If a head says xx watts into xx or xx ohms?

Discussion in 'Amps and Cabs [BG]' started by MCBTunes, Feb 6, 2005.

  1. Ok well, if an amop head says it will play 350 watts into 4 ohms or 200 watts into 8 ohms does it mean

    if you have one 8 ohm cab it will shoot 200 watts into that cab and if you have 2 8 ohm cabs it will push 350 total so 175 into each cab? I can see how that would be a little louder but not much....

    what if you run it strait into a 4 ohm cab, thats 350 watts would that be the loudest?

    am i right? where did i go wrong here? :)
  2. ESP-LTD


    Sep 9, 2001
    All things being equal (which they are not) the 2 8 ohm boxes would probably be the loudest (more surface area). It might be a pretty subtle difference however; it all comes down to speaker efficiency and the 4 ohm model and 8 ohm model are probably different.

    Otherwise, you have a complete grasp of the issue.
  3. tommytoughnuts


    Jan 26, 2005
    do a search for ivan mikes post called Ohms FAQ. he'll answer all your questions
  4. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    You aint wrong dude, you got it!

    BTW, spec is specifications by the manufacturer in your manual.


  5. fdeck

    fdeck Supporting Member

    Mar 20, 2004
    Madison WI
    HPF Technology: Protecting the Pocket since 2007
    The acoustical power at a given distance is roughly proportional to the amp power times the total speaker cone area. For instance, start with 200 W into the 8 Ohm cab. Now plug in the second cab. You get 350/200 or 1.75X the power, but 2X the area, so the acoustical power goes up to 3.5X where you started from. This is 5 dB louder.

    Straight into a 4 Ohm cab would not be as loud as 2 cabs, "all other things being equal" which they are not.

    I am giving this rule of "power times area" as a rule of thumb, and there are a lot of factors involved if you are not comparing identical speakers. I actually consider cone area to be a better prediction of bass speaker efficiency than the rated efficiency, because the latter is subject to how it is defined by each manufacturer. The best thing would be a sensitivity versus frequency curve for every speaker on the market, but now I'm being idealistic.