Parallel/series/parallel..possible ??

Discussion in 'Cabinets & Speakers' started by kook, Mar 7, 2019.

  1. kook

    kook Active Member

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    Ok i have i have a 4x12 cab...i have two g12m at 16ohm each and two vintage oxfords at 4ohms each...i think they would sound great together so here is what im thinking...wire the g12's in parallel for 8ohms and wire the oxfords in series for 8ohms.. then wire each pair parallel to each other for 4ohms...does this make sence ? Would either pair take the brunt of the power (jcm800 100w)...
    Thanks guys
     
  2. Jon C

    Jon C Well-Known Member

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    That works …… The efficiency may be better with one of those sets but the math works
     
  3. kook

    kook Active Member

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    Can you alloborate on that ?..i dont want to blow either pair
     
  4. Jon C

    Jon C Well-Known Member

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    You won't blow anything up …… you'll have to experiment to see if you can even hear a noticeable volume difference……
    More importantly, That would be a combined resistance of 4ohm
    Just make sure your amp can safely handle only 4ohm of load ( That's Full Power Dump on your JCM800 ) !!!
     
  5. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    are all speakers the same wattage?

    the power rating is where you'll go awry.

    When mixing speakers you'll run into different scenarios.

    Some speakers are more efficient than others.

    example 1: a 16 ohm GB25 will have a 97db while a 16 ohm V30 will be 100 ohm. That means that the GB will be less efficient & will always play 3 db lower than the V30. Now, on top of that, the power rating is different for each speaker, so, when you mix speakers, you have to use the lowest power rating (25 watts, for the GB25) & multiply that by the number of speakers. So, in a 4x12, you would keep the maximum cabinet rating at 100 watts, even though the V30 can handle more than the GB25.

    example 2: you can have all GB25 speakers. a 4 ohm & a 16 ohm, if you wire them together, the speaker w/ the least resistance will be more efficient & always drown out the speaker w/ more resistance. So, when you push the speaker at "x" ohms, the 1 speaker will always be pushed harder & the other speaker will just be pushing air in the background. It will be supporting the overall volume, but not heard.

    This is not the most efficient way to mix speakers. It's better to match them. If you mix, it's best to match what you can & bi-amp, so that each amp is running the speakers matched, for maximum efficiency.

    There are rules that can be broken, as guitar amp's aren't always about running clean & efficient, but, in this case, you'll be running some speakers clean & efficient, while running others not, but, they won't be heard over the clean efficient one(s)

    Hope that makes sense...
     
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  6. Jon C

    Jon C Well-Known Member

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    So kinda what the Dog said is …… You won't blow anything up……:drool:
     
  7. JohnH

    JohnH Well-Known Member

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    I agree it looks fine on paper. And as described, all speakers get nominally the same power, so what you hear is down to relative efficiency. So your overall cab power rating is 4x that of the lowest speaker.
     
  8. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    What power rating are the Oxford speakers? As long as they are greater than 25W it may be ok.
    :photos:
     
  9. kook

    kook Active Member

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    Thanks guys so the oxfords are the 1960s 12t6 speakers (25-35watt)..not efficient at all and have a very dark sound..so i already assume i will hear the g12m more predominantly..which is fine with me..im more or less doing this so i can use the 2 greenbacks with my marshall the oxfords are basically helping take the load so i dont blow the speakers..keep in mind the g12m's(16ohm) will be wire a parallel and the oxfords (4ohm) will be wired series, then each pair will be wired parallel to each other for 4 ohms....being that the oxfords are not as efficient as the greenbacks im worried power distribution wont be even and the g12m's will take the brunt of the power
    Thanks guys..hope that made sence
     
  10. chuckharmonjr

    chuckharmonjr Well-Known Member

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    Another simple tip..mount them in a X configuration so you have one of each on top and on bottom
     
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  11. junk notes

    junk notes Active Member

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    Those Ox's are really nice in a BF Bassman piggyback rig.
    Sounds like a nice setup you are trying with GB's.
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    wire the g12's in parallel for 8ohms and wire the oxfords in series for 8ohms..
    ..then wire each pair parallel to each other for 4ohms..

    yes
    It depends on speaker efficiency which one (or 2) is going to be louder...
     
  13. kook

    kook Active Member

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    Thanks..i do have a blackface bandmaster..i have some older jensen vibranto speakers in it...i have a silverface bassman 10, with 4 tens...what a great sounding amp it is...my 800 is just to bright with the 75s..the sidewinders are an improvement but im really curious to hear it with the GBs
     
  14. GIBSON67

    GIBSON67 Well-Known Member

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    Marshalls and Oxfords...probably one of the few combo's I haven't tried.

    Those old Oxfords handle the watts pretty well, so I am thinking they will rock, and especially with a pair of GBs!
    I had a large 2x12 Bassman cab with Oxfords a while ago, but no Marshalls at that time...definitely regret selling that cab.
    One of the best in my opinion.

    As far as your wiring, I'd go with series for the two pairs and make it 16 ohms if you're only using it with your Marshall.
    4 ohms is better for Fenders, so I understand where you are coming from, though.
     
  15. kook

    kook Active Member

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    Ty..i actually changed my mind about 4ohms im going for 16..i may remove 2 powertubes drop it down to 50w and if my cab was at 4ohms it wouldnt work...i originally bought the greenbacks for my 1965 EKO viscount..(modeled after ac30) they just dont mesh
    Thanks again
     
  16. Scumback Speakers

    Scumback Speakers Well-Known Member Sponsor

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    The Oxfords are going to be less efficient, and since they're that old, they're likely going to get hurt. Their old glues and voice coils weren't meant to handle the kind of signal a JCM 800 100w puts out, which is 115w clean signal around 3-4 and 170w at 8 on the volume knob. Here's the JCM 800 manual so you can check yourself.

    I wouldn't even run four 25w G12M's with that past 4-5 before I got nervous. What Dogs of Doom said about the 4 ohm speakers getting more power due to less resistance is correct as well. Generally I think you're going to wind up real unhappy, even if you yank two power tubes, as that amp will still put out 50w clean and over 90w cranked.

    [​IMG]
     
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  17. kook

    kook Active Member

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    Ty scumback...im taking eveything in...so about the efficiency...if i have g12 pair at 16ohm each wired parallel for 8 and the oxford pair 4ohm each wired at series for 8..since each pair is wired for 8 would one set still be getting the brunt of the power ? Also..one oxford is fresh recone and i had the other done in the 90s...
    Ty
    Im still undecided just considering everything at this point...i rarely get over 4 on volume , dont even get to 2 at practice
     
  18. Scumback Speakers

    Scumback Speakers Well-Known Member Sponsor

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    kook, the problem is the uneven ohm ratings. The lower resistance speakers will get more power than the higher resistance ones. When I break in speakers, I have to put the 8 ohm speakers all in one cab, while I put the 16 ohm speakers in another. They're wired in parallel, but even so the lower ohm rating speakers move more from a bigger signal getting through than the higher ohm rating speakers. That tells me the 8 ohm speakers with their lower resistance, get a bigger signal than the 16 ohm. The same thing will happen in our cab with this wiring setup. It's got to do with ohms law, current, etc, but in a nutshell, the lower the ohms, the more signal is sent to them. So they'll get more power than the higher ohm rating speakers, regardless of the wiring setup. Your best bet is to have all the same ohm rating on the speakers.
     
  19. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    I am sorry guys but I have to interject.
    Both Dogs of Doom and whoever is Scumback (there is no name or qualifier of person) are somewhat incorrect, not right or whatever in the statements about lower impedances.

    Every case may be different and all need to be deciphered but most musical cabinet setup/loads are common and not hard to figure out.

    Ohms Law in accordance to series/parallel circuitry applies here.

    There would be two parallel 16's plus two series 4's. Lets use 50V RMS. The current is determined by by total resistance which equates to 16 ohms.
    So 50V / 16 ohms = 3.125A

    16 in parallel divide 3.125A for 1.5625A per speaker
    two 16 in parallel is half of load at 8 ohms dropping half the voltage = 25V
    each 16 is 25V x 1.5625A = 39.0625W

    each series 4 drops 12.5V
    each 4 is 12.5V x 3.125A = 39.0625W

    So you now see that each speaker is handling the same wattage in this scenario, about 39 watts.

    The more efficient speaker will of course be louder but I am going to say the old Oxfords are around the mid 90's SPL pretty much or almost as much as some G12M.

    Also speaker ratings are given in RMS.
    You are using musical power which is twice that in handling power.
    A 25 watt RMS rated speaker handles 50 watt in musical power.

    Still, be careful with old speakers because of their age and material breakdown.
     
    Last edited: Mar 9, 2019
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  20. BowerR64

    BowerR64 Well-Known Member

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    ...crickets chirping
     

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