The omnidirectional microphone polar pattern is perhaps the simplest polar pattern and is one of the three main polar pattern types (along with bidirectional and cardioid). Understanding the omnidirectional pattern and how omnidirectional microphones perform will give you a solid foundational knowledge of mic polar patterns and microphones in general.
What is an omnidirectional microphone? An omnidirectional microphone has an omnidirectional polar pattern and is equally sensitive to sound from every direction. Unlike their directional counterparts, omni microphone capsules have only one side of their diaphragms open to external sound pressure.
In this in-depth article, we’ll discuss the omnidirectional microphone polar pattern in great detail in order to answer any questions you may have about omnidirectional microphones!
This article focuses specifically on the omnidirectional 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 Omnidirectional Polar Pattern
- Omnidirectional Microphone Generalities
- How Is The Omnidirectional Polar Pattern Achieved?
- When Should You Use An Omnidirectional Microphone?
- List Of Miking Techniques With Omnidirectional Microphones
- Omnidirectional Microphone Examples
- All The Different Microphone Polar Patterns
- Related Questions
The Omnidirectional Polar Pattern
A picture is worth a thousand words. Let’s start with a diagram of the omnidirectional microphone polar pattern:
The ideal omnidirectional polar pattern (shown by the darker outer ring of the above diagram) is equally sensitive to sound from every direction. In other words, it has an acceptance angle of 360° about its primary axis, which is shown about the 0° point in the above diagram.
Omnidirectional mics work on what is known as the pressure principle. The pressure principle is an acoustic principle that basically describes a microphone capsule that only has one side of its diaphragm exposed to sound pressure.
Pressure is a scalar quantity rather than a vector quantity (it has no direction). Since external sound pressure can only act on one side of the omnidirectional diaphragm, it, in theory, has no directivity.
Omnidirectional Microphone Generalities And Characteristics
Though every microphone is different, those mics with an omnidirectional polar pattern all exhibit some of the same qualities. Understanding the general characteristics of omnidirectional mics allows us to make better decisions as to whether we use them or not.
Let’s look at the general characteristics and typical truths of omnidirectional microphones:
- Equally sensitive to sound from all directions.
- Achieved with the pressure principle in single-diaphragm microphones.
- No null points.
- No lobes of sensitivity.
- Does not exhibit proximity effect.
- Resistant to vocal plosives.
- Resistant to wind noise.
- Most natural sounding polar pattern.
- Prone to feedback (low gain-before-feedback).
- Becomes more directional at higher frequencies (becoming more subcardioid or even supercardioid).
- The larger the microphone body, the more difficult it is to achieve the ideal omnidirectional polar pattern.
- Common pattern in top-address pencil, lavalier, handheld, and conference microphones.
Equally Sensitive To Sound From All Directions
As stated previous, the omnidirectional polar pattern, as the name suggests, it sensitive to sounds in all directions. This is the simplest way to describe the omnidirectional pattern.
Omni mics generally only have one side of their diaphragms open to external sound pressure, which creates this omnidirectional pattern.
Note that at higher frequencies, the body of the microphone will begin to affect the directional sensitivity of the sound waves reaching the diaphragm (due to the shorter wave length of these waves at higher frequencies). Therefore, it’s best to expect slight unidirectionality in omnidirectional microphones in the upper frequencies. This typically isn’t overly noticeable, but a physical trait of the mic pattern.
Achieved With The Pressure Principle In Single-Diaphragm Microphones
The pressure principle is an acoustic principle that basically states that only one side of a microphone’s diaphragm is open to external sound pressure. The other side (rear side) is closed off in a constant pressure chamber that approximates standard atmospheric pressure.
The diaphragm, then, moves according only to the differences in [sound] pressure at its front side. If the sound pressure is greater than atmospheric, the diaphragm moves inward. If the sound pressure is less than atmospheric, the diaphragm moves outward.
The movement of the diaphragm coincides with the mic signal.
Since pressure is a scalar quantity (it has no inherent direction), having only one side of the diaphragm exposed creates a directionless (aka omnidirectional) polar response pattern!
Related article: Pressure Microphones Vs. Pressure-Gradient Microphones.
No Null Points
Because the omnidirectional mic is ideally sensitive to sounds in all directions, it has no null points. This affects its capability to isolate sound sources, to reject unwanted sound sources, and reduces its gain-before-feedback.
No Lobes Of Sensitivity
Being sensitive in all directions means there are no lobes of sensitivity to watch out for in omni microphones.
Does Not Exhibit Proximity Effect
The proximity effect only takes place in pressure-gradient microphones (those mics that have both sides of their diaphragms open to external sound pressure).
The proximity effect’s bass increase at close distances has to do with the increasing difference in low-frequency amplitude between the two diaphragm sides relative to the difference in low-frequency phase between the two diaphragm sides.
This is completely avoided by having only one side of the diaphragm open to external sound pressure.
To read more into the proximity effect, please check out my article What Is Microphone Proximity Effect And What Causes It?
Resistant To Vocal Plosives
Omnidirectional mics are much more resistance to vocal plosives than their directional counterparts.
This, again, has to do with the omnidirectional mics only having one side of their diaphragms exposed to external sound pressure.
As plosive energy passes a pressure-gradient mic, it builds up pressure at one side while greatly reducing pressure at the other. This causes an overloading of the diaphragm and a “pop” in the mic signal.
Having only one side of the diaphragm open, as with pressure principle omnidirectional microphones, greatly reduces the risk of vocal plosives.
For a better explanation of vocal plosives along with methods of reducing/eliminating them from mic signals, check out my article Top 10 Tips For Eliminating Microphone Pops And Plosives.
Resistant To Wind Noise
By the same token as above, the pressure principle allows omnidirectional mics to be less sensitive to wind noise and gusts of wind than their directional counterparts.
Most Natural Sounding Polar Pattern
Because the ideal omnidirectional microphone is equally sensitive to sounds in all directions, it has no off-axis colouration.
No off-axis colouration means the omni mic will capture sounds with the same frequency response from all directions. With no sound quality differences in sounds from various angles, the omnidirectional mic will sound more natural than its directional counterparts.
Not that, in reality, omni mics will exhibit some colouration at high frequencies.
Prone To Feedback (Low Gain-Before-Feedback)
Omnidirectional polar patterns have no null points and no angles of decreased sensitivity. This makes them very prone to feedback in live sound reinforcement situations.
Directional mics will generally have null points which can be directed toward loudspeakers or monitors (think of positioning a cardioid mic’s pointing away from a stage monitor so its rear null point rejects the sound from the monitor while the mic remains sensitive to the singer in front of it).
Omni microphones, conversely, are equally sensitive in all directions, so positioning an omni mic near a foldback monitor or loudspeaker is a recipe for feedback.
For more information on microphone feedback and how to avoid it, check out my article What Is Microphone Feedback And How To Eliminate It For Good.
Becomes More Directional At Higher Frequencies
As with all microphones, omnidirectional mics become more directional at higher frequencies.
In pressure principle omnidirectional microphones, this is due to the nature of short wavelength/high frequency sound waves. The high end sound waves have a harder time getting around the physical microphone body from the rear in order to effectively move the diaphragm.
The Larger The Microphone Body, The More Difficult It Is To Achieve The Ideal Omnidirectional Polar Pattern
As discussed above, higher frequency sound waves difficulty moving around physical microphone bodies. This affects the directionality of omnidirectional mics at high frequencies.
If an omnidirectional mic becomes directional, it is no longer “ideal.”
Generally speaking, smaller omni microphones (like lavalier/lapel mics) are capable of holding a more consistent “ideal” omnidirectional polar pattern than their larger counterparts.
Common Pattern In Top-Address Pencil, Lavalier, Handheld, And Conference Microphones
The omnidirectional polar pattern is easily achievable and a common pattern in the following mic types:
- Top-address pencil mics: many small-diaphragm condenser and moving-coil dynamic pencil mics have a pressure gradient capsule with an omnidirectional polar response.
- Lavalier mics: lav/lapel mics often benefit from omnidirectional patterns due to their natural and wide pickup, capturing consistent audio as the talent moves his or her head. Lavalier/lapel mics do not usually need to be directional when positioned correctly on the talent.
- Handheld mics: handheld mics, especially those used in reporting or interviews (rather than on stage), are omnidirectional. An omni pattern reduces the need for moving the microphone drastically every time someone new begins speaking.
- Conference mics: an omnidirectional polar pattern is the way to go when choosing a conference microphone. That way everyone around the room can be heard equally.
How Is The Omnidirectional Polar Pattern Achieved?
The omnidirectional pattern is achieved via the pressure principle: an acoustic principle that exposes only the front side of the microphone to external sound pressure. The rear side of the diaphragm is closed off in a “chamber” of fixed pressure that approximates the atmospheric pressure.
Sound pressure is a scalar quantity. So although sounds may move in somewhat defined directions, sound pressure itself does not have directional properties.
Note that the directional characteristics of directional mics (all non-omnidirectional mic) are achieved through phase and amplitude differences in sound pressure on their diaphragms and not from any inherent directionality of sound pressure. For the most part, sound itself is also omnidirectional.
So with only one side of the diaphragm for sound pressure to react with, the angle at which a sound waves hits the diaphragm is not a critical part of the equation. Rather, the amplitude of the sound pressure is what causes the diaphragm to move and give the omni mic its all-encompassing polar pattern.
When there is a lower-than-atmospheric pressure at the front of the diaphragm, the omnidirectional mic’s diaphragm moves outward. When the exterior pressure is greater than atmospheric at the front side of the diaphragm, the diaphragm moves inward. These differences are what causes the typical omnidirectional microphone to produce and output a mic signal.
Achieving The Omnidirectional Polar Pattern In Multi-Pattern Microphones
Things change in multi-pattern microphones. It’s not overly practical to add a pressure-style capsule within a multi-patter microphone that would only be engaged in ‘omnidirectional mode.’
The vast majority of multi-pattern microphones have either a single dual-membrane capsule with back-to-back diaphragms or two back-to-back capsules. These capsules/diaphragms nearly always have cardioid polar patterns, which are unidirectional (sensitive on-axis/to the front and insensitive 180° off-axis/to the rear.
In order to achieve the omnidirectional pattern, then, the mic signals from each diaphragm are summed together in-phase and at equal amplitudes. The result is not a true omnidirectional pattern based on the pressure principle, but approximates and acts as an omnidirectional pattern just the same.
When Should You Use An Omnidirectional Microphone?
There must be some best practices or preferred applications of omnidirectional microphones or else they wouldn’t sell. So what should someone choose an omnidirectional mic instead of a mic of any other polar pattern.
The truth is, you should get creative with the kinds of microphones you use in different applications. However, there are some tried and true method and miking techniques that are popular for good reasons. Let’s get into common practice with using omnidirectional microphones.
Best Applications For Omnidirectional Microphones
- When a most natural recording is preferred.
- On single sources in isobooths to eliminate proximity effect issues.
- On single sources in isobooths to rid of vocal plosive issues.
- Overhead stereo and surround sound techniques for larger rooms and larger ensembles.
- Mono of stereo pair miking techniques to capture more room sound.
- Natural pick up for lavalier recordings.
- When recording a moving target.
- For conference calls.
- In intercom systems.
- To reduce wind in outdoor ambience recordings.
- To help reduce the amount of handling noise.
As with all microphone types, there are the best practices, and the worst practices. Next up the ways in which omnidirectional mics do not perform well.
When Shouldn’t You Use An Omnidirectional Microphone?
- In live reinforcement situations that call for high gain-before-feedback.
- In noisy environments.
- For close-miking/isolating single sound sources.
List Of Miking Techniques With Omnidirectional Microphones
Here is a list of miking techniques that include omnidirectional microphones:
- Close-Miking (mono)
- Olson Wing (stereo)
- Stereo Ambient Sampling System (stereo)
- Spaced Omnis (stereo)
- Decca Tree (stereo)
- AB Technique (stereo)
- Ball Boundary Technique (surround sound)
- Fukada Tree (surround sound)
- Hamasaki Surround System (surround sound)
- Omni+8 Surround (surround sound)
- Polyhymnia Pentagon (surround sound)
For more information on stereo miking techniques, check out my article Top 8 Best Stereo Miking Techniques (With Recommended Mics).
Omnidirectional Microphone Examples
Each of the above-listed brands are featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.
Neumann M 150
The Neumann M 150 is based on the design of Neumann’s legendary vintage M 50 microphone. It is a side-address small-diaphragm tube condenser microphone with an omnidirectional polar response pattern. Just like the M 50 it emulates (and replaces on the Neumann product line), the M 150 performs its best on orchestral recordings and is a go-to in the Decca Tree and many other stereo-miking techniques.
The Neumann M 150 Polar Response Graph
As we see above, the polar pattern of the M 150 is very consistent, which is a common trait in small-diaphragm condenser mics. It holds its omnidirectional pattern, arguably, up to 8 kHz, which is very impressive.
It’s worth noting that the Neumann M 150 polar response graph is drawn on a split diagram. The lower frequencies (125 Hz – 1 kHz) to the left and the upper frequencies (2 kHz – 16 kHz) on the right.
Above the standard 1 kHz measurement and below the 16 kHz pattern, the M 150 slowly morphs into a more subcardioid polar pattern. This is completely expected, since microphones naturally become more directional at higher frequencies.
At 16 kHz, we see that the M 150’s polar response curve resembles more of a lobar/shotgun-type polar pattern. There isn’t much sonic information above 16 kHz (often referred to as the “air” band of frequencies). We can therefore intuit that the M 150 is certainly an omni mic and will behave like so across the vast majority of the sound spectrum!
DPA d:dicate 4006A
The DPA 4006A combines DPA’s modular 4006 omnidirectional capsule with its long pencil-like amplifier. The 4006A is a top-address small-diaphragm electret condenser mic. This mic is the most popular in DPA’s d:dicate line and is marketed as an ideal mic for A-B stereo pairings, studio vocals, and for close-miking instruments.
The DPA d:dicate 4006A Polar Response Graph
DPA makes incredibly high-quality microphones with impeccable consistency. Looking at its polar response graph, the 4006A is no exception.
Starting at the standard 1 kHz, we find that the 4006A exhibits a perfect omnidirectional patter. As we would expect, the mic slowly become more directional above 1 kHz, but not overly directional.
Even at 8 kHz, the 4006A’s rear (180°) pickup is only attenuated 2.5 dB. This is just bordering on subcardioid and could certainly still be considered omnidirectional. Most other omni mics would be getting quite unidirectional at this point, but not the 4006A.
We see that at the high end of the sound spectrum (16 and 20 kHz), the 4006A does become fairly unidirectional, which is to be expected. All in all, the 4006A is a prime example of an omnidirectional microphone.
The Audio-Technica AT4022 is another top-address small-diaphragm “pencil” condenser microphone. Its electret-style capsule yields an omnidirectional polar pattern. The AT4022’s small diaphragm yields a flat frequency response, consistent polar pattern, and accurate transient resposne that makes it an excellent choice for studio and live applications as well a great option for recording ambience.
The Audio-Technica AT4022 Polar Response Graph
Audio-Technica’s polar response graphs are a bit less involved than the previously mentioned Neumann and DPA graphs. Nonetheless, it shows us the most important frequencies in the AT4022’s polar response.
As expected, at the lower frequencies (200 Hz and 1 kHz), the 4022 shows an ideal omnidirectional pattern. However, as we approach 5 kHz and 8 kHz, the microphone becomes more and more directional. At 8 kHz, the AT4022 exhibits more of a subcardioid polar pattern than an omnidirectional one.
The Rode Reporter is a handheld top-address moving-coil dynamic microphone with an omnidirectional polar response pattern. This microphone is a great choice for single-microphone interviews in the field. The omni patterns allows for a more consistent capture of sound without having to immediately point the mic at a person as soon as they start speaking.
The Rode Reporter Polar Response Graph
Rode shows us even less than Audio-Technica in terms of frequency rings in their Reporter microphone polar response graph.
The information gathered from the above graph tells us what we already know: The Rode Reporter exhibits a clean omnidirectional polar pattern at low frequencies (500 Hz), and, as the frequencies increase, the mic becomes more and more directional.
That being said, the Reporter is arguably more omnidirectional than subcardioid at its highest given rating (4 kHz). This may, at first glance, make the Reporter look more omnidirectional than it truly is.
DPA d:screet CORE 6060
The DPA d:screet CORE 6060 is a top-of-the-line electret condenser lavalier/lapel microphone with an omnidirectional polar pattern. This microphone is ideal for any situation that would call for a lav mic. Whether that’s on video, on the theatre stage, or during a hands-free presentation.
No polar response graph available for the DPA d:screet CORE 6060. Because this microphone is so small (and DPA makes very high quality mics), it can be assumed that it exhibits a polar response approximate to the ideal omnidirectional polar pattern.
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 is a unidirectional microphone? A unidirectional microphone is most sensitive to sound in one single direction, known as its “on-axis.” These mics are less sensitive to and may even completely reject off-axis sounds. The cardioid is the most popular unidirectional pattern, though there a many others, including:
What is the function of a microphone? A microphone is a transducer of energy. Its function is to convert mechanical wave energy (sound waves) into coinciding electrical energy (audio signals). In other words, mics turn sound into audio. There are various methods to achieve this conversion, but all have some sort of vibrating diaphragm.
To learn more about all the microphone polar response patterns, check out my article The Complete Guide To Microphone Polar Patterns.