It may be piezoelectric film or a piezoelectric disc; will try both as must be very thin.
If the disc resonates at ~4KHz; it should be good for an intended 300Hz to 3KHz, as from this graph, right ?

----> https://upload.wikimedia.org/wikipe...ezoelectric_sensor_frequency_response.svg.png

It will be fixed not very distant from lips, about 1 inch. Considerations, please ?

 

Considering the mass of a piezo disc it may not be very sensitive as a voice mic (but ok as a drum-kit mic!). Any reason for not using a cheap electret mic capsule?