Find the thread started by Halcro on the "Copernican Theory". The theory does not expressly deal with your question, but Halcro is a devotee of the open, non-plinth plinth. Good arguments pro and con to be found there.
What you say about low rpm equating to low vibration is probably true enough, but belt-drivers would say that the belt affords isolation from the motor. Most direct-drivers (like me) prefer very very heavy plinths, but then there is argument about what is the best material: wood, exotic wood, slate, granite, etc. |
Viridian et al, You guys may be missing the point of what Atma-sphere wrote (at least as I see it). The point is that whatever the resonant signature, it is critical that the tonearm and platter be "connected" so they resonate as one piece. The problem with outboard arm pods (again, as I see it) is that they separate the tonearm from the bearing/platter, and no matter what you do after that, the two entities are independently subject to environmental energy sources; they'll then move or vibrate differently in response. Best you can do is make them very very massive so that most energy is dissipated as heat rather than movement. This is/was essentially my longstanding argument with Halcro vis a vis outboard arm pods. My metaphor or thought experiment is: Think of yourself trying to cut a diamond while seated in a row boat floating on water. Now think of yourself trying to cut a diamond whilst you are sitting in one rowboat and the diamond and all your tools are in another separate rowboat. Which is easier to do accurately? |
Hi Henry, I was hoping you would come out of your recent shell. Once again, you've written nothing that comes remotely close to changing my mind about outboard arm pods. However, I do agree with you on some of the other issues... Where was it exactly that I was talking about "airborne feedback". That's your pet bugaboo; you raise the issue in order to beat it to death. I've never used the term.
The way I read Atma-sphere's post, I should think you would have to disagree with some of it. He is saying what I have always said. To wit, "To this end, the coupling between the bearing and the base of the arm must be as precise and tight as possible; IOW of a singe piece which will not respond to vibration, as if any differences can occur they will be interpreted by the pickup as coloration."
Take a look at an L07D some time. There is the epitome of what I and Atma are talking about in terms of "coupling".
All of this folderol aside, I have come to think of you as a friend and I would love to argue these silly issues with you over a Foster's, if and when I ever make it back to Oz.
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I want to stay out of this discussion, because it's all been said before, but I wanted to point out, with respect to the argument regarding whether the arm pod moves due to stylus drag, that the mass of the arm pod, no matter how great, is not the major determinant of its being moved by stylus drag. Rather, the major determinant is the coefficient of friction between the base of the arm pod and the shelf. (Think, if the shelf were made of ice and the arm pod was of the mass of a curling stone [38 to 44lbs, according to Wiki], the pod would move easily.) I am not pointing this out in order to take sides in the discussion. I really don't care whether the arm pod moves or not, because I don't use an arm pod.
Second, I must agree with Richard, the Timeline says nothing about whether the arm pod moves. It only says that IF the arm pod moves, the mechanics of the tt (motor/servo/mass of the platter) are such that the Timeline read-out is unaffected. For all we know based only on the Timeline, the arm pod could be swinging around the whole circumference of the platter as if tethered to the platter, and the Timeline won't tell us this is happening unless the motor/servo/platter is not up to overcoming the resulting drag (call it "arm pod drag"). This is as obvious to me as is the opposite view to Halcro. |
CT, I am glad someone appreciates my sense of humor. |
Timeltel, Who can disagree that the first choice is the tonearm? I certainly don't. But I think the controversy surrounds the question of how best to mount a given tonearm in relation to the tt proper, assuming a priori that the choice of tonearm was suitable. And I think we're talking about a pivoted tonearm, not an SLT. Should the tonearm at its pivot be firmly mechanically joined to the tt bearing/platter, or should it be mounted outboard on a separate "pod" for optimal results?
So, has Henry actually listened to a version of either of his tt's wherein the very same cartridge/tonearm combos are mounted to satisfy the "firm mechanical connection" group of us? I really don't think he's done that. And even if he did, must we accept his subjective opinion as gospel? Like you, however, I agree that whatever floats your boat is just fine, for all of us. |
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Parrotbee, That's a rather subjective decision. You'd have to make two plinths, one with Panzerholz and one with acrylic and then do your own listening tests. However, if you're talking about all-acrylic vs all Panzerholz (no mixing of disparate materials), I personally would choose Panzerholz or some other hard wood. Acrylic in layers with other materials can be used to effect constrained layer damping, nicely.
Basephysics, Perhaps you have some deeper understanding of how the Timeline works. I am not an owner of one, but I have borrowed one and long ago returned it to its owner. As I understand it, the Timeline is an idiot. It just flashes its laser(s) at a regular pre-determined interval such that if the platter is rotating precisely at 33.333... rpm, the laser "spot" on a nearby flat surface will not appear to move. In other words, the laser does not "sense" movement per se, it just flashes at a regular interval. If I am incorrect, please educate me. Now, if my understanding of the Timeline is NOT incorrect, then will you or someone please tell me how the Timeline can show us anything but the fact that the platter is or is not rotating at correct speed? If it only senses correct speed, how would it also be telling us about arm pod "movement", if such were happening? Let's say you put your finger against the side of the spinning platter, adding drag, and let's say that the Timeline continues to tell you that the speed is exactly correct. Does that mean you are not touching the platter, despite what your eyes and your senses tell you? "Arm pod drag" is no different from that.
I should add here that I do NOT think that the very large, well constructed, and well thought out arm pods used by most of the arm pod aficionados is actually moving. Henry, for one, made some beautiful constructions that are very massive, and his shelf is not a sheet of ice in fact. This has devolved into an argument about hypotheses.
As to "basic physics", Basephysics, you must be familiar with Newton's Third Law of Motion: For every action, there is an equal and opposite reaction. We all seem to accept the notion of "stylus drag". This is due to friction between the stylus tip and the vinyl groove. Correct? If stylus drag is real, then it stands to reason that the groove is also exerting an opposite force on the stylus tip which is in effect pulling on the tonearm. If the tonearm is mounted on an outboard free-standing arm pod, then the arm pod is subject to the theoretical possibility that it could be dragged by this force. (Again, I emphasize that I do NOT think this is a real world issue for a well built arm pod, until proven otherwise.) But in theory the arm pod might move. If this additional drag on the platter were to be overcome by the motor and servo so as to maintain exact speed, in spite even of the fact that the arm pod may be moving, then the Timeline would be oblivious to the whole thing. That's my point. The Timeline tells us nothing, zero, zilch about whether the arm pod moves or does not move, due to arm pod drag. The Timeline might be affected or might not be. It depends as always upon the tt motor and servo mechanism or other elements of the drive system.
That's my story, and I'm sticking to it. |
Henry, Life is short indeed, and you're too smug to learn anything new. Instead of the snide remarks, I beg you to think about what you're saying when you say that the Timeline can show you whether your arm pod is moving or not moving. That's the only question we're debating, and I've spent enough effort to show you why it cannot. It can only show you whether your tt is running at correct speed (within its own limits to do that), or not running at correct speed. It cannot show the cause, in either case. But if you disagree, and you're really sure I am wrong, perhaps you can launch a logical response in lieu of sarcasm. I invite you, in other words, to tell me WHY I am wrong. |
Ct, For what it's worth, I built two plinths of the type you describe. Both from slate slabs, and I was motivated not only by the principle that there should be a rigid association between tonearm pivot and bearing/platter but also by the simplicity of the design. Simplicity is a virtue when you work with slate, because it is so tricky to cut slate without having a disaster. On the other hand, my favorite Einstein quote is to the effect that the solution to a (physics) problem should be as simple as possible, but NOT simpler. As a result of my perhaps too simple plinth design, I am limited to tonearms that bolt to the top surface of the plinth and which do not require a pass-through for a vertical shaft. Thus I have a collection of such tonearms: Reed 2A, Triplanar, Dynavector DV505 (two of the latter, in fact), RS Labs RS-A1 (the funkiest but actually sounds great). Both my Denon DP80 and my Lenco L75 reside in such plinths. For my SP10 Mk3, I did revised the basic idea so as to accommodate removeable tonearm mount boards, made of slate or aluminum. Yet the Reed 2A is king of the Mk3. And the Mk3 plinth uses constrained layer damping; the bottom half is solid cherrywood.
For the TT101, I took the base QL10 plinth and extensively re-vamped it with heavy alu supports below deck to stiffen it and with an alu arm board to replace the supplied particle board one. I further stiffened the tonearm mount by bolting the alu "board" through to a heavier piece of alu below deck such that the wood of the QL10 is squeezed by the alu arm board from above and the stiffening alu support below. We shall soon see whether the TT101 will continue to function reliably when I re-install it in nude form into this plinth. |
