Wiring Cabs, Speaker OHMS all in one thread

Discussion in 'The Squawk Box' started by JakeM, Feb 19, 2011.

  1. bobarino

    bobarino Senior Member

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    Jan 17, 2011
    i'd do it like this:

    internal 2x12 @ 16ohm connected to one of the 8ohm outputs
    external 2x12 @ 16ohm connected to the other 8ohm output
  2. Powermetal

    Powermetal Junior Member

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    Jun 14, 2012
    Hi, newbie here. Came across this forum and looks great with a wealth of info. I have been literally confused from other forums so hoping to get a straight simple answer,please? I have two - 2 x 12 cabs and want to stock them with the Celestions G12T - 75 watts. I'm looking to buy the QSC GX3 power amp. I would like one cab one the left of stage and the other, well the right of stage. Daisy chain them. So, do I need the speakers at 16 ohms or 8 ohms, wired in parallel or series and will the QSC be too powerful and fry these speakers? Should I look for another power amp? Any input appreciated, thank you all.
  3. Longtailweasel

    Longtailweasel Junior Member

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    Dec 5, 2011
    Ok guys, I know this is an old thread but I don't want tot start a new post.
    Question 1:
    I have a 2x12 cab, with 2 output jacks, with 8 ohm speakers wired in parallel to get an 8ohm cab. Only one jack is wired right now. i have a 4 watt vox that runs at 16ohms and a 65 watt egnater renegade that i can choose between 4, 8, and 16. I run my egnater at 8 ohms because i want it to be louder. I also love the sound of my vox but a lil 8'' speaker doesn't cut it. Is there a way i can have one jack be 8ohms and the other be 16ohms so i dont have to re wire my ab every time i want to switch amps?

    Question 2: I want to get new speakers. A greenback (25w) and a vintage 30 (60w). This would make a 50 watt 2x12 cab right? So would i blow the greenback because im using a 65 watt amp. My amp has a 65 watt and a 18 watt switch so should i just use the 18 watts if im going to go with this setup? thanks
  4. ashbass

    ashbass V.I.P. Member

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    May 3, 2007
    Old topic, I know. I've searched and read. I'm trying to straighten out what is safe for my gear, not necessarily what sounds best. Here's what I think is right.

    A 4 Ohm amp can drive a 4, 8, or 16 ohm speaker.
    (8 and 16 will not be optimal performance-will likely have less volume.)

    A 8 Ohm amp can drive a 8 or16 ohm speaker.
    (16 will not be optimal performance-will likely have less volume.)

    A 16 Ohm amp can drive a 16 Ohm speaker.


    A 4 Ohm speaker can be driven by a 4 Ohm amp.

    A 8 Ohm speaker can be driven by a 4 or 8 Ohm amp.

    A 16 Ohm speaker can be driven by a 4, 8, or 16 Ohm amp.

    Am I right?
  5. ltfullert

    ltfullert Junior Member

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    Dec 27, 2010
    Hey guys, I was wondering if it's possible to easily swap the lugs about in the back of my Fender Twin to switch the wiring between series and parallel?

  6. Comanche

    Comanche Senior Member

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    Mar 5, 2012
    Hello, I have a Lil Night Train that is 2 watts.
    It has one 1/4 speaker output.
    I want to run two 10 inch marshal cabs that I have.
    I would like to run the 1/4 mono output into a two 1/4 split.
    [ame=http://www.amazon.com/Hosa-YPP111-inch-Dual-Cable/dp/B000068O53/ref=sr_1_1?ie=UTF8&qid=1347244863&sr=8-1&keywords=1%2F4+jack+splitter]Amazon.com: Hosa YPP111 1/4 inch TS to Dual 1/4 inch TS Y Cable - 6 Inch: Musical Instruments[/ame]

    If the 8 ohms output from the amp is split does it make the the output 4 or 16 ohms?
    Are the speakers in series or parallel?
    Thank you.
  7. picoman

    picoman Senior Member

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    Feb 4, 2010
    Can all this conusion be avoided if you buy amp that has variable ohm cabinet option?
  8. Greenman1976

    Greenman1976 Member

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    Dec 18, 2011
    One thing I have yet to see is wiring two amps to one speaker. I've searched google and almost all the forums and havent found a thing. I have a few ideas to be able to do this but i can't draw out schematics. so I have the two amps slet up on a DPDT switch that is set up to direct the unused amps volume through a resistor of equal value of the speaker. would this work? build it into a power supply case where i can plug each amp to it with a speaker cable, maybe add an attenuator?. Im planing on doing this to a Fender super champ xd and the new Marshall DSL15h (if i can get it) with both going to the fenders cab. Ideas?
  9. martin H

    martin H Senior Member

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    May 16, 2012
    Ok time for a quick treatise: Hope this is helpful

    [1] Speaker impedance, amp impedance and power

    Discussing what cabinet to uses with what amp, the first thing to remember is that tubs amps and transistor amps react differently to the impedance of the speaker cab.

    The lower the total speaker impedance, the more current (and hence more power) the amp will provide. The relationship is roughly linear, i.e., an amp that will provide 20W in 16 ohms, will provide 40W into 8 ohms and 80W into 4 Ohms. The limiting factor is the minimum impedance that the amp can drive. Going below that will likely damage the amp, became too much current will flow from the output transistors. This is why transistor amps usually specify a minimum speaker impedance ( “4 ohms total” or “4 ohms minimum”) Running a lower impedance my damage the amp. Running a higher impedance does no harm, but reduces available power. A transistor amp is not damaged by running a signal through it with no speaker. Therefore, it’s best to run the transistor amp into its stated minimum impedance. Remember the example above. That amp rated at 80w 4 ohms produces only 20W into a 16 Ohm cabinet.

    Different ball game. Unlike the transistor amp, the tube amp does not produce more power if you just drop the cabinet impedence. The tube amp produces maximum power into the specified impedance set by the output transformer. An amp rated at 100w with the output transformer tapped for 8 ohm speakers will produce less power into either 16 ohms or 4 ohms than it does at 8. This is why tube amps often have tapped output transformers to allow maximum power into 4, 8, or 16 Ohm cabinets. The tube amp is not likely to be damages by a short in the speakers, but can be damaged by running a signal through it with no speaker

    [2] Impedance of multiple speakers: There are two ways to wire speakers, SERIES AND PARALLEL.

    In series, the wire goes from the amp to the + of the speaker, then from the – of the speaker to the + of the second speaker, then from the – of the second speaker back to the amp. The current flows first through one speaker, then through the next, in series.

    In parallel, the wire goes from the amp to the + of both speakers and the - of both speakers is connected to the other wire from the amp. The current splits and flows through both speakers simultaneously, in parallel.

    Speakers in series have a higher impedance than the individual speakers. Two 4 ohms in series give a total impedance of 8 ohms. Two 8’s in series gives 16 ohms etc,

    Speakers in parallel have a lower impedance than the individual speakers. Two 4 ohms in parallel give a total impedance of 2 ohms. Two 8’s in parallel gives 4 ohms etc.

    [3] Distributing power among speakers

    I see a lot of questions about how power is distributed among multiple speakers: In a two speaker setup the distribution of power is identical as long as the speakers have the same impedance, irrespective of whether they are connected in series or parallel. Two 25W speakers of the same impedance will always handle a total of 50W, and the power is distributed evenly among the speakers, 25W each. Things only get strange if you start mixing speaker impedances in the same cab. For example:

    Mismatched impedances in series: if you put a 4 ohm speaker in series with an 8 ohm speaker, 2/3 of the power will be generated across the 8 ohm speaker; Therefore the 8 ohm speaker must handle twice the power of the 4 ohm speaker

    Mismatched impedances in Parallel: Works the other way; if you put a 4 ohm speaker in parallel with an 8 ohm speaker, 2/3 of the power will be generated across the 4 ohm speaker. Therefore the 4 ohm speaker must handle twice the power of the 8 ohm speaker.

    [4] What is the output impedance of the amp?

    Working all this out can be tricky with amps that have multiple speaker output jacks and cryptic messages on the back like “8 ohms.” If there are two jacks, does this mean that you can plug more than one 8 ohm cab into the amp? Again the answer tends to vary between tube and transistor amps.

    The speaker output jacks on a transistor amp are almost always in parallel. The amp manufacturer is relying on you to do your own calculations of the total impedance of what you are plugging into these jacks. Remember how parallel speakers work? – It’s the same with cabs. Two 16 ohm cabs in parallel = 8 ohms. Two 8 ohm cabs = 4 ohms. Two 4 ohm cabs = 2 ohms. If the amp says “4 ohms” on the back, the last combination is bad.

    Tube amps can be trickier. If the amp has an impedance selector on the back, the jacks are usually in parallel, and you have to do the same calculation above; Two 16 ohm cabs in parallel = 8 ohms. Two 8 ohm cabs = 4 ohms. Set your impedance selector to 4 ohms or 8 ohms accordingly.

    If it doesn’t have an impedance selector on the back, the amp can be wired in several ways. Some Fenders are wired in a clever way that actually changes the output circuits to account for the changed impedance if you plug in a second speaker. Some just put the second speaker in parallel without changing the transformer tap. A few put the second speaker in series. In these cases, it’s best to ask the manufacturer how it’s supposed to work.

    Hope this was of some help
    3 people like this.
  10. Buzd

    Buzd Junior Member

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    Feb 9, 2013
    Hi guys

    I'm a newbie out here and I apologize if this question has already been asked but I have a 2x12 custom built cab with 2 x 8 ohm speakers. I understand wired in parallel would be 4 ohms and series 16 ohms. Is it possible to have 2 jacks in the back so 1 jack is wired in series (16 ohms) and 1 wired in (parallel 4 ohms)? I want to be able to connect 2 amps (one has 4 and 8 ohm out) and 1 has 16 ohm out only. I will then switch between heads using my tonebone VT only using 1 cab.

    I saw the attached image earlier but I'm not an electronics guy and do not fully understand it.

    Any help would be greatly appreciated.

    Attached Files:

  11. truckermde

    truckermde Senior Member

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    Oct 21, 2012
    It is definitly possible to have multiple jacks for various impedance. Several cabs come standard that way.

    And welcome:wave:
    1 person likes this.
  12. Buzd

    Buzd Junior Member

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    Feb 9, 2013
    Thanks Trucker

    Would anyone have a simple diagram how to do this by chance?

    Thanks again.!
  13. jumpinjackf1ash

    jumpinjackf1ash Senior Member

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    Sep 18, 2008

    I have a Kustom Coupe 36 amp that has one 12 inch 16 ohm speaker in it (eminence cannabis rex). i also have a 4x12 kustom cab that holds 4 12 inch 16 ohm speakers (2 eminence swamp thangs and 2 texas heats) wired in series/parallel so that the cabs rating is 16 ohms.

    The amp has a selector switch for the 2 output jacks. I know that if i want to run the internal speaker alone, i plug that in and set the switch to 16 ohms. I know that if i want to use just the 4x12 cab i plug that in and set it to 16 ohms, and leave the combo internal speaker not plugged in.

    Here is the question...what if I want to run all 5 speakers, the internal 16 ohm combo speaker and the 4x12 16 ohm cabinet? I think I could set it to 8 ohms on the amp and be fine...but it makes me think the combo internal speaker will get half the power of the amp, then the 4x12 cabinet will get the other half and each speaker of the cabinet will only be 1/4 as loud as the combo speaker and things wont be matched or sound right. Anyone have any ideas or tried this before?
  14. mr_mer

    mr_mer Senior Member

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    Mar 8, 2010
    Hopefully folks are still monitoring this thread...

    I have an opportunity to buy a 2x12 cab to match my Germino Classic 45, but I do run a 16 ohm attenuator (otherwise it is too loud/can't get the tone I like). This 2x12 cab is parallel wired (Pair of Celestions, one G12H and one G12M), making it effectively 8 ohms.

    Am I right in thinking that I won't be able to use the attenuator?
  15. IronWeso

    IronWeso Senior Member

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    Jan 12, 2008
    OK I've been searching for answers on this:

    I have a modded DSL100 head on the way. I have a 1960a with two V30s and 2 GT75s. I currently play it in stereo with my rack setup.

    HOWEVER - I want to add a 2x12 cab into the fold. I can get a deal on an empty Avatar cab. I will be putting speakers into it - looking at 25w greenbacks.

    Questions are: 1.) Can I mix all of this in my live setup using only the DSL?
    My thoughts are no because I may blowout the Greenbacks since they only handle 25W each.

    2.) If it is possible, what OHM speakers (8 or 16) would I get the Greenbacks in? Also, how would I connect the outputs/inputs OHMs from the Head to the cabs?

    3.) If its not possible to mix all this into a live setup. What OHMs should I get the Greenbacks in just for home recording?

    My head hurts... thanks!:applause:
  16. DrBGood

    DrBGood Senior Member

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    May 17, 2013
    I have a FM65 combo (65W - 1X12" 8ohm) and want to use my Crate GTX212 combo speakers (120W -2X12" 8ohm) as a cabinet. It could cut off the FM speaker or use the 3 of them. Can it be done ?

    I think I would have to add an output jack to the FM and a cut off input jack to the Crate.
  17. antihater48

    antihater48 Junior Member

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    Dec 31, 2013
    I generally try to read though all the posts if I have the patience.. only made it halfway throungh the fourth page..
    I have a v30 and a greenback light that im going to run with an egnater tweaker 15, and maybe my ashdown fallen angel 60 dsp..
    Although I might try it out with the speakers in paralel, I was thinkin Id run them ay 16 ohms. Does it make a difference which one gets power first? should it be the v30 cus its a higher wattage? Or the g12l cus its a smaller magnet to try and balance the volumes? What woukd the jack wiring look like if I wanted to be able to daisy chain it?
    Lastly, since there are two output speaker jacks, as long as they're the same ohm rating, would there be any benefit to running them sperately? Or is that the exact same as running them paralel at for ohms? Sorry for the million questions.
  18. SteveGangi

    SteveGangi V.I.P. Member

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    May 20, 2010
    Check with the manufacturer. If that were a 4 Ohms parallel cab, I'd say just rewire it in series to get the 16 Ohm load.

    You could always disconnect one speaker, but that defeats the whole purpose of a 2x12
  19. xSinner13x

    xSinner13x Senior Member

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    Feb 17, 2012
    What, IF any difference does either circuit make, or is it just splitting hairs?


  20. Big John

    Big John bigger is better V.I.P. Member

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    Mar 18, 2007
    Thought I'd add this to the collective here. A pair of switching jacks gives ya a few options...


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