Electret microphone

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Electret microphone [Copy link]

Electret Condenser Microphone (ECM) Currently, we are basically using active MIC, because we need to power the microphone; passive microphone, do not need to power it, but need to borrow external power amplifier. For example, the dynamic microphone we use, the microphone used in KTV is a passive microphone. 1. Sensitivity Generally defined as: the efficiency of microphone sound-to-electric conversion. Expressed in dB. In the test standards of relevant microphones, it is set as 0dB=1V, so the sensitivity value of the microphone is negative. For example: -58dB The sensitivity of the microphone is generally selected between -28-----66 dB, and different uses have different sensitivity requirements. For example: the sensitivity value requirement of a laptop is relatively high, about -27db, while the sensitivity of a Bluetooth headset is relatively low, as long as it is about -62db. It must be mentioned that the sensitivity of the microphone is not only determined by the sensitivity of the microphone itself, but also related to the resistance R in the circuit and the power supply. The size of this resistance directly affects the sensitivity of the microphone. The same microphone, if using different R values, will have completely different sensitivities. For example, when the R value is 1k and 2k, the sensitivity can differ by nearly 7db! Therefore, sensitivity is conditional. Microphone manufacturers generally give test conditions, usually: 2.2k, 3v. 2. Frequency response Generally defined as: the consistency of the sensitivity of the microphone corresponding to each frequency point in audio transmission. The frequency response range of the microphone is generally called 20-----20khz. It is generally believed that the more consistent this consistency is, the flatter the entire frequency response curve is, the better. But this is not the case in actual use. For example, in a telephone, it is hoped that the frequency response curve of the microphone is a haystack type with the head and tail cut off. This can overcome low-frequency noise and high-end howling to the greatest extent. The microphone in the aviation earmuff is required to cut off the components below 700hz to avoid the low-frequency noise frequency of the aircraft engine. In general conference transmission, it is hoped to reduce the frequency above 4000hz to overcome the howling. In ultrasonic transmission, the microphone frequency response is required to be above 15khz. The higher the high-end sensitivity, the better. Therefore, the frequency response of the microphone should also vary depending on the use. 3. Current and impedance There is a field effect transistor inside the microphone, which is used for impedance conversion and signal amplification. Therefore, a DC voltage must be added to the microphone to work, which can be selected between 1.5--6v. Under normal circumstances, the current value of the microphone depends on the current value of the FET (field effect transistor). Generally, it is between 0.15--0.5mA. Here, FET is a constant current source. When the external voltage and resistance of the microphone change, the current value remains basically unchanged. Therefore, we can think that the current value of the microphone is the current value of the FET. The FET current value is related to its own amplification gain index, namely the transconductance (equivalent to the amplification factor of the transistor), and its own impedance value. It is generally believed that within a certain range, the larger the normal current value of the microphone, the lower the impedance, the higher the amplification ability, and the higher the sensitivity of the microphone. The impedance of the microphone is generally calibrated by the manufacturer as: 2.2k. In fact, the impedance of the microphone is a range value, not a point value. In practice, the impedance of the microphone is between 700 ohms and 3000 ohms. It is actually wrong for many users to use a multimeter to measure the impedance. The multimeter only measures the DC resistance of the microphone FET. 4. The impact of voltage changes on sensitivity is generally -3dB.