The polar pattern of each microphone indicates how sensitive it is to sound coming from different directions. Taking a look at any of the polar patterns below, each of them illustrates a series of points (shown as a solid continuous line in the shape of oblong circles) that produce a certain signal level if sound is sent in that direction. The illustration of each polar pattern in reference to the orientation of a microphone depends on the direction in which they were meant to be used. For large membrane microphones that have their diaphragm on its side, the polar patterns must be read in that side orientation as well. These types of polar patterns are known as “side fire” or “side addresses” since they represent the side view of the microphone. Smaller microphones that have their diaphragms at their very tip have polar patterns known as “end fire” or “top/end address” since the pattern is in reference to the very top of the microphone. Pretty much, the polar patterns of each mic are drawn out in the way the mic faces you while using them. A novel idea, but it works.
If you ever took a look at a normal, inexpensive stage microphone with its characteristic rounded end, chances are its omnidirectional. These kind of mics are used for a variety of applications where capturing sound from every direction is important such as with groups of singers or instrumentalists, a meeting with multiple participants, recording the sounds of the great outdoors – pretty much any situation where you want to capture sound in all directions without having to move the mic around calls for one of these. Anyways, these types of mics can theoretically pick up sound equally from all directions, but the reason I say theoretically is because in the real world, there are far too many variables for anything to work perfectly, as is the case with this one. First of all, the body of the microphone itself can get in the way. Also, depending on the size of the diaphragm, certain frequencies will get cut off, not to mention if these are placed too close to speakers you will get that very annoying feedback loop. Not without its problems, but neither is anything else.
Although most musicians fair well with a run of the mill omnidirectional mic for their vocals, a unidirectional microphone will be your best bet at eliminating background noise by only capturing what is directly in front of it. So, why doesn’t everyone use these bad boys for vocals? Same reason why we all don’t drive a Ferrari – they are a bit pricier than your average microphone and tougher to set up properly. Although some of these mics literally do receive sound from only one direction, unidirectional mics for the most part simply have a certain side that is far more sensitive that the opposite end, so although it does pickup sound from more than just the front, its main focus is still faced towards a single direction. Within the classification of unidirectional, there are a few more sub categories named after the shape of their polar patterns.
This is pretty much the most common form of unidirectional microphones. As you can see from some of its polar patterns, these guys focus their sensitivity towards a single end making them perfect for speech or vocal microphones since they tend to reject sound coming from all other directions. This is especially helpful in avoiding feedback coming from the PA or speakers. Cardioid mics are essentially a combination of bidirectional unidirectional elements that are constructed in such a way to focus much of the sensitivity towards one specific end of the mic or tweaking it a bit until you get certain other polar patters, such as the subcardioid, supercardioid and hypercardioid variety.
This type of microphone is the most highly directional of all unidirectional microphones. Although most of their sensitivity is focused at the very top, they also have small spots of sensitivity on its left, right and rear, it is much less than any other unidirectional microphone. Because their area of sensitivity is so narrow, shotgun mics are perfect for situations where background noise is unwanted, such as in movie sets, stadiums or field recording of wildlife.
As the name suggests, these microphones pickup sound equally from both its front and rear as can be seen from its figure 8 polar pattern. Most ribbon microphones are of this variety. The reason they respond to sound equally from both front and back while nothing on its sides has to do with the way in which they interact with pressure along with their build. Technically speaking, these types of mics don’t respond to the sound pressure itself, but to the change in sound pressure between its front and back. Since sound coming in at the microphone’s sides reach the front and back at the same time, there is no change in pressure, therefore, no sound is picked up in that area, resulting in that figure 8 shape.