Digital Sound & Music: Concepts, Applications, & Science, Chapter 1, last updated 6/25/2013
Figure 1.10 Shure SM58 dynamic microphone Figure 1.11 AKG C-414 condenser microphone
Another way to classify microphones is by their directionality. The directionality of a
microphone is its sensitivity to the range of audible frequencies coming from various angles,
which can be depicted in a polar plot (also called a polar pattern). The three main categories
of microphone directionality are directional, bidirectional, and omnidirectional.
You can think of the polar pattern essentially as a top-down view of the microphone.
Around the edge circle are numbers in degrees, representing the direction at which sound is
approaching the microphone. 0 degrees at the top of the circle is where the front of the
microphone is pointing – often referred to as on-axis – and 180 degrees at the bottom of the
circle is directly behind the microphone. The concentric rings with decreasing numbers are the
sound levels in decibels, abbreviated dB, with the outer ring representing 0 dB, or no loss in
level. The blue line shows the decibel level at various angles.
We don't explain decibels in detail until Chapter 4, but for now it's sufficient to know that
the more negative the dB value (closer to the center), the less the sound is picked up by the
microphone at that angle. This may seem a bit counterintuitive, but remember the polar plot has
nothing to with distance, so getting closer to the center doesn‟t mean getting closer to the
microphone itself. The polar pattern for an omnidirectional microphone is given in Figure 1.12.
As its name suggests, an omnidirectional microphone picks up sound equally from all directions.
You can see that reflected in the polar pattern, where the sound level remains at 0 dB as you
move around the circle regardless of the angle, as indicated by the blue boldface outline.