1. Use of omnidirectional microphone: when there is no fixed direction between the sound source and the microphone and the sensitivity of the microphone in all directions is required to be the same, just open a hole in the front shell of the microphone's sound hole, such as telephone handle, mobile phone, hands-free headset, etc.
　　2. Use of unidirectional microphone: when there is a fixed direction between the sound source and the microphone, and the sensitivity of the microphone is different in all directions, the microphone has the highest sensitivity when the angle between the sound source and the microphone is 0 ° and the lowest sensitivity when the angle is 180 °, then it is necessary to open a hole on the shell before and after the sound hole of the microphone, such as car phone, etc.
　　3. Use of noise elimination microphone: when there is a fixed direction between the sound source and the microphone, the sensitivity of the microphone is required to be different in all directions. When the angle between the sound source and the microphone is 0 ° and 180 °, the sensitivity of the microphone is the highest, and when the angle is 90 ° and 270 °, the sensitivity is the lowest. At this time, a hole must be opened in the front and back of the microphone's sound hole, and a hole must be opened in the shell, wait.
　　4. Under the same conditions, the sensitivity of omnidirectional microphone is the highest, the sensitivity of unidirectional microphone is lower, about 6-8db lower than that of omnidirectional microphone, and the sensitivity of denoising microphone is the lowest, about 10-12db lower than that of omnidirectional microphone.