Vocal micing in Herbie Hancock: Possibilities

[Clueless]

A bunch of us got together last night to watch Herbie Hancock's Possibilities DVD, a collaboration to produce new music with a variety of contemporary artists--Chrstina Aguilera, Annie Lennox, Sting, Joss Stone, John Mayer, etc. There's a lot of footage of the studio sessions and it seemed to be different studios for each track, so lots of exposure to the similarities and difference between the studios and their approaches/abilities.

One question we all discussed afterwards related to the vocal micing technique. Virtually all the singers had two mics in their booth, usually either a Telefunken 251 or a U87 or a U47 and some other tasty mic. We are all familiar with the technique of having a close-up mic and another mic 5' back in the room to pick up ambience, but that setup was only in evidence once. What we saw and could not explain was the incredible variability of placement of the second mic. With Annie Lennox is was right next to the primary mic. With others it was 2' back, 3' back, down, up, etc. Our question was--what would drive this variety?

My hypothesis is that not all booths are created equal, and that in many cases the mics are pushed around more by what the room acoustics dictate than by what serves the singer. I.e., many booths don't have a spot 5' from the singer's primary sweet spot that's worth capturing. Any thoughts on (1) the two-mic technique, and (2) what factors influence how one implements that approach in the booths that vocalists sing in.

[JGP]

How do you know both mics were being recorded??

[Clueless]

Originally Posted by JGP

How do you know both mics were being recorded??

For the sake of this discussion, and because of the fact that using multiple mics to record a single source is a well-established technique, let's stipulate that they are. What I understand (rightly or wrongly) is that a mic positioned 5' away from a source in a properly sized room (doesn't need to be 1380 sq ft) provides a source for natural ambiance to balance out the sound of a close-up mic.