Each microphone type (see part 1) can have one of several ‘pickup patterns.‘ Omni, Cardiod, Super-Cardiod, or Figure-8. Each term describes the pattern of sensitivity of the microphone (measured at one specific frequency – usually 1KHz). At higher frequencies, each type of mic becomes more and more directional. Conversely, at lower frequencies, each type becomes more omni-directional. This can be used to your advantage if you carefully consider what you want to accomplish. An example is hanging an SM57 over the top of a Marshall cabinet so that it is in front of a speaker, but aimed at the floor. It still picks up the lower frequencies, since it becomes more omni-directional at lower frequencies. Meanwhile, it rejects higher frequencies from the Marshall cabinet, since the cabinet is ‘off-axis’ to the mic, since the mic is aimed at the floor. This helps a lot in getting rid of that JCM900 “buzz saw” effect.
Omni-directional means that that microphone is equally sensitive to sounds which come to it from any angle. Imagine the head of the microphone as being in the middle of a round balloon, with the surface of the balloon representing a graph line of sensitivity. Graphed on a 2D piece of paper, it would be a circle (or roughly so). These are good for recording environmental sounds outdoors, or possibly if you have a few people sitting in a circle that you need to mic, where multiple mics would be close enough to cause phase problems.. They are generally not good for use in an enclosed room, or where they will be located such that they will pick up the sound from whatever speakers are amplifying the sound.
Directional (or Cardioid) – Pickups up only in one direction at the front of the mic. Allows you to aim it at what you want to amplify and pick up only that sound, and rejects unwanted sounds -AT HIGHER FREQUENCIES. That is an important thing to keep in mind, since it will still pick up the low frequencies and midrange of any off-axis sounds, it will result in a very colored tone of that off-axis instrument being added to the mix. You can experiment with changing the mic angle, and/or moving the mic closer to the source you want to pick up (which will reduce the amount of sound picked up from the UNwanted instrument).
Another characteristic of directional microphone is ‘proximity effect.’ This is a change in the frequency response of the microphone as the sound source gets closer to the mic element, and is present in nearly every cardioid mic unless specifically designed out. You can easily hear this by holding an SM57/58 and start speaking while moving the mic closer and farther away from your mouth. You will notice that as your mouth gets closer to the mic, the low frequencies and low mids become more pronounced.
Hypercardioid (or Supercardioid)- As the pickup pattern narrows, it develops a smaller node at the back of the mic. This means: don’t point the BACK of the mic at a monitor! Typically, the least sensitive angle is about 120 degrees off-axis. Best feedback rejection.
Figure 8 – At the extreme, the node at the rear of the mic is as sensitive as the node at the front, and there is high rejection of sounds from off-axis. A graph of this polar pattern looks like a ‘figure 8.’
Each of the mic types discussed in Part 1 can have any of the patterns described in this section. However, you will find that typically, a dynamic mic is usually a cardioid (directional) or omni-directional.
A ribbon mic is usually a Figure 8, due to its construction.
Condensers are special: since they often have two elements, plus on-board electronics, they can be changed to different patterns with the flick of a switch. As an example, a Neumann U87 can be switched between Cardioid, Omni, or Figure 8.