In addition to those obvious differences, there are some less-obvious advantages to using certain patterns in certain situations.
For instance, an omnidirectional microphone exhibits little or no proximity effect, so if you have to have the microphone extremely close to a source and you want it to avoid the buildup of low frequencies that’s inherent with a directional microphone, an omnidirectional pattern would be a good choice.
In fact, the omnidirectional pattern tends to offer the most natural sound all around as it doesn’t have the off-axis coloration that’s a byproduct of directional patterns, which employ mechanical or electrical mechanisms to cancel out off-axis sounds. Not that that’s a bad thing…in fact, switching patterns on a microphone is often a good alternative to changing the color of the sound without resorting to equalization.
Most variable-pattern microphones will include frequency response charts for each of the patterns the microphone can be switched to as well as graphs that show the response to different frequencies with different patterns.
All microphones, for instance, become more omnidirectional at lower frequencies and more directional at higher frequencies…just to varying degrees. Also, different patterns are required for certain stereo microphone techniques, such as Blumelein, M/S, even Decca Tree configurations.
Finally, it’s probably a good idea to mention a few differences between variable-pattern microphones and fixed-pattern microphones. Most of what we’ve discussed here applies to both, but there are a few differences.
First off, there are obviously some advantages to variable-pattern microphones. As mentioned, not only will the pickup pattern vary as the different patterns are selected, but the frequency response and color will change as well, and it can be very handy to be able to try different colors without having to switch microphones out.
Some microphones offer just two or three patterns, some offer a few more intermediate steps, and some have continuously variable patterns, which can be great for dialing in specific sounds.
Multipattern microphones typically are condenser microphones with two capsules back-to-back, and the different patterns are achieved by applying different amounts of power to one or both diaphragms (as well as switching polarity for certain patterns). As such, a multipattern microphone set to the omnidirectional polar pattern…which is basically two cardioids back-to-back…may still exhibit a small amount of proximity effect.
Also, as mentioned earlier, all microphones become more and more directional at frequency increases, so while a “true” omnidirectional microphone’s pickup pattern will approach that of a cardioid at higher frequencies, a variable-pattern microphone’s response will approach that of a figure-eight microphone when set to omnidirectional.
And, depending on the level of quality control employed by the microphone manufacturer, the front and back capsules may sound quite different from one another, which could especially be a problem when using figure-eight microphones in a Blumlein or M/S configuration.