Electret microphones trap charge in material so no external voltage is needed

Evidence

A variant of the condenser microphone, the electret microphone, is based on using an electret material, which has electric charge trapped within, between the electrodes so that no external voltage is needed. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 482

Categorization

• DEFINE: Defines the electret microphone as a self-biased condenser microphone.
• corroborated: 3 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 482