4 cabinets with one head?

Discussion in 'Amps and Cabs [BG]' started by nutadactyl, Jan 12, 2009.

  1. nutadactyl

    nutadactyl Guest

    Aug 15, 2008
    I have a gk rb1001-2 700watt head and a 2x12, and a 4x10 avatar cab, the head only has 2 outs, but the cabs each have an in and an out, will it hurt anything if i run another two cabs with this head?
  2. rpsands


    Jul 6, 2007
    Yes, unless you get some series cables. The 1001-rb is stable to 4 ohms.

    Assuming all four of your cabs are 8 ohms, you should net 2 ohms when you wire them all together. This will not be good.

    The problem you're gonna have here is that if you have all 8 ohm cabs you're only going to get either 8 ohms or 2 ohms out of wiring (or 32 ohms, which is useless).

    So if you have 4 cabs, sharing around 500 watts @ 8 ohms, you're looking at 125 watts per speaker cab. That's enough to get something like +21 db. So say your cabs are all around 98db sensitivity, you're looking at:
    119db + 3 per cab == 128 db

    If you just run the two cabs at 4 ohms, assuming a realistic sensitivity of 98db again, you should get 700w @ 4 ohms, so 350w per cab.

    That will get you +24 db approximately for wattage, so 122db + 3 db for the extra cab, so 125db.

    Adding those two extra cabs should (if my calculations are correct) provide you with a not terribly audible increase in volume, due to the reduction in wattage.

    Edit: Plus the added expense of extra cabinets, buying series cables, and all that jazz. In short, I would not bother. Get a bigger amp if you need to run 4 cabs.
  3. rpsands


    Jul 6, 2007
    To add a little more info here, I think that the bare calculations of +3db per cab are probably not exactly correct here, unless we're assuming the exact same sensitivity. Even so I am not sure. Because you've got a drastically different number of drivers, I think there's going to be a lot of weirdness in the numbers I am not accounting for. My grasp of the db calculations is pretty tenuous when not dealing with only the same cab:p

    Regardless, this is probably a bad idea :)
  4. OnederTone

    OnederTone Aguilar Everywhere Gold Supporting Member

    Aug 15, 2002
    Thornton, CO
    Bad idea. Wave off Mavrick, wave off.
  5. Exactly, a good way so BBQ your amp or loose over half your volume if one side of a series string fails. Get a second 1001rb II amp slave it from the first head or get the 2001rb.
  6. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    my eden amp can handle 4, 8ohm cabs (equals 2 ohm load) if your amp only handles 4 ohm load min. then you can only run 2 8 ohm cabs or ONE 4 ohm cab...
  7. nysbob


    Sep 14, 2003
    Cincinnati OH
    If you had a kustom 400, no problem...:D

  8. How are you doing your calculations? Is it taking in consideration the excess heat that the wattage produces in the amp/speakers, thus output will be different to perceived volume? Also, more cabs move more air so is that taking this into consideration too?

    I don't know how it works exactly (forgotten a lot of stuff too), which is why I'm asking.
  9. rpsands


    Jul 6, 2007
    My numbers assume that the cabs are all the same and use standard formulas. I didn't think at all about heat or whatever, since from what I know it's a relatively minor concern.

    From my understanding:
    Doubling wattage nets a +3db increase in volume
    Doubling speaker cone area nets +3db increase in volume.

    1 watt into a 98db sensitivity cabinet nets you 98db.
    2 watts nets you 101db.
    4 watts nets you 104db.
    8 watts nets you 107db.

    And so on, until 128 watts nets you 119db.

    Then you double speaker area once, for 122 db. Then again for 125db.

    Haha, looks like I actually failed. You only get +3db when you double the speaker area, so if you follow the ideal scheme, you are getting exactly no increase in volume (+ or minus a couple db).

    This math is all idealized, and doesn't speak to things like on-axis/off-axis, and all that ******** that makes smart guys like BFM and Greenboy so popular :)
  10. JessyB96


    Dec 14, 2008
    Alberta Canada
    you should never run 4 cabs off one head neways u just shouldn't if u need more cabs run a slave of sorts its less dangerous. why do u need to be that loud anyways
  11. rpsands


    Jul 6, 2007
    There're plenty of amps out there that can push four cabs safely. Depends on the ohms the power amp is stable at, and whether it can crank enough watts to make it worth your while.

    I'd be pretty confident running four 8 ohm cabs out of a GBE 1200, for instance.
  12. Gruntollio Bass

    Gruntollio Bass Guest

    May 27, 2007
    Sydney (Australia)
    I would have no problem running 4 X 8ohm cabs through my Eden WT800B as I can run 4ohms per side.
    I'm usually plenty loud with just 2 410's though.
  13. Willem


    Dec 26, 2005
    To sum up: your amps can't handle less than 4 ohms. So you can run 1 4 ohm cab or 2 8 ohm cabs.
  14. IvanMike

    IvanMike TTRPG enthusiast, Happy, Joyous, & Free. Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    if you have more questions check out the ohms faq you can access by clicking the link in my sig. It sounds like you could use a primer on impedance.

    I wrote that because it seems like music stores and amp companies do a terrible job of informing the public (especially when purchasing). It always amazes me how so many people have equipment and never got any information on how to use it. :eyebrow:
  15. If you upgrade to the 2001rb you can run 4 8 ohms cabs per side (2X 540 watts = 1080 watts and 8 8 ohm cabs)
  16. Red Planet

    Red Planet Inactive

    May 29, 2005
    I'm cranky in my old age.
    Cool so now I can run home and hook up four 4 ohm cabs to my CA9 or RMX 2450 and kill anything in its path.

    Where is the Mad Scientist Smiley?
  17. And you base this opinion on what ?

    If your head can handle the ohms load, you can run as many cabs as you want off your head.
  18. MHensleyJr

    MHensleyJr Supporting Member

    May 5, 2008
    Redlands, CA
    Might be a dumb question, but what do you do if your amp only has 2 speaker jacks and you want to run 4 cabs? How do you go about doing it?
  19. Like others have said if the ohms don't fall below what the amp can run, then you're fine doing this. I use a Sunn Concert Bass Amp and a Concert Slave to run my 4 cabs(1x18,4x10,4x12,2x15). The amps are only 200 watts each, so chaining all my cabs to one amp would be pretty much pointless. But hooking it up this way if for some reason something went wrong with one cab, I wouldn't loose another one.

    Definitely check out the ohms FAQ in IvanMikes sig.
  20. You dont want to run 4 cabs do you. What you need to figure out is a cab configuration to give you a 4 ohm load, ie; one 8x10, two 4x10 (8 ohms each), 1x15 and 4x10 (8 ohms each), etc. The amp is more than powerful enough to deliver the volume.

    I am suprised there arent more amps that push a 2 ohm load though. Peavey and Carvins frequently do but most are 4 Ohm min.