New Audiomobile (Mass + EVO) dumax datasheets available.

Discussion in 'Archived Threads 2001-2004' started by Rick Chwiendacz, Oct 9, 2001.

  1. Rick Chwiendacz

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    http://www.audiomobileinc.com/xfiles.htm
    Check them out - some interesting information in there. Not the least of which is that some of Audiomobile's motors have more xmag than Blueprint's mighty '03 series motor design - what's holding them back right now seems to tbe the suspension more than anything. It seems kind of strange to have 27mm of xmag with only 20mm of xsus to me.
    Also it's interesting to note that Matt at Audiomobile didn't post the graphs for BL vs. X and Kms vs.X. I wonder why?
    - Rick
    [Edited last by Rick Chwiendacz on October 18, 2001 at 07:19 PM]
     
  2. Jack Gilvey

    Jack Gilvey Producer

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  3. Rick Chwiendacz

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    Sure, Jack.
    Most of the time, xmac and xmax are indeed one and the same, at least per DUMAX. When finding the final xmax for a driver, DUMAX takes the lower of xmax, and xsus. For most drivers, xsus is higher than xmag, so xmax just becomes equal to xmag.
    In this case, the audiomobile motors have excursion to spare, but it's their suspension that's the limiting factor, not the motor structure. In this case, at 20mm excursion, the audiomobile Mass drivers' suspension compliance has dropped to 1/4 of its normal value (the suspension has gotten 4x stiffer), but the motor is still going strong. Without posting the actual Kms/Cms vs. X curves, we can't tell whether that's due to progressive nonlinearity, or catastrophic failure, such as spider contacting the top plate, or voice coil hitting bottom.
    With most drivers, the goal is to design the suspension such that it's quite linear up until xmag, and then have it progressively limit the excursion above xmag to avoid damage.
    This isn't the case with these drivers, though.
    - Rick
     
  4. Jack Gilvey

    Jack Gilvey Producer

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    Thanks, Rick, got it. I had assumed that Xmax was purely a magnetic limitation/measurement based on the datasheets I'd seen, and this is first set of specs that illustrated the true DUMAX definition for me.
    Since Xsus seems to have been reached so "early", is the Xmag value just extrapolated from the Bl curves?
    [Conjecture] At first glance it appears that the suspension is compromising such a capable motor, but might the design purpose be to have the suspension limit excursion well before the precipitous drop in Bl seemingly endemic to underhung motors? Until which point,though,they are more linear than overhung, at least according to the figure in the LDC.
    As opposed to an overhung design, where the Bl is allowed its more gradual rolloff until the suspension begins to "kick in".[/conjecture]
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    [​IMG]
     
  5. Rick Chwiendacz

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  6. Rick Chwiendacz

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    While I'm not a driver engineer, I think that the fact that the surround is made of rubber isn't by itself a major factor. The particular surround profile Audiomobile chose may very well be limiting the excursion, but I have a feeling that the excursion limits would be very similar for foam and rubber surrounds, given the same overall profile. (similar molds)
    As I said, until we see the curves, it's quite difficult to extrapolate what the possible causes might be. Seeing the point where the voice coil hits bottom on a Cms Vs. X plot, for example, isn't very difficult. =)
    I have e-mailed Matt at Audiomobile about this, and hopefully I'll get a response from him about it.
    - Rick
     
  7. TerryC

    TerryC Stunt Coordinator

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    Jack,
    Here is a great write up about Dumax X-Max figures: http://www.diysubwoofers.org/misc/dumax/dumax.htm
    Rick,
    What's your definition of bottoming? Since the suspension(XSUS) limits the travel of the VC (XMAG)long before its limits its very hard to bottom the Mass's VC.
     
  8. Rick Chwiendacz

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    Well, the strictest definition of bottoming (and the correct one, I believe), would be when the voice coil former contacts the back plate. My comment about bottoming in the earlier posts was not directed specifically at the MASS woofer though - it was a general statment with regards to the Kms vs. X curve.
    As I said, it's hard to really see what's happening until we see the curves, which may be one of the reasons why we don't have them.
    When the voice coil hits bottom, you'll immediately see Kms increase to a very high number (since Kms = 1/Cms, and Cms just dropped to near zero.) This would of course be readily seen on the graph. Suspension limiting would not be shown as such a sharp increase in Kms, as suspension limits are going to be more gradual, although they can be quite steep as well.
    - Rick
     

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