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4 ohm cab to 8ohm?

Discussion in 'Amps and Cabs [BG]' started by dfinnegan71, Aug 30, 2012.

  1. I hope this is not a repost, cuz I looked around. But anyway, I am assuming I can rewire my 4 ohm cab to 8 ohm without to much trouble, right? I have a 2-12 cab that has 2 8 ohm speakers wired to 4 ohms. I just picked up a 15 cab I want to run with it. That has a 4 ohm speaker in it. I think if I just plug er in, I'd be running only 2 ohms and mught damage my head. What do you guys think?
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Two 8 ohm speakers can only be wired as 4 ohms or 16 ohms. There is no way to make two 8 ohm speakers into an 8 ohm load, other than removing one of them.

    Most amps will burn up at 2 ohms, but there are exceptions, so be sure to look up your specific amp.
  3. thanks, that's what I was afraid of
  4. FretlessMainly


    Nov 17, 2010
    Notwithstanding what Bongo posted, even if you could get your 2x12 to 8 ohms, if you'd be running a 4 ohm cab and an 8 ohm cab in parallel, you'd be at 2.67 ohms, which is likely to burn up most heads as well. You could run them in series at 12 ohms, but what's the point other than having the 15 moving more air but at reduced output? I can't comment on the loudness differences there.
  5. will33


    May 22, 2006
    He could solder up a series cable and get the load to 8ohms, that's about it.

    OP...what amp? A 2ohm stable mono amp, or 2 channel amp would make it no problem.
  6. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Not possible, even with trouble. The series cable idea is a pretty good one, though. Here's a schematic and a picture of one. If you're using Speakon[SUP]®[/SUP] plugs, tip=1+ and sleeve=1-.


  7. Bassmann1968


    Feb 17, 2009
    Which amp do you use?
  8. Sorry for the late, really late delay in getting back to you. I use a Genz Benz shuttle 9.0 it makes 900watts @4ohms and 500 watts @8 ohms.
  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Your amp is capable of operating into a minimum 4 ohm load.

    Your best bet is to find a more suitable speaker cabinet combination.
  10. +1 I agree with both statements. The rig you describe is not an optimal pairing for several reasons, but the biggest reason is the impedances of your drivers just don't give you many good choices.

    I also can not help but respectfully recommend you read up on mixed driver rigs. A subject that is regularly argued here on TB but that has a clear answer if you are willing to listen. The arguments persist because many bassists listen with their eyes and not their ears, or don't like being told that their expensive mixed driver rig could sound much better than it does, or don't consider physics to be relevant to bass playing...
  11. Rooster009


    Feb 27, 2008
    I like the idea of building the series cable the best. 500 watts to 2-12's and a 15 would be plenty for any situation. Not to mention, the series cable is a lot cheaper than buying a new cab.
  12. Rooster009


    Feb 27, 2008
    Here we go again on the mixed driver thing. Wow!
  13. the series cable is much easier...
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    If the cabinets are from our company, they have been designed from the ground up to be compatible between driver sizes. The phase response and relative sensitivities are compatible by design.

    Not knowing what cabinets the OP has, I can not provide more accurate information.
  15. With all due respect sir I believe your company has done its best to make a bad idea work. That doesn't mean it is now a good idea.
  16. If it sells and people like it, is it still a bad idea? :)
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    It also does not mean that it violates any laws of physics.

    IMPO, the entire (poplular) argument against mixing driver sizes has ignored much of the math, analysis and testing. When the design provides acceptable analysis results and phase coherency, offers no negative artifacts and customers like how they sound, why is this so bad. In fact, if you were to participate in a double-blind listening test, you would not be able to identify a mixed size pair of cabinets... confirming that the myth is generally stronger than fact when I have been involved in such tests.

    Before you suggest again that I read up on the subject and learn something, you should be aware that I am an EE, I understand the math, and have many, many years of experience in commercial speaker design, transducer development as well as DSP algorithems. This is not my first rodeo ;).

    Also note that my comments assume a proper design using like topology cabinets (ie. not combining a sealed box with a ported box, etc.) where a common response family between driver sizes was a specific design approach and not just happenstance.
  18. preside


    Aug 7, 2010
    Scottsdale Az
    I understand people have strong feelings , but TRY to keep it civil bassmeknik. Insulting people and thier professional credentials only hurts your case.
  19. 4-string


    Jul 23, 2006
    Hard to find an unspoiled thread in the amps forum these days. Geez.
  20. father of fires

    father of fires Commercial User

    Nov 29, 2006
    Chief of Medicine at Damnation Audio
    Holy crap people. Take that **** elsewhere.

    The series cable is your best bet.

    You could sell both cabs for one nice one too.

    Also...the only thing BFM ever said is that mixing speakers can have unexpected results.

    A properly designed system can make use of multiple speaker sizes. And yes...you can design a 15 for strong lows and you can design a 10 for fast highs.