Almost... done. Need help in figuring out whether to use damping or not in my box...

Discussion in 'Home Theater Projects' started by Javier_Huerta, Feb 24, 2004.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Hi all!

    Well, I finally got my box built (2 of them, actually). I have no clue what happened, but I just calculated the enclosure volume, and considering bracing and such, I'm left with 118L's worth of volume. I was aiming to get 150L's. [​IMG]

    Anyway... this is not so bad. Since I won't be using flared port ends, and since the port is rather smallish (4"), it seems I won't get any turbulence at the power levels I'll use. Besides, group delay dropped down considerably.

    Anyway... while I was playing around with Unibox, I found out using different damping techiques affects frequency response a lot. From "No fill" to "Heavy fill", apparently I end up losing around 10 Hz of F3. Not good. I think.

    Then again, why does Adire tells you to use "heavy fill" on their designs?

    I'm not sure about this. Should I use polyfill on my vented box? Cover the box walls with something? And, if I do so, what's the correct ratio to use?

    I'm a bit confused.... thanks for any help!

    Javier.
     
  2. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Help [​IMG]
     
  3. Chad B

    Chad B Stunt Coordinator

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    I experimented with fill on my DIY sub. Maybe some of this info will interest you.
    With heavy (near 100%) fill, the enclosure was tuned to 23 Hz and cabinet colorations were very low. The sub didn't draw attention to itself and localization was low, but bass output seemed fairly low, probably from too low of a Q around the tuning frequency. A lower Q results in more bass rolloff at low frequencies, but that rolloff is shallower than with a high Q alignment.
    With no fill, the tuning was around 25-26 Hz and the cabinet was lively. By that I mean certain frequencies rang and resonated in the cabinet- not a good thing. The bass was louder, but the sub didn't sound as good.
    I ended up compromising by putting in just enough fill to reduce the cabinet resonances, which worked out to about 1/4 of the box volume being filled with a mixture of fiberglass and polyfill. The tuning is between 23.5 and 24 Hz and the bass has a decent compromise between quality and output.

    Chad
     
  4. perry web

    perry web Stunt Coordinator

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    i am in the process of building a 115L vented box also.
    the adire plans do not say heavy fill.

    http://www.adireaudio.com/Files/Vent...plications.PDF

    page nine, second to the last paragraph says
    "all cabinets are designed assuming no polyfill is used."

    I am not going to line my walls or fill. I figure I can always add it later if I want to.
     
  5. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Chad, thanks for your explanation. I now have a starting point to tune my sub. I'll aim for 20 Hz, and I'll start adding fill.

    The walls will be lined with soft foam. I think it wouldn't huert, either....

    Perry, the Adire Audio plans I saw that said heavy fill were the Tempest ones.

    Thanks for your help! I'll start cutting PVC pipes ASAP. [​IMG]
     
  6. perry web

    perry web Stunt Coordinator

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    the tempest plans are all 194 l and up.

    that is very large. i guess it can afford to use fill when you have a box 340 l!
     
  7. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Done! I lined up the walls with foam, and filled my subs at 50%. I'll start testing from here.

    The subs aren't massive in size, but they are incredibly heavy... my local carpenter used countersunk screws, glue, and silicone everywhere... I'll try to take some pics of them. I just need to install their feet, so maybe tomorrow I'll be able to finish them! [​IMG]

    Thanks a lot for your help.
     

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