New project: Isobaric or compound subwoofer, 12" drivers, 250W power. Help, please :)

Discussion in 'Home Theater Projects' started by Javier_Huerta, Nov 6, 2003.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Hi all,

    After building the AA Tempest, I noticed I still have a bit to learn about building cabinets... [​IMG] (you might remember the cabinet I used developed some kind of crack / became unglued). The sub still works like a champ in my music-only system, so I'm very excited about my next project.

    I was thinking about starting small this time. Since the drivers I have available have a large Vas (198.6L), low Fs (22Hz), low Qts (0.384), Qms=13.36, Qes=0.396, and nice Xmax (17mm) (yeah, the old HED-12's I have in storage), I have two choices:

    1. Build a big (150L) cabinet, or
    2. Build a 75L isobaric subwoofer.

    Since I just got married, option #2 seems nicer and nicer.... [​IMG]

    I understand I'll lose 3dB when compared to a single driver big cabinet. I think I'm willing to make the trade-off, considering we (my friend, the carpenter and me) will get much needed experience in building speaker cabinets before trying to rebuild my AA box (yeah, I'll do so as soon as I can!).

    I was thinking about building an isobaric vented sub. Sadly, I have just realized this is a lot harder than I thought, especially when considering I'd need pretty big ports, or go with a 3" one.

    So I'm leaning towards isobaric, sealed, with a slight (+3 dB) bass boost. I'll probably move the subwoofer to a bigger box when I'm ready to do so, anyway.

    I have also been reading about compound subs. While I think I do understand the mechanics behind isobarics (lose 3dB's, cut box size in half, basically), I haven't been able to find much info about compound units. I think MartinLogan uses this configuration on their high-end hybrids, but that's as much as I know about this.

    If anyone can suggest how to proceed, or have any ideas on how to better define this project, I'll be very grateful. At the moment, I think the limitants are:

    * Small, easy to build box
    * Low Fs / F3
    * Not much SPLs required - as long as the sub goes waaay down deep.

    Thanks!
     
  2. MikeCTM

    MikeCTM Auditioning

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    well with isobaric, and more importantly sealed alignment you're not gonna go waaay down deep too quick large box better than small box is my thinking
     
  3. Javier_Huerta

    Javier_Huerta Supporting Actor

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    I know sealed isn't the way to go if you want deep bass. But I wouldn't want to risk building another huge box that will break down. [​IMG] Also, I'd like to try building a small, powerful sub.

    How about adding an LT to a single sealed sub? I'll start looking for info on that...
     
  4. AjayM

    AjayM Screenwriter

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    I don't know why you would say that. You will get the same response with isobaric as you will with a standard config. And saying sealed doesn't go low is WAY to general of a statement to be meaningful. My sealed tempest sub is -3db at 20Hz in room without corner loading, with corner loading in the last room I had it in I was -3db at 17Hz (and actually had a peak at 20Hz). With a BFD I basically have flat response (well +3/-6db...damn room modes) from 20Hz-80Hz. I have real usable response down to 16Hz (I didn't measure any lower).

    What you will lose is volume though, I can listen at a nice level with no issues, but it won't compete with these super-subs with a megawatt behind them. But it's no different than any other sealed tempest design except for the -3db whacked off the top due to the iso loading.

    Andrew
     

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