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Watts, ohms & impedance – what does it all mean?

Discussion in 'Amps and Cabs [BG]' started by Ozzel, Aug 17, 2004.

  1. I'm sure this question has been answered before, but I waded several pages deep in this forum and couldn't find anything. Can someone help me understand what these terms mean? I just want to have a basic understanding of amplified sound, and a simple definition of watts, ohms and impedance and how they relate to each other should help.

    Thanks, all!
  2. If you just looked back you might not find anything. Try the "search this forum" feature, because there has been many threads abou this subject.

    In the mean time read this tongue in cheek article. It really is based on some basic theory.

  3. Juddium


    May 24, 2004
    Haha, interesting article...not completely accurate, but close enough for a beginner.
    I'm assuming you don't know anything about a circuit at all. Basic DC circuits have components in them such as resistors, capacitors, and inductors. These can be used in AC circuits as well, but figuring out the numbers gets a little tricky.
    Basically, impedence is to AC circuits what resistance is to DC circuits (sort of. there's a little more involved, but that's the jist of it). The way it works in DC circuits is, voltage = amps x resistance. This resistance is measured in ohms.
    So if you have a 12 volt DC circuit with an 8 ohm resistor in it, you'll be pushing 1.5 amps through the circuit (provided the power source can crank that amperage out).
    Well that's for DC. But speakers are basically AC circuits. However, impedence is measured in ohms too...the same basic principle applies to AC circuits as DC circuits. You can add impedences like resistors - parallel resistors decrease the overall ohm rating, series resistors increase the overall ohm rating of the circuit. BUT, the impedance for each speaker doesn't change - the impedence of the whole circuit changes.
    (parallel is if you hooked the speaker wire from the positive terminal of each speaker into the amp, and likewise for the negative terminal - series is if you hook the positive of one into the amp, the negative of that one into the positive of the other, and the negative of the other into the amp. I think most speaker cabs are set up to run parallel, but this is useful for car stereos - my forte:)
    So, if you have 2 parallel 8 ohm speakers, the entire thing runs at 4 ohms (good for a 4 ohm amp) but each speaker is still 8 ohms. Your power gets cut in half for each speaker - the whole circuit runs at whatever your amp is set to run at for 4 ohms, but each speaker only gets half the power (power, measured in watts).
    I forget exactly how watts is computed in circuits, but if I'm not mistaken it's some factor of amps and volts. Actually, I think it's Power = Amps x Volts. Not really necessary to know that, but the basic concept is watts are the power to run speakers. You have to throw amps across the speaker to get it to move, some move with less amperage than others. Throw too much over the speaker, you blow it. Throw too little, you don't hear diddly squat.

    whew. and it's been a couple years since my last physics class, surprised I remember all that.

    Hope this helps, if there's anything I can clear up let me know
  4. All I know is if you buy two 8 ohm cabinets and put them together it makes them a 4 ohm stack which runs them louder considering your head can handle 4 ohm and 8 ohm loads. Same works with two 4 ohms becoming 2. Oh and the more watts you have the louder you can go. I'm so uneducated haha, but that's the way it works if you dumb it down a lot.
  5. Juddium


    May 24, 2004
    yeah, that's a good way of putting it
  6. CrazyArcher


    Aug 5, 2004
    Hahaha! One funny story :) Yet enough to make someone who doesnt kow anything understand the matter more or less...
  7. TheChariot


    Jul 6, 2004
    Boston, MA
    I'm a meer 17-year-old... and I was lucky enough to have a full-stack donated to me at the age of 15. The sound wasnt all that it was cracked up to be... until I educated myself and realized that the people who gave me the stuff gave me two 4ohm cabs and a head that doesnt operate at 2ohms.

    Where did I learn this?


    Analyze all of the specs of the heads and cabs... you'll start to put 2 and 2 together a little bit. Check out the FAQ section too. And DEFINATELY take a look at the owner's manuals for the B-Series and Pro-series heads. OBVIOUSLY I learned a lot more when I stumbled upon Talkbass... but Ampeg's website does a good job of laying out specs for beginners.... despite the crappiest forums I've ever been too. However, I'm indebted to those forums, because someone there turned my onto Talkbass... where I received (and still am receiving) an imense amount of knowledge about Bass equipment and technology.
  8. jiant.


    Jul 3, 2004
    Fort Mill, SC
  9. TheChariot


    Jul 6, 2004
    Boston, MA
    Oh.. you dont want it the way I got it, bro. Chemotherapy, radiation, surgery... 9 months of that. It's a crappy road, but I learned more than I lost.

    Not to mention a killer PA/Mixer, Guitar Combo, drumset, Bass rig, and a Stingray that I got so customized I came to hate it. :D

    ::3 Cheers for the Make-A-Wish Foundation:: :smug: