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Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
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Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
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In Reply to: So what you are saying is ... posted by garth on November 18, 2005 at 15:44:09:
You are missing the word effective. Equal moment of inertia is the same as equal effective mass. It is not the same as equal total mass.A big fat blob of a headshell is not at all the same as a big fat blob of a bearing housing. The headshell will increase the moment of inertia, and thus the effective mass, much more than the bearing will if they weigh the same.
Taking Klaus's example, an SPU (32 grams) substituted for our 7 gram headshell will increase the effective mass by 24 grams. Attaching an extra 25 grams to the bearing will increase effective mass by 0.1 g. Both will of course increase the total mass by 25 grams.
The position of the masses determines the final effective mass, so it is very important.
As a way into this consider an arm with which you are probably familiar. I have never taken a Rega tonearm apart but I guess the armtube alone would weigh around 30 grams, yet the effective mass of this arm is around 10 grams. Once you understand how 30 grams of magnesium, most of it forward of the pivot, has only 10 grams of effective mass you will be well on the way.
And no, I am considering the topic of effective mass very carefully for my new tonearms. I intend to make a version with about 10 grams effective mass and a version with around 15 grams. The second one will allow me to achieve twice the torsional rigidity of the first because I can beef up the armtube so much, as long as I make sure that I distribute the extra beef correctly.
Mark Kelly
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Follow Ups
- No again - Mark Kelly 11/18/0516:21:21 11/18/05 (1)
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