Electret microphone

An electret microphone is a microphone whose diaphragm forms a capacitor (historically-termed a condenser) that incorporates an electret. The electret's permanent electric dipole provides a constant charge Q on the capacitor. Sound waves move the diaphragm, changing the capacitance C, which produces a corresponding voltage change across the capacitor of ΔV = ⁠Q/ΔC⁠. The electret's constant charge eliminates the need for the polarizing power supply required for non-electret condenser microphones, though a preamplifier is typically incorporated to boost the audio voltage signal.