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is 2-4ohm cabinets better or is 2-8ohm?

Discussion in 'Amps, Mics & Pickups [DB]' started by Humph, Mar 24, 2005.


  1. Humph

    Humph

    May 23, 2004
    Warren, NJ
    Hey, I was wondering if it made any difference in loudness, efficiency or sound having two 4ohm cabinets into a iamp800(800watts@4ohm) or 2 8ohm cabinets.
    The amp can handle 2ohm loads so that wouldn't be a problem.
    Also having a combo like one 4ohm & one 8ohm is something like 2.67ohms. Is the 4ohm cabinet gonna be favored by the amp or will the cabs be equally favored? I don't even know if it makes a difference.
    I was thinking of getting an acme b-2(4ohm) & put it with an EA wizzy(8ohm).
    Any help is appreciated :help:
     
  2. Even if an amp is rated at 2 ohms minimum load, I believe it's not a good idea to run it there. Amps generate enormous amounts of heat when run at 2 ohms, and heat is the enemy of electronic components. If you want your amp to last forever, to always be 100% reliable, and never need servicing, then 4 ohms is the minimum, IMHO. I also believe (some may disagree) that there is a tonal degredation when run at 2 ohms. You can run at 2.67 ohms, but one cab will be favoured, and once again I believe two 8 ohm cabs is the optimum. Two 8 ohm cabs, each running at max efficiency, is going to be better sounding and probably louder than mismatched cabs. None of this is based on scientific analysis, just my 20 odd years as a gigging bassist.
     
  3. Isn't the wizzy a 4 ohm cab?
     
  4. Uncletoad

    Uncletoad

    May 6, 2003
    Columbus Ohio
    Proprietor Fifth Avenue Fret Shop. Technical Editor Bass Gear Magazine
    I have an IAmp 800. I've run it at 8,4,6,2.?, and 2 ohms full out all night on many different occasions.

    I'm pretty sure you can't break it. Sounds great no matter how it's hooked up.

    I'm not to sure about your speaker choices though. I'd try to demo that mix before I plunked my dough down. How about another Wizzy? I hear two sound really nice together although I've never heard that for myself. I rarely get good tones out of mismatched stuff. The EA cabs all sound great.

    Consult with Tom Bowlus for that evaluation.
     
  5. Kevinlee

    Kevinlee

    May 15, 2001
    Phx, AZ..USA
    I run a ai clarus-2 with two 4ohm cabs which puts it at a 2ohm load, all the time and I've never had an issue with it. I ocasionally run it at 4ohms with just one cab and I don't notice any difference as far as tone degradation.

    The clarus delivers 300 watts at 2ohms so I do this for the extra headroom. But the iamp 800 gives you 800 watts at 4ohms so I would think two 8omh cabs would be the way to go with that amp. And like Marty said the amp doesn't have to work as hard at 4ohms.

    I use to have one of the original iamp 500, the white one. Those Iamps are sure nice sounding amps.

    Kevinlee
     
  6. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    Assuming the amp can handle the 2 ohm load (and I have been assured that the EA amps can), you will be drawing twice as much current with the 2 ohm load as with the 4 ohm load. That translates, ideally, into twice as much power, and 6dB more perceived volume- not as much as you'd think ;-)

    Overheating is rarely a problem with switching amps (like the EA or AI amps) run at rated levels. The output transistors are always either fully conducting or totally cut off, so very little heat is generated. My Clarus doesn't get perceptibly warm running into a 4 ohm load for a few hours.
     
  7. Humph

    Humph

    May 23, 2004
    Warren, NJ
    Yeah, you are right.

    So it seems that 2-4ohm cabs are more power and sound efficent but 2-8ohm cabs are better for lessening the load on an amplifier. At least that is what I can assume.
    Mixing the 4ohm with 8ohm isn't necessarily bad for the amp but it isn't the most efficent way to bridge cabs. Matching cabinet impeadence is much better, whether it is 2-4ohm cabs or 2-8ohm cabs.
    I also think the EA iamp800 can handle a two ohm load pretty well. I do see your point about making the amp last as long as possible by not running a 2ohm load on it.
     
  8. robgrow

    robgrow Supporting Member

    May 1, 2004
    Cincinnati, Ohio
    Humph,

    I'm not sure if I understand your post, but keep in my mind that speaker efficiency and sensitivity are not directly related to rated impedance. While you can almost certainly develop more power with most modern amps into a 4-ohm dummy load resistor than you can into an 8-ohm speaker, the speaker is always going to be much louder(!), since the dummy load's efficiency is essentially zero.

    Like others have said, I'd want to hear the Acme and EA cabs together before buying. Might sound great, might not. Trying it is the only way to tell for sure. Specs alone don't tell the entire story.

    Also as others have said, you should be OK running any Class D amp at or near its rated minimum load impedance.

    Good luck.

    -bob
     
  9. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    Mmm... nope.

    If the amplifier is designed to handle the load, you're not doing yourself any favors by buying an amp and then only using a quarter of its power or dynamic range. A friend who posts here occasionaly had some conversations with EA's head tech, who assures him that you can run an i800 into anything shy of a dead short without problems.
     
  10. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    Untrue.

    At a given volume, with cabinets of similar efficiency, the amp doesn't "work harder" with lower impedance cabinets.

    Consider a 4 ohm cabinet rated at 103dB/Watt, and an 8 ohm cabinet rated at 103dB/Watt. (For instance, the EA Whizzy and the EA CXL-112).

    The amp will have to supply*exactly* the same power- 1 watt- to produce that 103dB with either cabinet. The current and voltage will be different, but the product- I*R - and thus the output load on the amp, will be exactly the same.

    Of course, with a lower impedance, the amp will be able to run closer to its rated power.
     
  11. I stand corrected. My comments were based on the use of conventional amps, such as my Eden. I'm not conversant with the latest generation of amps with switching power supplies, etc.