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Two 4 ohm cabs in series = rise in impedance???

Discussion in 'Amps and Cabs [BG]' started by PikeoftheLake, Jul 20, 2013.

  1. Hi,

    I'm hoping that some of the speaker gurus can help me on this one. I'm about to combine two cabs which are exactly the same, just one has a tweeter. They will be combined using a series cable so that the two 4 ohm cabs will make an 8ohm impedance for my tube head.

    I'm told that this combo will cancel out the tweeter because there will be a rise in impedance in the cabinet without the tweeter. Could someone spell out the science behind this? Is it that the cab with the tweeter doesn't actually see the high frequencies or is it that the high frequencies somehow get cancelled out during the output of the speaker?

    Many thanks!
  2. Johnnywad


    Jan 20, 2013
    Be careful bro. That would actually be a 2 ohm impedance. Not 8. Unless your all tube head can handle that kind of load your gonna fry your amp. DON'T DO IT!!!
  3. I'm using a series cable to let the amp see an 8 ohm load.
  4. Johnnywad


    Jan 20, 2013
    Even run in series, from one cab to another, it equals a 2 ohm load. Seriously. Go to your search function and look for the info you request. There are lots of players here that will tell you the same. Just wait for other responses before you try what your asking about.
  5. Rick Auricchio

    Rick Auricchio Registered Bass Offender Supporting Member

    No, the OP is right. Two 4-ohm cabs in series will present a 4-ohm load to the amplifier.

    If they were in parallel, it would be two ohms.

    My only warning about a series setup is that if you ever forget to use the special series cable, you're going to fry the amp before you know it. (Though most amps will start out working OK, then shut down after a while. This could be a real annoyance at a gig.)

    EDIT: The first sentence should read "...present an 8-ohm load..." Can't believe I mistyped that.
  6. majortoby


    Jul 2, 2009
    Tampa, Fl USA
    I'd be wary of the crossover, because I have heard before that series connections and crossovers don't mix.

    But yeah, series connection of two 4 ohm speakers will certainly yield 8 ohms. Hence the purpose of a series cable. If one was to not use a series cable, sure, it'd be 2 ohms, but he's using a series cable.

  7. rickster4003


    Feb 15, 2013
    Isn't resistance in series additive and parallel is R1R2/(R1+R2)?
  8. two 4ohm in parallel is indeed 2ohms, but the OP is combining the cabs in series, not parallel, hence the impedance will be 8 ohms. The OP is right.
  9. I believe the cab with the tweeter will have a shift in crossover frequency due to the 4 ohm load in series with it. Impedance changes affect the crossover frequency.

    Yes you ARE correct that using a special SERIES cable to connect two 4 ohm cabs will make an 8 ohm load to your amp.
  10. Johnnywad


    Jan 20, 2013
    So tell me how it is actually done. I'm not disagreeing just curious. Would I be able to run say four 112 cabs rated at 8 ohms and get just a 4 ohm load?
  11. No. 2, 8 or 32 ohms would be your choices.

    2 ohms parallel.
    32 ohms series.
    8 ohms series/parallel.
  12. Two 4 ohm loads in series equals 8 ohms.
  13. Johnnywad


    Jan 20, 2013
    So it is a special cable and would only yeild the 8 ohm load off of two 4 ohm cabs? Thanks B. Sorry for the miss info Muck.
  15. Not a problem, it was confusing as heck for me at first when I started considering this.
  16. I don't claim to be a crossover expert, but my understanding is: if a speaker in series was a pure resistor, the crossover would not be affected. However, speakers are inductors in the real world. So adding an inductor in series will block high frequencies a tad.... but I'm not much of an expert on LC networks
  20. Slade N

    Slade N Supporting Member

    May 28, 2005
    portland, or
    i have not heard of such a cable...where wence doth one aquire said witchcraft??