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Is my new enclosure STURDY enough?

Discussion in 'Home Theater Projects' started by BrianJ>Y, May 22, 2003.

  1. BrianJ>Y

    BrianJ>Y Stunt Coordinator

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    Well I finally finished my ported 3.5cu-ft downfiring av12 sub + Rythmik amp...and it sounds AWESOME. Only thing is when I play it at around -5 to -10 from reference levels in my 3000cu-ft room the sides and mainly the top of the box feel like they're really getting pounded from the inside. I can't feel any air leaks, nothing's moving, and the sub isn't close to bottoming, it sounds great.

    I used 3/4" mdf all around and attached the boards with glue and screws. I braced using 2 large pieces of the same mdf along with a lot of L-brackets. I guess my question is when you guys feel your boxes during loud volume levels does it feel like they're getting pounded or just vibrating? I tried placing about 40 extra pounds of weight on top, the pounding seemed to be reduced...I'm going to try adding even more weight.

    Thanks,
    Brian
     
  2. TimForman

    TimForman Supporting Actor

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    It's hard for me to relate to this one. I can't get near my sub at reference levels.[​IMG] Just kidding. My sealed Tempest is built with void free oak plywood and MDF internal cross bracing. The joints have no screws as I used biscuit joints and dowels. The top is inset with a piece of glass that doesn't appear to move at all. I've pushed it to the limits and never got the impression it was getting "pounded".
     
  3. BrianJ>Y

    BrianJ>Y Stunt Coordinator

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    By pounded I mean putting your hands on top of the sub and feeling as if somebody was punching the top from the inside... I'm worried that my enclosure isnt rigid enough, although I built it like everybody else does...atleast I hope I did.
     
  4. Pete Mazz

    Pete Mazz Supporting Actor

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    If, by "L" brackets, you mean the metal screw on variety, I'd say you may have problems. These brackets don't hold securely enough to withstand the internal forces the sub is undergoing. If you glued the braces and just held them in place with the brackets, then you should be OK, although from the sounds of it, you may need more bracing.

    Pete
     
  5. TimForman

    TimForman Supporting Actor

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    Here's how I did the cross bracing in mine.
     
  6. Justin Ward

    Justin Ward Supporting Actor

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    When I feel the panels of my 194L Tempest (especcially the top) while it is playing I notice the same thing. It feels as if there is someone trying to punch their way out of box. I notice it most with drums.
     
  7. Allen Ross

    Allen Ross Supporting Actor

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  8. Greg Monfort

    Greg Monfort Supporting Actor

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    No, it shouldn't 'pound' or vibrate. MDF is relatively weak, so to ~match the rigidity of 3/4" void free plywood requires it to be ~1.125-1.25" thick depending on who made it since it varies from brand to brand, and even between plants of the same manufacturer. Once you start bracing the plywood, it's stiffness goes up much quicker with bracing than does MDF, so as you've already found out your best bet is to mass load it to gain the necessary rigidity/damping. Laminating another 3/4" to it should be adequate.

    GM
     
  9. BrianJ>Y

    BrianJ>Y Stunt Coordinator

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    I just attached the braces to the panels using wood screws(drilled from the outside). I previously used only brackets, now I have both. I'm hoping that helps improve the rigidity. I'm going to just add more weight rather than more panels.

    I'm curious though, if I don't add any additional weight and didn't add the screws, would the enclosure really fall apart? Is there any really noticeable advantage soundwise to having such a sturdy/rigid enclosure?
     
  10. Bryan Michael

    Bryan Michael Supporting Actor

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    i used dubble thick 3/4 in mdfb i also got the better stuff. when my dual av15 thumps it bareley vibrates. you cvan bareley feel it. and this is at around 110 db
     
  11. Greg Monfort

    Greg Monfort Supporting Actor

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    Over time it could in theory develop air leaks, or creaking joints. A vibrating cab is out of phase with what the driver's outputting so there's some added audible distortion and additional power losses. Having a low distortion sub is a big deal for music (I can balance a quarter on edge on my dual 15"s and 16hz organ notes won't knock it over), but for HT special effects most folks seem to prefer a bit of added harmonics.

    GM
     
  12. TimForman

    TimForman Supporting Actor

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    Allen,
    That picture shows the Tempest with the metal grill that Adire sells. It didn't stay there long as it made a annoying buzzing sound.
     

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