Lining a sub with foam

Discussion in 'Home Theater Projects' started by Felix_F, May 25, 2004.

  1. Felix_F

    Felix_F Stunt Coordinator

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    I've seen many pics of DIY subs that were lined with acoustic/eggcrate foam on the inside. Please excuse the novice question, but why is that done?
     
  2. Patrick Sun

    Patrick Sun Moderator
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    It's to minimize upper frequencies that can still be present even with low pass filtering.
     
  3. Neil Joseph

    Neil Joseph Lead Actor

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    Does one use the egg crate foam, or, if you stuff with polyester pillow stuffing, does one still need to use the eggcrate foam as well? Once I get the amp for this box, I want to stuff it. I already have some eggcrate foam and some pillow stuffing, which would you recommend I use?...

    [​IMG]
     
  4. Patrick Sun

    Patrick Sun Moderator
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    Try one and then the other, whichever sounds best to you wins.
     
  5. Aaron Gilbert

    Aaron Gilbert Second Unit

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    Neil,

    As that's a vented box, I wouldn't stuff it. You can line the walls with the eggrate foam, and that should be sufficient to damp unwawnted mid/high frequencies. In many cases, even that is not required. Stuffing in a subwoofer is done only to increase the apparent volume of the enclosure, such as for a sealed box that's smaller than the size required. In a vented box, you don't want anything that can interfere with vent operation. So even if you were to use pillow stuffing instead of foam, you'd want to staple it to the walls.


    Aaron Gilbert
     
  6. Neil Joseph

    Neil Joseph Lead Actor

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    Sorry and I hope I am not hijacking the thread Felix, hopefully the answers to my questions will also provide you with answers as well...

    I will try eggcrate foam on approx 50% of the interior walls to begin with and see how that goes. I don't want to over dampen it either.

    Thanks,
     
  7. Aaron Gilbert

    Aaron Gilbert Second Unit

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    You don't really need to worry about overdamping it. Neither eggcrate foam nor polyester stuffing are good at absorbing frequencies below 100Hz. Lining all the walls will only serve to help reduce midrange and high frequencies, not cause you to actually lose bass performance.

    All that said, as both your woofer and vents are downfiring, midrange and high output are not that great a concern. Assuming the subwoofer is sitting on thick carpet, the carpet will tend to absorb any mid and high frequences that get by the crossover. And THAT said, my woofer is front firing and my ports are upfiring, I have zero stuffing/lining in my box, and can't hear squat out of the sub besides 80Hz and below, through the ports or driver, using a standard THX 80Hz/24db per octave crossover.

    My guess is that you'd have a tough time telling any difference at all between zero foam and foam lining all the internal walls, assuming your crossover is the same as mine. You might be surprised to learn just how many high end commercial vented subwoofers have no lining inside the enclosure.


    Aaron Gilbert
     
  8. Patrick Sun

    Patrick Sun Moderator
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    My old Infinity BU-120 had a piece of fiberglass as "stuffing" in a ported enclosure. Sub manufacturers will do anything to minimize the enclosure volume to satisfy SAF/WAF in terms of marketing.
     
  9. Felix_F

    Felix_F Stunt Coordinator

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    No problem at all. This is very interesting.
     
  10. Aaron Gilbert

    Aaron Gilbert Second Unit

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    Well, ThomasW, whose loudspeaker opinion I respect highly, recommends lining vented enclosures in this thread:

    http://www.hometheaterforum.com/htfo...hreadid=198933

    So darnit, now I am going to have to take out my woofer and throw some lining in the box and see if I can notice any difference. [​IMG] I suppose that unless you get exotic like Black Hole damping pads, adding foam or bonded polyester to the walls falls into the DIY category of 'it can't hurt, and it's cheap, so might as well do it!'.


    Aaron Gilbert
     
  11. JurgenV

    JurgenV Extra

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    Aaron,

    Just wondering how that turned out for you. Did you notice an improvement with the lining? Have you also tried it with stuffing?
     
  12. ross ish

    ross ish Stunt Coordinator

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    Those big vented sonotubes sound like a cave echo without lining on the walls:}
     
  13. James W. Johnson

    James W. Johnson Screenwriter

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    I have had good luck using R-13 fiberglass as a filler..of course I am lucky because I spent a few summers as a kid working in an Ownens Corning plant so I have grown immune to the ichiness. [​IMG]
     

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