Perhaps one of the most challenging sound reinforcement job – in terms of feedback – is amplifying the voices of children. It’s often hard to hear children in dramatic or musical productions.
That’s because most children don’t project. Since they produce a low volume on stage, you must turn up their microphones quite a bit to hear them, which all too often can resulting in feedback. Here are some creative solutions to help those young voices be heard – without resorting to wireless microphone systems.
Use A High-Pass Filter
Children’s voices seldom contain frequencies below 200 Hz, so you can filter out everything below that frequency. On each mic channel, switch in a high-pass (low-cut) filter set to 200 Hz, Q = 1.7 to 2.0.
Have a deeper-voiced child talk on stage while you listen to the PA system in use. Gradually turn up the high-pass frequency until the reproduced voice thins out, then back off a little. You’ve just prevented feedback for all the frequencies below about 200 Hz.
Try Temporary Close Miking
Close miking results in more gain before feedback than distant miking. When a mic is close to its sound source, it picks up a louder sound than at a distance. So, you don’t need to turn up the gain as much to achieve adequate volume in the theater.
Let’s say that a choir is singing near the back wall. Try placing a floor mic about 10 feet from the kids when they walk in, then remove the mic when they walk out. The lights could be dimmed during the changeover. This can provide more volume than mics near the stage edge.
Use A Hinging Mic
If the mic locations must be permanent, probably a hanging mic is the best solution. When the choir sings, turn up just the one hanging mic, then turn it off otherwise.
Try to group the children in a few rows so that the choir is narrow. That way the one hanging mic will pick up the far-left and far-right edges of the choir. Two mics are needed for a wide choir, resulting in 3 dB less gain-before-feedback than one mic. Mount the microphones as shown in Figure 1.
Place loudspeakers close to the audience because it makes sound stronger in the audience area. In other words, they’re louder simply because they’re closer to the audience. The result is more volume with no increase in feedback.
Many schools and theaters have loudspeakers permanently installed over the proscenium arch. However, this location tends to result in feedback more easily because the loudspeakers are close to the mics and far from the audience. A solution is to rent or purchase some smaller 2-way loudspeakers (with an 8-inch or 12-inch woofer) and mount them on the wall or on stands close to the audience area.
Another option is to deploy an extra pair of loudspeakers mounted near the back of the audience. The front loudspeakers don’t need to be turned up as much to achieve adequate loudness in the back. You might be able to get by with a single pair of loudspeakers if your sanctuary/auditorium isn’t very deep.
You also might want to delay the audio signal going to the rear loudspeakers in order to create the illusion that the sound is coming from the stage rather than from the nearest loudspeaker.
Try Anti-Feedback Devices
Either a 1/3-octave graphic equalizer or an automatic feedback suppressor can help achieve a little more gain before feedback from a sound system.
And when all else fails, solve the problem at its source: train the children to project.