1. Aluminum ribbon microphone
For aluminum ribbon microphones, the aluminum ribbon used is both a microphone diaphragm and a conductor that moves in a magnetic field. The aluminum strip is usually made of aluminum silk, with a thickness of 0 to 1 mm, a width of 2 mm to 4 mm, and a mass of only 0.2 mg, in order to achieve a better transient response.
In order to obtain an ideal resonance frequency between 2kHz and 4kHz, the aluminum strip is made into a corrugated shape to maintain a precise tension value. The aluminum strip as a conductor and microphone diaphragm is suspended in the magnetic field between the two magnetic pole faces, vibrating with the frequency of the incident sound wave, and at the same time, a certain voltage output is generated at both ends of the aluminum strip.
2. Capacitive type
Condenser microphones have two metal plates, one of which is coated with an electret film (mostly polyperfluoroethylene propylene) and grounded, and the other plate is connected to the gate of the field effect transistor, the gate and the source A diode is connected between the poles.
When the electret diaphragm itself is charged, the amount of surface charge is Q, and the capacitance between the plates is C, then the ground voltage U=Q/C is generated on the pole head, when it is vibrated or rubbed by airflow , Due to vibration changes the distance between the two plates, that is, the capacitance C changes, but the power Q does not change, it will cause the voltage change, the magnitude of the voltage change reflects the strength of the external sound pressure;
The frequency of this voltage change reflects the frequency of external sounds, which is the working principle of electret microphones.
The diaphragms of condenser microphones are mostly polyperfluoroethylene propylene, which has good humidity performance, produces more surface charges, and is less affected by humidity. Because this kind of microphone is also a capacitive structure, the signal internal resistance is very large, in order to draw out and amplify the voltage signal generated by the sound, the output terminal must also use a field effect transistor.