When we talk about live sound or recording with mics, we hear a lot about phase cancellation. We know it is bad, but what is it really? Let’s not confused phase with the guitar effect known as phaser(that is different). Phase becomes something we have to worry about when we have two microphones recording the same sound (one mic can also have phase issues but is not as common). Phase cancellation is when the same sound is played out of a speaker at a slightly delayed time.This causes the speakers to play nothing or distorted sound. We will try to keep this a pretty high level overview. With that said, please keep in mind that some of the descriptions we provide will not be 100% “technically” accurate but used to demonstrate the principles at work; Don’t worry we will tell you if we are making stuff up.
First we need to have a quick and simple understanding of how mics, ears and speakers work. Ears “capture sound”. Mics “capture sound”. Speakers “Play sound”. Guys named Mike will date your sister and break her heart. Simple enough. Speakers take the electric “sound” the mics captured and make it audible to you. If you have ever looked at a speaker with the protective crap off, you see the cone. The cone moves in and out pushing air to make a wave of sound to your ear. Your ear has an eardrum, the ear drums moves in and out with the vibrations of the sound and that is converted into electric pulses to your brain.
The mic basically works like your eardrum and the speaker. It has a small little diaphragm inside that records the sound as air hits it, moving in and out. It works just like the speaker, but in reverse. The important part to understand is the in and out movement. Basically a mic can be on (moving out) or off(moving in). If we put two mics on the same sound source at different distances, we might get phase issues. Since sound travels at a certain speed; the sound might hit one mic before it hits the other.
So now we have the same sound hitting two mics at different times. One mic diaphragm might be moving in, while the other is going out. When the speaker is trying to reproduce that sound; it can’t. The speaker is trying to move in and out at the same time. Phase issues. It can’t move both ways at the same time so the sound actually is canceled out and NO sound is played. This phase cancellation.
In real world applications the sound is hardly ever canceled out completely as the two signals will be slightly different but it WILL makes the sound softer and comb filtered (comb filter adds a delayed version of a signal to itself)
Now that we know what it is; how do we fix it. Easy- move one of the mics a little until it goes away.
If you have any questions on this or other sound topics, please post below!!!!