Impedance Matching

Discussion in 'Microphones (live or studio)' started by ThirdBird, Oct 3, 2013.

  1. ThirdBird

    ThirdBird Active Member

    Dec 4, 2007
    Toms River, NJ
    I just acquired the PreSonus Eureka Channel Strip. It has a pre-amp, compressor, and eq for one channel. One of the knobs is the Impedance. From reading the manual, it says to adjust the knob to the impedance for whatever microphone I am using. It also says to try different combos to experiment, but that is all it says.

    I haven't gotten around to experimenting yet, but I certainly will. I am interested in the why/science behind this knob. What are some general reasons why it would be important to match it, or some reasons to make it different. How does this physically alter the sound in the audio science realm?

    And last question, will this ever be bad for the microphone or the channel strip, if I repeatedly and purposefully mismatch it?

    Above all, I know I have to try different things out, and the sound is always the final answer, but I am looking for more information. The internet has yet to help me out, so thank you if you can provide any illumination!

  2. Kurt Foster

    Kurt Foster Distinguished Member

    Jul 2, 2002
    77 Sunset Lane.
    you can't hurt the mic mismatching the impedance.

    impedance will affect the sound. properly matched impedance will sound full and robust. it will get thinner or vice versa depending how far you tweak it in different directions.

    ribbon mics usually have a very low impedance and will benefit most from this feature.
  3. Boswell

    Boswell Moderator Distinguished Member

    Apr 19, 2006
    Home Page:
    What the pre-amp input impedance controls depends on the type of microphone and its internal circuitry. With dynamic mics (and that includes ribbons), the load impedance controls the damping factor on the moving part (diaphragm or ribbon element), and so changes the response to transient sounds. A lower impedance gives greater damping, and this may result in a "cleaner" sound. However, there is also a straight voltage divider effect, and decreasing the input impedance reduces the signal amplitude. When the input impedance is equal to the microphone's output impedance ("matched"), you halve the voltage output, i.e. get 6dB less signal, but the damping factor is optimal.

    With mics such as condenser types that have internal circuitry and no output transformer, lowering the load impedance makes little difference (other than some reduction of amplitude) up to a point where distortion sets in. A condenser mic that has an internal output transformer is more susceptible to tonal change as the load impedance is varied. However, the change is usually due to the saturation characteristics of the transformer and its drive circuitry rather than anything to do with the transducer element.

    Note that most dynamic mics incorporate a transformer but without active circuitry, so they may also exhibit transformer effects in addition to element damping as the load impedance is varied.

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