Question about DVC subwoofers, short circuiting a coil, and more

Discussion in 'Archived Threads 2001-2004' started by Javier_Huerta, Feb 14, 2003.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Hi all,

    I have a problem here. Due to the amount of subs I have (two Tempests or 4 Cerwin Vegas), if I wire the subs using both coils, I end up with a 2 or 8 ohm load. And I'm using a PE 300-794 amp, so neither one is a good choice (I think).

    I've been reading a bit about short-circuiting one of the coils, so that I end up using just one of them on each sub. That way, the total system impedance is 4 ohms.

    There is a rather strong variation on Qes (by a factor of two) and Qes (which drops drastically on the Tempest). Qts stays the same, though! (I think this might be a typo on http://www.adireaudio.com/Files/TempestWhitePaper.PDF, and Qes equals the other cases' Qes). SPL drops by a factor of 3 dB (which I think should be expected, since you are basically losing one voice coil).

    The installation will be done on an IB.

    My options are:

    a) Lose those 3dB in sensitivity and short circuit a coil. This lack of power won't be made up by the extra 70 or so watts the amp produces in 4 ohm mode.

    b) Wire everything so that total impedance is 8 ohms, and lose the 70 watts of extra power.

    c) Wire everything so that total impedance is 2 ohms, and hope the amp doesn't fry.

    Which one do you think would be the best option? I think I could get away with a 2 ohm configuration if the amp is properly ventilated. Then again, I would be willing to use an 8 ohm mode if there is no other option.

    It would seem to me short circuiting one of the coils would mean having two add twice the drivers for the same SPL level.

    Thanks for your help!
     
  2. Steven Kephart

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    I would recomend using "A". But try it the way Adire explains here: http://www.adireaudio.com/tech_papers/dvc_subs.htm

    By using a pot on that unused coil, you could actually tune your system. So if you have to lose some sensitivity, why not gain something back?
     
  3. Patrick Sun

    Patrick Sun Studio Mogul

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    Don't even consider C. Do B, and if that's not enough, give A a try.
     
  4. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Stephen, I'm curious about that link. I had read it before, but since the article doesn't state what kind of variation to expect from the parameters I was hesitant. I'll try to find more info on the matter.

    Patrick, will C fry my amp? If so, I would think option B is the right one, too. At least I don't have to assume anything by using it (other than knowing I'll lose those 70 or so watts).
     
  5. Owen Bartley

    Owen Bartley Second Unit

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  6. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Owen, thanks for the article! It's very well explained.

    Sadly, I've already gone through all posssible combinations.

    This is challenging... but fun [​IMG]
     
  7. Brian Bunge

    Brian Bunge Producer

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    I do know of someone locally that has stated he's used multiple subs configured for a 2 ohm load. He says due to the added sensitivity you really aren't pushing the amp very hard and stated that he never had any problems with the amp overheating.

    But I personally haven't tried it, so do so at your own risk.
     
  8. MichaelAngelo

    MichaelAngelo Stunt Coordinator

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    2 ohm load on the PE amp is fine. I've been running two
    subs, each with a 300-794, at a 2 ohm load, for about 8 mos,
    can't say I listen at full volume for hours on end, the amps have given me no trouble at this load.
     
  9. Jack Gilvey

    Jack Gilvey Producer

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    This week it's an IB? Cool.

    I wouldn't worry too much about "sensitivity", in an IB it doesn't take much at all to reach Xmax. Also, in an IB, the max SPL available with one coil or both is the same since Vd is the same, Pe never enters into it.
     
  10. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Yep, in the "Sofa riser" thread, Thomas convinced me about trying to go for an IB instead. Besides, carpenters around here simply CAN'T understand the Tempest (or any other) AutoCad files. It's too much of a bother, building a box - besides, I have the space for an IB, and my house is still under construction [​IMG]

    According to WinISD, my subs can handle 250 watts RMS of power without bottoming out. That's the reason I wanted to go as high as possible.
     
  11. Jack Gilvey

    Jack Gilvey Producer

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  12. Ted Kim

    Ted Kim Stunt Coordinator

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    Javier,
    Maybe you are talking with the wrong type of carpenters. Consult with some cabinetmakers -- there is no reason why any self respecting cabinetmaker should not be able to build you a subwoofer cabinet.
     
  13. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Jack: Yep. If I model a 15,000 liter cabinet, WinISD shows I have enough Xmax to handle 250W with 4 of those subwoofers.

    Ted, I'd have thought so myself, but all of the carpenters around here I have seen do not have a clue about measurements, CAD files or the like. What they do (amazingly good, BTW) is creating furniture out of photographs.

    Still, if this carpenter is coming in the next following weeks, I'm pretty sure I can tell him how to design the baffles fro my IB in no time flat. Besides, I've read all over the Internet how IBs deliver the best quality bass out there, as long as you have 2 or 4 drivers.
     
  14. Jack Gilvey

    Jack Gilvey Producer

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    So ~65 watts to each one...about right.

     

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