It is a microphone with a particular acoustic pattern that hears mostly from the front of the microphone, some from the sides and none from the back. Cardioid microphones come in many shapes and sizes.
Let’s see what is a cardioid microphone and why it is the most commonly used type of mic in recording, podcasting, radio and live.
What Are Cardioid Microphones?
Cardioid Microphones are microphones that pick up sound with high gain from the front and sides but poorly from the rear. Cardioid microphones are named for the fact that their directional pick-up sounds are roughly heart-shaped.
The Cardioid Polar Plot is a typical polar patterns plot response of a cardioid microphone. Polar plots show the gain of a microphone for all the various directions that it points to concerning a fixed sound source.
The sound source stays in the same position, but the microphone is rotated around from 0° to 360°. By doing this test, we can know what the gain microphones record in all of the various directions.
Cardioid microphones have polar patterns plot response that is heart-shaped. It picks up sound with high gain, or equally sensitive to sound, from the front and sides but steeply lower when sounds are from the rear.
Cardioid microphones are used in applications that were equally sensitive to sound needs to be picked up from the front and sides but reject sound from the rear.
An example of these microphones are used in musical performance where a singer may be singing in the front, a band playing instruments on the sides, and viewers in the back.
In a scenario, microphones may be desired only to record the acoustic guitar, the singer in front, and the band on the sides, but not the audience in the rear.
For this type of scenario, cardioid microphones have great use and application.
Cardioid Microphone Generalities And Characteristics
Most Common Mic Pattern In Studio, Stage, And Broadcasting
The cardioid polar pattern microphones are by far the most popular and commonly used.
Its simple unidirectionality combined with its rear reject sound makes it an excellent choice in most studios’ professional, stage, and broadcasting.
Any time we need a clean, isolated sound source (most of the time), a cardioid microphone should be considered!
The Standard Unidirectional Polar Pattern
Though the term unidirectional refers to any most sensitive to sound in one direction (cardioid, cardioid-types, and lobar patterns), the word is often used synonymously with a cardioid.
Perhaps this is due to the popularity of the cardioid pattern mics.
This may also be because the cardioid pattern is the quintessential unidirectional pattern. It is almost equally sensitive to sound in one direction and completely insensitive to sound in the opposite direction.
Other microphone patterns may be more directional than the cardioid pattern, but they are at the expense of the rear lobes of an equally sensitive to sound.
Null Point At 180° (Directly To The Rear)
As mentioned, the cardioid polar pattern is known for its rear-facing (180°) null point.
This rear rejection to sound makes cardioid mics easy to position. Point the microphone at the sound from the sides you want to pick up and away from the sound source, you do not want to picks up sound from the sides.
The most common exploitation of the rear-facing null point is with stage monitors. Cardioid mics excel when placed in front of but pointing away from stage monitors.
This allows the singer to sing into the mics (which point at them) with high gain-before-feedback (because the mics point away and reject sound from the monitor).
Roughly 6 dB Less Sensitive At The Sides (90° & 270°)
So far, we’ve established that the ideal cardioid polar pattern is a unidirectional pattern that is the most sensitive on-axis (we’ll call it 0 dB at 0°). We’ve also stated that the cardioid pattern is not equally sensitive to sound at all to its rear (we’ll call it -∞ at 180°).
As the angle changes to either side of 0° in the cardioid polar pattern (clockwise or counterclockwise), the sensitivity decreases symmetrically until we reach the rear null point.
There is a decrease of 6 dB (relative to the on-axis sensitivity) as we pass by 90° (and 270° due to symmetry).
Note that If we base our acceptance angle on the points of -6 dB in a microphone polar pattern, the cardioid mics will have a 180° acceptance angle. This means the microphone polar patterns will likely pick up equally sensitive to sound fairly consistently within 90° to either side of its on-axis line.
The cardioid’s acceptance angle is quite wide while remaining unidirectional.
Exhibits Proximity Effect bi-directional
The cardioid polar mic requires the back of the diaphragm to be exposed to external sound pressure (albeit through an acoustic labyrinth that alters the phase and sometimes the amplitude of the sound waves).
This exhibits proximity effect means that the large and small diaphragm moves based on the difference in sound between the front and back of the diaphragm. In other words, the cardioid polar pattern is based on the pressure-gradient acoustic principle.
Microphones that work on the pressure-gradient principle (essentially every mic that is not omnidirectional microphones) exhibit a proximity effect.
Since the cardioid diaphragm’s backside is encompassed in an acoustic labyrinth, the typical cardioid mic will not exhibit as much close proximity effect as, say, a bidirectional mic (which has both diaphragm sides equally exposed).
Sensitive To Vocal Plosives
Having both sides of the small diaphragm exposed to external sound pressure also makes the cardioid microphones sensitive to vocal plosives.
Vocal plosives are tiny gusts of wind that come from hard consonant sounds in spoken language. The plosive energy is very transient and can cause a big difference in sound pressure between the front and rear of the diaphragm.
These quick but large variations in pressure cause plosive pop to appear in the mic signal as the diaphragm/capsule is overloaded.
Similarly, cardioid microphones are sensitive to wind sounds.
Excellent Sound Isolation
Due to the reject sound from the rear and unidirectionality of the cardioid pattern, cardioid mics work wonders at isolating individual sound sources.
The wide (180°) acceptance angle of the typical cardioid microphone also gives some leeway to the dynamic positioning of or mic movement relative to the sound source.
By positioning a cardioid mic properly, we can essentially isolate a single sound source.
This works best when close-miking a source without any other sound sources near or behind it. It helps if the unwanted sound sources are behind the microphones in the direction of the cardioid’s rear null point.
Sound isolation is essential in loud environments like the live room ambiance of a studio. It’s also essential is noisy live stages and venues.
Isolation also plays a big role in the less-that ideal recording environments and even in soundproof rooms to hone in on a specific source, which brings us to our next point:
Great For Miking A Single Source
Cardioid microphones are a go-to for miking single sources. Common single-source cardioid miking situations include:
- Spot-miking single instruments in a large ensemble.
- Miking individual drums or percussion elements in a drum kit/ or percussion setup
- Capturing a single person’s voice in the studio or the field
- Close-miking instruments in the studio and on stage
The cardioid microphone, when positioned correctly, may achieve a great deal of gain-before-feedback in live sound reinforcement situations.
This is due to the rear null point, making it easy to position the mic: point it away from any monitors or loudspeakers.
Feedback loops are created when a microphone picks up sound from a loudspeaker emitting that same microphone’s signal.
Simply pointing the cardioid away from a live speaker will allow for excellent gain-before-feedback.
Very Common In Coincident And Near-Coincident Stereo-Miking Techniques
As we’ll discuss in the next section, cardioid microphones are very popular in coincident and near-coincident stereo-miking techniques. This kind of ties into the fact that cardioids mics work great close to their sound sources.
Becomes More Directional At Higher Frequencies
Like all mics, real cardioid microphones will generally become more directional at high frequency.
We’ll see in the microphones examples that, sometimes, the polar response pattern may begin resembling a supercardioid/hypercardioid pattern at higher frequencies with a rear lobe of sensitivity.
This is partly because, at higher frequencies, phase differences become sporadic between the front and back of the cardioid diaphragm mics, making amplitude differences more important to microphone directionality.
Becomes Less Directional At Lower Frequencies
In reality, mics become less directional at lower frequencies.
In cardioid microphones, mics may even lose their rear null point at lower frequencies and exhibit a more subcardioid/wide cardioid polar pattern.
Makes The Typical Default Patterns Of Each Diaphragm In Dual-Diaphragm Multi-Pattern Microphones
Multi-pattern microphones typically have a dual-diaphragm capsule that features two back-to-back cardioid diaphragms (with the proper housing and rear-side acoustic labyrinths).
The multi-pattern microphone is combined with the signal amplitudes and polarities of these two cardioids’ capsules yields various other microphone polar patterns.
The Mid Microphone In Mid-Side Techniques
A cardioid mic provides the mid-channel in the famous mid/side stereo-miking technique.
The side channel is provided by doubling up the signal of perpendicularly positioned bidirectional microphones. Panning the signals left and right and flipping the phase of one of them yields the side information that disappears when the mix is collapsed to mono.
Read more about what stereo miking is: https://ehomerecordingstudio.com/stereo-microphone-techniques/
Works On The Pressure-Gradient Principle
As mentioned, the cardioid polar pattern is only achievable with the pressure-gradient principle. This means that both the sides of the mic diaphragm microphones must be exposed to external sound pressure.
Only Achievable With An Acoustic Labyrinth Covering The Rear Of The Diaphragm
The directionality of the cardioid microphone is brought about by carefully adjusting the path of sound before it reaches the rear side of the diaphragm. This is done with what is known as an acoustics labyrinth.
A 1:1 Ratio Of An Omnidirectional microphones And Bidirectional Pattern
One way of explaining the cardioid polar patterns is to superposition the omnidirectional microphones and bidirectional polar patterns.
As we see below in the diagram/equation, the positive polarities of the Omnidirectional microphones and bidirectional polar patterns mics add up to give the cardioid essential +2 in phase at 0° on-axis.
Conversely, at 180°, the positive polarity of the omnidirectional pattern cancels out with the negative polarity of the bidirectional pattern, causing the rear null point of the cardioid microphones.
As we move further off-axis, the negative polarity of the bidirectional pattern’s rear lobe slowly combines with the positive polarity of the Omni. It reduces the sensitivity of cardioid symmetrically between 0° and 180°.
Omnidirectional + Bidirectional = Cardioid (Superposition)
This is indeed a clever way of explaining the cardioid polar patterns.
Most common cardioid mics
one of the most popular microphones in the world of audio. The dynamic microphone capsule is most sensitive to sound to makes it perfect for live shows and recordings, from vocals, horns, and brass to drums and acoustic guitar amps. The dynamic mic can take strong sound pressure. It has long durability and great cost-benefit.
Highly chosen among other diaphragm condenser microphones of cardioid pattern. The condenser microphone has a wide frequency response and low noise pick-up. Recommended for home studios and live recordings to block out any unwanted noises.
Shure SM57 dynamic microphone is a top-address, moving-coil dynamic microphone that features a cardioid polar pattern. This mic is a favorite worldwide and is known as one of the best microphones are used by studio workhorses.
This microphone is rugged and affordable, making it a favorite jack-of-all-trades for audio engineers working in studios worldwide.
Like most cardioid microphones, the Shure SM57 is close to ideal cardioid patterns at 1-2 kHz. As you can see, the pattern of the 57 is very similar to a subcardioid at lower frequencies (shown above at 125 Hz), while the SM57 develops a rear lobe that is reminiscent either of a hypercardioid/supercardioid at higher frequencies (4-8 kHz).
Nevertheless, the frontward response is the most critical aspect of this unidirectional microphone. The SM57 responds within 60deg of its on-axis response. This means that the cardioid pattern has a proximity effect in practice.
The SM57 does not have a high level of sensitivity in the high-end frequencies. Therefore, it is logical to omit the 16 kHz (octave over 8 kHz) pattern, commonly found in polar response graphs.
Neumann KM 184
The Neumann KM 184 small-diaphragm actual condenser microphone has a cardioid polar pattern and top-address.
The microphone’s flat frequency response, high transient response, and consistent polar response make it an excellent choice for studio use. The KM 184 is a versatile microphone that can be used in both close-miking mono techniques and near-coincident and coincident stereo-miking techniques.
Condensers microphones with small diaphragms are well-known for their consistency in polar patterns. This is evident in the Neumann KM 184, a high-end condenser.
The split graph above shows that even at 125 Hz, KM 184 maintains 16 dB (rear rejection) and 6 dB (side rear rejection). The rear null point is valid from 250 Hz up to 4,000 Hz. This covers a wide range. The KM 184 retains its cardioid pattern at higher frequencies very well.
Rode’s flagship microphone, the Rode NT1A-A, is made by Australian microphone manufacturer Rode. This microphone is large-diaphragm and has a cardioid pattern of polar response.
The NT1-A is an excellent choice for professional and home studios due to its low self-noise and accurate response.
Rode doesn’t give away too many details here, showing only three frequencies in its Polar Response graph.
Nevertheless, the NT1A is not as intuitive as we thought. The NT1-A becomes less directional at 4kHz than it is at 1kHz. The polar microphone patterns tend to become more directional above 1 kHz while becoming looser below 1 kHz. The polar response graph for the NT1A shows us that this is not true.
Shure’s WL185 cardioid line of subminiature lavalier/lapel-electron condenser microphones is now available in the Shure WL185.
Technically, the WL185 can be used as a top-address microphone. The WL185 is like most lav microphones. It’s usually attached to the clothing or hair of speakers for film and video applications.
The polar response graph for the Shure WL185 is shown above. It looks like a simple ideal cardiac pattern. There is no distinction between frequencies.
This is quite common with small lavalier/lapel mics. Manufacturers may not include a graph of polar response for their lav microphones because they are small and consistent, which allows microphones to be more ideal in all frequencies.
When should you use a cardioid microphone?
The most widely used microphone polar pattern worldwide is the cardioid microphone. A cardioid pattern would be most beneficial for any microphone role, from the studios to broadcast locations to the stage to the studio and everything in between.
Cardioid microphones are ideal for many situations because of their unidirectionality, rear rejection, and simple unidirectionality. Let’s take a look at some of the most critical applications for cardioid microphones.
The Best Cardioid Microphone Applications
- Directly in front of a foldback monitor in live sound.
- reinforcement situations.
- If high gain-before-feedback is required.
- To isolate/close-mic single sound sources in noisy ambiance.
- Mic individual sound sources that are close together (e.g., drums in a drum set).
- Clean audio capture in less-than-ideal environments.
- If proximity effect is desired.
- To ensure maximum rejection sound to the rear.
Many situations call for cardioid microphones. The other microphone polar patterns are often better than the cardioid. These are some situations in which a cardioid microphone (or microphone polar pattern) may not be the best option:
Why Should You Use a Cardioid Microphone?
- If the sound source is moving coil around the microphone (off-axis coloration).
- Vocal plosives can be a significant problem.
- If the proximity effect does not suit your needs.
- To capture the most natural ambiance/room.
The cardioid directional doll is a very versatile model and is great for all uses. Whether you are looking for microphones to record live, acoustic guitar, youtube, or big concerts, cardioid is one of the indispensable choices if you want other situations where noise reduction and feedback suppression are needed.
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