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Speaker Impedance vs Cab Impedance??

Discussion in 'Amps and Cabs [BG]' started by Vysous, Apr 22, 2005.


  1. Vysous

    Vysous

    Mar 29, 2005
    Please Help--
    Hows that with impedance of each speaker??
    I know each speaker has his own impedance, and those speaker fit together in one box = cab make one overall impedance of cabinet.
    Hows that counted??
    For Example, I have four 8 Ohm speakers in box, so what will be the resulting impedance???
    Thanks for advices....

    Vysous
     
  2. bigbeefdog

    bigbeefdog Who let the dogs in?

    Jul 7, 2003
    Mandeville, LA
    Well, the answer is..... it all depends. Depends on how the cab is wired.

    If drivers are wired in *series*, you add the impedance. So if you had four 8-ohm drivers, all wired in series, the cab impedance would be 8+8+8+8 = 32 ohms.

    Of course, no manufacturer does that (at least none I've ever seen). But the point - when you wire drivers in series, total impedance goes *up*.

    The other option is *parallel* wiring. If drivers are wired in parallel, the equation is:

    1
    ---------------------------------
    1/R1 + 1/R2 + 1/R3 + 1/R4 +......

    So, if you had four 8-ohm drivers wired in parallel, the cab impedance would be 1 / 4/8, or 1 / 0.5, or 2 ohms.

    You won't see this very commonly, either. But, as you can see, when you wire drivers in parallel, total impedance goes *down*.


    The most common wiring method I've seen in 4x10's is to first wire the drivers in two series pairs, turning your four 8-ohm drivers into the equivalent of two 16-ohm drivers (impedance added). Then the two 16-ohm loads are wired in parallel, giving a cab impedance of 1 / 0.125, or 8 ohms.

    The same wiring method using 4-ohm drivers gives, you guessed it, a 4-ohm cab.
     
  3. Vysous

    Vysous

    Mar 29, 2005
    All right!
    I think I got it....
    Thx a much!
     
  4. Ben Clarke

    Ben Clarke Liquidating to fund a new business. Buy My Gear!

    Jan 6, 2005
    Western NY
    It depends to a small degree on properties of the box, too.
     
  5. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Ben's probably referring to his Tuba 24, which has an 8 ohm driver that is raised to 12 ohms by the cabinetry. That is the exception to the norm. As far as wiring four 8 ohm drivers in a typical alignment is concerned your options are 2, 8 and 32 ohms total load, and since both 2 and 32 ohm loads are less than optimal 8 is the usual option taken.
     
  6. In a sealed box and open air, the impedance rises as the frequency moves down toward resonance. This will be significantly higher than the nominal/advertised impedance.

    In a vented box, there are two impedance peaks, one on each side of the tuning frequency. Impedance is lowest at the tuning frequency, and approaches that of the voice coil DC resistance.

    If the bassist is bridging the power amp, then taking an accurate impedance measurement of the system might avoid destroying the amp.

    Consider two Avatar B410 nominal 8-ohm vented cabs in parallel: the DC resistance of the Delta 10a is 5.42 ohms. Using the standard series-parallel wiring scheme, this presents 5.42 ohms DCR to the input jack of each cabinet.

    If two of these cabs were daisy-chained in parallel (nominal 4 ohm load), the actual load at the 50 Hz tuning frequency could be as little as 2.71 ohm. In practice it might be a bit higher, but I'm certain it will be less than the 4 ohm minimum required by a bridged amp.