EmRR just posted yesterday about his use of audience-facing wide spaced shotgun mics last weekend over in the
shotgun mics usage thread (< link points to his 1st post about it yesterday), and we've discussed some details about it over there since.
Shotguns used in that way seems be a commonly used technique, but as mentioned in that thread, I wonder if shotguns are really the most appropriate choice for the application. The intent is to maximize pickup of the audience with minimal pickup from stage and PA. Okay I'm onboard with that, but with the stuff being rejected being potentially louder than what is on-axis, I'd think supercardioids to be a superior choice due to the much better off-axis behavior of a supercardioid than a shotgun, in the interest of keeping the significant audible bleed that inevitably occurs more natural sounding. That way one should be able to use more level from them if desired before the rejected stuff becomes problematically audible.
The opposite (polar opposite, heh, heh) would be substitution with omnis like billydee mentions using. With no meaningful directional sensitivity, placement becomes a critical balance tool, but what is picked up is likely to sound more natural. If they can be placed appropriately and used like he mentions, getting a little bit of everything around them to good effect, that approach can work great. Its really more like an on-stage mic'ing thing that includes up front audience.
I found using the edge of the stage itself as sort of a baffle (directional mics placed below the lip facing out) to help significantly when the goal is to keep as much stage sound out of the audience channels as possible.
I think it was Mix magazine which printed an interview with Steely Dan's engineer Roger Nichols, who was mixing stage monitors when they first tried IEMs in the early 1990s.
The first show, Donald and Walter complained that the crowd hated it, because they didn't hear any reaction.
On night two, Roger placed left and right shotguns aimed some rows back and dialed those in, and they all realized that the first night was like wearing earplugs against the crowd![/font]
I heard the same idea was the driver behind the origin of the "Healy method" of placing on stage two back to back LD omnis spaced about the same as one's ears angled 180 degrees apart - not so much for recording, but rather for feeding the then new highly-isolating IEMs the band had started using in place of monitor wedges with a bit of on-stage and audience sound.