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4 Ohms + 8 Ohms = 6 Ohms??

Discussion in 'Amps [BG]' started by jmac85, Jul 8, 2008.


  1. jmac85

    jmac85

    Joined:
    Mar 22, 2008
    Location:
    Duluth, MN
    I'm looking to add the Avatar B212 cab to my stack but not sure if I should get it in 4 Ohms or 8 Ohms. My head is only rated at 4 ohms and 8 ohms, so I'm not sure if this would be ok to do. Any help would be great thanks!!!!
     
  2. hpebass

    hpebass

    Joined:
    May 28, 2008
    8 ohm + 4 ohm = 2.667 Ohm

    If you have an 8 ohm cab, get another 8 ohm cab.
    If you have a 4 ohm cab, you're out of luck unless you get a head that can do 2 ohms.

    I've heard people connecting cabs in series but read a lot of people saying that it's impractical.
     
  3. touchdown!

    touchdown!

    Joined:
    Jun 2, 2008
    4 ohms + 8 ohms = 2.6667 ohms
     
  4. KJung

    KJung

    Joined:
    Apr 9, 2005
    Location:
    Wisconsin and Upper Michigan
    combining a 4ohm and 8ohm cab results in a total nominal impedance of 2.67 ohms, and the 4ohm cab will get more wattage from the head than the 8 ohm.

    So, this makes sense if you have, for example an 8ohm210 and a 4 ohm 410, and a head safe down to 2ohms.

    What head do you have?

    K

    Edit: If you current cab is 8ohms, get another 8ohm cab, which will result in a total nominal impedance of 4ohms, which is where most SS heads like to run.
     
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  6. JMDT

    JMDT

    Joined:
    Jan 30, 2008
    Location:
    Louisville, Ky
    2.6 ohms

    1/4+1/8=1/total
     
  7. scuz

    scuz You can't be angry ALL the time!

    Joined:
    Mar 24, 2008
    Location:
    Minneapolis, MN
    4 ohms + 8 ohms = ~2.6 ohms. Mixing ohms is usually a bad plan.
     
  8. fenderhutz

    fenderhutz Supporting Member

    Joined:
    Jan 28, 2007
    Location:
    Harpers Ferry WV
    Unless you have a SVT.
     
  9. Stingray_EB

    Stingray_EB

    Joined:
    May 1, 2006
    Location:
    Edinburgh, Scotland
    Also no one has actually said that your head will not be able to handle a load of 2.6667 ohms so do not add a 4ohm or 8ohm cab. I'm afraid you are stuck with only one 4ohm cab or 2 8ohm cabs. Sorry.
     
  10. jmac85

    jmac85

    Joined:
    Mar 22, 2008
    Location:
    Duluth, MN
    I've got the Hartke HA4000 and soon plan on getting the GK 700RB-II once I start gigging again (our drummer works on the Great Lakes Ore Boats :rollno:)
     
  11. KJung

    KJung

    Joined:
    Apr 9, 2005
    Location:
    Wisconsin and Upper Michigan
    Actually not true at all. A head has no idea if each cabinet has a different impedance or the same... all the head 'cares about' is the total nominal impedance, which in this case would be 2.67 ohms. As long as the head is safe down to 2ohms (which the OP's heads are not, now that he listed them), you would be fine.
     
  12. KJung

    KJung

    Joined:
    Apr 9, 2005
    Location:
    Wisconsin and Upper Michigan
    Actually, from what I understand, tube amps are more sensitive to exactly matching the impedance of the cab (2, 4, 8, or 16 ohms, depending on the head) with the correct 'output' tap. A SS head doesn't care at all, as long as you don't go below the safe operating nominal impedance level.
     
  13. WillInDenver

    WillInDenver An ounce of perception, a pound of obscure. Supporting Member

    Joined:
    Mar 9, 2005
    Location:
    Denver, nee Austin
    +1. The head doesn't know that there is more than one cabinet connected to it at all.
     
  14. Jaco who?

    Jaco who?

    Joined:
    May 20, 2008
    The 700 RB-II runs at a minimum of 4 ohms. You neglected to mention the impedance of the cab you have now - it's kinda important, since a 4 ohm cab combined in parallel with anything else you buy will total less than 4 ohms.
     
  15. touchdown!

    touchdown!

    Joined:
    Jun 2, 2008
    From what I have been told, a 4 ohm cabinet will get twice the amount of power as an 8 ohm cab if they are hooked up together
     
  16. KJung

    KJung

    Joined:
    Apr 9, 2005
    Location:
    Wisconsin and Upper Michigan
    Correct. That's why an 8ohm 210 and a 4ohm 410 with a SS head that is safe down to 2ohms (or at least 2.67 ohms like the Glock Heart Rock, for example) is a very cool modular rig, with each of the 6 10" drivers getting the same power.
     
  17. Baird6869

    Baird6869 Supporting Member

    Joined:
    Feb 16, 2007
    Location:
    Toronto, Ontario, Canada
    Disclosures:
    Nobody is stupid enough to actually pay me to play their gear.
    Sorry for the sidetrack, but if one has an SVT head (2 or 4 ohms) can the head be hooked up to one or even 2 8ohms cabinets?

    I am using an SVT with a Sadowsky 4ohm cab but my various Ampeg cabs are all 8ohms.

    Thanks!
     
  18. hpebass

    hpebass

    Joined:
    May 28, 2008
    2 8 ohms + 1 4 Ohm= 2 ohms
     
  19. ErnieD

    ErnieD Supporting Member

    Joined:
    Nov 25, 2004
    Location:
    Atascocita,TX.
    KJung, I see where a couple times you mention the smaller cab, such as a 210 is better at 8 ohms. Is there a benefit to this? I run a 215 w/ 212 and they are both 4 ohm cabs, bringing my GBE750 head to 2 ohms. Is there a downside to this setup or is the former just your preference? I only have 3-4 ohm cabs that I mix n match but based on another thread you posted similarly. I wondered if my next, possibly 210 cab, should be a 8 ohm? Just wondering, why you suggest this.
     
  20. KJung

    KJung

    Joined:
    Apr 9, 2005
    Location:
    Wisconsin and Upper Michigan
    No, I'm only talking about combining a smaller and larger cab. It would make very little sense to combine a 4ohm 210 and a 4 ohm 410, where the 210 gets the same power delivery as the 410.

    As a stand alone, most 210's and 112's can be easily driven to 'full power' by the 8 ohm output of most amps. Of course, lower SPL 210's like the Acme's and the older Bergantino models cab benefit from 4ohm versions in stand-alone use.

    My 8ohm 210 deal was only in context that 210/410 stack with a SS head capable of 2.67 ohm operation.
     
  21. Tim1

    Tim1

    Joined:
    Sep 9, 2005
    Location:
    New Zealand
    To Baird6869: as I understand it, while tube amps do prefer to be correctly matched to the right impedance, the rule of thumb is that if you must mismatch make sure that the speaker impedance total is lower than the tap (opposite to a transistor amp). There are many posts on this - probably hundreds. That is, if you are running into a 2.67 ohm load from a tube amp you should connect it to the 4 ohm output, not the 2 ohm. A tube amp will give you its rated output no matter what the speaker load. When I had my SVT2 I asked Ampeg if I could run an 8 ohm cabinet and they said it would be fine and to use the 4 ohm output tap - I have since learned that this was not the best advice. You will be fine running two 8 ohm cabs as they will equal 4 ohms, so use the 4 ohm output. Note: I am not a techie - most of my "knowledge" comes from listening to others such as PsychoBassGuy and learning from my mistakes. No doubt PBG or others will correct me if I have erred here.
     

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