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New Audiomobile (Mass + EVO) dumax datasheets available. (1 Viewer)

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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]
 

Jack Gilvey

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Thanks, Rick, those links were dead the other day.
When I click on the 2315, I get the sheet for the 2010, the link is screwey.
Could you define the difference between Xmag and Xmax for me? I thought they were more-or-less the same number, the point where Bl drops a certain amount. Are these underhung (I think so), and does that make the difference?
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[Edited last by Jack Gilvey on October 09, 2001 at 06:59 AM]
 
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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
 

Jack Gilvey

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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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[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]
It's possible, but unlikely. The drop in BL isn't quite as precipitous as people make it out to be, and at least in my opinion, there's no reason to make the suspension limit it THAT badly.
I'm going to steal some of John Janowitz's pics here - I hope he doesn't mind.
http://www.stryke.com/pics/overhung-bl.gif http://www.stryke.com/pics/underhung-bl.gif
These are the BL vs. X curves of both a typical overhung and underhung motor design. Note that the underhung is still doing pretty good 5mm past xmax in the rear direction, and 10mm past xmax in the forward direction. Even after that the BL doesn't really drop off that quickly, all things considered. It most certainly doesn't drop off enough to justify having a suspension that hard limits the motor at only 2/3 of xmax, that's for sure.
In any case, it's hard to speculate about what's what, becuase Matt cut the darn curves off all of the datasheets. I'm not quite sure why, since he said that he was going to post them when I asked him for them. He must have his reasons though - I'm just not quite sure what they are.
- Rick
 

Jack Gilvey

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It most certainly doesn't drop off enough to justify having a suspension that hard limits the motor at only 2/3 of xmax, that's for sure.
No, I'd have to say it doesn't. Interesting, to say the least. I wish we (you) had those curves.
Thanks again.
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Jack Gilvey

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You think the suspension characteristics might be partly due to the rubber surround? Given their car-oriented market, that's something a typical customer might demand.
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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
 
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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
 

Jack Gilvey

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Thanks for the link, Terry. I'd actually read that before
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, but it never sank in that the Xsus could actually be the lesser of Xmag/Xsus, and hence the Xmax value, until I saw these.
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