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What ohm rating is my cab?


TKel

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Hi,

 

I have a 4x12 cab with four Celestion 75 watt 8 ohm speakers. It has no switch, indication or information on the cab to tell me what ohm rating it is. It's a single 1/4" input jack with no options, so it is what it is and I don't know what that is. :)

 

I've drawn a crude diagram of the wiring quickly to give a visual so someone here might be able to tell me. I don't know if this equates to 4, 8 or 16 ohms. Please help, as I don't want to guess wrong or do the math/formula wrong and fry my output transformer. Thanks.

 

http://photobucket.com/albums/a206/terrykeller/?action=view&current=161373b4.png

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Originally posted by TKel

Hi,


I have a 4x12 cab with four Celestion 75 watt 8 ohm speakers. It has no switch, indication or information on the cab to tell me what ohm rating it is. It's a single 1/4" input jack with no options, so it is what it is and I don't know what that is.
:)

I've drawn a crude diagram of the wiring quickly to give a visual so someone here might be able to tell me. I don't know if this equates to 4, 8 or 16 ohms. Please help, as I don't want to guess wrong or do the math/formula wrong and fry my output transformer. Thanks.


http://photobucket.com/albums/a206/terrykeller/?action=view&current=161373b4.png




Using rational thinking if it has only one input it's probably 8ohm. It couldn't be 16 or 4 if it has 4 8ohm speakers and I doubt it's 2 or 32...so there you go.

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So, basically, depending on how you wire it, the overall impedance of a mono cab with all the same ohm ratings on each of the four speakers (being each the same as each other), it can only be the same ohm as a single speaker, 4 times the ohms, or one-fourth the ohms, so thus, it must be 8 ohms no matter what (since it's not 2 or 32 ohms). Is that the correct (basic) formula for any parallel or series wired 4x12 cab with four speakers of the same rating? I realize there are other methods, but for this, that is the basic logic, correct? Thanks again.

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Originally posted by TKel

So, basically, depending on how you wire it, the overall impedance of a mono cab with all the same ohm ratings on each of the four speakers (being each the same as each other), it can only be the same ohm as a single speaker, 4 times the ohms, or one-fourth the ohms, so thus, it must be 8 ohms no matter what (since it's not 2 or 32 ohms). Is that the correct (basic) formula for any parallel or series wired 4x12 cab with four speakers of the same rating? I realize there are other methods, but for this, that is the basic logic, correct? Thanks again.

 

 

Basically, your thinking is correct but only with regard to a 4x12 configuration.

 

In simplest terms:

Speakers wired in series = Add impedances (2 speakers of 8 ohms = 16 ohms total)

 

Speakers wired in parallel = Divide impedance (of 1 speaker) by the number of speakers (2 speakers of 8 ohms = 4 ohms total)

 

If you have MS Excel, you can download a spreadsheet from http://duncanamps.com/technical/impedance.html that will calculate impedance and power for different configurations of speakers.

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