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Thread: Multiple Cabs, Different Impedance Ratings

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    Name Manglin' Putz alantig's Avatar
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    Multiple Cabs, Different Impedance Ratings

    Okay, I know some of you are sick of reading this question, but since it's new for me, I'm asking it again.

    I have a Two-Channel C. Two speakers outs, switchable impedance. I just got a PRS Big Mouth cab, 8 ohms. I have an Orange 4x12, 16 ohms.

    Currently, they're stacked but not running together. If I would want to run them together, would I use the 8 ohm output setting? It seems to me I wouldn't want to pump 16 ohms into an 8 ohm cab.
    Alan

    "I watched approximately 45 seconds of 'Rock Of Ages'. It was like getting punched in the soul." - Abby Krizner

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    deus ex machina
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    Quote Originally Posted by alantig View Post
    Okay, I know some of you are sick of reading this question, but since it's new for me, I'm asking it again.

    I have a Two-Channel C. Two speakers outs, switchable impedance. I just got a PRS Big Mouth cab, 8 ohms. I have an Orange 4x12, 16 ohms.

    Currently, they're stacked but not running together. If I would want to run them together, would I use the 8 ohm output setting? It seems to me I wouldn't want to pump 16 ohms into an 8 ohm cab.
    When you plug two different cabinets into an amp, you are effectively wiring them in parallel. For cabinets that are the same impedance, the parallel impedance of two cabinets is half of the cabinet impedance. For mismatched impedances, we have to use the parallel impedance formula.

    Parallel Impedance = 1 / (1 / Cabinet-A-Impedance-in-Ohms + 1 / Cabinet-B-Impedance-in-Ohms)

    In your case, parallel impedance = 1 / (1 / 8 + 1 / 16) = 5.33 Ohms, which would mean that you would choose the 4 Ohm setting.


    With that said, power will be divided unevenly between the cabinets. The 8-Ohm cabinet will receive 2/3rds of the power.

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    Name Manglin' Putz alantig's Avatar
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    Thank you! Didn't think about them being in parallel - just thought that I didn't want to pump 16 ohms into an 8 ohm cab. Not sure if I'm even going to do this, but I wanted to make sure I did it right if I did.

    Effectively kills the idea of running either of my combos into this pair at the same time - they're both 8 ohms and no switching.
    Alan

    "I watched approximately 45 seconds of 'Rock Of Ages'. It was like getting punched in the soul." - Abby Krizner

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    Related question. I have two cabs, each is 8 ohms. My amp has two 4 ohm and two 8 ohm out. If I run from amp to cab one, then from cab one to cab two, would I be running in serial? If so, which ohm output on the amp should I use? I also have a 16 ohm output on the amp if that is needed. Thanks.

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    deus ex machina
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    Quote Originally Posted by tiboy View Post
    Related question. I have two cabs, each is 8 ohms. My amp has two 4 ohm and two 8 ohm out. If I run from amp to cab one, then from cab one to cab two, would I be running in serial? If so, which ohm output on the amp should I use? I also have a 16 ohm output on the amp if that is needed. Thanks.
    Most cabinets with two jacks are wired such that they daisy chain in parallel; therefore, you would plug the first cabinet into the 4-Ohm jack.

    When in doubt, measure the combined impedance with a multimeter. While impedance and DC resistance are both measured in Ohms, impedance is a not a synonym for DC resistance. Impedance is resistance to an AC signal. Impedance changes with respect to frequency.

    Impedance (Z) = SQUARE-ROOT( R^2 + X^2), where equals R equals resistance, X = reactance, and the symbol "^" denotes raised to the power of.

    If that formula looks familiar, it is because impedance is an application of the Pythagorean Theorem.
    Last edited by Em7; 10-01-2012 at 09:22 AM. Reason: grammatical error

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    A♥ hoards guitars A♥ rugerpc's Avatar
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    Quote Originally Posted by Em7 View Post
    If that formula looks familiar, it is because impedance is an application of the Pythagorean Theorem.
    Sometimes Wikipedia is actually useful... See the graphical representation:

    http://en.wikipedia.org/wiki/File:Complex_Impedance.svg
    Thbbbbbt...
    Check it out: Phillybri used to have a band: Resonance But he's soooo over them now!

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    Thank you Em7.

  8. #8
    Quote Originally Posted by alantig View Post
    Okay, I know some of you are sick of reading this question, but since it's new for me, I'm asking it again.

    I have a Two-Channel C. Two speakers outs, switchable impedance. I just got a PRS Big Mouth cab, 8 ohms. I have an Orange 4x12, 16 ohms.

    Currently, they're stacked but not running together. If I would want to run them together, would I use the 8 ohm output setting? It seems to me I wouldn't want to pump 16 ohms into an 8 ohm cab.
    Just out of curiosity, do you get to play venues where you are even allowed to deploy a stack like that?

    I was in a very loud band back in college (yes, 100 years ago) - so loud I had to daisy chain two amps and two cabs for a combo organ for some of the gigs we did - but in those days no one miked the amps, only vocals went through the PA, and there were no mix guys at venues, etc. People didn't make much of an issue over db levels.

    These days it seems most venues want to maintain more reasonable sound pressure levels. When I was gigging in recent years, the sound guy wouldn't have been thrilled if I'd rolled in a stack.

  9. #9
    Name Manglin' Putz alantig's Avatar
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    Quote Originally Posted by LSchefman View Post
    Just out of curiosity, do you get to play venues where you are even allowed to deploy a stack like that?
    Only when I dream. No gigging here - just in my basement recording. (Edited to add - given that my son had to help me move the Orange cab, I don't think it would matter what kind of venues I was at - if I had to move the cab myself, I'd be the guy playing "lead collapsed on the floor"!)

    Honestly, I don't know if I'll ever hook both cabs up at the same time or not, but I know me - I have two cabs, two speaker cables and two outputs. At some point, I'm not going to be able to resist. I'm still relatively new to the head/cab setup (the C is the first amp head I've had). And I don't want to ask myself "What's that burning smell?" while I'm playing. Again.

    True story - years ago, I had a 300W Spectra amp. Got it through my guitar teacher somehow. I decided to practice one day through headphones (they had volume control, so I didn't have it too loud). After about 10 minutes, I could smell something burny, but could not figure out what it was. Until my ears started getting very warm. Fried those puppies up good.
    Alan

    "I watched approximately 45 seconds of 'Rock Of Ages'. It was like getting punched in the soul." - Abby Krizner

  10. #10
    Quote Originally Posted by alantig View Post
    Only when I dream. No gigging here - just in my basement recording. (Edited to add - given that my son had to help me move the Orange cab, I don't think it would matter what kind of venues I was at - if I had to move the cab myself, I'd be the guy playing "lead collapsed on the floor"!)

    Honestly, I don't know if I'll ever hook both cabs up at the same time or not, but I know me - I have two cabs, two speaker cables and two outputs. At some point, I'm not going to be able to resist. I'm still relatively new to the head/cab setup (the C is the first amp head I've had). And I don't want to ask myself "What's that burning smell?" while I'm playing. Again.

    True story - years ago, I had a 300W Spectra amp. Got it through my guitar teacher somehow. I decided to practice one day through headphones (they had volume control, so I didn't have it too loud). After about 10 minutes, I could smell something burny, but could not figure out what it was. Until my ears started getting very warm. Fried those puppies up good.
    That's a great story. I was going to tell one about getting my mom her first cell phone, but I decided to go with this one, which is also true.

    From the late 70s 'til the early 80s I ran my law office word processing on something called an IBM mag-card machine. It was a very large computer tower that you'd stick cardboard cards into and it could read the card, then type a paragraph from the card onto a piece of paper from a special electric typewriter that was attached to it. It was state of the art. For the next paragraph, you'd stick in another card. My legal secretary had to be trained to use it, and we had a book of boilerplate documents that she saved a lot of time not having to retype. The software must have been built into the hardware. But I didn't have any idea how to run it.

    Sometime in the early 80s, my accountant came in and announced that I should ditch the mag card, and go with something new: an IBM Personal Computer. Much more powerful, he said, it can do anything. A computer! I couldn't believe that I could afford a computer! We bought two of these amazing machines.

    If memory serves, you'd load in a very large floppy disk in one drive, and that must have had the OS on it, because there was another floppy drive. So this thing arrived, with a monitor, and it came with a Microsoft manual that was as thick and impressive as a law book. I read that thing to get started, and didn't understand a word of it. There was simply no context. I'd never seen a real computer with a screen first-hand.

    Finally, we got it turned on. And we couldn't get it to do anything! Nothing!

    It just sat there with a black screen and this little white blinking <A>.

    I'd figured a computer, it would know pretty much everything. I expected it to give me answers! Needless to say, I was very disappointed. So I called my accountant. "I can't get it to do a thing," I said sadly.

    And he said, "Well, did you load in any programs...?"

  11. #11
    Name Manglin' Putz alantig's Avatar
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    We're showing our age, Les!

    My first year in college, we did everything on punch cards. No CRT to be found. My second year, they had CRTs, but only the second-year students (it was a branch campus, so only two years there) were allowed to use them.

    Transfer to Pitt. Take a COBOL course. One of the first assignments - everybody gets five data cards to punch. There were three punch machines on campus. So, on my way to another class, I pop into the computer lab in the basement of the Cathedral Of Learning. There's a guy at the punch card machine doing his cards. I wait. A few minutes later, his buddy walks in. They exchange a couple words, the first guy finally finishes. He comes back to the guy in line behind me, and the second guy says, "Well, was it hard?" First guy says, "Yeah. I don't know how anyone can use these things. They're impossible." I stood up, looked at the second guy and said, "All done. Your turn." They just stared...

    Fast-forward a few years later, I get a job at a public utility company. On one of the first days, they assign another programmer to work with me to teach me how to use the keypunch machine to do JCL decks. She started to give me a real basic-type intro and I said, "Wait - standard keypunch machine?" She said, "Uh, yeah." I said, "Okay. I know how to use it." She didn't believe me, so I had to pop out a few cards to show her. Apparently, very few people knew how to use them when they were hired.
    Alan

    "I watched approximately 45 seconds of 'Rock Of Ages'. It was like getting punched in the soul." - Abby Krizner

  12. #12
    Punch cards...that's really some programming! The mag card machine had little magnetic strips on the cardboard, kind of like the strips on a credit card.

    Two years ago I was asked to guest lecture at University of Michigan's music school, and for some reason this particular class was in the computer building. In the lobby they have panels from the first ENIAC computer in a glass case:

    http://www.waymarking.com/waymarks/W...Arbor_Michigan

    Of course, it's all tube! All I could do was stare at those tubes and wonder which ones might work in a guitar amp.

    You're right about showing age...hey, when you figure out how to NOT show our age, let me know!

  13. #13
    A♥ hoards guitars A♥ rugerpc's Avatar
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    My first computer programs were punched out on paper tape and taken by my 7th grade math teacher to the only computer Baltimore County owned at the time in the Board of Ed HQ...
    Thbbbbbt...
    Check it out: Phillybri used to have a band: Resonance But he's soooo over them now!

    ísɹǝqɯǝɯ uɐıןɐɹʇsnɐ oןןǝɥ

  14. #14
    Quote Originally Posted by rugerpc View Post
    My first computer programs were punched out on paper tape and taken by my 7th grade math teacher to the only computer Baltimore County owned at the time in the Board of Ed HQ...
    Wow, 7th grade? Big respect from me on that!

    When I was in 7th grade, all I was thinking about was what to say to a girl, just in case I could get one to talk to me.

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