Electret Microphone Question

Discussion in 'General Electronics Chat' started by aeson25, Jul 29, 2010.

  1. aeson25

    aeson25

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    In an electret microphone, what is the purpose of the resistor (lets call it R2) in series from the power supply to the mic? Does this have an effect on sensitivity? I've seen a lot of site saying that it can be 1-10kOhms and that the internal load resistance of the mic has an effect on the sensitivity, but not much on why the R2 is there and if it effects the output. I understand that it limits current if too high, but is that it? Can I just connect an electret without the resistor? It's also confusing since some sites call this the load resistor while others call the resistance between the output and ground the load resistor.

    Thanks
    aeson25, Jul 29, 2010
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  2. aeson25

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The electret microphone has only 2 connections. It required power. It also has to output a signal. Without the resistor, the microphone would have to load the battery to create a signal (and that's either undesirable, or impossible, or both).

    The resistor limits the current available to the microphone. As its resistance changes the electret and the load resistor act as a potential divider and the signal is produced at the junction of these 2 resistances.
    (*steve*), Jul 29, 2010
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  3. aeson25

    aeson25

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    Ok, so the electret mic and the resistor "R2" act as a voltage divider and basically determines where the static output voltage will lie. Will this effect the sensitivity of the mic? Again, I understand the limiting part, but will there be any other effect? I need to get the pressure measurements and want to make sure different resistors won't effect sensitivity.

    Thanks again.
    aeson25, Jul 29, 2010
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  4. aeson25

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Different resistor values will affect the voltage swing you get for a given sound level.

    Using the same value resistor (and the same voltage supply, and the same type of electret microphone) would be the first step in building multiple circuits with the same response to sound. Another step would be calibrating them (even if just against each other) as there is also bound to be some additional variation due to component tolerance etc.

    This has the following statement:

    (*steve*), Jul 29, 2010
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  5. aeson25

    trobbins

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    trobbins, Jul 30, 2010
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