18' high ceiling and 45' spread of instruments.... That is a change.

For cardioid microphones to get an even coverage of an area you want the microphones 4 feet apart for every 3 feet from the source. If you can place them 9 feet high, and 12 feet apart you will get even coverage.

However....
It probably sounds good to the conductor, so a XY or ORTF above the conductor.

Because of the number of instruments in a relativity small space I would go with the NT5 pair in XY configuration above the conductor, and if you have time set up some other microphones above the sections with the 9 and 12 foot spacing. Lots of microphones = phasing, so you may end up using mostly the XY.

Sorry - typo on the height - its about 13' not 18

I have recorded some wacky things over the years. This sounds like quite a challenge as this is a fairly tight scenario. While XY & ORTF may be viable? I think the acoustics of the space, along with its dimensions will cause you considerable problems? In this situation, I would consider utilizing 3 PZM's on the wall, behind the conductor, in a spaced left, center, right placement. These particular microphones with their hemispherical pattern can truly knockdown unwanted walls in unwanted places. I think I would take the fourth PZM and place it in the center on the wall behind the rear of the ensemble, directly across from the conductor. I'd then place a pair of XY or ORTF highlight microphones in the middle of the ensemble such as on the woodwinds. Then I would use the last two for spots or mid-ensemble on the left & right for a larger stereo spread. Can you say SURROUND?

And as I have mentioned before, since you'll have to record the ensemble & the choir separately, you'll be able to use the same technique as I have described before in other threads to eliminate your playback sound from being recorded with your choir. This will require a second pass of the choir recording, without the choir & without moving your microphones. You can do this before or after the choir. Flipping the phase on the second pass eliminates the ensemble playback speakers. This will truly give you much more control over the final product to not be recording playback of a PA system. But like I said, no playback speakers nor microphones can be moved. People versus no people will change the acoustics of the space but will have less of an impact than timing problems if speakers or microphones are even moved 1 inch.

Now I'm not suggesting you release this in SURROUND but you could have fun doing so. Obviously, the acoustics will be rather dubious and I don't believe you get a satisfactory sound by utilizing a primary pair of XYor ORTF over top of the conductor. It'll sound like you recorded them in a box. I can already see the way that sounds.

Seeing the sound inside your 45 x 45 box
Ms. Remy Ann David

I think Remy's idea with the PZMs is very interesting, and if you try that I would love to hear how it turns out.

I have recorded my daughter's HS wind ensemble on stage several times using a pair of NT5s in ORTF as the center pair with 414s as omni outriggers. In a room like you describe I'd put the outriggers 10-15' from center.

With this setup and the PZMs on the wall you would have all the cables at the front of the room. (With 70 kids in the room, logistics and safety are probably as big a consideration as sound.) If it is feasible, the K2 and the 421s might make nice spot mics, but simplicity is a virtue in this situation. If the main pair and a little bit of the outriggers gives you a good sound don't try to get too fancy.

Thanks for the suggestions,

I'll give it a dry run with just strings (they normally rehearse here) and see if it flies. (speaking of flying)

If it makes a difference the wall is brick (not cinder block) It used to be an outside wall. I have flown the PZMs in the past on wooden mounts that I've attached mic clips to. I got a very open/natural sound in a nice acoustic. But haven't done so in this room. Is it ok to just gaff tape them on the brick wall? How about mounting them on wood on a mic stand or mount the wood on the brick - does it matter? I could even mount them on the fiberglass baffles? I like the neutral quality of the PZMs but the science always gets in my way. (One might say I'm blinded)

I know I can and will experiment, but I'm also teaching and doing the 50 other jobs that teaching demands (and truth be told, I've never claimed to be anything more than a pretty good hobbyist at this).

Don't use the h-word in anything the IRS might read.

Advice from a fellow "dedicated (and fully professional) weekend warrior."

After a trial run with just the orchestra - the 3 PZMs on the wall weren't great. I could get an ok sound, but in looking at the set-up (because of other stuff against that wall) I couldn't space the 3 properly when all students were in the room. And closer together just made the space problems worse.

Because I really couldn't take the time to move mics if I mounted them directly on the wall while the students were in the room (time limitations)- I went back to a system I hadn't used for several years.

I flew 2 PZMs that I mounted on 2'x2' boards attached to boom stands.
I ran them up about 9.5' high and spaced them about 12' apart (slightly behind the conductor. The plan was to move these as needed, but I really didn't need to. They warmed-up and I hit record and then started conducting with a colleague watching levels.

In trying to spot mic the woodwinds I had phase problems and bleed problems with brass and percussion so I wound up with the 2 414s in omni about 25' apart (guestimate- students were all over the place) but about midway of the ensemble(10-12' in front of the PZMs). We did a dry run this morning and I think we'll wind up better than I anticipated.

If I can figure out how to attach a file I'll do so in the coming weeks. I'm also going to try to mic the choir with the playback live in the room. My plan is to set up monitors as in a live show facing the choir and record them as usual. I will try the inverted phase technique, but my sense after a few test runs today was that I created a much more cohesive mix - the two groups sounded more like they were recorded at the same time if we just sang along.

I still may have to spot mic for flute/clarinet solos within the mix, but I'll just try an N5/ or a 421 up close.

Phil

Here's what I ended up with. For all the problems, including missing a bunch of senior sopranos who were on an unannounced field trip - and recording the instruments seperately. I think the final product is pretty good. Let me know what you think. My monitoring system is pretty good, but the room and the monitoring room isn't.

It was entered in a local radio station's competition, so it's easier to hear it there. Our recording is of "Do You Hear What I Hear" arranged by Emily Crocker and John Moss.

Opus 3#2

What's that little click in one side at 15 seconds? It's the right side on my system but I'm not sure I have my amp hooked up right.

Well done, Phil. This is really nice. (esp after everything you went through to create this!)

I'm listening on laptop speakers, and it reminds me of the old radio broadcasts (in a VERY GOOD way, I mean) where they'd have orchestra and singers in one big room and let 'er rip. People sure knew how to make recordings in those days with what they had. I might be inclined to add a smidge of reverb overall, but that too could be my speakers. The choir sounds smooth and very well blended. All of the instruments were clearly defined and easy to discern in the mix, too.

I poked around and listened to some of the other recordings, and I still like yours the best for both the recording quality and the performance itself.

I think the contest is a brilliant idea, and more folks should be doing this sort of thing, IMHO. It also got me to thinking about the sheer number of local choral groups all over the country doing this sort of thing. Not too shabby for the state of choral music in general, if this many can contribute a song AND get it recorded as well.

Bravo!

Greener wrote: What's that little click in one side at 15 seconds? It's the right side on my system but I'm not sure I have my amp hooked up right.

I'm not sure, but it wasn't digital. I think it may have been an orchestra member adjusting music on the stand (or a finger snap or ????) 70 orchestra members, 100 singers it could be anything.

Thanks for the kind words Joe. They started the contest last year and we won, so we're trying to stay undefeated! :D . I got to know the producer last year so we're also doing a bit of bumper and promo-type stufff for the radio station during the contest. A little extra work for me but a lot of fun for my singers.

Phil

Phil- Very nice job in what I know are very trying circumstances. . I thought the stereo field give a good feeling of space and you got a good ensemble feel with enough detail for clarity. As Joe said, a nice natural feel. Of course, the best thing you did was get a good performance out of your students. Good luck with the contest!

As it happens, I have to go over to the high school in an hour and record their winter concerts (wind ensembles). Hope my recording turns out as well as yours