Famous in the world of film and broadcast but rarely used in the studio, the shotgun microphone has perhaps the most interesting direction polar pattern. To truly understand these mics and to get the most out of them, it’s critical to known the ins and outs of their polar patterns.
What is the lobar/shotgun microphone polar pattern? A shotgun microphone has a lobar polar/pick up pattern (an extension of the supercardioid or hypercardioid polar patterns). Interference tubes are placed in front of the diaphragm to achieve extreme directionality. These unidirectional mics generally have small side and rear lobes of sensitivity.
In this in-depth article, we’ll discuss the lobar/shotgun microphone polar pattern in great detail in order to answer any questions you may have about shotgun microphone patterns!
This article focuses specifically on the lobar/shotgun microphone polar pattern. For an in-depth definition of microphone polar response along with descriptions of every mic polar pattern, check out my article The Complete Guide To Microphone Polar Patterns.
Table Of Contents
- The Lobar/Shotgun Polar Pattern
- Lobar/Shotgun Microphone Generalities
- How Is The Lobar/Shotgun Polar Pattern Achieved?
- When Should You Use A Lobar/Shotgun Microphone?
- Lobar/Shotgun Microphone Examples
- All The Different Microphone Polar Patterns
- Related Questions
The Lobar/Shotgun Polar Pattern
A picture is worth a thousand words. Let’s start with a diagram of the cardioid microphone polar pattern:
Of all the standard microphone polar patterns in existence, the lobar pattern is perhaps the most intriguing.
It is unidirectional, meaning that it is most sensitive in a single direction. This is shown at 0° on-axis in the polar response graph.
However, there are three other lobes of sensitivity in the lobar polar pattern: one to either side (90° and 270°) along with one to the rear (180°). These lobes are less sensitive but nearly as narrow/directional as the main on-axis pickup.
The lobar pattern is intriguing, yes, but mostly theoretical. Most shotgun mics will certainly exhibit both the front and rear lobes, but only a fraction of them will have the side lobes of the “true” lobar pattern.
The shotgun polar pattern is typically created from a hypercardioid or supercardioid capsule, but only truly achievable with a long interference tube fastened in front of the capsule.
The interference tube is a long slotted tube that acts as a type of acoustic labyrinth in front of the mic capsule. Sound directly on-axis can pass through the tube with no issue.
Sounds that enter the tube from an angle do not have it so easy. The slots in the tube are designed to phase-cancel sound waves at different frequencies along the tube’s length.
This essentially narrows the pickup pattern of the already directional hypercardioid or supercardioid capsule, turning it into a lobar/shotgun polar pattern!
The acceptance angle of a shotgun mic polar pattern depends on the tube’s length and other design factors as well as the design of the mic capsule itself.
Lobar/Shotgun Microphone Generalities And Characteristics
- Only achievable by physical acoustic labyrinth (interference tube).
- Extension of supercardioid/hypercardioid patterns.
- Unidirectional (most sensitive to sounds in a single direction – on-axis 0°).
- Works on the pressure-gradient principle.
- Very common in film and television (on camera and boom poles).
- Most directional pattern.
- Rear lobe of sensitivity that yields 10 dB less sensitive at 180°.
- Sometimes has side lobes of sensitivity (18 dB less sensitive that on axis or more).
- Becomes more directional at higher frequencies.
- Becomes less directional at lower frequencies.
Only Achievable By Physical Acoustic Labyrinth (Interference Tube)
The shotgun/lobar pattern is only achievable by adding an interference tube in front of an already directional microphone capsule.
The interference tube effectively narrows the polar pattern by allowing on-axis sounds to pass through but phase cancelling much of the sound entering the tube at an angle.
An interference tube does this with carefully designed slots that cancel out various frequencies of sound at various points along the tube.
Extension Of Supercardioid/Hypercardioid Patterns
Although the interference tube is necessary to achieve the extreme directionality of a shotgun microphone, it also requires an already directional capsule.
Supercardioid and hypercardioid capsules are the base of the vast majority of shotgun microphones. Starting with these highly directional polar patterns makes for better directionality in the shotgun mic.
Although the lobar pattern does show multiple lobes of sensitivity, it is certainly a unidirectional pattern, having the greatest sensitivity on-axis.
Works On The Pressure-Gradient Principle
As previously mentioned, shotgun mics are built with hypercardioid or supercardioid capsules. The capsules with these polar patterns work on the pressure-gradient principle, which states that both sides of their diaphragms be open to external sound pressure.
In fact, every directional microphone and mic capsule works on the pressure-gradient principle.
Very Common In Film And Television
Shotgun/lobar mics are staples in the world of film and television. They are the mics typically found at the end of boom poles, hovering above the head of the actors. They are also often mounted directly to cameras to provide a pickup that’s narrow enough to match the camera frame.
Most Directional Pattern
Shotgun/lobar patterns range greatly in their on-axis narrowness (directionality). That being said, they are more directional than all the other microphone polar patterns.
Rear Lobe Of Sensitivity
Because shotgun mics use hypercardioid or supercardioid capsules, they have rear lobes of sensitivity.
The interference tube affects the overall polar pattern of the shotgun mic but it is not capable of removing the rear lobe inherent in hypercardioid and supercardioid capsules.
Sometimes Has Side Lobes Of Sensitivity
As we’ve seen in the ideal lobar polar response graph, there are side lobes of sensitivity in the polar pattern.
However, most shotgun mics will not show lobes at their sides. It all depends on the design of the mic and especially on how the interference tube connects with the rest of the mic.
Becomes More Directional At Higher Frequencies
Like all microphones, shotgun mics become more directional at higher frequencies. At the high-end of their frequencies responses, some shotgun mics nearly lose their rear lobe of sensitivity while others become a bit more sporadic in the way they capture directional sounds.
Becomes Less Directional At Lower Frequencies
By the same token, shotgun mics become less directional at lower frequencies.
How Is The Lobar/Shotgun Polar Pattern Achieved?
The lobar/shotgun microphone polar pattern is achieved by physical means via an interference tube.
The typical capsule of a shotgun microphone is either supercardioid or hypercardioid. It is the interference tube (effectively a front side acoustic labyrinth) that narrows the polar pattern even further in order to create the lobar/shotgun response.
An interference tube is a long tube designed to be in front of the microphone capsule. This is why shotgun mics look like elongated pencil mics.
The interference tube generally has an open top and cleverly positioned acoustic slots along its length.
An open-top allows direct on-axis sounds to pass through the tube to the diaphragm with no extra impedance.
The slots on the sides of the interference tube act to cancel out sounds entering from various side angles. by combining them out-of-phase. Different slots are often responsible for different sound frequencies.
So with an interference tube, manufacturers effectively increase the directionality of the already narrow supercardioid and hypercardioid polar patterns. This yields the extreme directionality of the microphones we call “shotguns.”
When Should You Use A Lobar/Shotgun Microphone?
Shotgun mics are often considered specialty mics. They excel in certain situations and are not even considered in most others. Let’s discuss when to use them and when not to use them:
Best Applications For Lobar/Shotgun Microphones
Shotgun microphones are popular in film but rarely see use in the studio. These specialty microphones are praised in their niche and practically ignored elsewhere. Let’s discuss each end of the spectrum.
Best Applications For Shotgun Microphones
- For film applications, whether as a boom microphone or camera-mounted microphone.
- For recording a narrow-angle of audio.
- For recording directional sounds from far away without the diffusion of off-axis sounds.
And now for the times when it’s like not appropriate to use shotgun mics:
When Shouldn’t You Use A Shotgun Microphone?
- To record natural ambience or room sound.
- Directly in front of foldback monitors in live sound reinforcement.
- Any time a microphone needs to be concealed.
- As a stationary mic to record close moving sources.
Lobar/Shotgun Microphone Examples
- Schoeps CMIT 5U
- Audio-Technica AT897
- Sennheiser MKH 60
- Rode NTG-2
- Shure VP89L
Schoeps CMIT 5U
The Schoeps CMIT 5U is a top-address small-diaphragm shotgun microphone with a supercardioid capsule. It measures 251 mm long and has unusually low colouration of off-axis sound for a shotgun mic. The CMIT 5U is very lightweight, making it an excellent mic for film (on-camera and boom alike). Its narrow pattern and natural sound also make it an ideal choice for spot-miking individual instruments in noisy environments and within large ensembles.
The Schoeps CMIT 5U Polar Response Graph
As we can see, the Schoeps CMIT 5U is very directional, as promised. By examining the 1 kHz null points at ~233°, we may infer that the capsule of the CMIT 5U is supercardioid. The 5U, like many shotgun microphones, does not exhibit the true lobar polar pattern in practice.
The rear lobe of the CMIT 5U shrinks, as expected, as the frequencies increase. The more important frontal lobe remains very consistent across the mic’s frequency response, becoming only slightly more directional in the upper-frequency range (noted by 16 kHz).
The Audio-Technica AT897 is a Line + Gradient (shotgun) electret condenser microphone with a hypercardioid capsule. It measures 279 mm long with an interference tube long enough to achieve its high directionality, but short enough that it doesn’t enter frame when mounted on-camera and fits inside most general boom pole shock mounts and blimps. The AT897 is a go-to choice for film and television for its natural on-axis pickup and excellent sound rejection from the rear and sides.
The Audio-Technica AT897 Polar Response Graph
The polar response graph of the Audio-Technica AT897 is a bit hard to read due to its wide lines. Let’s do our best to interpret it.
The null points seem to be at 110° and 250° at lower frequencies, which solidifies our understanding that the 897 has a hypercardioid capsule.
At 200 Hz, the AT897 shows its largest rear lobe, which yields about 10 dB attenuation at 180°.
At the standard 1 kHz, the 897 has a very tight shotgun pattern with a small rear lobe of sensitivity. This is what we want in a typical film shotgun mic.
Above 1 kHz (at 5 kHz and 8 kHz), the patterns are harder to discern, but seemingly take on a more standard lobar pattern with rear and side lobes to go with a narrowing on-axis response.
Sennheiser MKH 60
The Sennheiser MKH 60 is marketed as a “lightweight short gun microphone.” It is a small-diaphragm RF condenser microphone with a hypercardioid capsule. This highly directional mic measures 280 mm. Like most shotgun microphones, the MKH 60 is a great choice for reporting applications and in film (as a boom mic on camera-mounted mics).
The Sennheiser MKH 60 Polar Response Graphs
From the low-end to the high-end of the MKH 60’s frequency response, we see the microphone’s polar pattern become more and more directional.
At about 2 kHz, the hard null points fade while the frontal sensitivity begins to narrow. By 8 kHz and especially 16 kHz, the MKH 60 exhibits a more lobar-type polar pattern.
The Rode NTG-2 is a small-diaphragm shotgun microphone with a hypercardioid capsule. It measures 180 mm long and its lightweight design makes it a go-to in film, video, and television production industries. Its interference tube effectively narrows its on-axis acceptance angle while rejecting wind noise and sounds from the sides and the rear of the microphone.
The Rode NTG-2 Polar Response Graph
Rode only gives us 3 frequency points in the polar response graph of their NTG-2 microphone. From the above diagram, we gather the information we expect:
At lower frequencies, the rear lobe increases in size/sensitivity while the frontal lobe widens. In other words, the mic becomes less directional.
At higher frequencies, we see that the NTG-2 becomes more directional. Its front sensitivity pattern narrows while its rear lobe of sensitivity shrinks.
The Shure VP89L is the longest model in the VP89 line of shotgun microphones. It boasts the longest interference tube (the mic measure a whopping 386 mm in total length) along with the tightest pickup pattern (given as a 30° cone of sensitivity at the end of the interference tube.
The Shure VP89L Polar Response Graphs
Shure gives us 2 graphs to explain the polar response of its VP89L. Note that the VP89L is by far the longest shotgun mic on this list and, therefore, exhibits the narrowest directionality at the expense of potential off-axis phase issues in its sensitivity.
Even at the low frequencies on the left graph, we see that the VP89L is very directional. The rear lobe of sensitivity is really only present at 250 Hz (and below). At 500 Hz and above, the microphone begins to exhibit a more lobar polar pattern.
The right graph shows us the extreme directionality of the Shure VP89L.
All The Different Microphone Polar Patterns
Here’s a list of all the different polar patterns you’ll likely encounter when using microphones:
By clicking the links of each polar pattern title, you’ll be brought to a mynewmicrophone article that focuses on that specific polar pattern.
- Omnidirectional: picks up sound equally in all directions.
- Bidirectional: picks up sound symmetrically in the front (0°) and back (180°) with equal sensitivity but opposite polarity. Bidirectional patterns have null points at their sides (90° & 270°), which yields a “ring of silence” in 3D space. Their polar pattern looks like a figure-8 in 2D.
- Cardioid: unidirectional pattern with a null point at the rear (180°) and roughly 6 dB decrease in sensitivity at its sides (90° & 270°) compared to on-axis (0°).
- Supercardioid: unidirectional pattern with a narrower on-axis response than “regular” cardioid. Null points at 127° & 233°, which yields a “cone of silence.” There’s roughly a 10 dB decrease in sensitivity at its sides (90° & 270°) and a rear lobe of sensitivity with 10 dB less sensitivity (at 180°) compared to on-axis (0°).
- Hypercardioid: unidirectional pattern similar to supercardioid with a narrower on-axis response than “regular” cardioid. Null points at 110° & 250°, which yields a “cone of silence.” There’s roughly a 12 dB decrease in sensitivity at its sides (90° & 270°) and a rear lobe of sensitivity with 6 dB less sensitivity (at 180°) compared to on-axis (0°).
- Subcardioid/Wide Cardioid: A unidirectional pattern with a wider response than “regular” cardioid. Subcardioid can be thought of as a midway point between cardioid and omnidirectional.
- Shotgun/Lobar: An extension on the supercardioid and hypercardioid polar patterns. The use of an interference tube in front of an already highly directional capsule yields the extremely directional shotgun/lobar pattern. These patterns generally have a rear lobe of sensitivity and sometimes even have small side lobes of sensitivity.
- Boundary/PZM (Hemispherical): The hemispherical polar pattern found on boundary and pressure zone microphones. These patterns are achieved by placing the mic capsule flush to a flat surface and then placing the microphone itself at a surface/boundary within an acoustic space. The capsules themselves can be any polar pattern, though omnidirectional capsules are often preferred.
For an in-depth definition of all the polar response patterns listed above (and much more), check out my article The Complete Guide To Microphone Polar Patterns.
What are the three main types of microphone polar patterns? The three main mic polar patterns are omnidirectional, bidirectional (figure-8), and cardioid. Omnidirectional is based on the pressure principle and bidirectional, on the pressure-gradient principle. The unidirectional cardioid is a superposition of omnidirectional and bidirectional patterns.
For more information on the three main microphone polar patterns as well as all the other mic polar patterns, check out my in-depth article The Complete Guide To Microphone Polar Patterns.
What is a shotgun microphone used for? Shotgun microphones are typically used in film as boom mics and camera-mounted mics. Their extreme directionality makes them ideal candidates for capturing individual sources within a camera frame while rejecting the sounds from outside the camera frame.
To learn more about all the microphone polar response patterns, check out my article The Complete Guide To Microphone Polar Patterns.