A microphone’s polar pattern can be a powerful tool when trying to control what the mic hears, what it doesn’t hear and where you can put it without compromising the sound. There’s more to mics than cardioid.

Brief Summary

Cardioid is cool but if you’ve ever wondered why when you choose another pattern other than cardioid you usually go back to cardioid, maybe it’s because if you change the pattern you probably need to move the mic too?

Going Deeper

Pretty much anyone who has used a microphone will be aware of microphone pickup patterns. Not all mics are equally sensitive from all directions. These ‘Polar Patterns’ are extremely useful to people who use microphones but most people stick with one pattern pretty much all of the time. Are they missing out?

What Is A Polar Pattern Anyway?

The most familiar microphone pattern is probably cardioid. It’s easy to understand how it works. Cardioid mics are sensitive from in front and progressively less sensitive until you reach the back of the mic. The other most commonly encountered mic type is omnidirectional, meaning that the mic is equally sensitive from all directions. So far so easy. And for many people that’s as far as it goes, with a cardioid mic you can control what gets recorded by pointing it in that direction. Therefore cardioid mics are best - right?

Not right. There is a whole range of polar patterns available in what are known as the first order of polar patterns and each has its particular strengths and weaknesses. It is possible to make great recordings with just cardioid mics, but a working knowledge of the other patterns can help with all sorts of microphone placement issues.

Consider What You Don’t Want In the Mic As Well As What You Do

Hypothetical example - Someone has a mic with two polar patterns (as it’s hypothetical let’s make it a U47!) They audition it in cardioid. It sounds dry and full. They listen to it in Omni and it sounds thin and distant. Cardioid must be better. That person uses cardioid on everything from that point forward.

This is a tongue in cheek example but it’s not all that far fetched (apart from the U47). Many people neglect these alternative patterns because Cardioid seems the best choice. If you could only have one polar pattern then Cardioid probably is the best choice but you can use any polar pattern you have available, so why not use them?

Some stereo recording techniques require use of specific polar patterns but on individual, mono sources the main reasons for choosing a polar pattern other than cardioid is either to keep unwanted sounds out of the mic or to minimize unhelpful characteristics of an alternative pattern. Not all polar patterns sound the same. It can also of course be to control what gets captured but in my experience I’m usually looking to control the spill from unwanted sounds through use of polar pattern more than anything else.

So looking at the polar patterns in turn:

Cardioid

The most common, easy to describe, much more complicated to explain how it works, the cardioid pattern, so called because its plot is heart shaped, is most sensitive from the front and rejects most fully at the back. It isn’t the most directional of the patterns and the rear null isn’t the deepest null you can get. But it’s very convenient, and extremely popular. If you have a single pattern condenser mic it will almost definitely be cardioid and the most popular stage dynamics are all cardioid.

Does it have potential downsides? Yes. All directional mics, including fig 8 and the various varieties of cardioid, exhibit a behaviour known as ‘proximity effect’. This is an increasing bassiness which increases dramatically as the mic is placed closer to the source. This is common to all mic patterns apart from Omni’s. The other potential drawback is that the frequency response changes as you move ‘off axis’. Sounds captured from the sides, rear or above and below will sound coloured compared to sounds arriving from directly in front.

Returning to my hypothetical example. The Cardioid mic sounded dry and full. This was because the polar pattern captured less of the reflected sound from in the room, giving a dryness to the sound, and it sounded full because the mic was close to the speaker, allowing the proximity effect to lift the bass for a full sounding voice.

The Omni mic in that example sounded thin because it lacked proximity effect (although omni mics actually have better bass response than cardioid, they just don’t exaggerate it), and it sounded distant because of the room reflections the polar pattern picked up.

Omni

So on to Omni. The hypothetical U47 owner seems to have proved that cardioid is best. What is the point of Omni?

Firstly, Omni mics don’t exhibit the proximity effect, meaning that they can be used at any distance without the timbre changing significantly, particularly they can be used very close if necessary. Secondly, while there is more sound captured front the rear of the mic, that ‘spill’ from other sources isn’t coloured like it would be with a cardioid mic. It is ‘good’ spill. This is why Omni mics are often favoured by classical recordists. Many people are put off using omnis because they compare them with cardioid at the same distance. This is often not the best way to compare because of the mics differing Distance Factors. We’ll return to this later.

Fig 8

Figure of 8 microphones are equally sensitive from the front and back but are insensitive from the sides (and top and bottom, polar patterns work in three dimensions). One of the most useful things about fig 8 mics is that the side nulls they have are very deep. These mics are almost completely deaf from the sides. A cardioid mic by comparison doesn’t reject sounds from the rear nearly as well as a fig 8 does from the sides. It should be noted that the front and rear of a fig 8 mic are in opposite polarity from each other. This can be very useful, for example in Mid/Side applications, but needs to be kept in mind when using them.

There are other first order patterns. They all fall somewhere on a spectrum with Fig 8 at one end, Omni at the other and Cardioid in the middle. Between Fig 8 and Cardioid you’ll find Hypercardioid and Supercardioid, between Cardioid and Omni you’ll find the various flavours of wide and sub cardioid mics. Fixed pattern mics are common and many dual diaphragm condenser mics offer a variety of fixed choices but by mixing the outputs of the two diaphragms in a dual diaphragm mic you can achieve any pattern between omni and Fig 8.

So If Anything Between Fig 8 and Omni is possible, What Is Special About Cardioid, Hypercardioid and Supercardioid?

The reason Cardioid is a special case is that it is the point in this spectrum where the rear null is deepest. Beyond that point a rear lobe begins to develop and the cardioid mic begins to turn into a hypercardioid. A cardioid mic has the deepest rear facing null.

Hypercardioid is the first order pattern with the greatest directivity. This is measured by mic designers as its Random Efficiency or RE. it’s a measure of the on axis directivity relative to to its response to sounds arriving from all directions. A low number is more directional. Omni is least directional with an RE of 1, Hypercardioid is most directional with an RE of 0.25. See the table below.

Supercardioid is very similar to Hypercardioid. The distinguishing feature of this pattern is that it is the most forward facing, in terms of comparing its front to back sensitivity.

Subcardioid Mics. Lastly there are the patterns which fall between cardioid and omni. Wide or sub cardioid mics are a useful choice when something between these two would be useful, read about Luke’s experience with Subcardioid mics here.

Distance Factor

As alluded to earlier, the distance from which different mics should ideally be used varies with pattern. One of the things which dictates the best mic position on a source is the relative level of the direct sound from subject to mic, and the reflected sound which has bounced off another surface on its way to the mic. Because this reflected sound arrives from all directions, the polar pattern of directional mics reduces its level from some directions. So a cardioid mic sounds dryer than an omni at the same distance.

In a sense this isn’t really comparing like with like though. If you compare the sound of an omni which is 1m away with the sound of a cardioid which is 1.7m away you will be comparing the same ratio of sound from directly in front of the mic with sound arriving from all directions. This ratio, comparing direct to reverberant sound is a useful measure of a mic’s ‘reach’. The mic’s ability to capture direct sound relative to indirect sound is important and sometimes polar patterns other than Cardioid offer a solution to placement issues.

Distance factor - The measure of ‘reach’ of a microphone in a reverberant environment relative to an omni. A higher number is a ‘dryer’ mic.

Random Efficiency - The measure of on-axis directivity relative to sound arriving from all directions. A lower number is more directional.

So the principal characteristics of polar patterns when using microphones are the reach of the mic, based on its ability to capture direct sound relative to indirect sound. If you are too distant in a reverberant space your recording might be too ‘wet’. The forward acceptance angle, a pattern has to be wide enough to capture the entire sound of the instrument and if you are close you might lose an aspect of that sound, for example miking a piano too close will favour certain strings over others, and the rejection of off axis sound. Keeping out the sound you don’t want. For example using fig 8 mics to keep a singing guitarist’s vocal out of the guitar mic.

Polar patterns are a powerful aspect of mic use and choice. As well as where the mic is, we should always consider where the mic might be able to be if it were in a different pattern. This doesn’t happen all the time. Often a great sound can be found using cardioid and that’s that. But for those times when placement is tricky, an alternative pattern might be the answer.

Image Credits

Nicoguaro, CC BY 4.0, via Wikimedia Commons

Galak76, CC BY-SA 3.0 , via Wikimedia Commons