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Yet another Ohmage question

Discussion in 'Amps and Cabs [BG]' started by Gomex, Mar 24, 2005.

  1. Gomex


    Jan 7, 2005
    My current rig is a warwick Pro Fet 4 (400 watts@ 4 Ohms) and an Eden cx410 (500 watts@8 Ohms) I am currently looking to buy a 15" extension cabinet. My question is that while it would be nice to find an 8 ohm cabinet it will be hard to do so on my budget, so If i were to get a 4 ohm cab it would bring the total ohmage to 6 ohms right, would my amp be okay running at 6 ohms?
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    FWIW, the correct term is Impedance (which is AC resistance).

    Connecting an 8 ohm and 4 ohm cabinet together in parallel (the common connection for multiple speaker jacks on cabinets and amps) will result in a total load impedance of 2.67 ohms.

    If the amp is rated for 4 ohms minimum, using a 2.7 ohm load runs the risk of damaging the power amp section due to over heating.

    I would have guessed that 8 ohm cabinets are more common than 4 ohm ones for single driver cabinets...
  3. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    1st, its not ohmage, it's impedance ;) 2nd your cab isn't 500 watts @ 8 ohms, it's an 8 ohm cabinet that can handle up to 500 watts. :D

    anyhow, adding a second 8 ohm cab will give you a total impedance of 4 ohms which is fine. adding a 4 ohm cab will give you a net impedance of 2.67 ohms which will fry your head. :meh:
  4. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    aw crap ya beat me to it.............. :p

  5. Nuh uh...it's omageosity. Eveybody knows that. :rolleyes:
  6. One thing i dont get tho . . . most of the time a 4ohm cab = the same price as an 8 ohm cab, well, with the peaveys it is anyways
  7. Why would it be any different? A 4ohm cab has just as many speakers, as much wood, electronics and labor in it as the same 8ohm cab does.
  8. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    I don't see how the two are related... Eminence usually offers any given driver in both 4 or 8 ohms (for 15s and 18s) and 8 or 16 ohms (for 10s and 12s)...the price is the same.

    Peavey probably offers a number of 4 ohm cabinets because most of their bass amps can drive 2 ohm loads. As we know from IvanMike's well-written Ohms FAQ thread (is that thread a sticky yet?), two 4 ohm cabinets in parallel equal a 2 ohm total load.

    Avatar's line of cabinets is usually available in a number of different impedances. Unfortunately, Avatars aren't easily available to our friends in Australia...
  9. fretlessrock

    fretlessrock Supporting Member

    Aug 8, 2002
    Dood, yer payin for half the ohms! You are so totally getting ripped off with a 4 ohm cab when you could be getting 8 for the same price.

    :bassist: :bassist: :bassist:

    Do I actually need to put a winking smiley at the end of this?
  10. Damn, I hadn't thought of that.
  11. Joe Beets

    Joe Beets Guest

    Nov 21, 2004
    I saw two 16 ohm ten inch speakers in the used gear pile at a local music store. But I didn't buy them. I feel so stupid. :rolleyes:
  12. Sutton


    Mar 3, 2005
    Plainwell, MI
    haha, damn, never thought of it like that....I've been getting ripped off for so many years :(
  13. If you're amp puts out 400W @ 4 ohms, it probably doesn't put out much more than 200-250W @ 8 ohms. You aren't coming close to driving the Eden to its full limits.

    Here's what adding a speaker does for you:
    Current setup: 250W into 1 cabinet.
    Proposed setup: 400W into 2 cabinets.

    I propose getting a bigger power amp, rated around 500-600W @ 8 ohms. That gives you:

    Better setup: 500W into 1 cabinet.

    This will give you more power, more volume, less weight, as most power amps are lighter than bass cabinets, and possibly cheaper as well, haven't priced speakers/vs/ power amps lately. That's assuming the speaker you want to get is the same efficiency as the Eden.

  14. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Maybe, but he's also tricking the amp into putting out more power than it was probably planning to... ;)
  15. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    i'm so buying 512 ohm speakers from now on.
  16. Haha, yeah, i was stating that they were the same, i thought the first post said something about 8 ohm ones being more expensive or something, damn, i gotta learn not to post on the net that early in the morning, my mind makes things up!
  17. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    ah, it's ok, we were laughing WITH you :p ;)

    it's not often we get something like that to chuckle over, although i think the cat that wondered if the transistor (actually a capacitor) that fell out of his cab was important, and if he should just shove it back in the port to see if it would magically re-solder itself in the right place wins. :D
  18. jjimm


    Mar 22, 2005
    I was driving ohm when I thought of this....
    Is impedance the only electrical factor for speakers? Wouldn't it make a difference if you have two speakers, both with the same impedance, but different sizes? Like a 810 cab on one side and 115 cab on the other side.

    If both are 8 ohms, the total impedance would be
    4 ohms (given, a parallel circuit). But wouldn't the resistance be different, making the larger speaker resistance (the 810 cab) draw more power, and be louder on that side?
  19. the individual impedance of speakers is not what is measured on the back,
    4x10 cab rated at 4ohms, each speaker is 16 ohms, and with an 8x10 rated at 4ohms, each speaker is 32 ohms, so it all cuts down to each cabinet taking the same, its not the individual speakers that are rated, its the overall impedance of the cabinet

    i may be talking ****e

    more than likely
  20. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    A loudspeaker system's impedance is by no means constant. It varies wildly with frequency. The number marked on the cabinet is the nominal impedance...hopefully (for our solid state amp's sake) the minimum impedance.

    In the 1x15 + 8x10 case, each cabinet would theoretically receive the same power. Each 10 would receive 1/8th of the power that the whole cabinet receives.

    The 8x10 has about 4 times more cone area than the 1x15 and is likely to be much more efficient...so it will be louder.

    The sensitivity rating of a cabinet will give you some insight to how loud it will be relative to other cabinets of the same impedance. Remember that sensitivity ratings are usually measured at 1 KHz.