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What would the ohms be?

Discussion in 'Amps and Cabs [BG]' started by xring, Jul 4, 2005.


  1. xring

    xring

    Sep 16, 2003
    Ohio
    ...if I ran 3 - 8 ohm cabs?
    Is the formula 8x8x8/24 or 8+8x8/24? Probably neither. :D
    Thanks, Randy
     
  2. xb100

    xb100

    Mar 24, 2004
    NH, In
    well 2 8ohm cabs will equal 4 ohms. Then if you add another 8ohm cab it will be somewhere around 2.62 ohms, or something.

    heres how it goes

    2 32ohm speakers will =one 16ohm load
    2 16ohm speakers will =one 8ohm load
    2 8ohm speakers will =one 4ohm load
    and 2 4ohm speakers will =one 2ohm load.
     
  3. xring

    xring

    Sep 16, 2003
    Ohio
    Quick math! Thanks! That's great as I have a 2 ohm capable head. Randy
     
  4. paintandsk8

    paintandsk8 Pushin' my soul through the wire...

    May 12, 2003
    West Lafayette, IN
    all three in parallel = 2.67
    all three in series = 24
    two in parallel plus 1 in series = 12
    two in series plus 1 in parallel = 5.33
     
  5. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    I believe it is Rt=1/((1/R1)+(1/R2)+(1/R3)). You can throw as many 'cabs' (1/Rx) in there as you like

    So that means for three 8ohm cabs Resistance total = 1/((1/8)+(1/8)+(1/8))

    or Rt = 1/(.125+.125+.125)

    or Rt = 1/.375

    or Rt = 2.666666666

    or Rt = 2.67 ohms

    :D

    Joe.
     
  6. xring

    xring

    Sep 16, 2003
    Ohio
    Alright now, You two are just being wise guys. :D
    Now come down to my level and talk sloooowly.
    If I daisy chain the 3 cabs, it is 2.67 right? :eyebrow:
     
  7. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Sorry to have contributed to your confusion!

    (But the formula is real.)

    Yes, you are correct.

    2.67ohms

    :D

    Joe.
     
  8. Also easier formula could be (R1xR2)/(R1+R2). Since the first 2 8's = 4 (easy enough to do in your head) just do (4x8)/(4+8)=32/12=8/3=2.67.

    For combining equal impedance cabs, i.e. all 8 ohm, the formula breaks down to just ohms/# cabs. 3 8 ohm cabs = 8/3 ohms. 4 8's = 2 ohm (8/4).

    Randy
    P.S. The formula above (R1xR2)/(R1+R2) does NOT expand to more than 2 cabs. You can't do (R1xR2xR3)/(R1+R2+R3).

    The formula mentioned earlier post (1/(1/R1+1/R2+...1/Rn) )can be expanded to add as many cabs as you want.
     
  9. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    Actually the formula is really simple if *all* are the same ohms:

    R/n

    Where n is the number of cabs :) So 8 / 3 = 2.67.
     
  10. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Nice!

    :D

    Joe.
     
  11. xring

    xring

    Sep 16, 2003
    Ohio
    OK guys, this is sort of related and I'm not quite sure. I have an Ampeg B4R head and the ratings are this:
    (2 ch. amp)
    500w X 2 @ 2 ohms
    350w X 2 @ 4 ohms or
    1000w Bridged @ 4 ohms.

    On the 500 X 2, is that 2-2ohm cabs or 2-4ohm cabs? Makes a big difference in my application. I totally get the bridged application (2 8 ohm cabs= 4 ohms), but I lose it going seperate channels.
    I believe the parallel vs series difference applies here, thus my total lack of understanding.
    Thanks for the help, Randy
    ps: I realize now that I can't daisy chain the 3 8 ohm cabs bridged as I can only go as low as 4 ohms bridged.
     
  12. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA

    Each side of your amp can go down to 2 ohms in any speaker configuration.


    It's easy...when bridged, you have one amp that can go down to 4 ohms. When operating with two channels you have two amps. Each one can go down to two ohms.


    Not sure what you mean about parallel/series. That has to do with speakers, not amps.

    :D

    Joe.
     
  13. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    AND...if you want to use all three cabs use two cabs on one side (4 ohms) and one cab on the other side (8ohms). That is perfectly o.k....as long as you are in 2 channel mode, NOT bridged.

    :D

    Joe.
     
  14. xring

    xring

    Sep 16, 2003
    Ohio
    Great. I think I've come away from this a little wiser. Nevermind the series/parallel question. :rolleyes:
    It's a bummer though. I was hoping to get max wattage stereo with 4 ohms per side, but that ain't 'happenen!
    I think 2 cabs per side at only 350w won't let the cabinets speak as they are rated at 1700w rms per side!
    Much appreciated.
     
  15. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Yeah, bummer. Max wattage per side is definitely 2 ohms.

    But...max wattage bridged is 4 ohms. You can run 2 8ohm cabs and get max wattage.

    What cabs are you using? That sounds real high. Are you sure you are not referring to peak wattage instead of RMS wattage?

    If your peak wattage is 1700w then your rms wattage will be anywhere from 425 to 850w depending on how the manufacturer measured it. Commonly it would be 425w

    Or are these custom cabs?

    :D

    Joe.
     
  16. xring

    xring

    Sep 16, 2003
    Ohio
    Well the cabs are the Avatars. B212 Delta is rated 1000w rms. Also a B210 Delta for 700rms. I was going to get another cab for tonal options, but since that wouldn't really be feasible, I considered getting two more cabs for a monster rig. It would require more power for that, and realistically, I don't need it. I already do bridge them for the 1000w, but the B4R offers so many hook up options, I just got to thinking. (I ought not do that!)
    I could run a separate power amp in at say...2500watts, but I think I'll pass!

    r
     
  17. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    i think i'm gonna unstick the FAQ and all the threads linked in it like the OHMS FAQ because apparently, no one reads them. :rolleyes:
     
  18. xring

    xring

    Sep 16, 2003
    Ohio
    Don't unstick it on my sorry account. I just blew it and will shut up now...
    Randy
     
  19. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    Man, I don't really wana calculate how many watts each speaker would get in those set ups... :smug: