The Case for Matched Pair Microphones

You’ve probably come across the terms
“matched pair” or “stereo pair” in reference to small-diaphragm condenser mics
sold as a two-microphone set. What do these terms actually mean?

Modern computer-assisted design and manufacturing processes ensure that the specification tolerances for today’s electronics are considerably tighter than they were, say, three decades ago. Still, any two microphones fresh off the assembly line will likely not measure identically even though they are both within the manufacturers’ spec’d tolerances. Therefore, to be able to offer matched-pair microphones, the manufacturer must identify two mics that do measure identically (more or less). [It should be noted here that some manufacturers do not offer matched pairs, feeling that their tolerances are tight enough that any two mics are matched closely enough for stereo recording.] Some companies then take the process a step further with additional bench testing to ensure matching to even tighter tolerances. This may result in capsules or other components that don’t make the grade being discarded. These extra steps in the production process are why you’ll often pay more for a matched pair versus simply buying two single microphones of the same model. Plus, matched pairs usually come with a premium storage box or flight case and perhaps even shockmounts or a stereo bar that facilitates stand mounting for popular stereo pickup configurations. But why all the fuss over specs? Wouldn’t any two of the same modern mic model be effective at capturing a stereo image? Perhaps, but your satisfaction with such an arrangement depends on how persnickety you are. It will likely not pass muster with golden-eared engineers working in professional studios with state-of-the-art monitoring.

sE7 Small-diaphragm Condenser Microphone – Matched Pair

Why All the Fuss?

Why stress over minute specification variances? Photography offers a good analogy. Let’s say you were going to create a panorama by stitching together images captured simultaneously by two interchangeable-lens digital cameras. (Yes, we know smartphones and cutting-edge cameras can do this automatically, but bear with us.) The photographers among us would start with two sturdy (and preferably identical) tripods. Next, you would choose two identical DSLR camera bodies and set them up identically to capture the highest resolution. You would fit them with two identical lenses. By our repeated use of the word “identical,” you see where we’re going with this. You wouldn’t use a high-end DSLR to capture the left side of the image and a lesser, merely respectable camera for the right because you’d want the image quality to be the same. And, by the same token, you wouldn’t use two lenses with different focal lengths. You would want everything to be identical. And so it is with stereo audio capture. The left and right sides of a stereo image contain common source information captured by their respective microphones. The fractional timing/phase differences between the two are what lends a sense of spatial realism to the stereo image. Slight divergences in specs (most critically, frequency response) between the left and right sides of a stereo image can be detrimental to this delicate arrangement, smearing the crisp detail we all strive for. This is why a matched pair of microphones is your best bet for capturing a perfect stereo image.

PM-2 Small-Diaphragm Condenser Microphone Matched Pair

Capturing the Perfect Stereo Image

Most professional engineers take great care when capturing a source in stereo — be it a grand piano, drum overheads, room mics, or stereo guitar — as a component of a multi-mic, multitrack recording. More critical still are “purist” recordings that rely wholly on one matched pair (or a stereo microphone), eschewing “helper mics” that are typically added to spotlight various instruments. If this purist approach seems needlessly restrictive, then keep in mind that the fewer microphones you use, the fewer phase anomalies are present in your recording. Popular stereo mic techniques such as spaced pair (A-B), XY, and ORTF array rely on matched pairs of omnidirectional (A-B) or cardioid (XY, ORTF) microphones, while Blumlein (named for EMI engineer Alan Blumlein, who was granted a patent in 1933 for his groundbreaking work on stereophonic sound) is an XY technique that uses two matched bidirectional (figure-8) mics. Many types of acoustic events can be captured effectively using these techniques, but mic placement (and the acoustics of the room) is critical. For larger sources such as symphony orchestras, a spaced pair is often used with a center mic to fill in and strengthen the center image, as in the venerable Decca tree array, which uses three (identical) omni microphones. In such cases, stringent matching of the left and right “outriggers” is no less crucial. Given all the caveats involved in various stereo miking techniques, you may be thinking that a stereo microphone might be a preferable solution for stereo capture — and, for many situations, you’d be correct.

Stereo Microphones: The Ultimate Matched Pair?

With the exception of spaced pair, the other configurations mentioned in the previous paragraph are either coincident (meaning in the same plane, such as XY, Blumlein) or near-coincident (ORTF), referring to the proximity of the capsules to each other in the microphone array. Within the coincident category, an alternative to a matched pair of condenser mics would be a stereo microphone — which may be considered the ultimate matched pair. Stereo condenser and ribbon mics are fitted with two optimally positioned capsules or ribbon elements, and, as you would expect, they are typically matched within minuscule tolerances. Some of the most sophisticated stereo mics offer multiple pickup patterns like their high-end monaural counterparts do, and there have even been models that offered remote capsule positioning to widen or narrow the stereo field from the control room sweet spot. Another coincident array not previously mentioned because it entails using mics with two different polar patterns — cardioid and figure-8 — is mid-side (M-S). If you’re using a cardioid and a bidirectional mic, then matching them may seem irrelevant, but keep in mind that frequency-response linearity between the two microphones remains crucial. Mid-side requires an extra step of post production (an M-S decoder or equivalent summing in your DAW); nevertheless, the technique is quite popular and prized for its coherent phasing and bulletproof mono compatibility. If this approach makes sense to you, then consider the possibility of using a stereo mic with matched cardioid and figure-8 elements designed specifically for mid-side capture.

C414 XLII_ST Large-diaphragm Condenser Microphone

Next Steps: Resources for Stereo Capture

So, that about wraps it up. To bone up on the most popular stereo microphone techniques, check out this informative article: “7 Stereo Mic Techniques You Should Try.” And as for gear, Sweetwater carries an exhaustive selection of the best microphones for any recording or live sound application. To find the right mics for your upcoming stereo adventures, shop matched pair microphones at Sweetwater today. And, remember, should you need individualized expert advice, you can give your Sweetwater Sales Engineer a call at (800) 222-4700. You’ll soon be on your way to capturing amazing-sounding stereo performances!

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