Tempest PR Design input?

Discussion in 'Archived Threads 2001-2004' started by Chris Popovich, Mar 11, 2001.

  1. Chris Popovich

    Chris Popovich Stunt Coordinator

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    Hello all,
    I've cooked up a design using a single Tempest and Dual Pr15 passive radiators that I'd like you all to critique if you could.
    The box is made of .75" marine-grade plywood and exterior dimensions are 30*20*29 (hwd). Internal volume after bracing and drivers is approx. 8.05cubic feet.
    The two passive radiators each have 400 grams added.
    The sims I'm using show:
    -3dB @ 22Hz
    -6dB @ 17Hz
    -10dB @ 14.5Hz
    Group delay is coming up as
    24msec @ 20Hz
    10msec @ 30Hz
    6msec @ 40Hz
    5msec @ 50Hz
    I'm looking for good transient response, with good output availability as well. Do you think I'd be better off with dual shiva's instead?
    Thanks for the response,
    Chris
     
  2. Greg Monfort

    Greg Monfort Supporting Actor

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    What program are you using? For good transient response at rated power, I get ~25.6ft^3/14Hz, and ~294gr/PR, and a severe dip in the FR in the ~16-27Hz BW due to running out of Xmax, though it shouldn't bottom out.
    GM
    ------------------
    Loud is beautiful, if it's clean
     
  3. Chris Popovich

    Chris Popovich Stunt Coordinator

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    25 cubic feet? Wow. That's a big enclosure...
    The program I'm using is BassBox 6.0, whcih seems to do ok for vented, but I'm not sure about with PR's.
    -chris
     
  4. Greg Monfort

    Greg Monfort Supporting Actor

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    Yes it is. Trying to get good transient response with a ~high Q driver means a big cab.
    I'm not very familiar with BBP6. Does it allow you to select for VC heating like Lspcad? This dramatically increases cab volume. If not, then increase Qes ~50%, assuming you plan on using an amp rated at least as much as the driver, 750W. If you limit power to
     
  5. Julian Data

    Julian Data Second Unit

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    Greg,
    Do you have anymore LspCAD tips? I have received mine several weeks ago.
    thanks!
    Julian
     
  6. Greg Monfort

    Greg Monfort Supporting Actor

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    Hi JD,
    Hmm, tips? I'm not sure what you mean. What I mentioned about increasing Qes doesn't apply to Lspcad, as it's built in when you check the VC heating box in the Config window. It's how I do quick sims in BoxPlot. I don't use Lspcad til I get serious, as it slows down my old n' slo machine too much. If you plan to run the driver past Xmax, then the BL/Cms non-linear boxes should be checked.
    GM
    ------------------
    Loud is beautiful, if it's clean
     
  7. Julian Data

    Julian Data Second Unit

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    Ok..
    When I create a new driver that has DVC, I usually double the QES and let the program auto calc the QTS value. At times, when using the auto calc feature, I get some "funny" looking results when I don't have a value for. ie. MMd for the Tempest and I don't understand why.
    Julian
     
  8. Chris Popovich

    Chris Popovich Stunt Coordinator

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    Ok, I've given up the idea of playing with PR's, and decided to go with a simple vent.
    I'm now looking @ an 8.5 cubic foot box tuned to 18Hz. Does this make sense? Bassbox gives me a higher f3 than lspCad does, but Bassbox predicts better (slightly) transient response. Port being used will be 6" in diameter.
    I'm still thinking about that 25cubic foot box... wow....
    chris
     
  9. Greg Monfort

    Greg Monfort Supporting Actor

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    >Ok..
    When I create a new driver that has DVC, I usually double the QES and let the program auto calc the QTS value. At times, when using the auto calc feature, I get some "funny" looking results when I don't have a value for. ie. MMd for the Tempest and I don't understand why.
    Julian
    ======
    Hmm, you need to load it with the data for a single VC, then check the DVC box.
    ======
    >Ok, I've given up the idea of playing with PR's, and decided to go with a simple vent.
    I'm now looking @ an 8.5 cubic foot box tuned to 18Hz. Does this make sense? Bassbox gives me a higher f3 than lspCad does, but Bassbox predicts better (slightly) transient response. Port being used will be 6" in diameter.
    ======
    This doesn't allow for much VC heating. How much power are you listing? Are you checking the VC heating box in the config window? This driver will need a big box regardless of whether it's vented/PR'd due to its ~high Qts, if good transient response is required. At minimum, 15ft^3/16Hz IMO, and this is only Qb = 0.7 for half power. At 8.5ft^3, it needs a ~12.5Hz Fb for decent TR (PRs req), but
     
  10. ThomasW

    ThomasW Cinematographer

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    Chris
    If you're still interested in PR's make sure to download the latest upgrades to BBP6 from http://www.ht-audio.com they have "fixed" the PR modeling problems.
    I now get very similar results modeling the same driver in BBP6 or LspCAD. LspCAD does provide more flexibility with regard to modeling other aspects of speaker design though.
     
  11. Chris Popovich

    Chris Popovich Stunt Coordinator

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    This doesn't allow for much VC heating. How much power are you listing? Are you checking the VC heating box in the config window? This driver will need a big box regardless of whether it's vented/PR'd due to its ~high Qts, if good transient response is required. At minimum, 15ft^3/16Hz IMO, and this is only Qb = 0.7 for half power. At 8.5ft^3, it needs a ~12.5Hz Fb for decent TR (PRs req), but
     

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