1. Omnidirectional microphone
The omnidirectional microphone senses sound pressure changes in all directions and accepts sound from all directions with equal sensitivity. Its pickup characteristics are a sphere.
2. Directional microphone
Directional microphones only receive sound from a particular direction, and sounds in other directions are suppressed, which is good for improving speech resolution in noisy environments.
The directional microphone has two sound holes, and sound waves can be transmitted to the microphone from both sides of the diaphragm. The inside of the microphone is divided into two by the diaphragm, and the two sound holes transmit the sound to the two chambers. The diaphragm only senses the difference in sound pressure between the two chambers and converts it into an electrical signal output. When the intensity and phase of the sound pressure in the two chambers are the same, the output is zero. A very fine acoustic delay filter is added to the rear sound hole. The time from the rear sound wave to the diaphragm through the front and rear sound holes will be substantially equalized and the output from the front sound wave will be strengthened. Therefore, it shows a certain degree of directivity. In the free field, the deaf person's psychology, its directivity presents a heart-shaped polar coordinate pattern.
Compared to omnidirectional microphones, directional microphones have lower low frequency sensitivity. Coupled with the directional reception of the sound source, the patient's speech reception ability in a noisy environment is greatly improved.
Although directional microphones have many advantages, they are not very popular. Until the introduction of programmable hearing aids, in order to realize the conversion of omnidirectional and directional reception between different programs, people changed their minds, and manufacturers introduced dual-microphone or even three-microphone technology to improve the selective reception of sound sources in a certain direction. The idea of improving the signal-to-noise ratio has been re-emphasized.
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