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Old 1st April 2008, 10:03 AM   #1
allears is offline allears  United Kingdom
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Default tonearm absorbant bearings?

Sorry if I'm questioning the obvious but regarding tonearm bearings I wonder why the following :
If the stylus has moved in response to the groove and via the mechanics of the cartridge sent a signal down the wires , then all the vibratory /resonance problems are due to reflected vibrations coming back from the bearing / counterweight or within the armtube.
If this is so , why aren't highly absorbant bearings the norm rather than extremely solid ones ? And absorbant counterweights rather than brass or other solids?
Perhaps there is a site explaining these things that I have yet to find , if so , could someone point me to it (& stop me posting dumb questions!).
Thanks
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Old 1st April 2008, 10:24 AM   #2
YNWOAN is offline YNWOAN  United Kingdom
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It's not a silly question and there isn't a web site that answers (any better than this one) these kinds of questions. Most (though not all) arm designs work on the principle that mechanical energy produced from the stylus is communicated via the cartridge body, into the arm and through the bearings to be dealt with by the chassis of the turntable. However, some arms like the Well Tempered do seek to terminate this energy at the bearing point. Designers of rigid bearing arms would probably suggest that your suggestion would result in increased colouration as energy would not pass through the bearing but be reflected back to the cartridge and stylus.
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Old 1st April 2008, 12:38 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

The acoustic (as oppposed to mechanical) design of generic tonearms
is very limited, they are built to look like they do a job, and anything
radical generally goes straight into the niche market bucket.

The bearings have several jobs to do and they are in fact a very
poor point to try and absorb / dissapate energy in most arms.

A "well tempered arm" clone with a proper tube and headshell
would be one way of addressing the issue, the "Townshend trough"
is another.

Click the image to open in full size.

Click the image to open in full size.

/sreten.
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Old 1st April 2008, 03:29 PM   #4
oshifis is offline oshifis  Hungary
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Another example is the Mayware Formula IV unipovot with silicone grease damping at the bearing pin.
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Old 1st April 2008, 05:27 PM   #5
mandym is offline mandym  Philippines
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I am glad allears brought up this nebulous subject which has been vexing me ever since I started making my own tonearms!

YNWOAN, I have come across this argument before, that the best way to "drain" tonearm energy is through a mechanically sound and solid connection. On the other hand, I have also read about "recoil" mechanism where I imagine the vibrational energy is reflected back to the source as it hits a solid obstacle (analogous perhaps to a ball hitting a solid wall). My interpretation might not be correct, a little elucidation will be greatly appreciated.

sreten, I would also appreciate if you could expand on your statement that bearings are a poor point to absorb/dissipate energy in most arms.

At the moment I am doing work on wood tonearms specifically to address this issue. Wood has a very high internal damping and seems to work quite well in taming unwanted energy. Excess energy is also more efficiently "drained" to the plinth through use of like materials in order to enhance conduction. This necessitated the use (of course) of a unipivot bearing made of wood!

All I can safely say is that I am so much in the dark here. Air bearings, unipivots, string bearings, magnetic bearings, knife edge, etc,etc! Some of them seem to work on diametrically opposite principles yet put out magnificent performances. Black Magic?
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Old 1st April 2008, 06:37 PM   #6
YNWOAN is offline YNWOAN  United Kingdom
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I have not (yet) experimented with tonearm design so all my knowledge is hypothesis (on my behalf) or the thoughts of others. I do know that supporters of gimbal bearing arms often believe that this solution provides a broad band mechanical link between the arm base and the arm tube. Detractors of gimgal bearings suggest that the nature of ball races means that they are not absolutely tight (or they would not rotate) and this causes bearing 'rattle' at certain frequencies, or that the construction of this type of bearing creates an impedance mis-match which means that certain frequencies pass through the bearing whilst others are reflected or only partially attenuated. Often detractors suggest that a unipivot is the answer. Supporters of unipivots point to their inherently low friction levels and claim that mechanical 'connection' is greater than with ball races citing that surface pressure is proportional to surface area. Detractors claim that unipivots are unstable and lack geometric accuracy - they also claim the exact opposite of unipivot supporters, and believe that unipivots suffer from bearing 'chatter' and lack rigidity. Somewhere amongst these clashing belief structures and divergent interpretations of the relevant forces, some truth must lie.
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Old 1st April 2008, 08:16 PM   #7
EC8010 is offline EC8010  United Kingdom
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I haven't made a gimballed arm, but I have made unipivots. There are various ways of making unipivots, and it is possible to make one that chatters. Oddly, I find that a slightly lossy bearing works well - I use a ballpoint pen in PTFE as my bearing. I also use viscous damping elsewhere. There is no reason why the geometry of a unipivot need be anything less than perfect.
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Old 2nd April 2008, 02:49 PM   #8
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by mandym
I

sreten, I would also appreciate if you could expand on your statement
that bearings are a poor point to absorb/dissipate energy in most arms.


Hi,

My point is that given the job they have to do in practise if they do
this well you will find it difficult to disippate energy at that point.

/sreten.
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Old 3rd April 2008, 09:50 PM   #9
allears is offline allears  United Kingdom
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Hmm , interestingly diverse ways of looking at this business of vibration. I think it's going to come down to finding the right compromises , the ones that work musically , and that there will be no more "wrong" ways than there are wrong ways of making a musical instrument- if it sings it sings. I'm going to have to get some trial and error under my belt before I try to post again on this subject I think , but there is one more question regarding tonearm vibration that I'll put up as a new thread.
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Old 8th April 2008, 12:30 PM   #10
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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?
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