Confused about WinISD Pro prediction of excursion

Discussion in 'Home Theater Projects' started by Tim Bargar, Jan 15, 2004.

  1. Tim Bargar

    Tim Bargar Agent

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    I've been playing around with WinISD pro to see what I can do with the two drivers (ACI SV12 and DV12) I have. I've been puting them in vented boxes in the software because I want to get as much low end extension as possible (F3 at 20Hz or below). What confuses me is the linear excursion predicted by WinISD exceeds the Xmax at 20W of input power? I wouldn't expect that to occur since these drivers are rated at over 100W. I guess I don't understand something about the significance of the excursion plot, the power input in WinISD, or how much power the driver actually sees.

    Could somebody please explain this to me?

    Thank you!
     
  2. Chris Carswell

    Chris Carswell Supporting Actor

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    If your sub has a x-max of 10mm, check linear excursion at 20mm or peak to peak.
    Remember, the larger the box the faster the sub will un-load.
     
  3. Isaac C

    Isaac C Stunt Coordinator

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    That 100W figure is the thermal rating of the voice-coil. It really takes little power to mechanically-overload a subwoofer; especially at low frequencies; and especially using pure sinusoidal signals.

    hth [​IMG]

    Isaac
     
  4. Eric Eash

    Eric Eash Second Unit

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    yes, the cone excursion is peak to peak. i just plotted the SV12 @ 100W in a 4 cubic foot vented box tuned to 20Hz and it doesn't exceed xmax til 16Hz. i don't have the T/S measurements for the DV12 but i'm sure they are really close. anyone else have some advice.

    eric
     
  5. Troy R

    Troy R Stunt Coordinator

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    I have a question about xmax. Does the driver only acheive xmax at max output?

    I'm trying to design a sub with an old SVS driver and it's very hard to keep it under the 28-29mm (peak to peak) xmax. So I'm wondering if this will only happen if I'm playing the sub over 100+ db's.

    Any help/info would be great!

    Thanks,
    Troy
     
  6. Jack Gilvey

    Jack Gilvey Producer

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    What level is your design program showing when Xmax is hit? At what frequency is Xmax occuring?
     
  7. Troy R

    Troy R Stunt Coordinator

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    I'm trying to tune the sub around 20hz. Right now with a 16" dia. sonotube I can go 128 liters with a 6" port 34-35" long. The SVS driver has an xmax of 14mm and I'm getting excursion of around 29-30mm at about 28hz or so.

    So I'm thinking since I never listen at really loud volumes I'll be OK. What do you think?

    Thanks,
    Troy
     
  8. Tim Bargar

    Tim Bargar Agent

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    Thank you all for trying to help me out on this one. [​IMG] Currently I am not at the PC on which I've downloaded WinISD Pro, I am on a MAC which I don't believe is capable of operating that program. So, I'm sorry Jack, but I can't tell you right now the specifics of the alignment or the frequency relative to excursion. I will have to wait until Monday before I am able to do that.

    Please let me try to understand the interpretation of the excursion plot. If the plotted excursion is peak to peak, then if the xmax is stated as 11mm, then a reading of 21mm excursion on the WinISD excursion plot indicates the driver is operating within the normal limits. But if the plot indicates 23 mm of excursion, then the driver is going beyond it's capabilities? Is that correct?

    As far as the input power in the program, is that essentially the amplifier power rating?

    Since I'm at home, I found the DV12's TS data, I tend to be something of a pack rat and hold onto things. Here they are:

    BL 7.8 Tm
    Fs 17Hz
    Qms 5.101
    Qes 0.481
    Qts 0.44
    Vas 380L
    Xmax 10.54mm
    Rms power 150W

    Ironically, WinISD Pro doesn't have the DV12 T/S while WinISD does.

    Thanks,
    Tim
     
  9. Jack Gilvey

    Jack Gilvey Producer

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    It's (the "power" box under the "Signal" tab) the wattage rating of the amp you intend to use, not the Pe of the speaker.
     
  10. Sebastian

    Sebastian Second Unit

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    Troy,

    With that alignment and with 200W to the driver you should be safe to about 17 Hz. With sub sonic filter that should not be a problem with Xmax. You should be looking good to ~105dB (probably more, being safe) before that sub starts to bottom out at 28Hz. Over 200W the driver is going to bottom out giving the right source material. That looks like a good alignment, almost identical to mine, go for it! You will be able to bottom that sub no matter what alignment you go with (that is one of reason SVS invented the ISD) unless you tune it to around 25Hz but then you lose some of lower frequencies. Loud frequencies below 20Hz you would have problems, it’s a trade off. Higher tune, louder SPL, lower tune deeper but lose some output.
    Good luck! It’s plenty loud at first until you get bit by that stupid upgrade bug!
     
  11. Sebastian

    Sebastian Second Unit

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    Hmm, interesting Troy, I think I may like you alignment better. I think I may try a 20 Hz tune I never checked cone excursion when I modeled mine. It looks a little safer.

    Ah, nevermind I forgot I have an AV-12 in the closet waiting for the new house!
     
  12. Troy R

    Troy R Stunt Coordinator

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    Thanks again for the info Sebastian!

    I can't decide if I should go with a 4" flared (shorter sonotube) or 6" PVC port. I guess it depends on how cheap I can find 6" PVC...

    Thanks again!
     

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