mass-damping and fluid-damping are probably accomplishing about the same thing. But - as is actually contained within the implication of my last post - there might be a difference extending beyond that initial event, as it concerns inertia. Fluid-damping is essentially free from interial effects. In other words, both mass-damping and fluid-damping will resist being set in motion, but once they are, the mass will tend to want to remain in motion, whereas the fluid will always tend to resist further motion. This suggests that the ideal horizontal mass for accurate transcription of the groove modulation by the stylus/cantilever would be infinitely large, but that the ideal mass for accurate tracing of the groove path (which affects coil-centering) by the cartridge/tonearm would be infinitely small.
I know - no duh! The same is actually true in the vertical plane as well (although here gravity comes into play [and is exploited] as well), and this just brings us back to restating one of the central dilemmas of designing a record playing machine in the first place.
But it does have me fantasizing about things like: A truly ultra-low mass cartridge-carrying system which depends on fluid damping in *both* planes and uses a spring arrangement or equivalent for VTF; Or, how about attempting to capitalize on cutting-edge technology to create an ultra-fast, tonearm-less sensor/processor/actuator system which 'reads' the position of the groove path and record surface height via a laser sensor just in front of the cartridge, and then uses a microprocessor controlling an utra-quick precision actautor mechanism of some sort to positively locate the cartridge body in the optimum position and attitude to enable the stylus to extact the maximum information from the groove modulation through continuous real-time adjustment, possibly incorporating processor monitoring of the cart's signal itself to constantly calculate correct coil-postioning via the electrical L-R separation and phase info? Whew, boy!
(BTW, Twl, I also didn't understand some of your comments responding to my last post, about the run-off groove and degrees and such, or their relevance to my post. Maybe my post itself wasn't clear. Then again, I am eminently unqualified to know what the hell it is I'm really talking about in relation to all this stuff, so rather than worry about incomprehensability due to runaway pedantic excess, I should probably worry about acute embarrassment due to runaway ignorance flaunting! :-)
P.S. Edit: Basement, I wrote this prior to your latest post. |
Zaikesman, I used poor terminology in my last post regarding the term "run-out". In machine shop lingo, the "run-out" is the amount of eccentricity in a rotating piece, like a rod on a lathe. If there is "run-out on a LP record, that means it is rotating eccentrically(ie, off-center hole). I'll avoid that term since it confuses things with the run-out or lead out groove on the LP.
Ok, now my point was that with both fluid and mass methods, the rotational variations caused by the off center hole, happens relatively slowly over a long arc of the record. Both the fluid and mass methods can trace this movement easily, with no disastrous results. There should be no erratic movement of the stylus in the groove as a result of this. The arm still has relatively free movement in tracing slow arcs with both fluid and mass damping.
Now to move on, I think this discussion is very productive, and with a little care to make sure we are all on the same page, I'll comment on your input, and Basement's.
What you say about the mass staying in motion once it starts is very true. The amount of mass needs to be looked at real hard to make sure we don't get a swinging gate effect. That is important. On the other hand, once the fluid gives way to some movement, the paddle is also resisted from returning to center by the fluid. So this needs to be taken into account also. We have not come upon the perfect solution yet. But, we are making some headway.
I am still of the opinion that using both methods is somewhat redundant. But there may be some middle ground. Perhaps a mass increase, along with a tuned fluid damping could provide high inertial resistance, with the mass being controlled from overshoot by the fluid damping? IMO the mass provides a static increase in the resistance to movement, while the fluid requires at least some small dynamic movement and velocity, to come into play. So with both, there may be better control. Maybe we need to look into this possibility.
Regarding the sophisticated servo-operated control systems you mention, it has been my experience that mechanisms generally muck-up the works. I like to go by the simple route, if possible.
Now, Basement has done some experiments with his Immedia, and had some negative sonic results in some areas. From his description, my feelings are that the weight hung on the paperclips created a vibrating mass on the ends of the thin paperclips, and caused sonic impairments. My belief is that the shafts needed to be very rigid to preclude this problem. My weights are 3/8" solid lead shafts, and they are firmly pressed onto the bearing nuts and glued, so the mechanical connection is secure. There is no thin shaft with a heavy weight on the end. This may have led to Basement's problems. I don't know. |
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. |
