General index of the electret microphone microphones microphone general index (mi) : 1, the sensitivity (sensitivity) generally defined as: microphone acoustoelectric conversion efficiency. With the dB table. In the test standard of related microphone set to 0 db = 1 v, the sensitivity of the microphone as negative. For example: - 58 dB microphone sensitivity in between - 28-66 dB choices, the sensitivity of different USES have different requirements. The sensitivity value requirements such as: notebook computer is higher, to around - 27 db, and bluetooth ear machine is relatively low, as long as - 62 db. Must be mentioned is that the discretion of the microphone sensitivity is not only the sensitivity of sound transmission device itself, also related to the resistance R in the circuit. The size of the resistance directly affects the microphone sensitivity. Also a microphone, such as using different R values, sensitivity is completely different. For example: the R value of 1 k and 2 k, the sensitivity can be a difference of nearly 7 db! the With sensitivity is conditional, microphone manufacturers typically given test conditions, usually in the form of: 2.2 k, 3 v. 2, frequency response, Generally defined as: microphone at various points in the transmission of audio frequency sensitivity to should be by the consistency of the state. Microphone wide frequency response range of trophies Called 20-20 KHZ, it is generally believed that the consistency is aligned, the frequency response curve is as flat as possible. But in actual use is not the case. Such as: in the telephone, he hope microphone frequency response curve is cut hay head to tail. This can maximum limit to overcome the low frequency noise and high end the noise. Air in the ear label microphone will cut off 700 hz, in order to avoid the low-frequency noise frequency of jet engines. In the general meeting microphone, hopes to reduce the frequency of above 4000 hz, take noise in grams. While in the transmission of ultrasonic, requires microphone's frequency response, current and impedance microphones inside a field effect transistor, its effect is impedance conversion and signal amplification, so microphones work must want to add a dc voltage, can choose between 1.5-6 v. Microphones current value is normal Under the condition depends on the current value FET (field-effect tube). Generally between 0.15-0.5 mA. Here, the FET is a constant current source, when the microphones of the applied voltage, resistance change current value basically remain unchanged. Therefore, we can think of microphones current value is the current value of the FET. FET current value and its the transconductance amplifier gain indexes of (phase When the transistor magnification), is related to the impedance value itself. As a thought: in a certain range, the greater the normal current value of microphones, impedance is lower, higher magnification ability, the higher the sensitivity. Microphones impedance manufacturers general calibration for: 2.2 k, in fact, the impedance of the microphones is a range of values, rather than a point value. Practice microphones impedance between 700 ohm - 3000 ohms, many users use multimeter impedance measurement is wrong, actually multimeter measure only the dc resistance of microphones FET. Microphones impedance values not only affect the sensitivity of microphones itself, more important is to use microphones to affect indicators, that is to say, the output impedance of microphones must use microphones and the amplifier's input impedance match, the maximum sound transmission gain can be achieved. 4, noise generation and overcome microphones noise points and their own local noise, and the interference of outside noise. Because microphones field-effect tube current value is small, local noise is very small. Metal case bad earth, encapsulation, is the main noise source. Especially in high frequency equipment such as mobile phone, when the microphones shell and PCB version of the contact resistance is greater than 1 ohm, can produce significant high frequency modulation interfered, known as the current sound, mosquito singing. See chapter a below overcome method. Second, the capacitor microphone (microphones) equipment is used for the production of 1, interesting. In the production of ordinary microphones basic equipment investment is not large, 300000 yuan can get one month production scale of production capacity of 1 million only ordinary microphones. It should be pointed out that is dense LaoDongXing, most of the work order is under manual mechanical condition. Automatic production line is much more expensive, at least more than 1.5 million. There is no need for, there are interested I can provide from the starting project budget 00000-500000. 2, process Both intensive LaoDongXing and automatic production line, cleaning is the most basic technical requirements. Consistency is the key to the microphones production and difficulties, mid-range rate is top priority. Process is not complicated, general technical content.