How do I mic a 13-member a cappella singing group?

glad I could help - if you think of it I'd love to hear how the project turns out.

you can create a very serviceable MS rig with three cardiod capsules - you'll probably want to record all three tracks and process later, but it works just fine. I've even tried to do Blumlien (two figure-8 patterns at right angles) with four capsules - it got a little crowded<G>!

A spaced or coincident pair fairly close to the ensemble think in terms of where the conductor would likely stand - just behind and above is a great starting point), and then an M/S or Blumlein pair a little further back and a little higher - depending on the space.

A LOT of placement will come from walking around the space while they warm up. I recorded a small choir in a church several years ago where the coincident pair ended up about 2 feet above the conductor's head (I told her she had to be very quiet!) but the Blumlein pair (in this case a stereo ribbon) ended up 16 feet in the air and about half way across the right hand side - I happen to have a couple of very tall boom stands, but let me tell you, getting the stand in between a row of pews is not something I ever want to do again. But that was the sweet spot - the sanctuary was shaped oddly!

And don't worry - most of the time it doesn't get all that tricky.

Jeff Evans
I have found that putting the mic up higher than normal can work well too. Put the stand on a table if you cannot get a high mic stand. Some of the vocal sound can go upward a little.
 
No need to get too far back either as you may just end up with all room and no detail.
 
M/S also works great because the M mic is facing directly forward and the S mic is getting the sides. M/S gives you nice coverage over the ensemble rather evenly and you have some control after.
 
Co-incident and near co-inceidnet can work well too if you are working with matched pairs.

What Jeff say's here is correct, sound does indeed travel up for some strange reason.  If you can, just use a stereo AB pair in the middle and above the choir.
 
Ben

 
https://www.youtube.com/watch?v=Pa11QYLci2I
 
https://www.youtube.com/watch?v=TN80JSWZGCY
 
https://www.youtube.com/watch?v=VTrPSBuYVJk
 
https://www.youtube.com/watch?v=Pa11QYLci2I

rumleymusic
What 4 mics do you have?

I'm new at this, and mics are the one thing I've (so far) spent little money on. Good mics are on my list, but at least a year away.
 
So, what's cheap and ubiquitous? Yeah, MXL. I have 3 990's and 2 991's, all cardiod. And bright. My Mogami Gold cables are better than the mics. 
 
In my defense, all I can say that I spent less than $200 on the lot.
 
Gibson SG bass to back up my Fender J Bass. Good mic. Gibson SG bass. Good mic.
 
Guess what won. Unh hunh.
 

TheMaartian

Rbh
People are suggesting placing the mics when you haven't described the room dimensions. So, my suggestion is : group them in an equidistant arc, close X-Y pair about 5' in front of them - eye level. if you have 12' or higher ceilings then raise the mics to maybe 7'.

Thank you for generalizing it. Helpful, since I don't have a clue yet about the room. It could be anything from a small studio to an auditorium.
 
I'll be seeing the Pres. of NAU shortly (I may be a major donor, but I've had her and her husband over for dinner; we get along well) and plan to ask her for help getting connected to the Dean of the School of Music and then go from there. If at all possible, I'd like this to fit into not only their academic schedule, but also their studies. I'd love to get an original piece done just for this recording session. Networking has its benefits!

You might also have them staged 2 ppl deep - tactfully wamp the loud ones on the forehead until they wander to the back row.

Thanks Bitflipper,
 
You are right, with a good group and a good room, it takes little effort to get a good recording, and can be done convincingly with even cheapo Chinese condensers. (Though this was with Sennheiser MKH8040's and Josephson C617set mics, and that certainly makes things sound better)
 
The height of the mics was in consideration of the depth of the chorus.  It is a little better perspective and more even front to back.  It probably did help with the organ as well though it wasn't very intricate on this piece.  
 
As far as perspective, personally, I say to heck with the audience, the best seats in the house are above the group.  

rumleymusic
What 4 mics do you have?
 
I usually mic choral groups with a stereo pair at a reasonable distance (10-15 feet) back and space a couple to three wide cardoid or omni microphones closer up.  That way you can pick and choose your balance later on.  
 
If you are using cardioid mics, I would suggest the NOS pattern in a so-so room, or ORTF in a good room.  If there are soloists, make sure they stand center and closer to the main pair and you may be able to do without a spot.  If it is pop-like music, a spot may be necessary.   
 
For some miking examples:
 
This is a recent concert with just an ORTF pair on the ensemble and some instrument spots.  A little bit of bleed from the choir in the spots was a nice mix. (Choir on first two pieces only)
http://www.instantencore.com/music/details.aspx?PId=5123698
 
Here is a video of a professional choir with ORTF mains and some omni spots.
https://www.youtube.com/watch?v=-C2hkZpIiUM
 
Lastly here is a small baroque choir of 10 with 4 spots in conjunction with the main pair.
https://www.youtube.com/watch?v=cRFwfEMjQI4

OK, so I pulled the plug on a couple of new mics, the CAD GXL3000 multi-pattern condensers. Chinese-made, but got good reviews for audio and structural integrity. With the BP (Black Pearl) version shipping now, I found a couple of the non-BP versions for $91/each. Not the $69 price MF had on SDotD a couple of years back, but way better than the street price of $139 for the current BP (exact same innards, different look). And they come with shock mounts, so $90 seemed pretty good to me.
 
I plan on using them in an M/S pair, with one configured figure-8 and the other cardiod. If I can find some tall mic stands, I'll run a pair of 990 or 991 MXLs. That will max out the 4 mic pres on my audio i/f and give me two different perspectives to pick from and work with.
 
I've already ordered the mics, but any comments would, as always, be appreciated.

Mics are here. They've spent the last couple of days on COLD UPS trucks, so they're just sitting in their boxes coming up to ambient. Testing starts tomorrow. First time recording with an M/S pair. I plan to use my mobile recording rig.
 
Help an aging engineer out here if I've missed anything obvious. My planned test sequence follows. If you don't give a crapola, and I expect most or all not too , you can stop reading now.
 
1. Using my PC, SONAR and Tascam i/f, test each mic (all 3 patterns, the -10 dB pad, and the HP filter).
 
2. Set them up as an M/S pair, connected to my Nexus 10 tablet, Audio Evolution Mobile for Android and PreSonus i/f (mic inputs 1-2) and record some audio at 48/24.
 
3. Export the Mid and Side stems to WAV files and copy to the PC.
 
4. Open SONAR and create a three-track project (Mid, Side, phase-inverted copy of Side) with appropriate routing to a stereo buss.
 
5. Make sure all of that works.
 
6. Set up the track and buss FX I want to start with, and save as a template.
 
7. Set up two MXL mics as a stereo pair (PreSonus mic inputs 3-4), and record some audio at 48/24.
 
8. Repeat steps 3-6, except for a stereo pair.
 
Once that's done, I can use either a pair of 990's or 991's (depending on which sound better in situ) for the stereo pair.
 
I'm finding the following table (from Shure) helpful:
 

Ewph.  You have to be careful with those charts like the ones from Shure, especially when it comes to a spaced pair.  I know it is in every textbook and some big name studio guys do this because in the studio, a spaced pair, typically used for drum miking can be extremely wide, but this is not the use for orchestral or choir recording.  The AB or spaced omni pair should, in reality, be between 40 and 60cm.  It is the phase relationship between the two mics that creates the stereo image, not the proximity to the source.  Any wider than 3 feet, and you will have a massive "hole-in-the-middle" sound and increased phantom imaging (you won't know what direction the sources between the mics are coming from, sometimes they flip from left to right depending on the context), not to mention you will loose the phase relationship completely.  
 
I would take a look at DPA microphone's "microphone university" on their web site.  It lists the proper usage for an ensemble recording context.  
 
Regarding MS.  Most advocates for the technique in large scale ensemble recording will tell you the center mic should also be figure-8, not cardioid.  I whole-heartedly agree.  This will give you the same pickup pattern as a Blumlein pair, which is fantastic for choral recording because of the wide, realistic front image, and the equal ratio between direct and room sound.  You could also, and I prefer this, just use crossed figure 8's in a Blumlein pattern.