Fundamentals Of Microphone Polar Patterns
Have you ever come across the terms Cardioid, Omni-directional and Bi-directional microphones? If you are looking for a microphone to buy, chances are you must have stumbled across these words. But what do they mean and which one is right for you? In this post we discuss microphone polar patterns and why they are so important when choosing a microphone.
So what is a polar pattern?
Simply put, it's the 3D space around the mic capsule in which it picks up sounds with most sensitivity. To get a visual representation check out the illustration below.
Uses Of Cardioid Mics
1. Recording A Drum Kit: If you would like to achieve good isolation between your kick, snare, toms and other parts of the drum kit, the cardioid can work extremely well when placed strategically. You can also use some overhead mics to capture the sound of the room and then blend it into your production.
2. Recording A Solo Vocalist: If you're a solo artist recording vocals or any other instrument, cardioid would probably be your best choice. It captures the source which is in front of the microphone and rejects most of the sound from behind the capsule. Most singers and solo musicians therefore like to use cardioid microphones. If you're recording one singer or musician at a time, the cardioid pattern works like a charm. Just be aware off the off-axis coloration and the proximity effect which is discussed below, so you can get the best of your recording.
Cardiod microphones have the following salient features:
- Off-axis coloration – With most cardioid mics, you see a drop in high frequency sensitivity as sounds move further off-axis. This is something to wary of, especially if the singer has a tendency to move the head position during the recording. Ideally, you don't want to be moving around much in front of the microphone, so that you can get a stable tone.
- Proximity effect – This phenomenon is exclusive to cardioid mics. The proximity effect is a boost in bass frequencies that results from extreme close-miking. While this can be desirable at times, it can also lead to a blobby sound without proper definition. Therefore, it is important to be aware of this effect too and use it only when intended. Experiment with moving back and forth to find the sweet spot.
Uses Of Omni-directional Mics
Omni-directional mics are not as popular as cardioids since they are extremely prone to off-axis leak. In other words, since they pick up sound from all around the capsule, they tend to pick up a lot of undesirable sounds like the room sound and noises within the recording space. However, they are still very relevant in certain scenarios as mentioned below:
1. If you're recording a wide source like a choir, grand piano, omni-directional microphones might be the best choice. When recording a small choir, you could make the singers stand around the microphone and use an omni-directional pattern to make sure the microphone is equally sensitive all around the capsule.
2. When doing stereo recording using the A-B mic placement technique, or any other stereo recording technique omni-directional microphones help you achieve a well balanced sound emanating from all directions around the microphone.
3. If you want to record the sound of a room, an omni-directional mic will be able to give a very accurate representation since it will pick up sounds from all around the capsule equally. This is a great choice when recording spaces for use in convolution reverbs.
Uses Of Bi-directional Mics
The bi-directional mic is preferred if you'd like to have the strongest signal captured in front and behind the mic, with maximum off-axis isolation (so your mic doesn't capture the sounds from the sides). This is particularly useful in the following scenarios:
1. When you're recording a duet of singers facing each other.
2. When you're doing a stereo recording using the mid-side technique.
Rather than requiring a separate mic for every job, engineers came up with an ingenious idea to cram a ton of versatility into just one mic.
They realised that by using combinations of signals you could recreate virtually any polar pattern imaginable.
- By combining two cardioid signals, you get an omnidirectional pattern.
- By combining two cardiod signals but reversing the polarity of one of them, you get a bi-directional (figure-8) pattern.
- By turning off one, and using the other, you get a cardioid pattern.
And that’s how multi-pattern mics were born. These microphones have a simple switch so you can easily change your desired polar pattern.
If you're interested in doing all these kinds of things with just one mic, its worth checking out multi-pattern microphones.
That's all you need to know about polar patterns!
So now that you know the fundamentals of microphone polar patterns, it’s time to decide which microphone to buy and get the one that will serve you best!
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