How do bidirectional microphones work?
In: Technology
They measure the the difference of the sound from front (+) to back (-).
This causes the sound wave from the front to be picked up as usual.
From the back the sound wave is inverted (does not matter in most cases).
And from the side both of the above happen, which causes them to cancel out.
bonus:
This makes this microphone pickup the sound relative to the position differently, the bidirectional mic is also named a figure 8 mic for this reason.
An omnidirectional is O shaped.
And if you mix in the characteristics of an omnidirectional microphone with those of a bidirectional you get a cardioid shaped response.
If you look at the inside of a bidirectional mic, the capsule (the “sensor”) is going to be a [flat disk with a diaphragm inside of it](https://www.gear4music.com/us/en/Recording-and-Computers/sE-Electronics-X1-S-Large-Diaphragm-Condenser-Microphone-Box-Opened/2PDQ). Since it’s open at both sides, it detects air movement from either side.
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