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  • A Visit from the Wizard of Ohms

    For those of you who want to know what the heck an "Ohm" is, but were too shy to ask, here's a great explanation from the Row's own DaveB.

    "Ohms are the unit of measurement for electrical impedance in alternating current (ac) circuits. The omega symbol
    Ω
    is often used to specify ohms on spec sheets instead of spelling out the word "ohms." In order to operate at peak efficiency, the output impedance of the source (bass amp) must match the impedance of the load (speakers). You may have noticed that speaker cabinets are generally either 4 ohms or 8 ohms. If you hooked up two 8 ohm cabinets to the amp you would have a total impedance of 4 ohms. Likewise, two 4 ohm cabinets would be a 2 ohm total impedance load. The reason that the total impedance is less than the individual impedances of the individual cabinets is that they are connected in parallel. Think of it as if the amp is a bucket of water. If you punch a hole in the bucket the size of the hole will determine the amount of impedance to the flow of water. Bigger holes equals less impedance. Likewise, multiple holes of the same size will also decrease the impedance to the flow.


    The switch on this particular amp allows you to match the output impedance of the amp to the total impedance of the connected speakers."
    DaveB
    Comments 5 Comments
    1. Elmeaux's Avatar
      Elmeaux -
      This was indeed a great explanation. He was referring to the Bassman 300 Pro amp I had seen in the music store. When it said it had a switch on it to adjust the ohms, I had asked if one of our beloved "gear heads" could explain what that meant to those of us (meaning me) who are electronically challenged.

      Thanks, DaveB.
    1. thunderman's Avatar
      thunderman -
      Thanks, DaveB! Good stuff!
    1. slejhamer's Avatar
      slejhamer -
      We should note that the amp rating is usually the MINIMUM impedance. For example, you should not attach two 4 ohm cabs (a combined 2 ohms impedance) on an amp that specifies a minimum 4 ohms. I like fog effects on a stage, but smoke from an amp is not a good thing ...
    1. DaveB's Avatar
      DaveB -
      Slejhamer,

      That's because smoke is the magic that makes electronics work. When you let the smoke out the amp stops working. :-)

      Seriously, that is an excellent point. One that I should have made in the original post.

      Cheers,

      DaveB
    1. TobiasMan's Avatar
      TobiasMan -
      You can normally use a cab that has greater impedance (like an 8 ohm cab on a 4 ohm minimum amp) without any damage, it just results in lower power to the cab.
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