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In Reply to: RE: Suspicious calculation for arm/cart compatibility posted by hesson11 on June 25, 2009 at 21:08:45
If that's the static compliance you can bet the dynamic compliance is less. If the dynamic compliance were say 10 um/mN the arm mass would be 19.8 g.
BTW if you have a small speaker and a signal generator you can measure the effective mass of the arm directly.Mark Kelly
Some makers report the value at 100Hz, whereas the meaningful frequency range is between 5 and 20 Hz.
charlie s.
The Grado specs just list "Compliance," without specifying dynamic or static. I assumed it was dynamic because that seems to be the more common spec.
They also specify it in "cu" (i.e. "20 cu"), rather than the more common "cm/dyne". I don't know if there's a difference or if there is, what the significance is.
-Bob
CU = Compliance Unit. In the old "CGS" system the unit was 10^-6 cm/dyne. In the modern SI system the unit is um/mN. All the units are the same:
1 cm / dyne = 1 g ^-1.s^2 = 10^3 kg^-1.s^2
thus 10^-6 cm / dyne = 10^-3 kg^-1.s^2
1 um = 10^-6m
1 mN= 10^-3 kg.m.s^-2
therefore 1 um / mN = 10^-3 kg^-1.s^2
the two units are thus identical
Mark Kelly
"BTW if you have a small speaker and a signal generator you can measure the effective mass of the arm directly."
this is interesting. can you share how to do so.
Thanks
LT
This was a collaborative effort: I came up with the original idea which was refined by a couple of contributors on DIYaudio.com. Unfortunately I cannot find the original thread so I can't give credit where it is due.
The full description is rather long and involved so I might write it up properly and post it later.
Mark Kelly
Hey, I'd love to see that too!
Thanks Mark
if you can write this things up then it should be benefit for most around here as I found it to be helpful for some tone arm DIYER.
cheers
LT
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