Coincident microphone pairs provide common methods of capturing audio inside and outside the studio. These setups are cherished by audio engineers for many reasons.
What is a coincident pair of microphones? A coincident pair is a pair of microphones that are positioned with their capsules as close together as possible. The capsules are pointed in such a way that a stereo image is possible when panning each microphone. There are several coincident pair techniques which are all stereo miking techniques.
Coincident pair miking techniques include:
- Blumlein Pair
- XY Pair
In this article, we’ll discuss coincident microphone pairs in greater detail and describe the specific types mentioned above.
Before we get into coincident pairs specifically, you may want to check out my article Top 8 Best Stereo Miking Techniques (With Recommended Mics).
Definition Of A Coincident Pair Of Microphones
To easily understand the term “coincident pair,” let’s break down each word in the phrase.
A pair means that we’ll be using two identical microphones in these miking techniques. At the very least, we’ll use two microphones will very similar specifications (polar and frequency responses, sensitivity ratings, etc.).
It’s also worth running each microphone through the same model of preamp with the same amount of gain applied to the signal.
Coincident means to occur together in space or time. Of course, two microphones cannot occupy the same space at the same time so this really translates to positioning the pair of microphones as close together as possible. To be more specific, this means placing the capsules of the microphones as close together as possible.
Applications Of Coincident Pairs
Why would we want to utilize a coincident pair microphone technique?
Coincident pairs are utilized for capturing a stereo image of close sound sources, distant sound sources, and entire acoustic environments. These miking techniques are perhaps the most versatile among the stereo miking techniques because of their close-miking capabilities and relative phase coherence.
The coincident pair miking techniques also provide us with a compact method of recording stereo audio. This allows them to excel in smaller acoustic environments like small iso-booths.
Although coincident pairs may not be as wide as spaced pairs, the coincident nature of the microphone capsules eliminates many of the phasing issues inherent in spaced microphone pairs.
The phase coherence and small footprint allow for stereo audio while close-miking. At close distances from a sound source, phasing issues can be plentiful. The coincident pair reduces these phasing issues considerably when compared to spaced pairs at close range.
Because of this phase coherence, coincident pairs typically do a great job of capturing the low-end frequencies of an environment or sound source. Microphones naturally become more omnidirectional at lower frequencies and have two capsules placed as close as possible means few, if any, phase issues in the low-end.
Close miking captures a great amount of direct sound versus diffuse sound and often sounds much cleaner than distant miking.
For these reasons, you’ll often find coincident pairs close-miking acoustic guitar, piano, and other stringed instruments for a nice stereo image.
Why would we want a stereo image?
A stereo image creates realism, width, and depth in a mix. We hear sound in stereo and so it’s natural for us to hear music (whether live or recorded) in stereo as well.
Coincident pairs add excitement and space to a mix. Even when close-miking, these techniques really bring out the sound source in the mix, making it sound large and wide.
When distanced from the sound sources, coincident pairs add depth and width to a mix and bring out the character of the acoustic environment.
The issue with coincident pairs at a distance is that they may sound unnatural and may not provide as much stereo width as space pairs. This is because our ears are not coincident, rather they are spaced a bit apart. This is a minor detail but can leave something wanted from these stereo miking techniques.
For more information on microphones and phase, check out my article Microphone Polarity & Phase: How They Affects Mic Signals.
Common Coincident Pair Techniques
Let’s now take a look at some common spaced pair miking techniques:
- Blumlein Pair
What is an XY microphone pair? An XY pair has two cardioid microphones (typically top-address pencil mics) positioned with their capsules together but pointing 90° to 135° from one another. The capsules can be placed one on top of the other or right next to one another but should be positioned very closely together.
The XY is a very common stereo technique. This is especially true for close-miking techniques on guitar and piano.
Because of the cardioid pattern and the close proximity of the mic capsules, the XY pattern actually captures a decent centre sound along with its stereo image. This pattern also does a decent job at rejecting sound from the rear null points of each microphone, allowing for greater isolation when the XY pair is pointed toward the intended sound source.
The 90° angle offers less stereo width with a more cohesive centre capture. As we increase the angle between the two microphone axes, we develop a wider stereo image at the expense of a weaker centre and, generally, weaker mono compatibility (though phasing shouldn’t pose too dire an issue with this coincident pair).
Note that coincident pairs can be positioned narrower or wider than 90° and 135°, respectively. However, an angle less than 90° leads to a narrower stereo image while an angle greater than 135° leads to strange imaging and interference (maximizing at 180° where the mics simply point at each other).
XY stereo pair placement benefits greatly from stereo bar mic stands. I personally recommend the K & M Stereo Microphone Bar (link to check the price on Amazon).
Some stereo microphones operate on the XY coincident pair. One such example is the Audio Technica AT2022 XY (link to check the price on Amazon). The AT2022 has a user-selectable 90° or 120° stereo operation for narrow or wide pickup patterns.
Other handy recorders, such as the Zoom H4n Pro (link to check the price on Amazon), have built-in XY coincident pairs. The H4n also has a user-selectable 90° or 120° stereo operation for narrow or wide pickup patterns.
What is the Blumlein pair microphone technique? The Blumlein pair miking technique is a stereo miking technique that utilizes a coincident pair of bidirectional microphones pointed 90-degrees from one another (45-degree left and right of centre or the “front direction”).
The Blumlein pair is great for capturing a stereo image in the front and rear of the microphones’ position. This makes it an excellent choice for a compact stereo room mic pair.
The on-axis response of one bidirectional mic covers the null points of the other, effectively capturing audio from every angle. This means that each microphone essentially picks up its own side of the stereo acoustic field. Panning each mic to its respective side leads to a respectable stereo image with nicely isolated channels.
Depending on the positioning of the mics, the Blumlein pair can pick up more or less room ambience.
Ribbon microphones, by their bidirectional nature, lend themselves nicely to the Blumlein pair technique and are typically the microphones used in this coincident pair.
Usually, the mic will be stacked one on top of the other with the ribbon elements as close together as possible. This typically means the bottom microphone will be right-side-up while the top microphone will be up-side-down.
Like the XY setup, there are some dual-element stereo microphones designed with the Blumlein pair. One such example is the Cascade X-15 stereo ribbon microphone (link to check the price on Amazon).
A Note On Mid-Side
What is the mid-side microphone technique? Mid-Side is a coincident stereo miking technique with a cardioid “mid” mic pointing at a source and a bidirectional “side” mic placed above or below facing left/right. The mid mic is mono centre. The “side” mic signal is duplicated: one channel panned left, the other panned right and phase flipped.
The mid-side miking technique is coincidental but does not feature a pair of microphones. It is sometimes lumped in with the coincident pairs, though, and so I’ll describe it here.
The mid-side technique is designed to yield a stereo image that is perfectly collapsable into mono. This means that, unlike nearly every other stereo miking technique, the mid-side arrangement allows for perfect mono compatibility.
Mid-side does so by having the side information completely out-of-phase and so when the signals are summed to mono, the side information is completely eliminated, leaving only the mid (centre) signal.
The routing of the mid-side configuration is as follows:
Typically the duplicating process takes place within the routing of the mixing console or digital audio workstation.
As we can imagine, summing these three channels to mono would have the side microphone signals completely cancel each other out (due to the phase flip), leaving us with the mid (centre) mic signal only.
How do you hold a cardioid microphone? When holding a cardioid microphone, know where the on-axis direction of the mic is (where the microphone “points”). Point the microphone toward the sound source (often your mouth) and away from any live speakers that are projecting the mic’s audio.
To learn more about properly holding microphones, check out the following My New Microphone articles:
How To Hold A Microphone When Public Speaking And Presenting.
How To Hold A Microphone When Singing Live.
How To Properly Hold A Boom Pole And Microphone.
What is a stereo microphone? A stereo mic is a microphone designed with at least two capsules in a stereo configuration. Analog stereo mics output two (or more) mono signals (one from each capsule) that must be panned properly for the intended stereo image. Digital stereo mics tend to configure the stereo signal within mic before the output.
For more information on stereo microphones, check out my article Do Microphones Output Mono Or Stereo Signals?