A condenser microphone, which is also called capacitor microphone or electrostatic microphone, is an acoustic to electric transducer or sensor that converts sound into an electrical signal. Condenser microphones are used in a wide variety of applications, for example telephones, mobile phones, studio microphones and headsets.
The condenser microphone comprises a moveable membrane and an electrode or two electrodes. The membrane is arranged in parallel and spaced apart from the electrode or between the two electrodes. The arrangement of membrane and electrode(s) is called capsule. The membrane as well as the electrode are electrically conducting. Thus, a capacity is constituted. The value of the capacity depends on the area of the membrane and the electrode, and a distance between the electrode and the membrane. Intruding sound makes the membrane swing and thus the distance between the membrane and the electrode is changed. There are two operating modes for evaluating the change of capacity: The direct current (DC) biased mode and the radio frequency (RF) or high frequency (HF) mode. With the DC-biased mode the membrane and the electrode are biased with a fixed charge and a voltage maintained across the membrane and the electrode changes with the vibrations of the membrane. The RF or HF mode uses a comparatively low RF voltage generated by a low noise oscillator, at a frequency of several MHz, for example 8 MHz. The membrane and the electrode are part of a resonant circuit that modulates the frequency of the oscillator signal. Demodulation yields a low-noise audio frequency signal with a very low sound impedance.
However, due to the small distance between the membrane and the electrode, a dynamic range of the condenser microphone is limited and distortions are present when the membrane is largely deflected or touches the electrode. Furthermore, as microphones in general are sensitive to wind noise or acoustic pressure of high value and low frequency, also condenser microphones are sensitive to wind noise.
Therefore, there is a need for an improvement in operating a condenser microphone which makes the condenser microphone more robust against wind noise, increases the dynamic range of the condenser microphone, and reduces distortions.
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