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Old 8th April 2008, 01:12 PM   #11
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My gimbaled arm uses a cup and cone arrangement, and the cups appear to have a white plastic insert. I know that if the bearings are slop free, even if the arm moves freely for all intents and purposes, the sound suffers. Loosening the pivots ever so slightly, so the bearings have some noticeable looseness, improves the sound greatly. IMO, reducing friction may be more important than coupling energy into the arm support- possibly the arm itself needs enough internal losses to deal with that issue, as we don't want arms that ring.
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Old 8th April 2008, 08:48 PM   #12
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Ahh Haa! Now we're talking the same lingo (pardon the Pun on the Linn Power Supply!). You could probably lose the plastic insert. I frequently pry out the metal rings from so-called sealed bearings, which cause stiction. Then I flush out the heavy grease packed in there. Then use Tri-Flu, RemOil, or some other low viscosity synthetic lube. Some people swear by Dextron II ATF fluid. Here's what's happening when you loosen the bearings up. As the groove pulls on the stylus, the whole tonearm wants to move forward, which racks the cone pivot or axle against the balls nearest the forward end of the armtube. Towards the barrel of the rifle, not the butt. So when the balls are up against the wall, all slack is taken out of the system, and the cone is most likely only in contact with two of two of the balls. A very low friction condition, with a minumum of vertical inertia. Most of the inertia is probable due to the mass of the counterweight. One oof the commercial tonearms uses a system that only has three balls, and a cone. Clever. Another one has the counterweight suspended on a cable (very thin) to reduce the inertial forces, and to allow it too swing in response to the warps in the disc. As the stylus goes up the hill, the weight swingss back, reducing down force, preventing the cartridge suspension from bottoming out. The reverse happens when the cartridge crests the hill and starts its downward journey to sea level. Sorry for the prolix answer, but better to get a lot out there than responding four times to the nearly obvious follow up questions.
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Old 10th April 2008, 09:10 AM   #13
allears is offline allears  United Kingdom
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Thanks for your interesting responses , I think I just have to experiment so I can start to hear the physics happening so to speak. Otherwise , when I asked about absorbent bearings and counterweights it was just from thinking about my experience with musical instruments , in that with those one is trying to maximise resonance , whereas in a tonearm the opposite is true . So a big lump of brass in a guitar bridge will increase the resonance , a big lump of blu-tack will deaden it . So I wondered why the former was used for counterweights rather than something like blu-tack (only more rigid and massier of course , like a stiff blu-tack with bits of lead in it). And then looking at the Schroeder tonarms which have only a thread connecting the arm mechanically , so not draining the energy through a fixed bearing but with magnetic damping going on , I suppose I wondered what was wrong with trying to work with that "soft" bearing idea in the hope that it will offer a resonance-free arm at the expense of some rigidity, rather than a rigid arm that has to be damped . And then I keep coming across suggestions from highly-regarded designers that some element of "tuning" is involved in a good arm , that it is not after all completely different from a musical instrument , and it is in fact more of a case of choosing which frequencies need allowing and which need killing to make the music work.
So , I think onward and into the workshop is the way forward !
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Old 10th April 2008, 10:38 AM   #14
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makinson1 said

"As soon as you make an "Absorbent" bearing, the vertical inertia will go up (Kiss of death). I'm not sure what you mean by absorbent bearing. Could you give an example?"

Can you elaborate please? How is the inertia affected if you don't know "what it means" ?

sp
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Old 10th April 2008, 08:17 PM   #15
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Think of what the heavy brass bridge does. It acts as a sink for the string vibration and releases the stored energy over time increasing the sustain, reflecting the sound over time. The tonearm counterweight does the same thing, so that the vibration from the cartridge is delayed and attenuated before it reflects back down the arm tube. Anything of substantial mass will store that energy preventing it from being reflected immediately back to the cartridge which would result in a smearing of the sound. So we look for counterweights, arm posts, and tonearm sound boards which have a low acoustical impedance at the frequencies in question. But high impedance under 20 Hz to filter out rumble and low frequency noise.
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Old 10th April 2008, 10:44 PM   #16
mandym is offline mandym  Philippines
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Quote:
Originally posted by makinson1
Think of what the heavy brass bridge does. It acts as a sink for the string vibration and releases the stored energy over time increasing the sustain, reflecting the sound over time. The tonearm counterweight does the same thing, so that the vibration from the cartridge is delayed and attenuated before it reflects back down the arm tube. Anything of substantial mass will store that energy preventing it from being reflected immediately back to the cartridge which would result in a smearing of the sound. So we look for counterweights, arm posts, and tonearm sound boards which have a low acoustical impedance at the frequencies in question. But high impedance under 20 Hz to filter out rumble and low frequency noise.
Now I'm more confused as ever
I better stay out of this
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Old 11th April 2008, 01:52 AM   #17
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Mandym, coming from the land of Manny Pacquiao,


you should know that you don't have to actually get in the ring to enjoy the fight. The physics of the tonearm can only be understood by taking it in small bites. Start with some basic articles such as this one at TNT:

http://www.tnt-audio.com/sorgenti/armdesign_e.html

Then progress up to some in-depth reviews of tonearms that focus on the mechanics of the arm rather than the subjective listening tests. Check out the Theory and Design paragraphs of this one for instance:

http://www.tnt-audio.com/sorgenti/belladonna3_e.html
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Old 11th April 2008, 03:44 AM   #18
mandym is offline mandym  Philippines
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Ah yes, I enjoy boxing specially if my man is winning. I wish though that I knew more about the sport so I can enjoy it better.

Thanks much for the instructional links you provided. I briefly glanced at it and it seems I'll have to do some wading in deeper waters but I am sure (I hope) I can learn something from it. From Paquiaoland, thanks again Makinson1.
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