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  1. #1
    Eruption mk5's Avatar
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    04.30.16 @ 03:52 PM
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    Default Need help with cab/speaker wattage

    I've got a Mesa Boogie vertical 2x12 cab that originally had 2 Celestion Vintage 30's. It was stamped "140 watts" on the backplate, and the Vintage 30 is a 70 watt speaker. So obviously, 70 +70 = 140 watts.

    I recently changed out one speaker to a Celestion G12H30 that's 30 watts. All I did was re-solder the posts and bolt in the speaker. My logic is that now the cab is 100 watts (70 for V30 and 30 for G12H30).

    Now I am confused, because I was reading on another site that the cab wattage, when wired like this, is double the wattage of the lowest watt speaker. So instead of the 100 watts I thought I had, I might only have 60 watts.

    Can any techies shed some light on this and help me decipher how many watts my cab now has? I've been running a 100 watt head (lately in 50 watt mode).

    Thanks in advance.
    How open-minded do I have to be before my brains start spilling out?

  2. #2
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    12.19.16 @ 05:15 PM
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    The impedance is the important thing. I assume your speakers are 8 ohms. It sounds like you are confusing watts and impedance. Watts ALWAYS is cumulative and impedance is NOT.
    If you wired your speakers plus-to-minus-to-plus-to-minus then you have wired them in series. 8+8=16 ohms.
    If you wired it plus-to-plus and minus-to-minus then you have wired it in parallel. That formula is the reciprocal of the sum of the reciprocals. 1/(1/8 + 1/8)= 4 ohms.

    Series=add them together
    Parallel=reciprocal of the sum of the reciprocals

    Isn't that cool?
    Next week: series/parallel, or, "how the hell do I wire my Marshall cabinet?"

  3. #3
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    03.30.13 @ 09:28 AM
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    I'm assuming that you're not concerned about your speaker's resistance because you matched the ohms of both speakers so they remained the same as before. The cab is either 16 or 8 ohms, as long as they're matched it's unimportant.
    What is important is that you've matched a 30 watt speaker to a 70 watt. The 70 watt speaker will NOT take the overload to help the 30 watter like some believe. If you pump in a little too much power the 30 watter will sound flubby, warning that the coil is working too hard. The original G12H 30's could be pushed up to 40 or even 50 watts at times, but the reissues are much more sensitive to power fluctuations and shouldn't be pushed the same way.
    What you have is a 50-60 watt cab.
    I'd be careful with that combination.

  4. #4
    Eruption mk5's Avatar
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    Quote Originally Posted by cyberfiddl
    The impedance is the important thing. I assume your speakers are 8 ohms. It sounds like you are confusing watts and impedance. Watts ALWAYS is cumulative and impedance is NOT.
    If you wired your speakers plus-to-minus-to-plus-to-minus then you have wired them in series. 8+8=16 ohms.
    If you wired it plus-to-plus and minus-to-minus then you have wired it in parallel. That formula is the reciprocal of the sum of the reciprocals. 1/(1/8 + 1/8)= 4 ohms.

    Thanks cyberfiddl & tribb. I was coherent enough to make sure I matched the ohms. Both speakers are wired parallel, and are 16 ohms each.

    I'm going to have to either get another cab or swap out my G12H for a Classic Lead 80, I guess.

    Shoulda taken some electronics courses...

    Thanks again guys.
    Last edited by mk5; 05.25.05 at 06:43 AM.
    How open-minded do I have to be before my brains start spilling out?

 

 

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