The noise of an electret condenser microphone
mostly comes from:
1. Impure current source
If the direct current mix with the alternating current signal, we
will hear a stable level, low frequency and continual noise. We
can lead the power to the microphone directly, or set a non-join
circuit to filter the AC signal to improve the situation.
2. Mechanism design
The faulty mechanism design might cause the wind sheer sound or
resonant sound. Normally a deep curved sound hole is good to prevent
the ESD, but it has some bad influence on the sound; for example,
it is good for some frequency but some other frequencies might be
declined. Therefore we may get unnatural sound with buzz or noise.
3. The noise from signal
Microphone is a component to receive sound, which can receive wider
frequency range than human ears. Both high and low frequency signal
will transform into noise as a form of harmonic waves after being
received. An obvious example is that the noise happens when the
cell phone and the blue tooth are set too closely. Therefore when
we design the microphone circuit, we should keep it away from the
antenna or other components which might radiate signal.
4. Outer noise
Generally, the main noise is the sound of the wind. The users complain
about the unclear sound because the higher join capacity receives
the sound of the wind or breath. Modifying the join capacity (normally
around 0.022~0.1 u) can solve this problem.
On the other hand, if the outer sound (exclude the main sound) is
too louder, it means the sensitivity of the microphone or the loading
impedance is too high, what we can do is change to a low sensitive
microphone or to decrease the loading impedance.