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What are the concerns of running a 4ohm bass head into a single 8 ohm 4x10?

Discussion in 'Amps and Cabs [BG]' started by jcburn, Nov 2, 2010.


  1. I dont quite understand. Looking at picking up a cheap Peavey T Max. 350 watts at 4ohms, 500 watts at 2 ohms but I only have 8 ohm cabs.
     
  2. thats fine, you just wont get the full power, 2 8 ohm cabs will be running the amp and 4 ohms and 3 8 ohm cabs will bring it down to 2 ohms.
     
  3. Cabs, plural? Run 'em together! There's no real concern except the wattage limitations. You might not be able to crank the head as much as you would with a 4 ohm load. Some people say that running at 8 ohms chokes the tone of the bass but I don't think there's any scientific basis for that and I haven't heard any significant difference if at all. Supposedly you'll be able to get louder with a 4 ohm load as well but according to some smart folks on TB the volume difference would be marginal.
     
  4. Minor correction................

    Two 8 ohm cabs = 4 ohms

    Three 8 ohm cabs = 2.67 ohms

    Four 8 ohm cabs = 2 ohms
     
  5. Selta

    Selta

    Feb 6, 2002
    Pacific Northwet
    Total fanboi of: Fractal Audio, AudiKinesis Cabs, Dingwall basses
    Read the FAQ :eyebrow:

    You have no worries since it's a solid state amp...
     
  6. Thanks guys - and a minor correction on my behalf. I understand how to calculate impedance, just thought that the amp might damage the speakers, although I cant say what I was basing this on. This is the part I didn't understand but got it now.
     
  7. It can damage the speaker if you run the thing at 11. But as long as you aren't hearing any farting out or distortion you should be safe though.
     
  8. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    There are none.
     
  9. I love Talkbass. Thankyou all.
     
  10. +1 :D
     
  11. keyboardguy

    keyboardguy Supporting Member

    May 11, 2005
    For future reference (From Carvin)

    SPEAKER COMBINATIONS and OHMS ( Ω ):

    Four x 8Ω cabinets = 2Ω
    Three x 8Ω = 2.66Ω
    Two x 8Ω = 4Ω
    Two x 4Ω = 2Ω
    One 8Ω and One 4Ω cabinet = 2.66Ω
    Two 8Ω and One 4Ω = 2Ω
    One 2.66Ω and One 8Ω = 2Ω
    Two x 2Ω = 1Ω
    Three x 4Ω = 1.33Ω
    Two x 4Ω and One 8Ω = 1.6Ω
    One 2.66Ω and One 4Ω = 1.6Ω

    Mike
     
  12. Selta

    Selta

    Feb 6, 2002
    Pacific Northwet
    Total fanboi of: Fractal Audio, AudiKinesis Cabs, Dingwall basses
    This assumes parallel wiring only.
     
  13. This... the master has spoken.
     
  14. loopee

    loopee Supporting Member

    May 12, 2009
    Surrey, B.C. Canada
    would 2.66 be bad for a 2ohm head?
     
  15. Marginal Tom

    Marginal Tom

    Apr 28, 2010
    O'Fallon, IL
    No. Read the posts above yours.
     
  16. My understanding is if the head has a minimum impedence of 2ohms then anything equal greater than this is fine.
     
  17. JAUQO III-X

    JAUQO III-X Banned

    Jan 4, 2002
    CHICAGO,IL.
    Endorsing artist:see profile.
    If you have an amp that runs 350 watts at 4 ohms and you run it into a single 8 ohm cab, you will not get the full 350 watts.
     
  18. Bassmec

    Bassmec

    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    Your 8 ohm cab is in fact a cunningly disguised 2 ohm cab
    all you need to do is rewire it all drivers in parallel.
    The crossover for the tweeter is probably just a simple high pass only, does it have a level control.
    So how much are you going to pay me for all this knowledge to get you from a 175 watt bass rig to a 500 watt rig.:hyper:
     
  19. staindbass

    staindbass

    Jun 9, 2008
    the concern is that you wont get full power from the amp. i would consider that a concern. someone had pointed it out already, but 150w may not be enough. i hope it is. johnny a / staind
     
  20. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    99% of the time a cab can't make use of more than half its rated power anyway, if that much, so 'getting the full watts' is seldom a concern.
     

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