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Matching Speaker Ohms to Amp

Discussion in 'Amps and Cabs [BG]' started by Koiman, Apr 27, 2006.


  1. Koiman

    Koiman

    Aug 19, 2005
    Just for the heck of it I decided to check the resistance (ohm value) of my 4 ohm cabinet and found that it was a 3.1 ohm cabinet. My amp is rated for 4 ohms. I installed a 10 watt/1 ohm resistor in series with my speakers and now have a 4.1 ohm cabinet. It makes me feel better but I'm not sure if it was really necessary and can't hear any difference. Has anyone else encountered this situation or done anything about it? Thanks for any ideas.
     
  2. 12bass

    12bass

    Jan 2, 2003
    Victoria, Canada
    The DC resistance is nominally around 3 ohms with a 4 ohm cabinet. All you are doing with the resistor is burning up your amp's power as heat.

    Check out this link: http://www.epanorama.net/documents/audio/speaker_impedance.html

     
  3. Koiman

    Koiman

    Aug 19, 2005
    Kevin, thank you for the education. I didn't know that there should be a difference between D.C. resistance and nominal resistance. I'll be removing the resistor from my speaker cab tonight. Glad to hear that my 4 ohm cabinet really is a 4 ohm cabinet and not burning up my amp.
     
  4. Koiman, remove the resistor.

    Impedance is the total load presented to the amplifier. It is not just simple DC resistance as you measured, and is always higher. It is frequency dependent, as well as responsive to cabinet tuning (sealed, vented, horn loaded).

    Impedance is a function of the driver operating as a system in the cabinet, and under real world load. If you cab is spec'ed as 4-ohm nominal, the cab is just fine for an amp rated at 4 ohms. If the amp requires 8 ohms, your cab will fry the amp.
     
  5. 12bass

    12bass

    Jan 2, 2003
    Victoria, Canada
    You are welcome!

    He mentioned in OP that his amp is rated at 4 ohms minimum.... so no problem here.
     

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