Cardioid Polar pattern of a SM 57
This is one of the more common polar patterns. It's fairly directional. (The 0 in the picture above is the direction the mic is facing.) If you look at what would be the back of the mic (180 degrees) you can see that the sound pick-up is down quite a bit.
You may have noticed that there are several different line patterns on the drawing above. They are the different frequencies and the different pick-up patterns that those frequencies make. As the frequency goes lower the pattern becomes more and more omnidirectional.
Listen to this example of the Cardioid Pattern as I walk around it.
If you listen closely, not only will you hear the amplitude (volume) drop off as I go around the microphone but also the timbre (tone) of my voice changes. That's because it's hard to make a cardioid microphone that affects the amplitude without affecting the timbre. This is call "off axis coloration".
Omni Polar pattern of a KM 130
Unlike the cardioid pattern above, this omni pattern is fairly non-directional. As is with most things in life this can be both good and bad. Since it picks up sound equally well in all directions it would not be the ideal polar pattern for a P.A. system. But if you're recording something and you want to capture the sound of the room too--this might be the pattern you want.
Listen to this example of the Omni Pattern as I walk around it.
As you can hear, no matter where I'm standing in relation to the microphone, there isn't much of a difference in sound. Though, if you did listen closely (this might be a job for headphones!) you should notice a slight drop in the high end. Still, this pattern has no way near the "off axis coloration" that a cardioid pattern can suffer from. (As a side note, you can also really hear the extended low frequency pick-up of the omni pattern compared to the cardioid in these examples.)
There's more to microphone polar patterns than just cardioid and omni but that will have to wait for another day.
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