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3 cabs, one amp?

Discussion in 'Amps [BG]' started by Murph_Orpheus, Jun 16, 2010.

  1. Murph_Orpheus

    Murph_Orpheus

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    I've never really gotten into this territory before so I'm unsure about how it works and whether it would be dangerous for my amp. I have 2 8ohm cabs and a 4ohm cab. My amp is a Mesa BB750 which does go down to a 2ohm load so I'm curious is it possible to run 3 cabs with this head?
  2. BassmanPaul

    BassmanPaul Gold Supporting Member

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    If the cabinets are the impedance you state you will indeed have a 2Ω load. If the BB750 is 2Ω stable then you can run all three cabinets at one time. However the power will be distributed 50% to the 4Ω cabinet and 25% each to the 8Ω cabinets. Depending on what cabinets you own, you should keep an ear out for the 4Ω one.

    Paul
  3. Murph_Orpheus

    Murph_Orpheus

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    Cheers Paul. I'll give it a go tonight running the 2 8ohm cabs in series and then the 4ohm cab parallel. I'm anticipating a wall of sound :D
  4. mulchor

    mulchor

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    Flip that around. 2 8s in parallel will give impedance of 4.

    The 8s in series would be 16. :rollno:
  5. Murph_Orpheus

    Murph_Orpheus

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    Ho hum! This is where my inexperience comes in! Cheers for that.
  6. BassmanPaul

    BassmanPaul Gold Supporting Member

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    Yes, if you are daisy chaining from cabinet to cabinet that is still parallel.

    Paul
  7. Murph_Orpheus

    Murph_Orpheus

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    So how do you hook it up in series?
  8. ~ignited~wings~

    ~ignited~wings~

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    Most bass cabs can't be connected in series without modification. Some of my Eden cabs can if I use the banana connectors.

    But for your case, daisy chaining is still parallel, and will still be a 2ohm load. What configurations are each cab?
  9. Rick Auricchio

    Rick Auricchio Registered Bass Offender Supporting Member

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    A series connection would require a specially-wired cable assembly.

    The jacks on all cabinets, unless otherwise specified, are simply parallel connections.

    The common confusion is a lingusitic one: Although the cabs are physically connected serially (one after the other), they are not electrically in series.
  10. BassmanPaul

    BassmanPaul Gold Supporting Member

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    You don't want to hook them up in series. All have to be in parallel.

    Paul
  11. Wes Whitmore

    Wes Whitmore

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    He can run 2 ohms on that amp.

    In a perfect world, your cabs all have the same drivers, same cab size/tuning, crossover points, etc. If your cabs are (2) 2x10 8 ohm cabs, and (1) 4x10 4 ohm, then you basically made a 2ohm 8x10, each driver getting about the same power. Turn the horn off 2 of the 3 cabs. If you just have a hodge podge of cabs with different drivers, cab tunings, etc, your amp will be happy at 2 ohm, but it might sound bad...or it might work well. You will just have to try it and see if your combination works for you.
  12. FunkMetalBass

    FunkMetalBass

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    Endorsing Artist: J.C. Basses
    And then he could run it in parallel with the 4ohm cab to get a 3.2 ohm impedance! :hyper:
  13. Murph_Orpheus

    Murph_Orpheus

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    Ok, so if I run one output from the amp to one of the 8ohm cabs, then daisy chain that to the 2nd 8ohm cab, then use the 2nd output on the amp to run to the 4ohm cab will they all be running parallel? And what impedence would that give me? 2ohms?
  14. BassmanPaul

    BassmanPaul Gold Supporting Member

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    Yes and yes.
  15. Oci-One Kanubi

    Oci-One Kanubi

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    Actually, with all three cabs paralleled, I think he would have 1/8 + 1/8 + 1/4 = 1/8 + 1/8 + 2/8 = 4/8 = 1/2 = 2 Ohms total impedance.

    If the Mesa BB750 is a 750 Watt head optimized for 2 Ohms impedance he could be putting up to 375 Watts into the 4 Ohm cabinet, so he needs to check the to be sure the 4 Ohm cab can handle such power.

    Also, he would be putting only 187.5 Watts into each of the 8 Ohm cabinets, so he'd need to think hard about whether he wanted to carry all three to a gig, or only two. With one 8 Ohm cabinet and one 4 Ohm cabinet he would have a total of 2.65 Ohms impedance, so a 750 W head would probably deliver about 600 W if he dimes it. Of these approximately 600 W, the 4 Ohm cab would be carrying about 400 W. If 600 W will do the gig and if the 4 Ohm cab can handle 400 W, then he should probably carry only two cabinets. Unless he just wants to look mighty.
  16. Murph_Orpheus

    Murph_Orpheus

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    I don't want to bring all 3 to gigs it's just something I wanted to play about with at practise for fun. But I wasn't sure of the possible outcomes etc. And the 4ohm cab can handle it no problem as it's rated at 600 watts.
  17. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

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    Funk was saying that the OP would end up with a 3.2-ohm load if he wired the 8-ohm cabs in series (for 16 ohms), then paralleled that with the 4-ohm cab. As others have pointed out, you have to go way out of your way to connect cabs in series. A novice wouldn't be able to figure it out, and there's no chance of it happening by accident.

    Also, as someone else pointed out, be careful not to overdrive the 4-ohm cabinet. It will be receiving twice as much power as each of the other cabinets.
  18. Rick Auricchio

    Rick Auricchio Registered Bass Offender Supporting Member

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    But you should still listen and turn down if you hear any of the cabs farting out.
  19. jeonnie

    jeonnie

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    what about 3, 8 ohm cabs.. Two of them daisy chained. with an amp rating at 2 ohms
  20. B-string

    B-string Supporting Member

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    Three 8 ohm cabs = 2.667 ohms and will be fine. all cabs will share the power equally.

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