The Blumlein XY pair captures reverberance fully but causes phase artefacts from side sound.

Evidence

A particular XY technique is still known as the Blumlein pair, where the positive lobes of the two dipole microphones are in the directions 45◦and −45◦azimuth. The sound source(s) to be recorded is situated between the directions of the positive lobes. The technique reproduces the sound energy equally in all directions and does not suffer from attenuated capture of the reverberant field. However, the sound arriving from the sides produces a 180◦phase reversal between the microphone signals. The sound is thus reproduced in loudspeakers out of phase, which may produce colouration and directional artefacts. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1841

Categorization

• DEFINE: Defines the Blumlein pair XY microphone arrangement and its side-lobe phase reversal quirk.
• QUESTION: Would be worth chasing: how severe are the colouration/directional artefacts in practice, and does it limit Blumlein pair use?