Posted by Jim_E (A) on October 26, 2009 at 11:29:11

In Reply to: RE: Musings on true-ribbon roll-off points for 3-way Maggies - corrected!! :-)) posted by andyr on October 24, 2009 at 02:53:58

Andy,
I finally had a chance to run the full 3.3R high pass filter (Lars values, 3 ohm driver) in Matlab. The component values are not correct for a fourth-order Butterworth filter, and provide some low freq peaking. The actual roll-off point is close to yours.

Does your analysis tool show the same peaking characteristic as well?

regards,
Jim

Edits: 10/26/09

• RE: Musings on true-ribbon roll-off points for 3-way Maggies - corrected!! :-)) - andyr 14:16:46 10/27/09 (0)
  In Reply to: RE: Musings on true-ribbon roll-off points for 3-way Maggies - corrected!! :-)) posted by Jim_E on October 26, 2009 at 11:29:11

  Hi Jim,

  Further to Davey's comments, if you compare the 3.3 with the 3.5, you can see that the mid LP filters are similar - except the 3.3 has 0.955mH as the first inductor in the 18dB LP filter, whereas the 3.5 has 0.355mH.

  lspCAD produces a very nasty mid-range frequency response for the 3.3... could Magnepan have made a mistake with the 3.3 (and it really should be 0.355mH)? After all, it's the same driver. :-))

  Regards,

  Andy
  
  
  
  

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  Edits: 10/27/09
• RE: Musings on true-ribbon roll-off points for 3-way Maggies - corrected!! :-)) - Davey 13:48:37 10/26/09 (2)
  In Reply to: RE: Musings on true-ribbon roll-off points for 3-way Maggies - corrected!! :-)) posted by Jim_E on October 26, 2009 at 11:29:11

  You have to be careful how you analyze that.
  
  The peaking is a result of being connected without the midrange crossover attached. The C1/L1 circuit driving the HP filter without the midrange filter attached will yield a big peak as you've shown.
  
  Try analyzing using just the two high-pass components and nothing else. It'll look good then.
  
  Cheers,
  
  Dave.
  

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  • RE: Musings on true-ribbon roll-off points for 3-way Maggies - corrected!! :-)) - Jim_E 13:36:40 10/27/09 (1)
    In Reply to: RE: Musings on true-ribbon roll-off points for 3-way Maggies - corrected!! :-)) posted by Davey on October 26, 2009 at 13:48:37

    Davey,
    The peak is a classic under-damped response. I agree that adding the midrange network will probably tame that some. Even with reduced magnitude, there will remain a pair of filter poles around 190 Hz introduced by the use of the common mid/ribbon filter. This pair of filters poles introduces an abrupt 180° phase shift which would remain. The roll-off is also limited to 12 dB/octave for most of the ribbon filter's operating range.
    
    The use of the common high-pass LC filter for both the midrange and ribbon reduced the cost, but is not an optimal configuration. Both filters are fourth order(24 dB/octave), but neither even close to classic Butterworth configuration.
    
    Getting rid of the crossover module, and going with the bi-amp configuration seems a far better solution.
    
    regards,
    Jim
    

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    • RE: Musings on true-ribbon roll-off points for 3-way Maggies - corrected!! :-)) - Davey 14:58:58 10/27/09 (0)
      In Reply to: RE: Musings on true-ribbon roll-off points for 3-way Maggies - corrected!! :-)) posted by Jim_E on October 27, 2009 at 13:36:40

      Yeah, I understand the way the filter works. (I wasn't sure you did in your simulation so was pointing that out.)
      
      There's an alternative tweeter connection in a schematic in the "tweaks" section that moves the tweeter filter connection point upstream of the midrange HP filter. (I think some users have performed this "tweak" previously since the page has been there for a long time.)
      
      http://www.integracoustics.com/MUG/MUG/tweaks/mag3.6xover.html
      
      
      It can be confusing analyzing electrical responses only on the Maggie crossover networks. The acoustic responses have to be factored in to yield approximate final results.
      
      Removing the crossover module and configuring for a bi-amp setup is a better solution, but you still have to design the electrical responses to achieve the proper final acoustic responses. Line-level crossovers require just has much design effort as high-level networks. Maybe a little more. :)
      
      Cheers,
      
      Dave.
      
      
      

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