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Mixing 4/8 ohm cabs

Discussion in 'Amps and Cabs [BG]' started by seanm, Aug 27, 2005.


  1. seanm

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

    Feb 19, 2004
    Ottawa, Canada
    So I purchased an EA 500c. This is a 4 ohm wizzy cab with a space on top for the iAMP500. Makes a nice light combo which is pretty loud.

    But I will be playing in a 7 or 8 piece band tomorrow and I wanted a bit more volume. So I tried it today with my other cabs, both of which are 8 ohms.

    Paired with the LDS 12"-6", there was no appreciable volume difference from the wizzy alone. However, with the CLX-112 there was a big difference!

    I would say that pairing the wizzy and the CLX also blends the strengths of the two. You get more mids from the wizzy and the CLX adds some of the bass that the wizzy lacks.

    I have some samples here: ftp://ftp.seanm.ca/shootout/

    The naming scheme should be obvious ;) However, the samples do not really do justice to the combinations. Especially the CLX/LDS pair. This is a *very deep* combination and the depth gets lost in the samples.
     
  2. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    yep been there, done that (almost - different cabs)

    if your head will do 2 ohms ok, then the 2.67 ohm load of a 4 and 8 ohm cab is no problem. what you discovered is the difference in power and sensitivity can be a problem. in the 4/8 setup the 4 ohm cab gets twice the power, so from watts alone it should be 3 dB louder than the 8. However, in mny cases the 8 may have a sensitivity greater than the 4, and if it is 3dB greater, it all balances out. Except, the voicing of different speakers of the same sensitivity can make one speaker sound louder than the other. So, ultimately, you have to put down the slide rule and actually fire up the cabs to see what's what. ;)
     
  3. seanm

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

    Feb 19, 2004
    Ottawa, Canada
    IvanMike, I agree. It all comes down to sound. Numbers just give you a *hint* at what a cab can do.

    Both cabs have the same sensitivity 103dB @ 1m. But that is probably at 1khz. At bass frequencies, they are probably much different.

    I am really enjoying the synergy between these two cabs. I suck at describing sound, so I won't even try. Maybe if Tom Bowlus catches wind of an EA thread, he will read this and describe them togeather :D

    And yes, the iAMP 500 is 2 ohm safe. You just don't gain anything: 350 watts @ 8 ohms, 500watts @ 4 Ohms & 2 Ohms.
     
  4. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I would think that you'd never want to mix cabinets of different impedance...one is sure to develop a severe case of impedance envy... :D :bag:

    In all seriousness (like I have any credibility now...) looking at www.euphonicaudio.com, the 500 head puts out 350 watts into 8 ohms and 500 into either 4 or 2 ohms.

    Maybe I'm reading something into those specs, but it seems like the amp's power supply runs out of steam below 4 ohms. The output section can handle the increased current draw of a 2 ohm load but doesn't produce any more power (than at 4) because the power supply can't muster the needed voltage swing to produce more power. Make any sense?

    In the end, it's how it sounds that matters (as long as you're within the mfr's specifications) and if it sounds good with your mixed impedance rig...run with it!!!
     
  5. boogiebass

    boogiebass

    Aug 16, 2000
    I've used a Wizzy with CXL110 on top powered by the iAMP 500. Very nice rig; plenty of bottom and a bit more upper register articulation than two Wizzy's (which also sounds good but is VERY warm).
     
  6. seanm

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

    Feb 19, 2004
    Ottawa, Canada
    Yup. I believe you are correct. So plugging in the second speaker does not give me more watts.

    My real problem is that my *gigging* bass has very low output. I like to keep the master volume at 12:00 or below. So I need to compensate with either a preamp or more speakers.

    The advantage of more speakers is you push more air. You also get the 2nd speaker up higher. I also like the sound of the passive bass straight to the amp!
     
  7. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Sorry that I missed this one! FWIW, I think you described the sound pretty well. Of course, I tend to prefer two Wizzy's... :p
     
  8. I don't think the lack of extra wattage at the lower ohms will be a problem. you are only running the amp at 1/2 anyways... plus the extra speaker will make it louder, so you won't need to push it any harded.

    The EBS 350 is similar in that it has no increase in wattage output at 2 ohms, but "the total peak power increases by nearly 20% if you load the amp down to 2 ohms."
     
  9. bill spangler

    bill spangler

    Mar 4, 2001
    Albany GA
    :eyebrow:
    If one of your cabs has two 8 ohm speakers & your second cab has one 8 ohm speaker, then each speaker will see approximately the same power. So the fact that the 'two speaker' cab sees 2/3 of the power is not a serious issue. You have to remember, however, that the rated speaker impedences are only nominal and are not static. They depend on the frequencies produced and the volume. If your woofers are of different makes or models, it is possible that your total combined impedence can dip below what your amp is designed to handle. I had this happen to me when I tried using two '210' cabs of different makes such that my nominal impedience was 2 ohms, which my amp is designed to handle. When I turned up too much, then my amp's safety features shut it down temporarily. As long as your amp operates safely at 2 2/3 nominal ohms, you're probably fine. In addition, many modern amps have features which protect the amp in case you attempt to operate it beyond its designed capabilities.
     
  10. Steve Clark

    Steve Clark Supporting Member

    Jan 9, 2004
    London ON
    I think Sean may agree with you on that point now. ;)
     
  11. Output of your bass should have NO effect on where the master volume is. You should be boosting the input gain to compensate for the bass signal levels.

    Theoretically, the input gain and pads adjust for all the variations in input signal strength from the bass, so the preamp section gets the correct signal level regardless of bass used. If the preamp signal is the correct level, then there is no need to adjust the master volume to "compensate" as there's nothing left to compensate for. Input gain/pad took care of that.

    Randy
     
  12. seanm

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

    Feb 19, 2004
    Ottawa, Canada
    I had (notice the foreshadowing) the gain maxed out, so the only thing left to do was boost the signal.

    Yes, the whole argument is just academic since I now have two wizzys and am very happy with them. Thanks Steve.
     
  13. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    I figured that I would let you drop that one. ;)

    Tom.
     
  14. Wow, that's pretty unusual... something wrong with your bass or preamp input? An input pad that should be turned off?

    Randy
     
  15. seanm

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

    Feb 19, 2004
    Ottawa, Canada
    I am starting to wonder too. I have mentioned that I max out the gain a few times and nobody has ever chimed in with "me too".

    It is an iAMP 500. There is a passive and active jack and I use the passive jack.
     
  16. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    I agree that this sounds rather unusual. At least with the 800, you wouldn't want to be in the same room if the gain was maxxed out driving two Wizzy's! :eek:

    Tom.
     
  17. Steve Clark

    Steve Clark Supporting Member

    Jan 9, 2004
    London ON
    Sean,

    Send me an email or post here detailing the problem. If you can use EA speak just so we are thinking the same thing for your settings, meaning 'Level' and 'Main'. We can work with Gary at EA to sort out the issue.

    Steve