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wiring diagram request - mixing ohms

Discussion in 'Amps [BG]' started by jlagross, Dec 14, 2013.

  1. jlagross

    jlagross

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    hey all!

    I ordered 4 speakers online from a guy, spoke with him personally and he sold me on them (literally). They are old marshall 10 inch bass speakers. Very punchy and crisp clear sound. All 4 were suppose to be 8 ohms, but 2 ended up being 4 ohms while the other 2 were 8. They are all the same brand, the logo being gone but look identical, and sound EXACTLY the same, so i do want to keep them, my problem is getting the impedance correct. I dont have any other info on them so if anyone has any knowledge of marshall bass speakers i can upload pics.

    This project is an empty 810 1971 svt cab,
    Is it worth wiring the two 8's and two 4's together in a 4x10 since they are the same brand ? if so anyone able to provide a diagram? I also have 2 cts 32ohm speakers i could use to in this config. I do plan no filling the other 4 holes in the cab just dont have the money at the moment.

    Thanks!
    Jason
  2. wighat

    wighat

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    Bottom line: you'll need 8 identical drivers designed for a sealed enclosure of a similar volume to the internal compartments for this cab to sound right.
  3. B-string

    B-string Supporting Member

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    You have a real mess there! You really don't have 4 speakers that will work well together.
  4. jlagross

    jlagross

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    yeah i was looking at this as 2 4x10's , since my peavy has 2 outputs, each 4 ohms. i was going to use these marshalls in the lower 4x10 , and 4 other identical drivers for the top. that way if im just playing with friends i can plug in to just the bottom/top if the jam calls for it. That was my thinking anyways. looks like im out of luck then..
  5. scottstephens

    scottstephens Guest

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    The previous posters are correct; mixing speakers of different impedances will not sound right, because they will not all be carrying the same load.

    If you just need to get through the next few days or weeks, you should run either the two eight ohm speakers in parallel or the two fours in series. That is, you will probably be limited to a 2x0 rig. Fortunately the old SVT cabs isolate the speakers in banks of 2 so it will work, but look wierd.

    IF you form both of those banks and are tempted to run them in parallel from the same amp, don't because it would be 8/3 or 2.7 ohms, and most amps can's take such a low output impedance.

    s
  6. Downunderwonder

    Downunderwonder

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    There is a specific problem with mixing drivers in series which stuffs up any odd scheme to equalise the power applied.

    If you ran a pair of 4ohm series and the 8 ohm ones parallel with them you get some very low total impedance which your amp may not handle. What is the amp exactly? Some Peavey are indeed 2 ohm stable Solid State, but not really recommended. If it's really a 2 channel amp you're golden.

    Your cab is 4 2x10 unless the early ones are different.
  7. JohnMCA72

    JohnMCA72

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    You don't mention the amp, which is pretty important.

    I wouldn't do it myself, but here's how you can make it work as well as it can:

    Wire one 8 ohm & one 4 ohm speaker together in series. Do this twice so that you'll have 2 pairs of speakers (1 @ 4 ohm & 1 @ 8 ohm), with each pair having an impedance of 12 ohms.

    Wire the speaker pairs together in parallel. You'll get a combined 6 ohms of impedance for the whole mess. Most amps will have no problem driving into a 6 ohm load, but since I don't know what amp you'll be using I can't say for certain.

    It's far from optimal, as others have noted, but if you don't have the money to do it right, at least this should keep you from damaging or destroying anything.

    Now, whether any of those speakers can handle the power that it's going to take to get you the sound pressure level (SPL, i.e. "volume") you want is another matter entirely. I don't have anywhere near enough information to answer that one for you.

    2 8 ohm speakers wired in parallel gives you 4 ohms for the pair. Wire the 4 ohm pair (of 8 ohm speakers in parallel) in parallel with both of the 4 ohm speakers & the combined mess will have a load of 1.333... ohms. Not many amps can handle such a light load without risk of letting some of the magic smoke out.
  8. Bassmec

    Bassmec

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    Disclosures:
    Proprietor Springvale Studios
    No real problem here. All the original poster needs now is three amps.
    Just wire the similar impedance speakers in parallel and then.
    Get one amp that delivers the pair of drivers max watts @ 2 ohm loads, one amp that delivers for 4 ohm loads and one that delivers at 16 ohm loads. Simples!;)
    PS. Lightweight power amps come in stereo with individual volume controls so it might be only two amps, one of them in bridge mode.
    :bag:
  9. JohnMCA72

    JohnMCA72

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    ^^^ Best answer so far.
  10. jlagross

    jlagross

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    haha thanks all for the witty posts and the intelligent ones.
    The amp can handle 2 ohms, its a peavey mark viii , i meant to put that in the OP , i apoligize.

    I test wired them and recieved 2.5 ohms, which is within my 2-4 ohm suggested impedance for the amp. They sound CRYSTAL CLEAR and are LOUD. I definitely want to keep them, if that means getting other 4's and 8's to put in with them i will.

    I wired the 4's together to get 8 ohms, then wired all together in parallel i believe. dont quote my my terminology may be wrong. iv been trying to learn it :)

    its a project for sure and im learning along the way. All i can ask for.

    thanks again

    Jason
  11. Downunderwonder

    Downunderwonder

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    Alrighty then, you can safely run the 2x 4ohm series, with the 8ohm ones in parallel as I suggested. That gives you equal power to each and 2.6ohm nominal loading. In the meantime.

    Personally, I'm anti 8x10 for carrying bar rooms. They are nice up the middle but muffled to the sides.

    If you get enough volume out of the frankenbeast you should build a couple of 2x10 cabs to stack vertically and carry on.
  12. jlagross

    jlagross

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    Thanks Down under.
    She may be a franken cab but shes mine and I can say I built her myself, even if she may not be ideal at this time.
    I will post pics when she's all finished.

    thanks
    Jason
  13. Downunderwonder

    Downunderwonder

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    It sounds like you understand series and parallel well enough if you measured 2.5 ohm dcr for the whole four Marshalls. I would use the middle two cab pairs rather than top or bottom ones. Gives you some height without decoupling and makes for a balanced frankencab.

    EDIT: the other four cts 32ohm can go in parallel, takes you down to 2ohm total, not my cup of tea, but keep your eye on the DDT light, if it lights up all the time back off or the amp will be getting hot. The problem is those 4 cts would only get a smidgen of the power, the other pairs get most of it. Depending on power handling the cts should go on the bottom.

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