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.