I defer to Gutbucket here, but I'd say the closer to the source 110, farther away 90. anything less than 90 isn't worth it. IF you are super close to the stacks, you can try 110 NORTF (spaced 17 cm) or stay with X-Y 110.
What kind of angle are you guys using in x/y? I am wondering when further back would it be beneficial or matter to close up the angle below 90* to get a more narrow field and let the omnis do their thing? Obviously 60-90* may not yield a useful recording on its own and the center card can be used, just curious how narrow and wide x/y fits into the pair.
I'm just trying to wrap my head around the possibilities here. With summer coming up and plenty of music, I really look forward to playing around with these 3 and 4 mic setups.
Ordinarily I'd not choose to run cardioids X/Y by themselves for an AUD recording. Instead, I'd run a near-spaced cardioid configuration.
If I were to run X/Y on it's own, I prefer supercards, hypercards, or 8's, but if running X/Y cardioids by themselves I'd probably use a rather wide angle like 120 degrees between microphones to achieve a more satisfactory stereo image. If I didn't want the mics angled that wide, I'd space them apart more, but then that would no longer be X/Y.
In this situation however, the X/Y isn't intended to be used by itself, but intended to work as a team along with the wide omnis. Combined with the omnis, we don't need to try and achieve sufficient stereo width from the X/Y pair alone. I actually want the X/Y cards to be more monoish and forward/center focused and less angle between microphones is appropriate. How much less? Instead of choosing an X/Y angle which best optimizes stereo image and width, I'd choose an angle that best optimizes forward focus and collection of direct arriving sound with optimum clarity- I'd point them directly at the stacks- PAS
X/Y PAS is probably going to call for a rather minimal angle between mics, usually significantly less than 90 degrees. In isolation, the X/Y recording will sound center heavy and not have much stereo spread. But it is probably going to work best in combination with the omnis- providing good clear forward focus with just enough stereo width to smoothly fill the center of the stereo image between the omnis. A bit of stereo width helps keep everything that is being contributed by the X/Y pair from being simply clumped together dead center like a single forward-facing center mic would do, but it doesn’t need to spread fully out to the sides like it would without help from the omnis.Aside- This is why 4 channel AUD mic setups which combine two stereo configurations that are each designed to work optimally on their own, will often produce less than optimal results. Each pair needs to contribute something different from the other so they don’t conflict with each other. Optimally configured for use in combination with each other, the X/Y or M/S pair in the center needs be significantly narrower than if it was to be used by itself, and the omnis should be a bit wider than one would want for them if used on their own. That's the logical extension of the idea to optimize the combination of the two pairs. So strive for that if possible, but no big deal if not- like if you can't space that far).
I think I mentioned previously that I've been playing around with a Mid/Side pair in the center between omnis. When listened to by itself in isolation, that M/S pair sounds best with plenty of Side in used in the Mid/Side to Left/Right conversion. Let's say it sounds best with a 50%/50% Mid/Side ratio or even more Side than Mid. When used in combination with the omnis, I’ll first determe a good level balance between the omnis and the Mid microphone (using 100% Mid and no Side). That’s exactly the same as if recording using just three mics- the two omnis plus the center Mid mic. Then, with both the omnis and center all playing back, I'll begin to play around with the Mid/Side ratio of the center pair, adjusting the ratio it until I find the smoothest imaging across the playback soundstage, where the center is still clear and direct, but evenly blends into Left and Right with more distinct image placement just off center and half-left/half-right. That may be a Mid/Side ratio closer to a ~90%/~10%. Mostly Mid, with just a touch of side.
So a narrow X/Y angle is equivalent to using more Mid and less Side. Point At Stacks X/Y with a narrow angle is going to be Mid heavy with little Side information to begin with, and will focus on other qualities which are desirable in the center (the clarity of direct sound from the stage and PA), while still getting sufficient Side information to provide a bit of width and work well in combination with the omni pair. The Mid/Side ratio can be always be adjusted further either way as needed, but PAS X/Y already gets us closer to the ideal, and may be close enough for those who don’t want to go to the trouble to adjust it.
If you are
tweaking the Mid/side ratio of the X/Y pair, I suggest setting the ratio to 100% Mid while finding your initial balance adjustments between the omnis and center. Once you have a balance you like, then play with the Mid/Side balance of the center pair by bringing in more Side. You may want to go back and forth a bit to find the best balance between the center level and center Mid/Side ratio.
This kind of flexibility after recording is partly what makes these techniques so useful.