Stuffing my ported subwoofer design - Couple of questions.

Discussion in 'Archived Threads 2001-2004' started by Javier_Huerta, Dec 7, 2002.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Hi!

    My design is finished... though I was wondering about stuffing a vented sub and its influence on overall system design.

    I have the material for a 60x60x60 cms. box. Braced, I calculated an approximate volume of 170 liters. But I forgot to consider the bracing, port and driver volume. So I end up with approximately 155 liters - I'd say at least 10 liters' short of an adequate design.

    If I decide to stuff my vented sub, can I gain a bit of perceived space? For example, if I use 4 pounds (2 kg.) of stuffing, would I gain back some 20% interior space - say, 30 liters? Then I would get a 180 liter enclosure, which would be ideal for my project.

    Can I get away with using even more stuffing than that? What's the limit? Any specific recommendations?

    Then, there's the issue of Adire's plans for the Adire Alignment box. I copied their design into WinISD for study, and the port size the software comes out with is completely different to the one Adire suggests (the program says 14" of a pair of 3" ports are needed, while Adire says a pair of 12" will do fine. All I can think of is that the stuffing is changing the port length. Any specific ideas about this?

    Thanks for your help!


    Javier.
     
  2. Chris Carswell

    Chris Carswell Supporting Actor

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    You got it, the stuffing is changing the port length.
    You will roughly get a 25 to 35 percent of "space gain" by using
    stuffing at a rate of 1 to 1.75 pounds per cubic foot of internal
    volume. 1 LB of polly fill per 1 cu ft = 100% fill rate.
    I also found that stuffing gets less effective as box size increases.
    The morale: The bigger your box is, the harder it is to fool your
    woofer. A few rules of thumb: Stuff small enclosures (those with up to
    about 3 cubic feet of internal volume or less) with 1.5 pounds of
    fill for each cubic foot of internal volume and you should get about a
    30-percent increase in box volume without seriously affecting other
    performance variables. For larger enclosures OVER 5 CU. FT, add stuffing
    at a rate of approximately 1 pound per cubic foot and you should get a
    virtual-space boost of about 20 - 25 percent.

    16oz - per ft^3 = 100% fill rate
    12oz - per ft^3 = 75% fill rate
    8oz - per ft^3 = 50% fill rate
    4oz - per ft^3 = 25% fill rate
     
  3. Jon Torres

    Jon Torres Second Unit

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    You might want to email Brian Bunge. I think he had a stuffed 175 liter vented box for a tempest.
     
  4. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Chris, thank you very much for your post! My box is actually exactly 6 cubic feet. So I'd guess 6 pounds would give me a 20% space increase (exactly what I was looking for - 7.2 cubic feet, or even a bit more space than I'd need.

    Would you suggest downsizing a bit the enclosure, or dialing a bit back on the polyfill? Also, can you please explain what is the fill rate? Maybe the relationship is pretty obvious, but being a metric system user, I can't understand the relationship between fill rate and perceived volume gain.

    A last question, if I may: If I stuff my subwoofer, I shouldn't pad the internal walls with acoustical foam or anything, right?

    Jon, I'll e-mail Brian. He has always been very helpful with ideas. Thanks!

    Thanks a lot!!!
     
  5. Brian Bunge

    Brian Bunge Producer

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    Javier,

    Chris has got you covered. Yes, I stuffed a 175L enclosure with 64 oz. of polyfil, but this was per Dan Wiggins' recommendations. I doubt adding acoustic foam will gain you much, if anything.
     
  6. Jacques C

    Jacques C Stunt Coordinator

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    Javier,

    My sub is almost the exact same size as yours (you can see a picture of mine in the Adire Audio Gallery). I have mine fully stuffed (1lb/cu. ft.) with no lining at all. Mine ended up being tuned to 21 Hz or so and right now in-room the -3 dB point is 15-16 Hz.

    In my opinion, the stuffing did its job pretty well, and this sub plumbs the depths very well.

    Only thing you have to worry about is stuffing right at the entrance to the ports. The first time you really pump it up you will be surprised how far stuffing can fly! ;-) Just make sure there is an open area for the port(s) to breath and you will be fine.

    Take care.

    Jacques
     
  7. ThomasW

    ThomasW Cinematographer

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