To get the most out of our microphones, we need to know their directionality. Understanding how microphones respond to sound at varying angles and the directions in which microphones point will be invaluable in our work as musicians and audio engineers/technicians.
What is a directional microphone? A directional mic, as the name suggests, is a microphone that is most sensitive in one (or more) directions. In other words, a directional mic has any polar pattern but omnidirectional. Directional mics effectively “point” in a certain direction and are very popular choices in the audio recording.
In this article, we’ll discuss directional microphones in great detail in order, covering the different directional polar patterns; the theory and design of directional mics, and, of course, real-life examples of directional microphones.
What Is A Directional Microphone?
A directional microphone has an obvious axis (direction) in which it is the most sensitive. Most directional mics have a single primary axis that points in a single direction. Bidirectional mics, which are also directional, have a single axis line that points in both directions.
Understanding The Primary Axis: Top-Address Vs. Side-Address
To understand the directionality of a directional microphone, we must understand the primary axis of the microphone.
The primary axis can be thought of as an invisible line extending out of the microphone in the direction the mic points toward. This line passes through the centre of the mic’s diaphragm and points outward from the mic capsule perpendicular to the diaphragm.
The primary axis is also referred to as the microphone’s on-axis response line and is denoted as 0° on a mic’s polar pattern response graph.
It’s critical to note that all microphone specifications having to do with the transducer element of the microphones (capsule, cartridge, etc.) reference a sound source on the mic’s primary axis. Directional microphones (and even omnidirectional mics to a lesser extent) will capture sounds differently than advertised if the sounds arrive at the mic from an angle!
The specifications that are based on on-axis sounds include the following (I’ve added links to in-depth articles on each of these specifications):
To learn about all of the microphone specifications, check out my article Full List Of Microphone Specifications (How To Read A Spec Sheet).
The polar pattern of a microphone gives us a great idea of the directional characteristics and angle-dependent sensitivity of the microphone. As mentioned, the polar pattern is based on the microphone’s primary axis.
So determining a microphone’s directionality becomes an exercise in finding the primary axis direction of the microphone. There are essentially two styles of microphones when it comes to the direction of the primary axis compared to the mic body:
- Top-address (also known as top-fire, end-fire, or end-address): the primary axis points out of the top of the microphone body.
- Side-address (also known as side-fire): the primary axis points out of the side of the microphone body.
Top address microphones are generally easy to point in the proper direction. Their bodies are typically long with the capsule at one end (the “top”) and the output connection at the other end (the “bottom”).
These mics are often small-diaphragm condenser pencil mics, handheld mics, and moving-coil mics.
Examples of top address microphones include the Shure SM58 and the Neumann KM 184:
Shure and Neumann are both featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.
Side-address microphones are a bit more difficult to point correctly but are typically easy to work with. A side-address microphone’s primary axis points out of the side of its body.
Side-address mics are often large-diaphragm condenser mics or ribbon mics.
The grilles and headbaskets of side-address mics often allow us to see the diaphragm and capsule/element of the microphone. Being able to see the capsule/element helps us to envision the primary axis pointing perpendicular from the centre of the diaphragm.
Sometimes we’ll mistake the back of the capsule/element as the front. Once the mic is plugged in, we should be able to hear and test/ensure the microphone is positioned frontward rather than backward (unless the mic is bidirectional).
Most side-address mics will have a symbol marked on the mic body to signify which side is the front.
Examples of side-address microphones include the Neumann U 87 Ai and the Royer R-121:
For a more in-depth read on microphone address types, check out my article What Are Top, End & Side-Address Microphones? (+ Examples).
Understanding Directional Microphone Design: Pressure-Gradient
There are basically two ways in which a microphone diaphragm reacts with the environment and sound waves around it. The two microphone types are known as:
- Pressure Microphones.
- Pressure-Gradient Microphones.
Pressure microphone diaphragms are only exposed to the environment on one side. The other side of their diaphragm is closed-off in a “container” that is designed to maintain ambient pressure.
Because pressure mics only have one side of their diaphragms open to sound waves, sound waves from any given direction will affect the diaphragm the same way. There will be no phase or amplitude differences to account for between the two sides of the diaphragm because the sound waves will not interact with the rear of the diaphragm.
Therefore, the pressure microphone exhibit omnidirectional polar patterns. Omnidirectional polar patterns, by definition, are not directional. With that, we’ll end our discussion on pressure mics and move onto pressure-gradient mics.
Pressure-gradient microphones have both sides of their diaphragms open to sound pressure variations.
This means that any given sound wave from any given direction will affect both sides of the mic diaphragm with varying amplitude and phase. It’s these phase and amplitude differences that cause the microphone to be more sensitive to sounds in some directions more than others.
All unidirectional pressure-gradient microphones are most sensitive to sounds on their primary axis in the “front” directional from their diaphragm.
Bidirectional microphones, which are the simplest form of the pressure-gradient mic, are equally sensitive to sounds from the front and back directions along their primary axis line.
So how do pressure-gradient microphones work?
To best understand how pressure gradient microphones work, we’ll have a look at a simple diagram of a bidirectional microphone. Remember that bidirectional mic diaphragms are equally exposed to sound at the front and the back.
With that in mind, we’ll look at sound waves coming at the mic directly from the front; directly from the back, and directly from the sides.
Sound From The Front: Bidirectional Mic
As sound arrives directly from the front of a bidirectional mic, it hits the front of the diaphragm and then, after time t, it hits the rear of the diaphragm. The time causes phase and amplitude differences in the sound wave between the front and back. These differences make the diaphragm move and the microphone output a [positive polarity] signal.
Sound From The Rear: Bidirectional Mic
Sound waves directly from the rear of the microphone will hit the rear of the diaphragm and after time t, will hit the front. This also causes phase and amplitude differences between the two sides of the diaphragm that makes the diaphragm move. Thus sounds from the rear cause the mic to create a [negative polarity] signal.
Sound From The Side: Bidirectional Mic
Sound waves directly at the side of the bidirectional microphone will reach both sides of the diaphragm at the same time with the same phase and same amplitude.
Equal pressure will be exerted on both sides of the diaphragm and the diaphragm will not move. The microphone will not produce any signal.
These are the 3 critical points to understand. However, between these points (at any angle other than 0°, 90° or 180°), the diaphragm will receive varying amounts of phase and amplitude difference when reacting to a given sound wave.
The result, in this perfect case, is a bidirectional polar pattern.
So what about unidirectional polar patterns? How are they achieved with the pressure-gradient principle?
Single-diaphragm unidirectional polar patterns are achieved by altering the path a sound wave must take to reach the rear of the diaphragm while leaving the front of the diaphragm as unobstructed as possible.
To illustrate this, let’s look at another oversimplified diagram. This time, of a cardioid microphone. In this example, we will, once again, look at the sound waves from the front, rear, and sides of the microphone.
Sound From The Front: Cardioid Mic
In this primitive diagram, we see that sound waves coming from the front of the diaphragm will hit the front of the diaphragm first. Then, after a general time 2t, the sound wave will reach the rear of the diaphragm.
This extra path length around the diaphragm and through the rear ports and acoustic labyrinth to the rear of the capsule is essential for the unidirectional polar pattern. We will see why when we look at the sound from the rear.
Sound From The Rear: Cardioid Mic
Here, we see that sound coming directly from the rear of the microphone reaches the rear ports of the diaphragm first. It takes time for these sound waves to pass through the acoustic labyrinth set behind the rear diaphragm. In fact, the rear of the capsule is designed so that it takes equal time (t) for sound waves to reach the front and rear of the diaphragm (if the sound waves come directly from the rear).
Therefore, rear sound waves cause equal pressure on both sides of the diaphragm and effectively cancel each other out. This creates a null point of sensitivity to the rear of the microphone (a characteristic trait of the cardioid polar pattern).
Sound From The Side: Cardioid Mic
Sound from the side of the cardioid pattern arrives at the front of the diaphragm and back of the diaphragm at different times (t1 and t2, respectively).
This results in some cancellation and about -6 dB relative to the on-axis response in a perfect cardioid pattern.
To illustrate the cardioid polar pattern we’ve been discussing, here is a basic polar response graph of the cardioid pattern:
For a full article on pressure-gradient microphones, check out My New Microphone’s post Pressure Microphones Vs. Pressure-Gradient Microphones.
Frequency, Proximity Effect, And The Pressure-Gradient Mic
When we’re dealing with pressure-gradient (directional) microphones, we must tune them in order to achieve a flat frequency response.
We must remember that a microphone moves according to the pressure difference between the front and rear of its diaphragm.
The distance the sound wave must travel between the front and rear of the diaphragm means a variation in phase and, therefore, localized pressure. This causes the diaphragm to move.
Higher frequencies have shorter wavelengths. These shorter wavelengths allow for a decent phase shift in the sound wave cycle as the sound wave travels from the front of the diaphragm to the rear (or vice versa).
If the frequencies are too high, the phasing becomes erratic and the directional pattern typically narrows. In general, pressure-gradient mics hold their patterns for all frequencies that have wavelengths 4 times the distance between the front and rear of the diaphragm
Low frequencies, however, have long wavelengths. When dealing with long wavelengths, the two sample points (the front and rear of the diaphragm) are only a small fraction of the wavelength apart. This means there will only be a slight pressure difference between them.
Pressure-gradient mics naturally have a frequency response that falls at 6 dB/octave as frequency goes down. This low-end roll-off is equalized out, either electrically or acoustically.
So most of the low-frequency sound waves produce very little movement in the diaphragm. However, they are typically boosted by the mic (through acoustic or electrical means) to be properly represented in the mic signal.
The Proximity Effect
This causes an issue though. The low-end boosting works well when the sound source is at greater distances. This is because the distance between the front and rear of the diaphragm is relatively insignificant compared to the distance between the mic and the sound source.
However, things change when the mic is close to the sound source and the distance between the front/back of the diaphragm is comparable to the distance between the mic and sound source. In this situation, the amplitude difference between the front and rear of the diaphragm is greater.
This is due to the Inverse-Square Law that states sound pressure level will drop by 6 dB for every doubling of distance from the sound source.
The boosting that once brought the low-end frequencies up to a respectable level now over-boosts the low-end, causing a muddy and distorted signal. This is known as the proximity effect.
To learn more about the proximity effect, check out my article In-Depth Guide To Microphone Proximity Effect.
Microphones naturally become more directional at higher frequencies and less directional at lower frequencies.
High frequencies have short wavelengths. When the sound wave wavelengths become close to or shorter than the distance between the front and rear of the diaphragm, the polar pattern becomes somewhat erratic. This is because the phase shift of the sound wave is no longer within the same period as the wave.
This erratic nature typically ends up causing increased directionality.
Low frequencies have very long wavelengths and so the phase shift between the front and back of the diaphragm is quite small. As we’ve discussed, the low-end response of pressure-gradient mics is typically boosted due to the -6 dB/octave roll-off.
The issue is that sound waves rarely ever completely cancel each other out by applying equal pressure on either side of the diaphragm. This truth of the real-world combined with the boost of the low end makes it so that the polar response widens at lower frequencies.
Directional Polar Patterns
Each microphone has its very own polar pattern that can be described qualitatively and quantitatively.
Qualitative Polar Pattern Types
Qualitatively, there is a list of polar pattern types. They include:
All the polar pattern types listed above are directional except for omnidirectional.
*Note that the hemispherical/boundary pattern is most often an omnidirectional pattern within a boundary mic. These mics are positioned against a flat boundary and pick up sound in a hemispherical pattern. In a way, these mics are directional but in most cases, we would consider them non-directional.
To learn more about the hemispherical polar pattern, check out my article The Hemispherical Boundary Microphone/PZM Polar Pattern.
Here is an example of a perfect cardioid polar pattern drawn on a polar response graph:
More on each of the directional microphone polar patterns later in this article!
In order to achieve each of these polar patterns, microphone manufacturers design their mic capsules/cartridges/elements carefully. The transducer elements have various physical offsets (acoustic labyrinths and foam, etc.) built around the diaphragms to adjust the phase and amplitude of sound waves before they reach the rear (and sometimes the front) of the diaphragm.
As we mentioned in the section on pressure-gradient microphones, the phase and amplitude differences between the front and rear of the diaphragm open up the opportunity for directional polar patterns.
Quantitative Polar Pattern Graphs
Quantitatively, polar patterns are described in a polar graph. Most manufacturers will provide polar response graphs to show the intricacies of their microphones’ directional responses.
A polar response graph represents a 2-dimensional plane around the microphone. The microphone capsule/element is at the centre of the circle in the polar response graph.
The primary axis of the microphone is shown on the graph at 0°. The polar graph then goes through 360° clockwise.
The outer circle is denoted by 0 dB. The on-axis response of a directional microphone always reaches this outer circle at 0 dB. Bidirectional microphones reach this outer circle at 180° as well.
Smaller concentric circles represent lower levels of microphone sensitivity.
A polar response line is then drawn over this polar system to represent the microphone’s angle-dependent sensitivity.
Continuing with our unidirectional cardioid microphone example, here is the polar response of the Electro-Voice RE20 (a cardioid dynamic microphone):
In the above example, we see the full polar response graph. The unidirectional polar pattern is drawn in two lines:
- A solid line represents the typical polar response above 700 Hz.
- A broken line represents the typical polar response below 700 Hz.
Because microphone polar patterns are largely frequency-dependent (remember that mics become more directional at higher frequencies), it is common to see multiple pattern lines in a single polar response graph.
Each of these lines reaches 0 dB at 0° (where the unidirectional cardioid pattern is the most sensitive). At the rear angles of the microphone, we see that the RE20 is more sensitive to lower frequencies. In other words, the RE20, like all mics, becomes less directional at lower frequencies.
Each concentric circle represents a 5 dB change in overall mic sensitivity.
Here is a picture of the Electro-Voice RE20:
It’s important to remember that this graph is simply a 2-D representation of directionality. The actual polar response of a microphone is 3-dimensional since mics operate in 3-dimensional space. This means that lobes of sensitivity are 3-D. It also means that if a polar response graph shows two null points, there is actually a ring (or cone) of silence around the microphone.
Microphones naturally become more directional at higher frequencies (and more omnidirectional at lower frequencies). No microphone exhibits a perfectly consistent polar pattern throughout its frequency response though some small-diaphragm condensers are quite consistent.
For this reason, mic manufacturers will often present their polar response graphs will multiple polar response lines. Each line represents a certain frequency and shows just how consistent the polar pattern is throughout the mic’s frequency response.
For example, the Neumann KM 184 has 8 different lines to show its frequency response at all octaves between 125 Hz and 16 kHz:
Note that the lower frequencies are listed and drawn on the lefthand side while the higher frequencies are listed and drawn on the righthand side.
Here is a picture of the Neumann KM 184:
From Most Directional To Least Directional
Microphone polar patterns are often described as being more or less directional as other patterns. The same is true for microphones themselves.
The more narrow the microphone’s response is according to its primary axis, the more directional it is. In other words, the sooner the mic’s sensitivity drops off as we move off-axis, the more directional the microphone is.
Let’s look at a list of microphone polar patterns from most directional to least directional:
Admittedly this list is rough. Placing the bidirectional polar pattern is tough. It is certainly more directional than the subcardioid in the front and rear directions. However, the subcardioid is more directional in the fact that it is most sensitive in a single direction.
With that, let take a look at the common qualitative directional microphone polar patterns:
The Shotgun/Lobar Polar Pattern
Shotgun microphones are the most directional mics on the market. The general shotgun polar pattern is shown below. Sometimes this is called the lobar pattern if the microphone exhibits side lobes (a side ring) of sensitivity.
The shotgun pattern often resembles the above pattern without the side lobes.
This pattern is achieved by extensive acoustic labyrinth design around the microphone capsule. Speaking of capsules, I’ll preface the shotgun design by writing that shotgun microphones nearly all have small-diaphragm condenser capsules.
These small-diaphragm capsules, by themselves, exhibit either supercardioid or hypercardioid patterns. The capsule is designed with its diaphragm exposed openly at the front but with a convoluted acoustic labyrinth in the back in order to phase shift the rear sound waves.
The rear narrowing comes from the long interference tube that is designed in front of the diaphragm. This tube has intermittent slots along its length. Each slot allows varying amounts of sound waves to enter the tube from each angle.
The sound waves that do enter the tube from off-axis angles largely cancel each other out via deconstructive wave interference before they ever have a chance to reach and react with the microphone diaphragm.
Sound waves that enter the top of the tube or slightly off-axis do not experience this cancellation or only experience slight cancellation at most.
The result of an interference tube placed in front of an already highly directional capsule yields the super-directional shotgun polar pattern.
To learn more about how interference tubes work, check out my article Why Are Some Microphones Long & What Are Interference Tubes?
To learn more about the shotgun polar pattern, check out my article The Lobar/Shotgun Microphone Polar Pattern (With Mic Examples).
The Hypercardioid Polar Pattern
The hypercardioid is arguably the most directional (though it’s not the most unidirectional) microphone polar pattern that is achievable within a practical microphone capsule body.
Let’s have a look at the typical Hypercardioid pattern:
The hypercardioid pattern is possible with a pressure-gradient microphone. A deeply complex acoustic labyrinth allows for this polar pattern.
For more information on the hypercardioid polar pattern, check out my article What Is A Hypercardioid Microphone? (Polar Pattern + Mic Examples).
The Supercardioid Polar Pattern
The supercardioid pattern is very similar to the hypercardioid pattern. The main difference is that the supercardioid has a wider frontal lobe and a smaller rear lobe. We could argue that this pattern in less directional but also less bidirectional and more unidirectional than the hypercardioid pattern.
Here is a graph of the basic supercardioid pattern:
The supercardioid pattern is possible with a pressure-gradient microphone. Like the other unidirectional mics, a deeply complex acoustic labyrinth allows for this polar pattern.
To learn more about the supercardioid polar pattern, check out my article What Is A Supercardioid Microphone? (Polar Pattern + Mic Examples).
The Cardioid Polar Pattern
The cardioid pattern is perhaps the most common polar pattern in professional microphones. It can be thought of as a combination of pressure (the omnidirectional pattern) and pressure-gradient (the bidirectional pattern). However, in unidirectional microphones with a single diaphragm, this pattern is produced by a complex acoustic labyrinth system in the capsule to the rear of the diaphragm.
Here’s a picture, again, of the cardioid polar pattern:
For more information on the Cardioid polar pattern, check out my article What Is A Cardioid Microphone? (Polar Pattern + Mic Examples).
The Subcardioid Polar Pattern
The subcardioid polar pattern is best described as a unidirectional pattern with an omnidirectional tendency. As we see below, this pattern has no bull points and is still relatively sensitive to the rear directions:
Once again, the subcardioid polar pattern requires the microphone to have a complex rear ports system and be tuned properly for this specific directionality.
To learn more about the subcardioid polar pattern, check out my article What Is A Subcardioid/Wide Cardioid Microphone? (With Mic Examples).
The Bidirectional Polar Pattern
As mentioned, the bidirectional (figure-8) polar pattern is the truest examples of pressure-gradient where both sides of the diaphragm are equally exposed to sound pressure variation.
The bidirectional pattern, to review, is shown below:
For more information on the bidirectional polar pattern, check out my article What Is A Bidirectional/Figure-8 Microphone? (With Mic Examples).
Directional Microphone Examples
To really get to know what directional microphones are, let’s run through some examples. Each of the examples below has a different directional polar pattern that we had mentioned above:
- Sennheiser MKH 416 (Shotgun/Lobar)
- Audix D4 (Hypercardioid)
- Electro-Voice PL35 (Supercardioid)
- Neumann KM 184 (Cardioid)
- Audio-Technica AT808G (Subcardioid)
- Royer R-121 (Bidirectional)
Sennheiser MKH 416 (Shotgun/Lobar)
The Sennheiser MKH 416 (link to check the price on Amazon) is our example of a shotgun microphone:
As you can see, this mic has the characteristic long interference tube with slots along its length. Let’s take a look at the polar pattern of the MKH 416:
As we can see, the MKH 416 is very directional and has a small rear lobe. At lower frequencies, the mic becomes less directional while at higher frequencies the mic becomes more directional a begins exhibiting strange lobes of sensitivity to its sides.
Audix D4 (Hypercardioid)
The Audix D4 (link to check the price on Amazon) is an example of a hypercardioid microphone.
The mic is a moving-coil dynamic mic designed for low-end instruments. Let’s have a look at its polar pattern graphs:
The rear lobe of the D4 is actually smaller and less pronounced than we’d expect from a hypercardioid mic. That being said, this is a highly directional mic that becomes more directional at higher frequencies.
Electro-Voice PL35 (Supercardioid)
The Electro-Voice PL35 (link to check the price on Amazon) is our example of a supercardioid microphone.
The PL35 is another moving-coil dynamic mic that is designed to clip-onto and captures the sound of drums. Here are its polar response graphs:
This microphone is nearly textbook supercardioid with its large frontal lobe and small rear lobe. As we’d expect, the PL35 becomes less directional at low frequencies and more directional at higher frequencies (it even begins exhibiting side lobes at 16,000 Hz).
Neumann KM 184 (Cardioid)
The Neumann KM 184 (link to check the price on Amazon) is a famous cardioid microphone.
This small-diaphragm condenser mic, like most high-quality SDCs, holds a consistent polar pattern throughout its frequency response:
Audio-Technica AT808G (Subcardioid)
The Audio-Technica AT808G (link to check the price on Amazon) makes the list as our example of a subcardioid microphone.
The AT808G is a dynamic microphone designed for studio talkback situations rather than for use on the podium. Its subcardioid pattern helps to capture the whole control room without capturing too much of the audio equipment (when positioned correctly). Here is the AT808G’s polar pattern graph:
Royer R-121 (Bidirectional)
The Royer R-121 (link to check the price on Amazon) is our example of a bidirectional microphone.
The R-121 is the flagship ribbon mic of Royer Labs, a major player in the game of ribbon microphones. Both rides of the R-121’s ribbon diaphragm are equally exposed to external sound pressure variation. Let’s have a look at the R-121’s polar response graph:
As we can see, there isn’t a whole lot of information but the 3 frequencies lines show us that the mic’s response is quite consistent.
A Note On Multi-Pattern Microphone Directionality
I cannot end this article without touching on the directionality of multi-pattern microphones.
Multi-Pattern Mics With Dual-Diaphragm Capsules
Multi-pattern microphones generally utilize a dual-diaphragm condenser capsule. These back-to-back diaphragms are separated by a short distance and generally have shared rear labyrinths and ports between them that make them cardioid.
Multiple patterns are achieved by combining the two capsules in different combinations of phase and amplitude. For example:
- Cardioid is achieved by turning off the rear diaphragm altogether and only using the front diaphragm.
- Omnidirectional is achieved by summing the two diaphragms at equal amplitudes and positive polarity.
- Bidirectional is achieved by summing the two diaphragm at equal amplitude but in opposite polarities (the front diaphragm in positive polarity and the read diaphragm in negative polarity).
- Supercardioid and hypercardioid are achieved by summing the front diaphragm with positive polarity and the rear diaphragm with negative polarity and less amplitude.
One such microphone that offers all 5 of the above-listed polar patterns (plus 4 intermediate patterns) is the AKG C 414 XLII (link to check the price on Amazon).
The Shure KSM9/SL (link to check the price on Amazon) is an example of a microphone manufacturer thinking outside the box when it comes to multi-directionality. This microphone has switchable polar pattern options of cardioid and supercardioid.
In the KSM9, the two diaphragms are contained within a single housing and both face forward.
The front diaphragm is tuned to between a cardioid and supercardioid pattern with the rear element connected in parallel to the front element.
The polar pattern switch on this microphone actually flips the polarity of the rear diaphragm signal. When in-phase, the overall pattern becomes cardioid. When out-of-phase, the overall pattern becomes supercardioid.
Multi-Pattern Mics With Two Capsules
Other multi-pattern microphones, like the Josephson C700A, have two separate but coincident capsules that point in the same direction. One of these capsules is omnidirectional (pressure) while the other is bidirectional (pressure-gradient).
These microphones output two separate signals and the directionality of the microphone is altered in the mixing stage.
Obviously, if we only use one capsule’s signal, we would get either omnidirectional or bidirectional.
By combining the omnidirectional and bidirectional capsules together, we achieve a cardioid polar pattern.
Supercardioid is attainable by summing the omnidirectional and bidirectional polar patterns together with an amplitude ratio of 5:3.
Hypercardioid is possible by summing the omnidirectional and bidirectional polar patterns together with an amplitude ratio of 3:1.
How does a microphone work? Microphones work as transducers, converting sound waves (mechanical wave energy) into mic/audio signals (electrical energy). Although there are various means of converting energy within different mics, they all utilize a diaphragm that reacts to sound and allows for the conversion to a mic signal.
For an in-depth explanation of how microphones work, check out my article How Do Microphones Work? (A Helpful Illustrated Guide).
What is a dynamic microphone? A dynamic microphone transducer converts energy via electromagnetic induction. A conductive diaphragm moves within a magnetic field to produce an audio signal. The term “dynamic” typically refers to moving-coil microphones though ribbon mics are also dynamic.