Vinyl Asylum

Posted by Mark Kelly (M) on June 25, 2009 at 21:49:02

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

• Another variable: at what freq is the measured compliance reported? - charlies824 11:22:12 06/26/09 (0)
  In Reply to: RE: Dynamic or static compliance? posted by Mark Kelly on June 25, 2009 at 21:49:02

  Some makers report the value at 100Hz, whereas the meaningful frequency range is between 5 and 20 Hz.
  
  charlie s.
  

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• Grado doesn't specify - hesson11 04:59:20 06/26/09 (1)
  In Reply to: RE: Dynamic or static compliance? posted by Mark Kelly on June 25, 2009 at 21:49:02

  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
  

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  • All units are equal - Mark Kelly 05:13:02 06/26/09 (0)
    In Reply to: RE: Grado doesn't specify posted by hesson11 on June 26, 2009 at 04:59:20

    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
    
    

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• RE: Dynamic or static compliance? - lovetube 04:24:42 06/26/09 (3)
  In Reply to: RE: Dynamic or static compliance? posted by Mark Kelly on June 25, 2009 at 21:49:02

  "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
  

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  • Measuring effective mass - Mark Kelly 04:57:24 06/26/09 (2)
    In Reply to: RE: Dynamic or static compliance? posted by lovetube on June 26, 2009 at 04:24:42

    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
    
    

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    • RE: Measuring effective mass - Old nuff 2 no better 10:40:40 06/27/09 (0)
      In Reply to: RE: Measuring effective mass posted by Mark Kelly on June 26, 2009 at 04:57:24

      Hey, I'd love to see that too!
      

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    • RE: Measuring effective mass - lovetube 06:22:16 06/26/09 (0)
      In Reply to: RE: Measuring effective mass posted by Mark Kelly on June 26, 2009 at 04:57:24

      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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