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Padding a slot port cabinet

Discussion in 'Amps and Cabs [BG]' started by Easy Rider, Nov 17, 2003.

  1. I'm finally coming round to padding my home built 2x10".
    I've done some searching and at one point I found that padding should stay at least 5 inches away from the port opening.
    However, my cab has slot ports and now I'm confused how to keep the padding 5 inches away from the port, because the left, right and bottom wall of the cab are part of the port.

    You don't want to hinder air flow to the port, so the padding on the bottom stays 5 inches away, easy.
    But the sides are different, I thought maybe to cut half a circle with 5" radius radiating from the port opening out of the padding on the side walls, to adhere to the rule, but that seems... odd to me.
    And can I pad the top of the slot port as well?

    In short: is there a particular approach to padding slot ported cabs?

    Thanks ahead.

  2. What kind of padding? (poly-fill style stuff? or eggcrate style stuff (cut your own panels)?)

    Don't pad the bottom panel of the cabinet, and cut off your padding where the port shelf (inside top panel of the port) is. If you want to get fancy, trace/cutout and extend the padding below the shelf, and taper it to the left and right sides of the cabinet.
  3. mje


    Aug 1, 2002
    Southeast Michigan
    Was this built to a specific design, using computed Thiel-Small parameters for the speakers? Or is it more of an empirically derived design?

    Whichever the case, the use of interior padding or stuffing can serve two purposes: One, to eliminate internal resonances. Two, to tune the box by increasing the acoustical impeadance of the box. Add more stuff, and you're effectively enlarging the box (although simultanously increasing damping). You may find you need to experiment a bit, even if you're using an exiting design.

    Is there a diagram of this box we can see?
  4. Well, here's a picture of the cab to start with:


    I calculated the cab myself to the parameters of the drivers. I wanted the cab to be as small as possible, because portability was my main reason for making this cab. The other reasons were fun (of course) and being slightly cheaper then buying one.
    But, this being my first cab ever, I made a horrible mistake. I calculated the box, and came up with this rather nice compact cab, but I calculated it for ONE speaker! :oops: My throat was sore for a week from all the cursing...
    But anyway, sound quality actually isn't a big deal, it's just a practise cab, and I'm not building another cab because this one fits *perfectly* in the boot of my car. So, I'm going to make it sound as good as it can get and be done with it.
    So, right now it's a really loud cab but lacks bottom end and it's a bit muddy and boomy. I'm going to try the padding, eggcrate foam BTW, to try to relieve that as much as possible.
    It's pretty much a 'damage control' thing.

    Patrick, thanks for the suggestions. I'm not sure I get the taper part though... I can't visualize it.

    mje, I'm not sure what kind of diagram you want to see, and my plans aren't the up-to-date with the cab I actually made. But I could whip something specific up, if you could tell me what you want to see.

  5. Calculate the diameter of the slot port area, as if it were a circle. Keep everything => 1 diameter from the port.

    You can use fiber fill stuffing to increase the apparent volume of the cabinet by about 30%. The fill ratio is 1 pound of material per 1 cubic foot of net internal volume. You will have to take steps with nylon netting or something similar, to keep the fiber fill away from the port. This is more tricky than doing it to a sealed box, but the theory is the same.

    Your box is booming because you have too-large drivers in a too-small box. Tuning will not help this. Only an increase in volume.
  6. Allright, and that's in ALL directions right? Like along the x, y and z axis?

    And stuffing it would be a good solution. I'm getting images of old nylon stockings and maybe some wire... yeah, that can work. :D


  7. Port Area (sq.in.) = Height * Width (inches)

    Diameter (in.) = Area / Pi

    In a slot port, the effective length is (tunnel length + 1/2 height). Keeping a free area one diameter from the tunnel opening will insure no interference with the slot port.

    I have a doubt about something as finely woven as nylon hosiery. I was thinking more open, such as nylon netting. You don't want to interfere with the air flow.
  8. Allright, thanks!

    And the point of stockings having to fine a mesh is well taken.

  9. Petebass


    Dec 22, 2002
    QLD Australia
    There's always fishnet stockings :)

    As for the honkiness, you could always EQ it out if you feel the need. But stuffing speakers into small cabs isn't new and indeed is the basis of Eden's speaker cab designs. Let your ears decide.

    What drivers are they?
  10. Perfect suggestion... I shoulda thought of that.

  11. Hmmm, it's already not much of a looker so it might look a bit trashy with fishnets... :)

    They're Beyma drivers, the SM110 model.
    150 watts each. Made in Spain, by the way.
    I wanted to go with two Celestions but these went lower and were a LOT cheaper.

    I'm not that upset about the sound quality as I am about the miscalculation actually. The sound's still pretty good. And loud. It sure turned out a louder cab than I thought. But that was the point, a loud, portable cab for practice.
    It's so loud in fact that I thought 'might as well try adding some dampening and see if it tightens up a little'.
    I'm gonna do so tomorrow I think/hope.

  12. Petebass


    Dec 22, 2002
    QLD Australia
    Let us know how it goes.

    And your cab needs a name. Maybe Frank-n-Furter?
  13. Oh but it has a name!
    It's the 'EZ Jammaster 2001' (Builder, model name, vintage). Or just 'Jammaster' for short.

    Didn't come round to buying the foam today, so tomorrow it shall be done.

  14. Just finished padding the cab with eggcrate foam.
    And that sure helped a lot!

    The muddyness is gone, I can finally really hear what these drivers can do. The sound is nice and crisp and well defined. All the unwanted reverb is a thing of the past.
    It's still a little boomy of course, with the open A being the fattest note and the open E being a bit thin.
    With a little EQ-ing to counteract that though (I didn't get an amp with a 12-band EQ for nothing!) I think I actually like the sound of the cab now.
    The padding does make it less loud, but because it was very loud to begin with and the sound is so much more defined now I no longer have to turn it up that much anyway.

    So, that was time and money well spent!