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Wacky Impedance Question...

Discussion in 'Amps and Cabs [BG]' started by Mike, Dec 10, 2002.


  1. Mike

    Mike

    Sep 7, 2000
    Cali
    4 ohms and 8 ohms create about a 3 ohm load, I think. I'm still and forever will be a techno idiot. If I had a 4 ohm cab and a 16 ohm cab what would my impedance be? (This sounds like a dumbass riddle.)

    What would be the drawbacks of running a system like this? I have a 4 ohm cab in transit. I'm hoping one cab will do it for me. (I think it will). But, if ever I wanted to try two cabs, could the above be a possibility? The (HUGE) problem would be finding a 16 0hm cab...

    Just curious.

    Thanks.
     
  2. Pacman

    Pacman Layin' Down Time Staff Member Gold Supporting Member

    Apr 1, 2000
    Omaha, Nebraska
    Endorsing Artist: Roscoe Guitars, DR Strings, Aguilar Amplification
  3. Mike

    Mike

    Sep 7, 2000
    Cali
  4. 4 ohms // 8 ohms = 2.67 ohms, here's why -

    Impedance in parallel:

    1/Rtotal = 1/R1 + 1/R2 + .... + 1/Rn

    So 1/Rtotal = 1/4 + 1/8 = 3/8, then flip it, so 8/3 = 2.67.

    Same thing with 4//16 gives 1/16 + 1/4 = 5/16, or 16/5 = 3.2 ohms

    Most amps are only 4 ohm rated. You'll need an amp rated at 2 ohms to be able to handle any cab in parallel with your 4 ohm cab.

    The drawbacks are that the 4 ohm cabinet will get twice as much power as an 8 ohm cabinet in parallel, and 4 times as much power as a 16 ohm cab in parallel. No way around this.

    It's best to just use (1) 4 ohm cab or (2) 8 ohm cabs.

    Chris
     
  5. Mike

    Mike

    Sep 7, 2000
    Cali
    I guess I lose... :)
     
  6. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    If a cabinet has multiple speakers, i.e. 4x10, 2x12, etc., you could rewire them internally to a different impedence. For example, a 4 ohm 2x10 has 2 8 ohm speakers wired in parallel, so you could rewire them in series and get a 16 ohm load. Your options depend on the impedence of the individual drivers. This is really only practical with 4 ohm multi-driver cabs; 8 ohm cabs are gonna end up at either 2 ohms or 32 ohms depending on the drivers and wiring scheme, and neither load is very useful. Example; 4x10 8 ohm cab has 4 8 ohm drivers in a series/parallel configuration. If you put them all in series, you get 32 ohms, if you put them all in parallel, you get 2 ohms.
     
  7. Mike

    Mike

    Sep 7, 2000
    Cali
    All right. I have a 4 ohm EBS 2x12 on the way. No idea wht the speaks are. Either 4 or 8 I suppose. I'm hoping this will be it. However, as you mentioned, I could rewire these for 8 ohms, add another 8 ohm cab and be set with a 4 ohm load? I'm hoping I won't need to do this but, if so, it could be done in this manner?

    Thx.
     
  8. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    Uhh, no....if the cab is 4 ohm, then it has 2 8 ohm speakers wired in parallel (technically, it could have 2 2ohm speakers wired in series, but I've never seen a 2 ohm speaker). You could wire them in series and get a 16 ohm load. There is no way to wire 2 8 ohm speakers to get an 8 ohm load.

    You can safely run a 16 ohm cab and an 8 ohm cab; the total load will be 5.33 ohms. BUT, the 16 ohm cab will not be recieving as much power as the 8 ohm cab.
     
  9. Mike

    Mike

    Sep 7, 2000
    Cali
  10. AndyGL

    AndyGL

    Nov 20, 2000
    Wellsville, NY
    What would 3 eight ohm cabs work out to be cabled one to the other?
     
  11. geshel

    geshel

    Oct 2, 2001
    Seattle
    Figure it out. . .

    1/8 + 1/8 + 1/8 = 3/8

    flip over, 8/3.

    Same as one 8 and one 4, which makes sense: put two of the 8s in parallel -> 4 ohms. Put that in parallel with the remaining 8 -> 8/3 or 2.67 ohms.