what's the farthest from the stage you can be and still get a good pull with omnis?
What's the best configuration to use?
There's no simple answer. It depends a lot on the type of sound one enjoys and appreciates and the environment in which one records. Some people like widely split omnis. Some like a smaller split. Others prefer baffled omnis (e.g. Jecklin disc). Some people have a certain tolerance and/or appreciation for a degree of ambient / reverberant sound. Others have a much higher a lower tolerance.
In general, I found I could get away with omnis from a farther distance outdoors v. indoors, since there's usually less reverberant sound outdoors.
General consideration: However it sounds to your ears from the recording location, omnis will sound similar. So if it's boomy, or muddy, or distant, etc., you'll likely achieve a similar result running omnis.
Spot on, Brian. Well put.
I use omnis a lot, both indoors and out. It’s tricker to use them indoors and usually requires placing them closer to the stage for the reasons mentioned above. In general it’s easier to use them outdoors so that’s a good place to try first if less familiar with them, also because they have some advantages outdoors such as less susceptibility to wind noise. They work well at a distance outdoors, yet closer is still usually better, simply because it sounds better closer. But that’s usually the case regardless of pickup pattern for a lot of reasons: higher signal to noise ratio (aka- music to blabber ratio), less frequency attenuation by the air itself, less distance for wind to push the sound around before it gets to the mics, more enveloping sound when the source is wider as viewed from the mic position, more focused crowd energy, etc.
I'll mention a couple unusual distant mic’ing scenarios where omnis have been superior, just to emphasize 'it depends':
1) Boundary mounted omnis indoors on the back wall or front balcony surface of a venue has sometimes worked better for me, with less boom and room reflection problems than cardioids from the same location. But boundary mounting them changes the nature of an omnidirectional mic to a more directional one and introduces other unique boundary mounting traits that help that situation, so it’s really a whole different pickup pattern and microphone response. It also isn’t a very common mic’ing approach for concert recording.
2) All the space shuttle or rocket launch recordings I’ve heard have been done with omnis at at distance of many, many miles, and the ‘talent’ is never mic’d through the PA. Same goes for most good thunderstorm recordings, trains through valleys and other far-ambient ‘takes you are there’ non-concert stuff.