It took me a long time to understand as well. Now I'm grappelling with mass and it's relationship with damping. If you are like me, you think about this stuff all the time, and things come to you, (obviously, look at whats come back at us). This part I think you might be missing- you mention that all (most) your records are not off center. While there are quite a few that are obviously off center, what we are talking about here within the cantilever/coils is microscopic. All records are off center, evan if just a fraction of a groove width, they aren't manufactured to the kind of tolerences we are striving for. If you dismiss this, then you shoot for the arm staying put at the cartridge. Really, what we want (in theory) is the arm to stay put directly over the cantilever. The key to this, with fluid damping, as stated by Z above, is the viscosity. Control the resistance selectively at selective speeds (traditionally, the speed being the frequency of the warp/wow). To see it, you definitely need to get in and look at the cantilever at the cartridge to see how much it is moving in relation to the cartridge. to measure it, you definetly need test records and the like. ( I don't have these resources, maybe you do). There is more to controlling frequencies then just keeping the coils centered, though. There are, I believe and suspect, differences and simularities between fluid damping and mass. We are not done with this yet. Last night, I put my immedia back on to test some of this. I drained some fluid out until the arm could tilt easily to one side but come back without overshoot. Then I weighed some pennies, came up with 5 pennies on each side to be about 12 grams with electrical tape, and slung them out with a paper clip. They are about 1.75" out on each side, just below the record height, slung out at the same angle as the cartridge, and just taped on the top with a piece of electrical tape, over the center of the bearing, and they swivel front to back because of the tape. archaic, but they increase the horizontal mass considerably with minimum effect on any other parameter. What I thought I heard was a wider soundfeild with more separation between intruments. But the induvidual instruments seemed more truncated, less air and detail around them. The high end seemed more recessed with a loss in detail. I didn't adjust damping at all between the two. I did notice more movement of the cantilever, at least I thought I did. Sounded similar to adding to much damping, and of coarse this experiment is extreme, I didn't play with it any further. One resource I don't have lately is too much time. I am currantly getting more enjoyment in the tweak factor by hearing your results. The immedia has damping, and it is easy to control and adjust/change, but it is also much heavier than the rega, I plan on starting another thread if you don't to see if anyone has tried fluid damping with the rega, and if any is readily available. This is a new tonearm you are designing, isn't it? You are changing the parameters of the design. Seems to me you are somewhere roughly as far from the rb-series as the ol 750 is. |
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). |