The Noise Reason of Electret Condenser Microphone

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.

Condenser microphone and Dynamic microphone

1. Transform sound into electric signal- The best design in theory:The design of electret condenser microphones is based on the theorem that we use charging and discharging motionbetween electric capacity conductors. When the ultra-thin or gold-plating Mylar diaphragm response to the soundpressure level, it changes the static electricity between the conductors into electric signal directly. Then we can gaina proper output of impedance and sensitivity by the electric circuit coupling.
2. The characteristic of reappearing the original sound:To reappear the original sound is the highest performance for the acoustic specialist to achieve. If we check the basicdesign of the microphone, we can find a electret condenser microphone can transform the sound into electric signaldirectly, because it is not only manufactured with accurate mechanism technique, but also combine complicated electriccircuit. Therefore, with the excellent characteristic in advance, the electret condenser microphone must be your best choice.
3. Very wild frequency response:Diaphragm is a main component of a microphone to sense the sound and to transform it into the electric signal.The material and the mechanical design of the diaphragm decide the acoustics of a microphone. Due to the materialof the diaphragm is very thin and light, and can transform the sound into electric signal directly; the range of thefrequency response can reach to the ultra-low frequency (under 10 Hz), and the high frequency can also gets tosupersonic easily, which shows the characteristic of wild frequency response.
The diaphragm of the dynamic microphone loads a sound coil which is hundreds times heavier than itself. (Left picture)The diaphragm of the electret condenser microphone works without any load. (Right picture)

Acoustic keyword

W ( Watt ): A watt = a voltage x an ampere. For example, 330 Watt= 110V x 3 A.
V ( Voltage ): V is the unit of voltage, when it needs one joule of work to sent one coulomb of electric from one point to another point, then the potential difference between these two points is one voltage. 
Ohm: Ohm is the unit of impedance in electronics, the higher the impedance is, the less electric current can pass through. 
Hz( Hertz): The frequency of the sound waves vibrate every second. For instance, 100Hz means 100 times vibration in one second. 
dB ( Decibel): dB is the unit of the sound pressure level, which is calculated with logarithm, because the susceptibility to the sound of human ears is not linear. 
Fo ( Resonance Frequency): Fo stands for the resonance point of the speaker. The lower the Fo is, the efficiency of the low frequency is better. 
S.P.L. ( Sound Pressure Level): The volume of the sound. 
Vo-p: The measurement from Vo to the peak, to drive the magnetic buzzer, the waveform is 1/2 square wave. 
Vp-p: The measurement from peak to peak, to drive the piezo buzzer. The waveform is square wave.

Microphone Sensitivity

The sensitivity of the microphone is one of the most important factors, which affects the receiving result. The higher the sensitivity is, the higher the SPL can be received.Different from the production process of other products, the microphone is selected and sorted by its sensitivity after producing. We cannot get 1000pcs of what we need in sensitivity from just inputting 1000pcs of microphones’ material on the production line. Therefore, in order to avoid discontinuing the production, we had better choose the spec. usually with the sensitivity of -40 to -44, which is popular and easily produced.About the volume, we can still improve it by modifying the circuit, such as the impedance, the voltage, and the amplification factor.We suggest that do not choose a special spec. with very high or low sensitivity at first, or the problem of lead time and lacking of material might happen.