Ask the Expert – Mic use for school play

Tim Thompson emailed a question regarding microphones for a school play.

“We don’t have the ability to mic every kid in the play and would love to have just a general mic on the stage that would pic up the kids as they speak. The stage is about 35 ft wide. What kind of mic and how many could we use. It is mostly speaking and a little singing. Any ideas?”

Tim Horton, Project Manager with SFL Group, replies:

The challenge with a “general mic” is that you only pick up “general sound”. As soon as you start to amplify this mic in the PA, you will get feedback.

The principle is this: every time you half the distance between mic and performer, you double the effective volume.

With this in mind, if you were to close mic someone (i.e. 2” from their mouth) you will get, let’s say 100% volume. As you move away to 4” you are at 50% volume. By the time you are 1-ft away, you are now at around 15% volume.

If you were to put the mic in the centre of your stage, you would be about 17-ft away from everyone. This is probably equal to a 1% volume capability…!

Of course, you could use a handful of mics spread out along the stage, but you would only achieve about 10% volume potential. Even if you were to use shotgun mics which are highly directional, you might only be able to increase this volume capability by a small amount more than this.

Encouraging the kids to “perform” and project their voices as best they can would get you off to a good start, but really without individual close mic’ing you will not be able to make a mouse shout…

The main use for these “general mics” is for recording or broadcast; basically to amplify anywhere except the room in which the mics / performance is being held.

I’m sorry that there is no easy answer to this question!

Tim