The opamp circuit shown in the first post here is not an amplifier because its gain is only 1 at low frequencies and it has a loss for frequencies higher than about 73Hz. An electret mic needs a gain of about 100 to 400 times.
The lowpass filter is very simple (only one RC) so its cut of high frequencies is very gradual. 364Hz is reduced a little. 3640Hz is reduced more. 36,400Hz is reduced much more but is still there.
An electret microphone has a Jfet inside that uses only 0.4mA. Its resistor to the positive supply should be 10k if the supply is 8V (9V that is filtered). A lower resistor value will load down the signal level because the output impedance of the Jfet is about 3.3k ohms.