Choir Miking Strategies
by Bruce Bartlett

In house-of-worship installations, one of the biggest challenges is miking the choir. We want to achieve a good balance, a natural sound, and high gain before feedback. Another goal is to
make sure that the mics are invisible! It's a tough assignment.

What mics work well for the choir? Where should the mics go, and how many are needed in each situation? The suggestions that follow should point you in the right direction.

Part 1 of this series offers tips for reinforcing large choirs. Part 2, to be published next on ProSoundWeb, covers small choirs and techniques for choir recording.

Mics for Choir Sound Reinforcement. The most popular type of choir mic is a small hanging mic. A few of these tiny microphones can be hung over the choir from the ceiling, from rafters, or on stands. They are almost invisible when viewed from the congregation.

An example of a miniature choir mic.

Choir mics are condenser types with a cardioid or supercardioid polar pattern. These patterns reject feedback yet have a wide enough pickup for good coverage of the singers. Condenser mics can be made much smaller than dynamics of equivalent bass response. Choir mics are built in three parts: mic head, cable, and power module. The mic head puts out an unbalanced, medium impedance signal which travels through the long cable. At the far end of the cable is a power module with an XLR connector or a terminal block. The module accepts phantom power and sends DC to an FET near the condenser mic capsule. Also, the module equalizes the mic signal and converts it to low-Z balanced.

In some choir mics, the power module takes the form of a flat plate that is mounted in the ceiling. In other mics, the module is a tube with an XLR-type connector.

Mic Placement for Sound Reinforcement. When placing mics to pick up the choir, a critical factor is gain before feedback. To get enough gain, you must to mike the choir much closer than you would for recording. Place the mics about 18 inches in front of the first row of singers, and about 18 inches above the head height of the back row (See Figure 1).

The mics are raised to prevent overly loud pickup of the front row, relative to the back row. The rows are equidistant from the raised mics, giving a well-balanced sound.

Figure 1: Typical choir mic placement.

To achieve uniform coverage, use one microphone in the center of every 20-foot span of singers. A choir of 30 to 45 voices should need only two or three mics. Given a fixed miking distance, you'll get less feedback with fewer microphones. You might want to mount the choir mics on tall boom stands to experiment with placement during choir rehearsals. Once this is done, hang the mics permanently.

In miking a choir, it might seem important to consider the 3:1 rule. When multiple mics are mixed to the same channel, the distance between mics should be at least three times the mic-to-source distance. This prevents phase interference between mics (comb filtering), which is a series of peaks and dips in the frequency response - a colored, hollow sound.

The 3:1 rule cannot be applied to miking a choir with a few mics. Why? Most of the singers are somewhere between the mics, and those singers will be picked up with some phase interference. However, since each singer is in a different position relative to the mics, each singer is heard with a
different coloration. The effect averages out over all the singers and so is not very audible.

Once the mics are placed, you need a way to hold them in position. Mic cables can lose their orientation as the mic cable uncoils over time, or the mics can swing back and forth in a breeze. Some choir mics have a built-in hanger which comes with a tiny crossbar or pipe. You thread a fish line through this pipe and attach the line to screw hooks in the side walls (See the example photo of a miniature choir mic above to view how this should look.). This guy wire keeps the mics oriented toward the choir.

If hanging mics is not an option, you might try making some clear plastic mic stands of Lexan corner molding. The stands can be cut to the desired height and mounted to or near the choir rail.

What if the choir is under a balcony? Try mounting some supercardioid boundary mics to the bottom surface of the balcony, near its front edge.

Other Considerations. Monitor loudspeakers can easily feed back into the choir mics. To keep feedback under control, try not to use monitors near the choir. Turn up the house loudspeakers instead. If the choir insists on monitor speakers, don't feed a monitor signal of the choir back to them becasue it will cause feedback with the choir mics. Instead, just feed them some music for accompaniment.

If the choir members complain they can't hear themselves, maybe the piano, organ, or music tracks are too loud in the choir monitor speakers. Have the choir sing a capella, with the air conditioning turned off. Can they hear themselves? Now turn on the air conditioning. Can they still hear? Turn up the piano or organ in the choir monitors. Then turn up the tape tracks. At what point can the choir no longer hear their voices? Turn down the offending sound source.

In some venues the choir mics pick up too much of the organ's sound. In this case, use supercardioid mics and aim them toward the middle row of the choir. Because the mics partly reject sound from the side, they will pick up less of the organ in this configuration. If the organ is still too loud, aim the mics straight down over the choir and filter out frequencies below 100 Hz in the choir mics.

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 at http://www.crownaudio.com/mic_htm/mic_pubs.htm.

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