QotD: What is Speaker Phase?
You may have heard of speaker phase before. Usually in reference to subwoofers. In short, when the signal asks for a driver to push out, and it pushes out, it is in phase. When it is asked to push out and and pulls in? Out of phase. But speaker phase is way more complicated than that.
Want to experience the importance of speaker phase? Queue up your favorite two-channel music. Now, switch the speaker wire on ONE of your speakers so that red goes to black and black goes to red. You only have to do this on one speaker and not at the amp. Don’t worry, this won’t hurt your speaker. Now play your music.
Sounds weird, right? Kinda like it is coming out of one side of your head? Yeah, that’s what it sounds like when one of your speakers is 180 degrees out of phase with the other.
How Speaker Phase is Used
When music is mixed, speaker phase and other tricks are used by technicians to manipulate how you experience the tracks. If both speakers in a two-channel mix, are getting the same information at the same time, the sound will appear to be coming from directly in front of you (or between the two speakers). If they put a little more in the left side than the right, it will seem to come more from the left. Obviously.
Where speaker phase comes into play is when technicians want to move the sound around the stage. By delaying one speaker, the technician can create phase cancellations (where the sound wave runs into other waves and cancels out the energy). This tricks the ear (your brain really, but we like to blame our ears) into thinking the sound is coming from somewhere other than the speakers.
It’s All About Your Ears
If you think about how your ears really work, this all starts to make sense. If a sound is coming from your right, the right ear gets the full sound. But what about the left ear? Not only is the sound delayed, it is also different. The big thing between the ears (i.e. your noggin) likely reduces the highest frequencies. Plus the sound will be quieter. Plus a bunch of other stuff.
Remember that test you did with swapping the speaker wire? Remember how it sounded like it was sort of inside your head? Well, sound technicians can use that to trick you into thinking the sound is coming from behind you. How? By adjusting the phase, it signals to the brain that the sound is not coming from in front of you. If the technician then quickly pans the speakers back into phase, it will seem like the sound passed from behind you, through your head, and to the front of the room! The effect is best with headphones or very, very expensive electrostatic speakers, but it is pretty neat when you hear it.
For more information on phase and sound design, check out. SageAudio.com.