closed vs vented small cab

Discussion in 'Amps and Cabs [BG]' started by Matthijs, Apr 13, 2012.

  1. Matthijs

    Matthijs Supporting Member

    Jul 3, 2006
    I have a serious DIY itch building up and plan to do a smallish 121266. I'm aiming for a sound with a very controlled low end, a mix between a modern hifi cab and the classic GK microbass combo's. My main instrument is double bass, and I double on electric and tuba occasionaly.

    I've done some modelling around two deltalite 2512-II's I used in a previous build. The freq spec's for a closed cab of about 80 to 90 litres seem pretty close to what I want, but I also can get close with an even smaller, heavilly dampened, vented cab. Pro's for the vented cab ar the even smaller size, better x-max figures and better cooling for the neo speakers. Pro's for the closed box are the simplicity and the slightly more gradual low freq rolloff I think I want.

    Anything else I'd have to consider?
  2. will33


    May 22, 2006

    Tuning a small box low has it's benefits, both in mimicking the sealed cab rolloff and obviously being a ported box, (assuming you're plugging one or more ports to achieve that). With DB, a more attenuated lowend is a plus.

    And I think you totally kick major ass for throwing a tuba in there.....props to you.
  3. Oobly


    Jun 19, 2008
    Have you considered a fEarful 1212/6 with half the port blocked? May fit your criteria and the design is tried and tested to be good. Small and light for a 2x12, gradual low frequency rolloff (with the half port block) and quite hifi. Good xmax and power handling, etc.

    If you don't need massive SPL, a 12/6 may even do the job for you :)
  4. Matthijs

    Matthijs Supporting Member

    Jul 3, 2006
    Thanks, but you might have to reconsider when you hear me on tuba, it still needs some work :)

    I'm at work so I don't have the exact details, but off hand: 2 tube ports tuned at somewhere between 40 and 44 hz probably at the back of the cab. And a cab somewhere inbetween 60 and 70 litres. I would probably have to compromise a bit on port size, that's part of the reason for having them at the back.
  5. Matthijs

    Matthijs Supporting Member

    Jul 3, 2006
    I have, but I also like figuring it out myself. Those deltalites are currently in two 12/6 cabs of my own design. I almost always need the two of them (I have a large and loud horn section to compete with). Ít's a good idea to model what would happen in my vented model when I block one of the ports, just like in the fEarfull.
  6. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Check out the article on a small 12" box at my website. It might be close to what you are looking for.
  7. Matthijs

    Matthijs Supporting Member

    Jul 3, 2006
    I did read it some time ago and found it very helpful. It was actually the reason why I started modelling a vented alternative for a closed cab. There's just also something appealing in the simplicity of a closed cab. I guess the main point of this thread is to find out whether there are more rational points to make for a closed cab.
  8. I second this motion :D

    If you want the sealed to avoid the too-high resonance and dropoff below you get out of many ported bass speaker cabs, the fEARfuls have already been designed to avoid this. If you want the gradual rolloff of the lows, the half-blocked method will get you there. I'm not sure how to rationalize starting from scratch to build 121266 when there's an excellent execution available that would seem to do what you're aiming for.
  9. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Gold Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    Looks to me like your analysis has been quite thorough.

    Let me toss this out for your consideration: Four 3" diameter ports, each 8" long, arranged in a rectangle on the back of the cab. With all four ports open, tuning frequency is ballpark 48 Hz. Plug two of them with expandable plumber's test plugs, and the tuning frequency drops to about 35 Hz, while the resulting response curve roughly emulates that of a Qtc = .85 sealed box, at least down to the tuning frequency. Plug all four, and you have a ballpark Qtc = .72 sealed box. Three tunings in one cab.

    I use these as removeable port plugs in my commercial cabs:

    Test-Tite 86390 Test Plug, Mechanical, T-Cone, 3 In

    This is just an example, modify to suit your situation (which probably includes going metric).
  10. Matthijs

    Matthijs Supporting Member

    Jul 3, 2006
    You can call it a hobby, its part of the fun :D I only have to come up with a rational-like explanation for the family about why the old cabs won't do.

    And thanks Duke, I think I like that option. 4 vents at the back might also limit the risk of vent resonances. In the design I was thinking off I'm almost using the whole back of the cab for two enormous rectangular vents.
  11. Matthijs

    Matthijs Supporting Member

    Jul 3, 2006
    I did follow Alex his suggestion and did some modelling with multiple ports and closing some of them. I found the effects to be either very small, or not gettong me much closer to the freq specs of my closed model. It did lead me on to a very straightforward solution. I modelled a cab in size inbetween the closed and the vented cab models i had and will build it in such a way I can close the vent and turn it into a closed cab. Interestingly this cab is extremely close in size and specs to a double version of fdecks 12" cab on his site. Maybe it is indeed not very rational, me always wanting to do it my own way :)