Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What are balance input impedence

  1. Aug 20, 2005 #1
    lm doing an assignment regarding resistance may caused an error in the magnitude of the output voltage.
  2. jcsd
  3. Aug 20, 2005 #2


    User Avatar
    Science Advisor
    Gold Member

    You can't possibly expect a productive reply based on a post like yours can you?
  4. Aug 25, 2005 #3
    input impedance refers to an impedance value designed or set to result in a desired transfer of voltage or current to one device/circuit from another source.

    For instance, in audio circuits 'good' input impedance usually means that as seen from the terminals where another output device is to be hooked up to it, the effective resistance of the input circuit of a device is 100 or more times the internal resistance seen backward at the output terminals of the source device. This ensures that little current flows, but maximum voltage transfer is achieved between the source and input of the next device.

    In power circuits, the ideal impedance is based upon maximum power transfer or maximum efficiency of power transfer, *NOT* maximum voltage. Here quality of the signal is not important but direct transfer of energy is the key idea. So here, you might find that the internal impedance of the input circuit is only a bit higher than the output terminal internal resistance.

    In RF (radio frequency) circuits again the goal is slightly different. Impedance must be exactly matched between source and sink so that there is no residual reflection or waste of power or loss of signal.

    Balance usually refers to equality of power or centralized perceived direction of sound in a stereo or quadraphonic (or 5 way) speaker system. It results from roughly matching the overall power output from each speaker so that a stereo image is maintained and the sound is evenly distributed to the listening area and results in a realistic illusion of the original sound-stage.
    Last edited: Aug 25, 2005
  5. Sep 6, 2005 #4
    You have a point: my response was productive, but will it be understood by someone who can't string a sentence together?
  6. Sep 6, 2005 #5


    User Avatar

    Staff: Mentor

    Nice writeup Nam. The OP's use of the word "balance" confused me, so I waited to try to reply. I couldn't tell if he meant balanced versus unbalanced transmission lines, or matched impedances or whatever. (I didn't even think of the audio multi-channel balance angle....) Hopefully your answer helps him.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook