Ohms question

Discussion in 'Amps and Cabs' started by Ishmael8765678, Dec 21, 2009.

  1. Ishmael8765678

    Ishmael8765678 Member

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    I need to explain to my friend that more ohms into less ohms is bad. He is just guessing that it's ok (he thinks that he knows EVERYTHING). I did some research and found that since the resistance is lower on a lower ohm cabinet, it cannot handle the power of the head and could possibly catch fire so that is bad. Am I right? I don't wanna sound like an idiot when I tell him this.

    On a kind of unrelated note, I have two 4 ohm crate cabs and an 8 ohm b-52 cab. Would it be ok if I used the 4 ohm output on the head to connect to the b-52 and then just link the crates from the b-52? They each have two inputs.
     
  2. SatelliteAmps

    SatelliteAmps Member

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    Two 4Ω and one 8Ω gives a 1.6Ω load. Not good. The reason not to mismatch impedances is that there is major potential for damage from flyback voltages. It's not that it will catch fire.
     
  3. Raybob

    Raybob Member

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    You could make up a special wire harness that runs the two 4 ohm cabs in series for 8 ohms. Then parallel that to the 8 ohm cab and you end up with 4 ohms total.
     
  4. Ishmael8765678

    Ishmael8765678 Member

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    I may just sell the cabs since the head is 120 @4 ohms and the cabs are 80w. Would I only blow the speakers if I turned it up past 80w?
     
  5. GCDEF

    GCDEF Supporting Member

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    How would you know when you turn it up past 80 watts?

    You should rewire your 4 ohm cabinets so they're a higher impedance, then you can use them together and they should handle the amp's power.
     
  6. KGWagner

    KGWagner Member

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    Fundamentally speaking, ohms are a measure of resistance or impedance to electrical current flow. Another way of thinking of them is they are the "load". So, you don't put ohms "into" anything. Things have ohms, or a load value.

    Sometimes it's confusing, because you'll see terms like "8 ohm output" or "16 ohm output". There's no such thing. You can't output ohms. What they're saying is the output is matched for an 8 or 16 ohm load.

    I don't want to get into a long discussion about impedance matching, but suffice it to say if you don't match them up, you'll suffer signal distortion and imbalanced current flow. Signal transfer won't happen efficiently, and may reflect back into the output, distort, or wreak other sorts of unpleasant havoc. It may not even be immediately noticeable, especially with guitar amps where you might be deliberately overdriving and distorting the output.

    So, best case is, it won't sound as good as it could. Worst case is you may force some components to source more current than they're designed to, which can overheat or even burn them up. In any event, there's certainly nothing to be gained by the practice, and possibly a lot to be lost.

    The solution is simple. DON'T DO IT!

    Why would you want to anyway? Just wire things right. It's not tough. There are only a couple simple rules: loads in series add and loads in parallel divide. So, two 8 ohm speakers in series will be 16 ohms, while two 8 ohm speakers in parallel will be 4 ohms. That progresses logically... four 4 ohm speakers in series would be 16 ohms, while four 16 ohm speakers in parallel would be 4 ohms. You can even mix and match - two 8 ohm speakers in series to get 16 ohms, wire in parallel with two 8 ohm speakers in series to get 16 ohms, and you'd have an 8 ohm load. On and on.
     
  7. riffmeister

    riffmeister Gold Supporting Member

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    I say power it up, turn on the video camera, and watch the flames.....BWAHAHAHAHA!!
     

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