Directional and Omnidirectional Microphones – What Are They Good For?

Do yo have a directional microphone or an omnidirectional microphone?  Are you even certain?  The directionality of a microphone, that is, whether it picks up audio best from the front only, or from all around it (or some other pattern of pick-up) is frequently called the polar pattern of a mic.  To get the best sound from a microphone, it’s important to understand the different polar patterns and how to use them properly. Polar patterns are also sometimes known as pick-up patterns, because their function is to ‘pick up’ the sound. There are three main polar patterns and each serves a different purpose.

Cardioid

This is among the most common polar patterns that you will encounter. Meaning ‘heart-shaped’, this type of pattern will give you a good pickup to the front, with a lesser amount to the sides, and a good sound rejection to the back.  Cardioids are also known as “directional” mics since they only pick up audio from one direction.
One of the main features (benefit sometimes and curse other times) of cardioids is that they can create a “proximity effect.” As the source gets closer, the audio sound will be “bassier.”  You should be aware of this if you want to make your audio sound a bit deeper, especially for voiceover actors.  Though sometimes you may want less bass in the audio.  Knowing that you have a cardioid mic, you might be able to fix the tone just by getting further from the mic (but beware of letting more bad room sound in if you do this!) instead of futzing with EQ or other editing tools in your gear.  Sometimes the simplest solution is the best.
Cardioid polar patterns are recommended for most vocal applications, recordings and live recordings. It is suitable for venues where the recording environment’s acoustics are good, but less than perfect.  This is because a cardioid rejects audio from behind it, so if you have reflections or other potentially unpleasant audio coming from behind the mic, its effect will be minimal.  Sometimes the area behind a cardioid mic is called the “null” because it is sort of an audio no-mans-land.  See picture on the right.
Hypercardioid microphones take the concept of cardioids one step further. It records from the front, and rejects everything to 120 degrees to the back. These work very well for on-stage live performances and live recordings that are in difficult or far-away situations.

Omni

Also called Omnidirectional, this type of polar pattern picks up sound equally around the microphone. These are meant to sound very natural and open are well suited environments that have good acoustics. They are also great in recording situations where natural, open sounds are the goal.  And obviously, the main use for an omni mic would be when you want record sound from several different directions.  One example of this would be if you had, say, a barbershop quartet in the studio.  They could gather around the mic and each voice would be picked up equally.  Setting up an omni in the middle of an acoustic group of musicians like a small classical string combo, bluegrass group, etc., is also a good use.
The biggest difference between omni microphones and cardioid microphones is that omni does not give the proximity effect. Omni polar pattern microphones are generally not recommended for live sound, as they can be prone to feedback issues, but they are great in recording studios, where the environment can be better controlled.

Figure-8

Also known as bidirectional, this polar pattern microphone will pick up sound equally from both sides of the microphone.  This also means that the nulls for a figure-8 pattern are on either side, as indicated in the picture on the left.
You’ll find that the majority of ribbon microphones are configured as figure-8s. They are commonly used in mid-size recording studios. They can be sensitive, and so are not recommended for high SPL or harsh environments. They are, however, best suited for acoustic instruments, and for live recordings of jazz and acoustic groups. They are also often used for drum overheads.
Another use for a bidirectional mic is for when recording an acoustic guitar player who is also a singer.  The mic can be set up so that one side is facing up at the singer’s head and the other side facing down toward the guitar.
Yet another really cool use of a figure-8 microphone is in combination with a cardioid mic to perform a stereo recording technique called mid-side (MS) stereo recording.

Mics with switchable polar patterns

If you cannot afford to own at least one microphone that can give you all three of these patterns, you can get a mic that is capable of doing all these patterns.  You just flip a switch and your mic goes from cardioid to figure-8 or omni.  This is the route I took since I rarely have need of the other patterns, but definitely want the capability for those special times.  The mic I use for this is called the Rode NT2-A.  Take a look at the picture on the right.
Knowing which microphone polar pattern to use in each situation will ensure you get the sound you want, every single time. A basic understanding of the main types of polar patterns will help to unravel the mystery of some of this technology and give you professional quality results.