Recording Sound - Microphone Choice [Part 2]

Click here for Part 1

Coming straight from part 1, there's a little more to learn about microphones. Obviously, we now know that dynamic microphones are great for high volume sounds, where as condensers are great for their dynamic range and sensitivity. What we're going to touch on next is the variation in sizes and shapes, as well as the 3D pattern at which sound is picked up relative to the diaphragm.

Rode NTG-1 with a smaller
1cm Diaphragm

Microphones are designed to receive sound. However, The way in which this is achieved varies widely depending on the size and polar pattern of a microphone. So what does this mean? Well imagine a set of speakers. The speaker cones come in several different sizes to help represent the broad range of frequencies. Tweeters are usually about 1" in diameter and deal with anything from 7-22kHz, with 4-5" cones handle the mids at 400-6Khz, which leaves large 10" cones that will delivery the very deep 20-300Hz range. This is no different for microphones.

AKG C414 with a larger
1" Diaphragm

The best way to think about this is setting up and recording a drum kit. The first part you may want to mic up is the snare drum. As the frequency range tends to be low to high mids (500Hz-5kHz), you won't need a large diaphragm microphone in order to fully replicate the sound realistically. Similarly, you won't want to use a pencil condenser microphone with a 1cm diaphragm; this would be more useful on the cymbals which create a lot of those higher frequencies. For the kick drum, which has a fundamental frequency ranging from 50-200Hz, the diaphragm on the microphone would need to be much larger: about 1" for most proprietary kick or condenser microphones. Some may even want to convert a medium sized speaker cone into a microphone, which would be able to pick up the sub frequencies of the kick (20-60Hz). However, I digress: can you tell which instrument I play yet?

The point is, before you pick a microphone, consider the frequency range that the source will be creating, or at least the frequency range that you'd like to use.

Now, polar patterns. Have you ever wondered why microphones are the shape and size they are? Why some are long and thin, where others can be cuboid-like or have the diaphragm exposed on 2 sides? These different designs have all been implemented for the purpose of creating a pick up pattern; better known as the Polar Pattern.

The Polar Pattern is a 3D shape (usually depicted in 2D) that highlights the area around a diaphragm that can pick up sound. There are 4 main patterns available for microphones, which are described below:

Omni-Directional Polar Pattern
credit:wikimedia.org

Omni-Directional - This is the simplest pattern available for a microphone and is the most basic to understand: it picks up sound from all directions equally. You can imagine the pick up pattern as being a large sphere around the diaphragm. This pattern can be found on a lot of vocal microphones and as a choice on many higher end condenser microphones.

Uses: As it works to pick up everything, it tends to give the most realistic representation of the sound, with both the source and reflections on the recording.

Cardioid Polar Pattern
credit:wikimedia.org

Cardioid - This pattern, much as the name may depict it to be, is shaped like a heart. Rather than picking up sound from all directions, it's only able to reach sounds on one side, with minimal 'leakage' of sound from the back. As you can see, there is a small amount from the rear, which is only due to the nature of a diaphragm being effected from either side regardless; for the most part though, this is a single direction pattern.

Uses: This pattern is particularly useful in both live and studio settings, where sound leakage may want to be avoided. For live purposes, you'll want to prevent as much leakage from other instruments as possible, so recording in this single direction very much helps. Similarly, if you want to record in a studio with as little reverberation as possible, the cardioid pattern should help with that.

Hyper-Cardioid Polar Pattern
credit:wikimedia.org

Hyper-Cardioid - Coming directly from the previous pattern, Hyper Cardioid is almost an exaggerated version of Cardioid, which is far more directional, leaving even less leaked sound or room tone to affect the source sound. However, what it gains in it's precision it looses in it's mono-directionality. I.e the pattern turns more into a figure-of-8 shape, which means sound is picked up from the rear. This shouldn't be significant enough to burden a recording though, especially with higher end microphones.

Uses: As this provides a more precise directionality, it is usually used for broadcast recording. For example, a lot of shotgun condenser microphones (such as the NTG-1 shown above) use this pattern so that the newscaster, who may be stood outside of a building or built up area, is picked up clearly at a distance without too much of the external noise being picked up.

Figure-of-8 Polar Pattern
credit:wikimedia.org

Figure-of-8 - Most common for condenser microphones which are exposed either side, figure of 8 is a fairly self explanatory recording pattern: sound is picked up equally from either opposite side of the diaphragm. By having this, two sources can be picked up either side of the microphone, without a large amount of spill that would otherwise occur on an omni-directional pattern. Similarly, a single source can be recorded, with a controlled amount of room tone to the desired effect.

Uses: One good example I read about recently was to use this pattern with a guitar amplifier either side of the microphone, with one guitar split and wired into both amps. As the distortion would be slightly different on either amp, this would create an almost doubled-up effect, which is naturally summed from either side of the mic to create a huge guitar sound. Also, for a lot of vocal work, you may want to record 2 singers either side of the mic for again the doubled up effect which is good for a pre-chorus emphasis.

Conclusion: These ideas are relatively simple to understand and are mostly common sense. However, knowing these simple steps and querying what your own microphones have can really change how you think about recording. Making sure the frequency response and directionality is accounted for can improve recordings greatly, especially with a combination of microphones and their respective polar patterns.

Next time, we'll go into the placement of microphones in relation to a source to make the most out of your recordings, as well as how multiple microphones can have adverse effects due to phase, with simple solutions to resolve this.

Thanks again for reading!

Alex.