The major advantage of the RF-principle is the low impedance of the capsule. For example, a typical condenser microphone capsule with a capacitance of 50 pF has an impedance varying between 160 MΩ at 20 Hz and 160 kΩ at 20 kHz. The same capsule in a 8 MHz RF-bias environment has an impedance of less than 400 Ω!
This makes the transducer far less sensitive to interference, moisture and other contamination, and easier to interface with solid state circuit topologies. Since the frequency deviations caused by the sound induced capacitance changes are relatively small, any potential artifacts are negligible and far lower than possible with conventionally DC-biased alternatives. Even without exotic design the self noise of RF-biased microphones is less than what can be achieved with equivalent traditional DC-biased circuits.
Furthermore, RF-bias enables push-pull microphone designs, completely symmetrical and balanced from capsule to output, which nicely does cancel all nonlinear capsule distortions.
A Sennheiser white paper written by their lead professional microphones development engineer and researcher Manfred Hibbing on the subject of RF-condenser microphones is available in PDF-format, but restrictions on this forum do not allow attachments in that format. Contact me for a copy at
[email protected]