I'm a little confused here, Ken. Are you talking about putting both mic sets in the same space; the omni right in-between or just above the ORTF pair?

If it's a large enough ensemble, I'd say go with the ORTF in the middle, and spread the omni's out (assuming you have two of them) on either side.

Otherwise, it sounds like (unless I'm misreading it) that you'll end up with a fairly tight, narrow image. A single omni, mixed in center/mono with your ORTF pair might not do much....

Otherwise, if you've got a gun to your head with really only three mics, I'd put the omni in the middle, and the two cardioid SDCs out on each side; all three at about the same height - a modified Decca tree, perhaps. Three stands, three cables, no muss, no fuss. You may have to adjust the angle and position of the cardiods, but you could probably pull it off; the omni may be just enough material to fill in the "hole" you'll likely get in the middle with the 2 cardioids.

Hopefully, you'll get at least a dress rehearsal in the afternoon to try out a few variations?

Thanks, Joe...I've got several LDC and SDC cardiods available, but only the one high end omni...kinda suspected all along what you said about running ORTF and an omni.

Not much time for experimentation, unfortunately...its gonna be pretty much set up and go...that said, I am familiar enough with my gear to know where to set them up....normal set up is LDCs on the far sides, ORTF pair in the middle, and a tight cardiod directed at the announcer's position....

Actually, I'm just looking for an excuse to try the 2247 out in an orchestral setting...dadgummit, if I only had two, I'd be in hawg heaven, but....

Thanks (again) Joe...and BTW: how ya been?

I did it once, but with NOS + omni in the middle and it turned up pretty well. It was arecording of about 50 piece orch. and 40 people choir i a large pallace with over 10 sec. of reverb and i was doing it for free because my brother was part of it(sang solo part)
I decided to go for such a setup because was affraid to go with the omnis (huge reverb)but wanted some bottom end and i didn't have time for rehersal.
To avoid narrow picture mix omni just a little bit to get some bottom end and thats it.

Followup: Show went well, but the director neglected to pass on one key thing during our preproduction meeting, nor did he mention it until 15 minutes before start time: A "special" event with 1/2 the string section strolling around the auditorium, with a house system mic'd up harp, the basses, and a short vocal acapella solo...

Of course, during the short time we had to mic check, set up, etc, we just ran our usual setup (C42s in ORTF, A51 Series III on sidefills)...good thing we always pack a couple of extras, plus a small POS sub mixer for such emergencies...

Monitoring playback, turns out all came out pretty well, but there's gonna be some serious editing during the strolling part....

Might even use this as an opportunity to dabble in a 5.1 mix...that would be tres cool, to hear individual instruments moving across the entire 2 dimensional field....

Lesson learned: continue to take twice as many mics, stands, and cables as you think you'll need...regardless of production meetings...information gets omitted, people "forget" etc...