Subwoofer Modelling

Discussion in 'Archived Threads 2001-2004' started by Patrick D, Nov 6, 2001.

  1. Patrick D

    Patrick D Stunt Coordinator

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    OK.. let me admit up front that I have no idea what i'm doing. I got a copy of LspCAD to act as a bit of a crutch since I'm not exactly satisfied with the existing plans out there. That said, here is the subwoofer configuration I am kicking around, presented to you all for ridicule.. [​IMG]
    [​IMG]
    [​IMG]
    This is using the Dayton 15DVC, since apparently the Tempest that I was going to use is out of stock (?).
    The box is 300 liters (~10.5 ft3), port diameter 6" and length 22". Ql is assumed at 7. According to the model the port airspeed hits a little over 2 m/s at the resonant frequency. I'm going to put that PartsExpress plate amp that was on special (the 250W one at 4ohms with the nifty remote) and cross it over at 80hz.
    Now, what I wanted out of this design was the impossible... I want my brains to leak out of my skull when there's an explosion in a movie, but to have the sub still have enough class to not embarass itself in the occasional music session. My concerns are for the group delay, while this appears to behave itself by staying under 20ms until 20hz, it does peak. Is this a problem?
    Will there be an issue with the impedence profile?
    It also shows a bass shelf response, which is -3db at 30hz until 17hz (from 80hz), I don't know if that's a problem.
    Also, how would I calcuate the Q for this box?
    I'm looking for advice to learn from, so please feel free to comment.
     
  2. Patrick Sun

    Patrick Sun Moderator
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    My only suggestion is to find a more optimal enclosure size/porting to make use of that Dayton 15" DVC because what you have now is not remotely desirable unless you were to EQ the top end of the bass (over 50Hz).
    ------------------
    PatCave; HT Pix; Gear; DIY Mains; DIY CC; Sunosub I + II + III; DVDs; LDs
     
  3. Jon Hancock

    Jon Hancock Stunt Coordinator

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    Hi
    That's a mighty large box for a 15" driver, and you do have it tuned quite low, at around 15 Hz. Maximal port output will be at the box tuning frequency, an octave above that, most of the output will have to be provided in "direct radiating" mode. Have you already purchased this driver?
    For a relatively few dollars more, you could go with a Blueprint 1503.
    BP 1503: Fs = 26.8 Hz
    Re = 3.6 ohms
    Qms = 7.9
    Qes = 0.32
    Qts = 0.3
    Cms = 143.5 uM/N
    Mms = 143.5 grams
    Sd = 804 cm sq
    Vas = 132 liters
    Xmax = 24 mm
    Pd = 1 kW
    For box modeling, I like Unibox; which is freeware, and gives you lots of information in an easy to use form. I like LspCAD, and own it, but I use it primarily for crossover design.
    http://www.danbbs.dk/~ko/ubmodel.htm
    Note the SPL capability in the 15-20 Hz region with 500 watts power. The upper light gray curve shows the maximum output capability based on box tuning and driver mechanical excursion limitations.
    There's still a gradual roll-off from around 100 on down, but depending on the room positioning and crossover, this is rarely a problem. The additional room gain below 100 makes up for some of this. Because the TC-Sounds sourced drivers have high VC inductance, they tend toward a hump in the 50-70 Hz region; this reqiured some taming with EQ for the Stryke HE-15, and may for the Blueprint.
    Unless you really want as much output in the 15 Hz region as possible, I'd consider a box more like our AS-15, 160 liters, tuned to about 18.5 Hz. It rocks, too, and the size is a little more manageable. Not a lot, I guess, but 25% smaller isn't trivial.
    Just some food for thought.
    Regards,
    Jon
    I'll know more after I test the ones I've ordered.
     
  4. ChristianT

    ChristianT Extra

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    Sorry wrong thread.
    [Edited last by ChristianT on November 06, 2001 at 03:51 PM]
     
  5. Patrick D

    Patrick D Stunt Coordinator

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    The 15-DVC is already in the mail with a handful of other Dayton drivers. I had heard about the Blueprint 1801 but I still can't find them via any of the usual sources. Are they under the MTX name?
    I'm not seeing the real pros/cons about the alignment I came up with versus the one you showed (aside from the overall SPL offset). I had wanted to try out UniBox but alas, no Excel 2k here.
    Looking at the response you give, it looks 6dB down from 80hz (which is where I was going to cross it over from the mains -- as if I have a choice with my receiver [​IMG]). My primary concern with my alignment was the shelving down of the response (4.5 dB) from 80hz, and the group delay and impedence peak coming well before the resonance frequency. What were the port values for your model?
    Changing my alignment to 200 liters, Ql=15, I get something around Fb = 18.7, with a max 2.5 dB drop from 80hz until Fb with 1 6"x22" port. I'm only feeding this 250W max (so less than that overall) from a plate amp. I'm not sure if this is too much better, group delay doesn't cross past 20ms now until below 20hz, however the response isn't as flat (with a small hump just before Fb).
    Anyway if anyone is still listening, what would be an optimal tuning frequency? Where do I start to not gain anything due to source materials just not going that low?
    (Thanks for the reply!)
     
  6. Brian Bunge

    Brian Bunge Producer

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    Patrick,
    The driver is the 1803. It's available directly from Blueprint. Try www.blueprintdrivers.com and click on the 03 series drivers.
    Brian
     

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