Omnidirectional Microphones

全向麦克风

Omnidirectional implies equal sensitivity in all directions, but because the microphone mechanisms inevitably have some directional character, a true omnidirectional microphone is not achieved in practice. It is practical to achieve "omnidirectional" behavior in one plane, and that is what is usually implied by the word in practice. A directional pattern such as the cardioid has its maximum sensitivity along the microphone axis, and that directional pattern is a figure of revolution with uniform sensitivity in every direction perpendicular to the microphone axis. Therefore, if a cardiod microphone is pointed at the ceiling, then it is omnidirectional in the horizontal plane. This is in fact a useful microphone technique if you wish to pick up sound over a wide angle without excessive focusing on one direction.

全向性意味着在所有方向上都有相等的灵敏度，但由于麦克风机制不可避免地具有一定的方向性，因此在实践中无法实现真正的全向性麦克风。在实践中，实现“全向性”行为在一个平面内是可行的，这也是“全向性”一词通常所暗示的含义。例如，心形指向性模式在其麦克风轴线上具有最大的灵敏度，而这种指向性模式是一个具有均匀灵敏度的旋转对称图形，其在麦克风轴线垂直的每一个方向上都具有均匀的灵敏度。因此，如果将一个心形指向性麦克风指向天花板，那么它在水平面上就是全向的。这种技术实际上在需要拾取宽角度声音而不过度聚焦于某一方向时是有用的。

Another physical fact that prohibits a truly omnidirectional microphone is the action of diffraction in limiting the high frequency response of a microphone at large angles to the opening port to the microphone transducer. A high frequency (short wavelength) sound arriving at the rear of a microphone cannot bend around the microphone to enter the port. So at extreme angles, "omnidirectional" microphones may lack clarity because of tipping the response toward the bass frequencies.

另一个阻止真正全向麦克风的物理事实是衍射作用，它限制了麦克风在大角度时的高频响应。高频（短波长）声音到达麦克风后方时，无法绕过麦克风进入麦克风换能器的开口口。因此，在极端角度下，'全向'麦克风可能会因为响应偏向低频而缺乏清晰度。

Microphone discussion

麦克风讨论

Index

Sound reproduction concepts

Reference
White & White
p299.

索引声学再现概念参考 White & White p299.

HyperPhysics***** Sound

HyperPhysics ***** 声音

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Figure-Eight Microphones

八角形麦克风

The "figure-eight" or bidirectional microphone pattern just refers to a microphone element which has symmetric pickup lobes to the front and rear. For a dynamic microphone where the air pressure moves a diaphragm attached to a voice coil, just providing equal air access to the front and back of the diaphragm will produce a figure-eight pattern.

‘八’字形或双向麦克风指向性仅指一个麦克风元件，其前方和后方的拾取方向对称。对于动态麦克风，当空气压力推动连接到线圈的膜片运动时，只要前方和后方的空气流通量相等，就会产生‘八’字形指向性。

One use of figure-eight is in a geometry called a "Blumlein pair". A pair of such microphones is place so that if you drew lines from the microphones to the sound source, they would intersect at right angles. This has been found to be a good microphone placement for live music in an acoustically desirable room, providing a pleasing ambience. It is also sometimes used for pianos and drums.

图八的另一种用途是在一种称为“布卢门菲尔德配对”的几何结构中。这样的麦克风对被放置成，如果从麦克风到声源画线，这些线会在直角处相交。这种布置在声学条件良好的房间中被发现是现场音乐表演中良好的麦克风布置方式，能够产生令人愉悦的混响效果。它有时也用于钢琴和鼓。