Coincident pairs: XY and Blumlein

A coincident pair puts two directional microphones as close together as the capsules allow, with their axes pointing in different directions. There is no spacing, so there are no arrival-time differences. Every bit of direction information comes from the level difference between the two outputs.

XY with cardioids

The classic arrangement: two cardioids angled apart, usually between 90° and 120°.

• A source straight ahead reaches both capsules at 45° off axis (for a 90° pair), so the levels are equal and the image is central.
• A source on the right axis is picked up at full sensitivity by the right capsule, and 90° off axis by the left, where a cardioid is 6 dB down.

For a 90° cardioid pair, a source on the right-hand axis therefore gives a level difference of about 6 dB. That is only a partial pan: the image sits roughly half way between the centre and the right loudspeaker. A wider angle gives larger differences, which is why 120° cardioid pairs have a narrower recording angle than 90° pairs.

Blumlein: crossed figure-8s

Two figure-8 microphones at 90° were the first stereo microphone arrangement (patented by Alan Blumlein in the early 1930s). Each capsule has a null at 90° from its axis, so the level differences grow quickly and the recording angle is narrow, about 76°.

It records the whole room, front and back, and the rear lobes arrive with inverted polarity. That gives a natural spaciousness and a precise front image, but placement is critical: sound from the sides is picked up out of phase.

Wide cardioid, supercardioid and hypercardioid pairs

More directional capsules have deeper nulls and greater level differences for the same angle, so at the same capsule angle they give a narrower recording angle. At 90°, cardioids give about 196°, supercardioids about 136° and hypercardioids about 109°. To keep the same coverage with more directional microphones, use a smaller angle between them. They also pick up less room at the sides but more from behind.

Advantages

• Precise localisation, because there are no time differences to blur the image.
• Mono compatible, because the capsules are at the same point and the sum has no comb filtering.
• Compact, easy to mount and move.

Disadvantages

• The images are less spacious than with spaced microphones.
• Low frequencies, where time differences carry much of the spatial impression, are less well represented.
• Coincident pairs depend completely on the pickup patterns being matched and the angle being exact.

Try it

Pick XY, Blumlein or the 120° preset in the stereo recording angle tool and compare their recording angles and level differences.

Draft: written by an AI assistant, awaiting technical review.