Rules:Laws

If you go to school to be an audio engineer, two of the rules they’re gonna teach you are the inverse square law and the 3 to 1 rule. When you understand what they mean, you’ll understand they’re pretty important and also really intuitive. Here’s the formula.

It means that as I move away from the microphone, I get quieter. If I double the distance, I quarter the intensity. Double it again, order again.

Keep that in mind the next time you use two microphones to record something. And that brings us to the 3 to 1 rule, and here’s why it’s important. Why on earth would anyone use two microphones to record one thing?

Maybe you’re trying to get a slightly different picture of that thing in two different places. When a second microphone is further from the source, it doesn’t just get the signal quieter. It gets it later.

A microphone here and a microphone here are both going to hear the signal coming from here, but they’re not going to arrive at the same time. And when they don’t, you’re gonna get some phase cancellation. And that’s why we use the 3 to 1 rule.

The farther these two mics are away from each other, the less of each other’s signals they’re gonna get. Making sure the mics are three times as far away from each other as they are from the source will ensure that by the time those signals combine, they’re not gonna do too much harm.