The term “Polar Pattern” relates to the directionality of a microphone. What is directionality? Sound sources can come from different positions and directions around the microphone. Polar patterns tell us from which direction the microphone is most sensitive to sound, and from where the microphone will be less sensitive, and even completely reject a sound. It is necessary to understand this concept and its implications when discussing microphone techniques. The most basic as well as the most advanced techniques make use of the directional characteristics of a microphone.

The above information tells us that a microphone has a front and a back, and sound sources coming from the front of the microphone will sound different from sounds coming from behind the mic or from the sides. A sound source located in front of the microphone is called an “on axis” sound, and sound sources on the sides or behind the mic are called “off axis.” When looking at a microphone, the first thing you have to understand is where the front of the mic is (where the on-axis sounds will be coming from).

The visual representation of a mic’s polar pattern is presented as a two-dimensional “slice”, where the circle around an axis shows the sensitivity (in dB) at the various angles around the microphone’s diaphragm. The farther away the line is form the center axis, the more sensitive the mic from in that direction (meaning, the sound will be louder coming from that direction) and the closer the line gets, the less sensitive the pickup of the microphone from that direction (meaning, less level from the sounds coming from that direction – also referred to as sound rejection).

 

In the above example, the diagram on the right shows a microphone that is equally sensitive from every direction. This type of microphone is called an “Omnidirectional” microphone (sometimes also called “Unidirectional”). The left diagram represents a microphone that is most sensitive to on-axis sound (the sound sources that are in front of the microphone), where sound coming from the back of the microphone is completely rejected (this means that in an “ideal” environment an instrument playing behind the mic isn’t picked up at all). This type of microphone is a directional microphone, and because the diagram looks like a heart, is called a “cardiod” microphone.

In reality the way microphones pick up sound is more like a three-dimensional spherical ball around the diaphragm. The illustrations below, found on the Shure website, give a nice representation on how the above polar patterns would translate to a real microphone:

As you can see, the polar pattern diagram is basically a two-dimensional slice from above the microphone (kind of like an MRI shows slices of your body from the head down).

The three common types of microphone polar patterns are “cardioid”, “omnidirectional”, and “bi-directional” (also called “figure-eight”). Some mics have a fixed polar pattern, while others have a switching mechanism where the engineer can decide which polar pattern he wants to utilize on a particular recording.

The bi-directional polar patterns looks like this:

A bi-directional microphone picks up sound equally from the front and the rear, while completely rejecting sounds coming from either side of the diaphragm. There are other types of polar patterns, and they are variations and combinations of these basic types. We will discuss those in future posts.

This was brief introduction to microphone polar patterns are. On the next post I will start to discuss some of the meanings, implications and applications for these different types of mics. Happy reading!