"I do use a particular micing technique I like for getting a big stereo acoustic guitar sound. I like getting the strings to pan across the stereo field. So you put one mic above the guitar angled down and one mic below the guitar angled up equal distances both pointing at the neck. The mic above gets more of the lower strings and the mic below gets more of the higher strings. I never really liked the thing of putting one mic near the bridge and one near the neck. The 2 mics sound too different and create kind of an odd irrelevant stereo image.
I really like being able to hear the placement of the notes across the stereo field kind of like a piano. Seems to be a more meaningful stereo image. The 2 mics are basically at a 90deg angle from eachother both pointing at the neck of the guitar. You can change the voicing of the pair by moving their orientation to the guitar. i find that pointing them at around the 15th fret seems to get the most natural balance. If you put them more in front of the sound hole it will get bassier and woodier, if you move closer to the 12th fret it gets brighter and more sparkly. I have used a variety of mics in this configuration: 67s, 251s, coles 4038s and more recently shoeps 221Bs. The shoeps were pretty wonderful. I didn't have to EQ them at all when recording, mixing or mastering.
The voice isolation thing is tricky. For the vocal mic it helps to use something the player/singer can get really close to like an SM7. I have also had some luck putting the guitar/voc mics in fig8 and orienting the position so the node is pointing at the player/singers mouth/sound hole. That definitely eliminates all of the low end of the voice from the guitar mic and visa versa.
Hope that helps!"
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