Help understanding WinISD

Discussion in 'Home Theater Projects' started by Eric_Ennis, Nov 13, 2003.

  1. Eric_Ennis

    Eric_Ennis Auditioning

    Aug 23, 2002
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    I have been trying to use WinISD to design a box that will work temporarily for some speakers I have laying around. I want to build the box to also practice my woodworking skills before I get serious about buying new drivers.

    Anyway, in order to familiarize myself with the program I have been playing around with it, entering various suggested boxes from the Adire site and looking at the responses graphs.

    I have noticed a peculiarity with the program regarding vents. The number and diameter of the vents is changeable, but the length changes with the cabinet tuning frequency. That makes sense. However, if I input the box values for say a tempest driver in the adire alignment, the vent lengths are not even close to what the white paper specifies. For instance, the Adire white paper on the tempest vented boxes specifies two 3" diameter vents with 11" tubes for a 214L box tuned to 15.4Hz. If I enter those values into the WinISD program, it tells me to use two 3" diameter vents that are 18.97" long.

    The one thing I might be missing is the polyfill stuffing, which I cannot find where to enter into WinISD, the Adire spec calls for 64 oz. of polyfill. If I use an assumption that one pound of polyfill will increase apparent box volume by 1 cubic foot and enter that volume into WinISD instead, I get much closer to the spec'd vent length. The actual ratio of weight to apparent added box volume appears to be around 1.1 or so, as I had to add 4.541 cubic feet to the box volume to get the port lengths to match.

    Is this a valid assumption? Should I use this conversion factor to factor in the effect of polyfill when using WinISD?

  2. ThomasW

    ThomasW Cinematographer

    Nov 6, 1999
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    There are differences in how programs handle damping. And generally speaking unless one is knowledgeable it's not a good idea to try and compensate for changes in box volume with damping materials. (Yes Dan Wiggins does it but he's a pro!)

    If you have MS Excel I recommend using Unibox. You'll find that it more closely tracks the better programs like LspCAD. Also grab the Adire copy of LspCAD and compare it to Unibox, there are some interesting differences.

    My final suggestion is to model boxes without damping materials, then build the box. Then fine tune it's performance with the damping. If you model the box with damping and build it accordingly (generally a smaller box) then there is much less 'wiggle room' when it comes to fine tuning with damping materials for optimal performance.
  3. michael-e

    michael-e Agent

    Sep 1, 2003
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    i designd my box with winisd pro.

    a mate compared it to his spreadsheets based on spreadsheet.

    Very similar results.

    its tuned within 1hz predicted


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