What must engineers adhere to when double miking an instrument on a live stage?

When double miking an instrument on a live stage, engineers must adhere to the 3:1 rule. This guideline helps to minimize phase cancellation and interference between the two microphones. The rule stipulates that for every foot of distance between the microphones, they should be at least three feet apart from each other. This distance ensures that sound waves captured by each microphone reach the microphones at different times, thereby reducing the likelihood of undesirable acoustic interactions that can muddy the sound.

In practice, using the 3:1 rule allows engineers to blend the outputs of both microphones effectively while maintaining clarity and fidelity. Adhering to this distance helps to ensure that each microphone picks up the sound of the instrument clearly without conflicting with the other, which can occur if they are placed too close together.