ELECTRET MICROPHONES

• An electret microphone is a specific type of condenser microphone that does not require a special polarizing voltage because its diaphram or back plate is permanently charged.
  
  
• Electret microphones are small, cheap, durable, and offer good performance at high frequencies. Most modern telephone handsets use electrets.
  
  
• The electrical equivalent circuit for a microphone is: Bridging refers to maximizing the output voltage by increasing the load impedance and/or decreasing the microphone impedance.
  
  
• Low impedance microphones have an impedance of 100 to 300 Ohms (more expensive); high impedance microphones have an impedance of 600 to 1000 Ohms (less expensive).
  
  
• Condenser microphones require a DC bias; balanced cables (XLR) are prefered over unbalanced lines (1/8" mini plugs) because the cables are more resistant to thermal and RF noise.
  
  
• Digital and wireless microphones are popular alternatives.