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2.67 ohm setup question

Discussion in 'Amps and Cabs [BG]' started by Happy MurphDay, Oct 1, 2004.


  1. Happy MurphDay

    Happy MurphDay

    Mar 9, 2004
    around
    Hey guys, I have done searches but couldn't find a quick answer for this question, If you have two cabs, one is a 8 ohm and one is a 4 ohm, when you put them together, the total load is 2.67.

    my question is, (if they are the same cabs, just different ohms) will there be a difference in sound and volume if you have a amp capable of driving a 2 ohm load.

    would there be a noticable difference or nothing big between the two cabs? or should i get a stereo power amp and turn up the 8 ohm cab a little more?
    thanks for the help
     
  2. basss

    basss

    Aug 27, 2001
    NYC
    It depends on the sensitivity and overall sound of each cab. When I used my EA wizzy and Cxl 112 together they actually were very close in volume with the 4 ohm wizzy being slightly louder. This is what you would expect when looking at the specs since they have identical sensitivity ratings. Furthermore, the sound of these two cabs are quite different so one wasn't covering up the sound of the other but rather filling in frequencies that that the other was lacking. I would guess that if you have similar sounding cabs and the 8ohm cab has a lower sensitivity you won't get a great balance.
     
  3. bigbeefdog

    bigbeefdog Who let the dogs in?

    Jul 7, 2003
    Mandeville, LA
    Good question.

    The output signal from your amp, like water in a plumbing system, seeks the "path of least resistance". So from a circuit standpoint, most of your power will be delivered to the 4-ohm (lower impedance) cab.

    However, watts vs. dB's (loudness) have a logarithmic relationship. A doubling of power results in a barely-noticeable 3 dB increase in volume. An increase in volume that sounds like "twice as loud" to your ears actually requires *ten times* as much power. So even though there may be a significant difference in power *delivered to* each cab, that doesn't always (or even often) translate to a significant difference in *volume out* (SPL) of each cab.

    In most instances I've encountered, sensitivities being equal, there's not a dramatic difference between the output of your two cabs in a 4/8 ohm rig.

    If the head can handle a 2-ohm load, as you said, you can go ahead and give it a try; you won't hurt anything.
     
  4. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Since Happy MurphDay wrote (essentially) identical cabinets except for impedance...like two Goliath IIIs or two Avatar B410s, etc... In theory, the 4 ohm cabinet would be 3 dB louder.

    With manufacturing tolerances and such, you may not even notice a volume difference. When you're playing in a band, I'm pretty darn sure no one would notice a difference.

    If you already have the two cabinets, don't worry about it (since your amp can handle 2 ohms). If you don't, I'd stick with 8 ohm cabinets.

    I find that I worry about this kind of stuff way too much...
     
  5. Happy MurphDay

    Happy MurphDay

    Mar 9, 2004
    around
    how much louder is 3 DBs?
     
  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
    Barely discernable by ear.
     
  7. Fuzzbass

    Fuzzbass P5 with overdrive Supporting Member

    What two cabs are you running?

    A not-uncommon 2.67 ohm stack would be an 8-ohm 2x10 over a 4-ohm 4x10. As noted, the 4-ohm cab will receive twice as many watts. But it has twice as many speakers... so, each speaker will receive the same amount of power.

    But even when running identical cabs, the difference is just 3db... so, you should be fine. Note that I often run a 2.67 stack from one channel of my amp (Berg 310 and Berg 115). The speakers blend very nicely.
     
  8. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    i thnk you know all of this but i love posting this link.... :p
    ohms info - check out the last paragraph on the 1st post
    thwe subject has pretty much been covered but i'll add my 2 cents.
    as long as your amp can handle a 2 ohm load i would experiment as much as possible. These things arent always intuitive. For example, a lot of cats used a stack of an eden 210 and 410, both 8 ohms, on a single 4 ohm head. If you thought about it too much it would seem like the 210's drivers would be louder than the 410's, but in practice it sounded fine. And fuzzbass presented the opposite scenario with a 4 ohm 410 and 8 ohm 210. In theory an 8 ohm cabinet with equal sensitivity wil lsound 3 dB quieter than the 4 ohm, which (as has been stated) is just noticeable. However, the tonal charactaristics of the cabinets also come into play. Sometimes cabs of equal sensitivites will sound louder or quieter depanding on how they are voiced.
    I just fried 1 side of my 2.1 this weekend. I was running a bag end 210 (4 ohm) on one side and a 115 (8 ohm) on the other side. As the stewart 2.1 will handle a 2 ohm load per side i plugged both cabs into the good side. The cabs are rated at the same sensitivity (or really close), but i heard the 115 just fine. The 115 does have a more present midrange than the 210 so i think that was a factor.
    The moral of the story? experiment.
     
  9. Happy MurphDay

    Happy MurphDay

    Mar 9, 2004
    around
    Thank you...

    Makes sense, gives me a great reason to fufill my G.A.S., experimentation...