Hmm, Ive been doing a bit of searching and I read that the resistor should equal the microphone impedance, which in this case is 680. Is this incorrect, an over simplification, or...?

 

Nearly every electret mic is powered from a decoupled 10k resistor from a 9V supply. Then their current is 0.5mA (like on their datasheet) and they have a voltage drop of 5.0V.
When the powering/load resistor is less then the output level is less. I measured many electret mics to have a 3.3k ohm output impedance that becomes 2.5k when in parallel with the 10k powering/load resistor.

Please post your complete schematic showing how you power the mic.

 

Here is what I currently have built. I guess I will replace the 680 ohm resistor with a 6.8k ohm and couple the power supply to ground through a capacitor.

EDIT: Will a 5V power supply be adequate, assuming I choose a resistor value to match the necessary current?
EDIT2: replacing the resistor with a 10k ohm resistor certainly made it more responsive.