Electret mic needs a pullup R to determine gain and DC quiescent point. (+) input needs to use same DC voltage rather than Gnd, but a bigger LPF <50Hz to remove audio, then Vout is near 0Vdc.
Thank you for your help. My purpose is to build a glass-break detector that want to put the voltage after the filter in A2D input of a microcontroller.
I doubt if I need to add something else to the circuit after the filter.