Choosing and using the right mic for the job is an important step in any video project, and understanding a microphone’s directional characteristics is one determining factor. In this segment, we talk about a microphone’s directional response and sensitivity, how to interpret a polar response chart, and we listen to examples of various mics to hear how response works in practice. Knowing how to determine the directional characteristics of a mic, and understanding how this affects the sound your mic picks up, can help you make an informed choice for your next project.
Choosing and using the right mic for the job is an important step in any video project, and understanding a microphone’s directional characteristics is one determining factor.
In this segment, we talk about a microphone’s directional response and sensitivity, how to interpret a polar response chart, and we listen to examples of various mics to hear how response works in practice
Knowing how to determine the directional characteristics of a mic, and understanding how this affects the sound your mic picks up, can help you make an informed choice for your next project.
All microphones aren’t created equal, and one key characteristic of every mic is its directional response, sometimes referred to as a polar or pickup pattern.
A microphone’s directional response determines how it responds to sounds coming into the mic from different directions. A polar response chart is a standardized way of displaying a microphones directional characteristics.
To determine a mic’s polar pattern, manufacturers play various frequencies aimed directly at the mic in an anechoic chamber, and then rotate the mic 360 degrees to measure the sensitivity of a mic at those frequencies.
The sensitivity of a mic refers to how much sound output it gives compared to the amount of sound input it receives. Mics with higher sensitivity to a specific frequency will reproduce it with a strong output signal, while mics with a lower sensitivity to a frequency will reproduce the sound at a much lower output level. Microphones often respond quite differently to various frequencies, and a polar response chart is a great way to see this.
This circular graph is a polar response chart, Beginning in the center ring moving outward, each step typically represents 5db of sensitivity. The innermost ring represents “low sensitivity”, while the outermost ring represents “high sensitivity”. The straight lines on the diagram represent the direction of incoming sound. 0 degrees represents sound heading straight into the diaphragm of a given mic. 90 degrees and 270 degrees represent sound coming into the side of a mic, and 180 degrees represents sound coming into the back of the mic diaphragm.
It’s important to understand that while this is displayed as a 2 dimensional graph, it actually represents a 3 dimensional pickup pattern.
There are two broad categories that most mics fall into, omnidirectional, and directional.
omnidirectional mics are designed to be equally sensitive to sound regardless of which direction sound comes from. Of course, in reality they don’t pick up all frequencies equally from all directions. Omnidirectional mics are great for picking up groups of people or an overall room sound, but can’t be aimed for selective sound pickup.
This is the polar pattern for the DPA emk 4071,which is an omnidirectional lavalier microphone. You can see that while the response does vary a bit depending on the frequency, it is still very sensitive to sound coming from all directions. Let’s see this mic in action.
In this setup, we’re starting with the mic diaphragm facing directly toward our guitar (amp). Let’s have a listen as we turn the microphone 360 degrees.
[DPA EMK 4071 demo]
You can hear that there is little to no falloff as the mic direction changed.
Unlike Omnidirectional mics, Directional mics are designed to be more sensitive to sound coming from specific directions.
The most common patterns that fall under this category are bidirectional, cardioid, hypercardioid, supercardioid, and lobar. Lets take a look at each one.
A bidirectional pickup pattern is sometimes referred to as a figure 8 pattern. These mics are designed to pick up audio from the front and back of the mic, while rejecting sound from the sides.
This is the pattern for the shure KSM 353. you can see that the mic picks up sound equally from the front and back of the diaphragm. These mics are most commonly use to record musical instruments.
The cardioid pickup pattern got it’s name from it’s heart-shaped appearance. It’s designed to pick up sound from the front of the diaphragm, and reject sound from the back.
This is the polar pattern for the shure SM7a. You can see that the cardioid pattern picks up mostly from the front of the mic, while rejecting most of the sound from the back and sides. Notice that it is a bit more sensitive to some lower frequencies from the back. Let’s take a listen.
[SM7a MIC DEMO]
Just as the polar pattern indicated, you heard a significant output fall-off as we turned toward the side and back of the mic.
A hypercardioid pickup pattern is a more directional version of the cardioid. The main difference is that it rejects more audio from the side, but also picks up a little more directly in the rear. These mics are sometimes referred to as mini-shotguns.
This is the polar pattern for the Audio Technica 4053b. If we compare it’s polar pattern to the sm7a, you can see that the sensitivity from the backside in this area is reduced, while the area directly behind the mic is more sensitive.
Mics with supercardioid patterns are similar to hypercardioid, but have even more pickup from the front, and less pickup from the back.
Some supercardioid mics use interference tubes that use phase cancellation to eliminate more sound from the sides. These are often referred to as shotgun or line and gradient mics.
Because of their narrow pickup, they require more accurate positioning to pick up the desired sound, but can also be further away from the source and still capture good sound, making them extremely useful for use in many video projects.
This is the polar pattern of the rode ntg-2 shotgun mic. You can see that the side rejection is significant, but the sensitivity from the back is also more pronounced. The difference between the sm58 cardioid pattern is very pronounced. Let’s take a listen
[ntg-2 example]
It’s clear that this mic has a very narrow pickup in the front, as well as a slightly increased sensitivity from the back.
When you want the extreme in microphone directionality, you’ve got the lobar pick up pattern. This pattern is only achievable in shotgun microphones. These mics will have long interference tubes to cancel out the sound from the sides.
This is the polar pattern for the dpa MMC4017. Notice how widely the pickup ranges depending on the frequency. Let’s take a listen
[dpa mmc 4017]
It’s easy to understand why it takes a skilled audio operator to capture great sound with this mic.
Getting great sound is a crucial component of high quality video production, and choosing the right mic for the job can be a tough one. Understanding how a pickup pattern affects a mic’s ability to capture sound in different situations can help you make the right decision for your next project. Thanks for watching.
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