Omnidirectional microphones: Magnetic, ceramic, and electret microphones are all omnidirectional microphones, that is, equal amounts of sound from all directions are accepted. At present, electret microphones are widely used in the field of acoustics. It is made of an insulating, permanently polarized material. When sound enters the microphone, the density changes of sound waves cause the negatively charged thin metal sheet to vibrate, which randomly converts sound energy into mechanical energy. The diaphragm vibration generates pressure on the electret and transmits it to the back plate of the electret. Both the back plate of the electret and the bottom of the diaphragm are connected to the field effect transistor preamplifier and have a terminal leading to the outside. When the distance and space between the diaphragm and the back plate of the electret change, a voltage is generated, and the mechanical energy is converted into electrical energy through the field effect transistor fixed on the microphone, and then transmitted to the amplifier through the terminal. The electret microphone has wide frequency, high sensitivity and durability, and the diaphragm is its only moving part.