Miking Strategies:
Small Choir Reinforcement, Recording
By Bruce Bartlett

The Smaller Choir. Suppose you want to mike a small choir of about 12 people. Of course, you want the most gain-before-feedback possible, but you also want to keep the number of mics to a minimum, both to reduce cost and to simplify mixer operation.

Should you use one close-up mic per person? One mic on every two people, or one every four people? How about one mic on the entire group?

There's a scientific way to answer these questions. It's possible to calculate the gain before feedback (GBF) of a chosen mic setup, given these variables:

Number of open microphones
Miking distance
Mic polar pattern
Angle of sound incidence to the mic

GBF drops 3 dB every time you double the number of open mics. GBF drops 6 dB every time you double the miking distance (not including proximity effect). Directional mics have more GBF than equivalent omni mics. With directional mics, on-axis sound sources produce more GBF
than off-axis sources.

The results of these calculations might surprise you. Listed below are several mic techniques and their calculated GBF, from best to worst. Note: The GBF of 12 close up mics was normalized to 0 dB.

12 cardioid handheld mics, each 1.2 inches from the voice, on-axis: 0 dB.

6 cardioid stand-mounted mics, each 7.2 inches from the voices, 45 degrees: -14 dB.

3 cardioid mics on mic stands, 2 feet from the voices, 0 degrees: -20 dB.

3 omni boundary mics on music stands, 2 feet from the voices, 0 degrees: -22 dB.

1 supercardioid hanging mic, 5.5 feet from the voices in three rows, on-axis: -23 dB.

1 supercardioid floor mic, 8 feet from the voices in a semicircle, on-axis: -23 dB.

What do the results show? If a facility can afford 12 mics, and can handle that many on the mixing console, go for it. Twelve close-up mics give the best GBF, by far. If six mics make more sense, you save cost and complexity, but give up about 14 dB GBF. That's not necessarily a problem, depending on the venue, mics, and loudspeaker placement.

When using six mics to pick up twelve people, the singers must be relatively far from the mics, and about 45 degrees off axis in relation to them. So six distant mics have much less GBF than twelve close-up mics.

If the customer wants the simplicity of a single mic on the choir, try either one hanging supercardioid mic or one floor-mounted supercardioid mic. Either should provide about 23 dB less GBF than 12 handheld mics, but this approach could work suitably anyway.

All of this is theoretical, and assumes that the mics have textbook polar patterns. Your real-world results may vary! But these findings might suggest some tendencies helpful to know.

Mics for Recording/Broadcast. For recording and/or broadcasting a choir in a live setting, three types of mics have proven to work well: cardioid condenser, omni condenser, and stereo condenser types.

A stereo pair of cardioid condenser mics is shown in Figure 3. This array reduces pickup of audience noise and room acoustics, and tends to provide sharp imaging.

Figure 3: A near-coincident stereo mic technique.

If mono compatibility is important, use two hypercardioid mics, angled 90 degrees apart, with their grilles almost touching and aligned vertically. This will prevent phase interference between the mics. A spaced pair of omni condenser mics is a good choice if you want stereo images to be blended rather than pinpointed. Omni condensers have superior low-frequency response, so they also excel at reproducing a pipe organ.

A stereo condenser mic combines two mic capsules in a single housing, for convenience. One stereo mic generally costs more than two mics of comparable quality. A special type of stereo mic is called "mid-side." It has one mic capsule aiming straight ahead toward the middle of the choir, and another capsule aiming to the sides. In a mid-side stereo mic, you can adjust the stereo spread by remote control.

Placement for Recording/Broadcast. Mic placement for recording must be determined by ear as the choir rehearses. Experiment with a pair of mics, or a stereo mic, on a tall stand. Once you've found a good-sounding mic position, hang the mics there.

Start by placing the mics about 12 feet from the choir. Raise them a few feet above the heads of the back-row singers, and aim them down at the choir. The setup shown in Figure 3 provides
excellent stereo. For convenience, you might want to mount both mics on a stereo bar or stereo mic adapter. This device mounts two microphones on a single stand.

A good starting position for two spaced mics is about 3 feet apart and 12 feet back. The wider the spacing between mics, the greater the stereo spread. But too-wide spacing results in an exaggerated left-right effect.

After setting up the mics, it's time to fine-tune miking distance.The farther the mics are from the choir, the more room acoustics you'll hear in the recording.

Listen to the mics’ signals, using either headphones or loudspeakers in a separate room. If the choir sounds too distant and muddy, move the mics about a foot closer and listen again. f the choir sounds too close, without much room sound, move the mics farther away.

Note: if the hall is acoustically "dead" (lacking reverberation), you might prefer to add artificial reverb. Use a digital reverb unit patched into the effects loop of your mixing console. If the organ overpowers the choir, or if air handling is noisy, you'll have to close-mike the choir and add digital reverb.

Simultaneous PA and Recording. Ideally, you'd use distant mics for recording and close mics for PA. But suppose you're limited to just the PA mics. Since PA mics are closer to the choir, their recorded sound will lack ambience unless you add some artificial reverb.

You'll want to send the reverb only to the recorder, not to the house loudspeakers. Here's one way to do it:

1. Connect busses 1 & 2 to the PA power amp inputs (or to the graphic EQ inputs). Connect busses 3 & 4 to the recorder line inputs.
2. Assign all mics to busses 1, 2, 3 and 4.
3. Connect the reverb returns to busses 3 & 4 (input).
4. Turn up the choir mics' effects sends while monitoring the recorder output.

You also could record “dry” to multitrack, then add reverb during mixdown.

Try out these techniques, and feel free to experiment with your own techniques too. In time, you’ll enjoy a beautiful choir sound for both recording and PA applications.

Bruce Bartlett is a microphone engineer with Crown, a recording engineer, and an audio journalist. He is also the editor of Crown's Mic Memo, a very useful technical and application tool available via the Crown web site.

Bruce Bartlett is a microphone engineer for Crown International, a recording engineer, and an audio journalist.