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In Reply to: RE: Counterweight Change posted by hahax@verizon.net on May 16, 2017 at 21:04:22:
My calculations indicate that for more-or-less traditional arm configurations the counterweight contributes only 4-5% toward the effective mass. We have to be careful to separate the concepts of mass and VTF, noting (carefully) that effective mass is that which affects arm-cartridge resonance. The counterweight is there and it's massive, but it has only minor **participation** in the cartridge dynamics.The bulk of effective mass (90%+) comes from the cart + headshell (> 75%) + armtube and the polar moment of inertia ( <20%). So, basically, all a counterweight has to do is establish the correct VTF, beyond that it's effect on cartridge dynamics is nearly negligible. As far as the sale of expensive custom aftermarket counterweights, people put expensive, custom rocks on their electronic equipment cabinets and funny little hats on their vacuum tubes too. Doesn't make these good ideas.
On a side note, as a structural dynamicist I decry all "rubber donut" isolation schemes in any part of the tonearm. They don't provide meaningful isolation, they introduce a spurious nonlinear element into the structure of the arm/counterweight which must dissipate the energy of the mechanical vibration that the cartridge throws up it, and the rubber parts fail in time.
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Follow Ups
- RE: Counterweight Change - mr.bear 05/16/1723:46:59 05/16/17 (0)