Microphone structure and working principle
The structure and working principle of common microphones
1. Moving coil microphone
Moving coil microphones are also called electric microphones. They are similar in structure to electric speakers and are also composed of magnets, voice coils and sound membranes, as shown in Figure 12-11. The voice coil of a moving coil microphone is in the magnetic field of a magnet. When sound waves act on the sound film to vibrate, the sound film drives the voice coil to vibrate accordingly, causing the voice coil to cut the magnetic lines of force to generate an induced voltage, thus completing the sound-electricity Conversion. Since the resistance of the voice coil is very small and its impedance is very low, the function of the impedance matching transformer is to change the impedance of the microphone to match the input impedance of the amplifier. The output impedance of a moving coil microphone is divided into high impedance and low impedance. The output impedance of high impedance is generally 1000-2000 Ω, and the output impedance of low impedance is 200-600 Ω. The frequency response of moving-coil microphones is generally 200 5000 Hz, and the high-quality ones can reach 30-18000 Hz. The moving coil microphone has the characteristics of sturdiness, durability, stable work, one-way directivity, low price, and is suitable for speech, music amplification and recording.
2. Condenser microphone
Condenser microphone is a kind of microphone that uses the change of capacitance to cause sound-to-electric conversion. Its structure is shown in Figure 12-12. It is a variable capacitor with a small spacing composed of a vibrating diaphragm and a fixed electrode. . When the diaphragm vibrates under the action of sound waves, the distance between the vibrating diaphragm and the fixed electrode changes, causing a change in capacitance. If there is a load resistance R and a DC polarization voltage E at both ends of the capacitor, when the capacitance changes with the sound wave, an alternating audio voltage will be generated at both ends of R. The output impedance of a condenser microphone is capacitive, because the capacitance is small, but the capacitive reactance will be large at low frequencies. In order to ensure low-frequency sensitivity, an impedance converter with an input impedance greater than or equal to the output impedance of the microphone should be connected to it. After impedance transformation, it is connected to the amplifier with a transmission line. This impedance converter generally uses a field effect tube. Condenser microphones have high sensitivity, high output power, simple structure, and good sound quality, but it is not convenient to use power sources, so they are mostly used in theaters and demanding language and music broadcasting occasions.
3. Electret microphone
The electret microphone is composed of two parts: acousto-electric conversion and impedance conversion, as shown in Figure 12-13. The key element of the acoustic-electric conversion part is the electret diaphragm, which is a very static plastic diaphragm, on which a pure gold film is evaporated, and then electretized by a high-voltage electric field, there are opposite charges on both sides. The vaporized gold surface of the diaphragm is connected to the metal shell outside, and the other side of the diaphragm is separated by a thin insulating gasket, so that a capacitor is formed between the vaporized gold film surface and the metal plate. The impedance conversion part is taken by the field effect tube, and its main function is to convert the impedance of tens of megohms into an impedance matching the amplifier. The G pole of the field effect tube is connected to the metal plate, and the D and S poles are connected to an external circuit. The output form is shown in Figure 12-14. Figure 12-14 (a) shows the source output connection. The output impedance of this connection is less than 2kΩ, the circuit is relatively stable, and the dynamic range is large, but the output signal is weak. Figure 12-14 (b) shows the drain output connection. This connection has a higher gain, but the dynamic range is smaller than that of the pole output connection.
The working principle of the electret microphone is that when the sound wave vibrates the electret diaphragm, the electric field of the capacitor formed between the vapor-deposited metal film of the diaphragm and the metal plate changes accordingly, generating an audio electric signal that changes with the sound wave. The signal is output through the field effect tube. Electret microphones have the advantages of small size, simple structure, good electroacoustic performance, and low price. They are widely used in cassette tape recorders, telephones, wireless microphones and voice control circuits.
In order to better understand customer needs, Changzhou Zhongce Instrument Co., Ltd. will provide you with more test programs to help you better choose
Please first determine whether the corresponding safety unit allows the tested product to use AC voltage or DC voltage, and it should be tested as required. Some products can be tested with AC voltage or DC voltage. Then the manufacturer can decide to use AC voltage test or DC voltage test according to the characteristics of the product. The user must understand the advantages and disadvantages of these two test voltages.
Moving coil microphones are also called electric microphones. They are similar in structure to electric speakers and are also composed of magnets, voice coils and sound membranes, as shown in Figure 12-11. The voice coil of a moving coil microphone is in the magnetic field of a magnet. When sound waves act on the sound film to vibrate, the sound film drives the voice coil to vibrate accordingly, causing the voice coil to cut the magnetic lines of force to generate an induced voltage, thus completing the sound-electricity Conversion. Because the resistance of the voice coil is very small. Its impedance is very low. The function of the impedance matching transformer is to change the impedance of the microphone to match the input impedance of the amplifier.
At present, the speaker aging life testers on the market are generally composed of a combination of signal source + power amplifier, which can no longer meet the increasingly stringent test requirements for product quality, and generally do not have the following test requirements and conditions: