Perhaps the ultimate B-Format recording microphones are the SoundField single point source microphone series. These microphones contain all the capsules you will need to make a complete B-Format reference recording in one pass, and include hardware to send the separate axis streams to individual Impulse Response Utility tracks. You will only need to swivel the mic once toward each speaker position, and the mic and processing hardware does the rest. For those who can’t afford SoundField mics, Impulse Response Utility provides additional microphone options for B-Format recording.
Capturing the W (sound pressure) signal requires an omni-directional microphone. Capturing the X and Y axis signals requires a microphone with a figure-eight pattern (to capture signal from the front and back of the mic). Therefore, with two figure-eight patterned microphones—one pointed directly at the speaker source (X), and another positioned perpendicularly (Y)—and an omni-directional microphone for the sound pressure (W), you can record each speaker position in one pass. Be sure to arrange the microphones so that their capsules are as close as possible to each other—ideally, you want to have a single, tight point of reference for each speaker position.
You will need to swivel each of the figure-eight pattern microphones to each speaker position. The omni-directional microphone will not need to be swiveled, as it has a 360-degree capsule.
Even if your budget is too limited for three separate microphones, you can still create B-Format impulse responses by recording each audio stream separately into Impulse Response Utility. All you need is a microphone that allows you to switch between omni-directional and figure-eight patterns. Many good microphones (at all budget levels) have this capability. You will need to do a significant amount of pattern-switching and microphone swiveling, but it can be done.