The directionality of a microphone refers to its sensitivity to sound arriving from various directions in a three-dimensional space at different frequency points. Visualized using polar coordinates, the directional sensitivity can be categorized as follows (note: these are cross-sectional representations; the actual patterns are three-dimensional):
Types of Directionality
- Omnidirectional: The microphone has equal sensitivity to sound from all directions.
- Bidirectional: Maximum sensitivity occurs at the front (0°) and rear (180°), while the sides (90°, 270°) show minimal sensitivity.
- Unidirectional: High sensitivity is confined to the front (0°) within a specific angle, with much lower sensitivity at the sides and rear.
Why Different Directional Microphones?
Different directional microphones are designed for specific applications. For instance:
- Unidirectional microphones: Ideal for interviews, they capture the interviewee's voice while minimizing ambient noise.
- Bidirectional microphones: Often called "noise-resistant," they exhibit strong directionality with a sensitivity difference of over 20 dB between the front/rear and the sides. They also feature a proximity effect, allowing control over output volume by adjusting the distance to the sound source.
- Omnidirectional microphones: Suitable for general use, such as in phones, voice-activated toys, and telecommunication devices, where directionality is not a priority.
Applications
Bidirectional microphones are advantageous in scenarios requiring selective sound capture and noise reduction. For example:
- Moving the microphone closer to the source can emphasize certain phrases or notes in singing.
- Increasing distance eliminates "popping" sounds from lip movements and reduces background noise beyond 0.5 meters.
Similarly, unidirectional microphones achieve noise reduction primarily through their directional focus, while omnidirectional microphones remain the default choice for general-purpose applications unless specific directional requirements exist.
