What is Phase?

[jboogie]

As the subjectline states, I am wondering what phase is. I see a lot of reference to it hear but I don't know what it is. Can someone fill me in?

Thanks everyone.

 

[Adam]

In regards to subwoofers, it involves the timing of the subwoofer versus the other speakers. It's like setting the time delay on your other speakers.

A recommendation (albiet a slightly complicated one, at least to me) on how to set the phase is included in one of the "Tips & Tricks" articles on bass located here.

 

[Adam]

There's another explanation at the Audioholics article here. A brief summary:

"A phase switch basically electrically reverses the polarity of the subwoofer and thus changes phase angle by 180 degrees. This is sometimes useful in cases where the Receiver/Processor subwoofer output is electrically out of phase with the speaker outputs. Use this option with caution, starting with the 0 degree as default. Let your ear be the judge as to which position allows your subwoofer and speakers to perform optimally. Usually there is a drastic and obvious difference between both settings. If you hear no difference, then I recommend keeping the switch set at 0 degrees."​

 

[pweller]

I am definitely not an expert, but as I recall phase was described to me in this way: If your speakers are 'in phase' that means that they both move in the same direction when given an electrical signal. If they are out of phase, one speaker moves out while the other moves in. (This is what happens if you reverse the red/black leads on one set of speakers.) I am sure there are people here who know more than I do about this, but this is a fairly simple way to understand the basics.

 

[Djizasse]

http://en.wikipedia.org/wiki/Phase_(waves)
http://en.wikipedia.org/wiki/Phase_cancellation

The way I see it, when two speakers are out of phase, they are at different stages of the wave signal (phase) which can cause destructive interference, where the signal from one speakers kills the signal from the other.

 

[Midcow2]

As the subjectline states, I am wondering what phase is. I see a lot of reference to it hear but I don't know what it is. Can someone fill me in?

Thanks everyone.

Electricity comes in direct and alternating current. The simplest example of direct current is a flashlight you connect a battery to a light and the light comes on. Alternating current varies with time ( frequency) and goes from a postive to a negative in a sinusoidal wave. See the image below:

Each different audio signal is a different frequency and the all add up to form sound.

However looking at the image above each frequecny has a total period of 360 degrees or a circle. A phase shift of 180 degrees means the waves exactly cancel each other out (the blue and violet sine waves are exactly 180 degrees out of phase)- this is the technique being using in noise cancelling headphones and nosies cancelling mufflers. In eact case a microphone picks up the original sound and then shifts the phase 180 degrees and output the shifted sound to cancel the original sound.

When you are listening to sound it is important that the speakers are in phase otherwise the sound from one speaker could cancel the sound from the other speakers.

Hopefully I simplified this enough so that it is understandable. If not, let me know and I will explain further.

 

[jboogie]

Thanks everyone. I think I had the basic idea correct. I just had no idea as to the complexity of it. Now I do.

Thanks again all.

 

[no. 5]

As the subjectline states, I am wondering what phase is.

Phase is the temporal relationship between waves. Not to be confused with polarity which is an electrical relationship.

A good example to illustrate the difference between polarity and phase is a balanced connection: there are three wires in a balanced connection, hot, cold and ground, the cold wire contains the same signal as the hot wire, but the signal the signal is inverted (i.e. the polarity is reversed). When the signal reaches its destination, the hot and cold are combined, but the cold is re-inverted so that the signal doesn't cancel itself out. The reason balanced connections are designed this way is because it provides superb interference rejection, any noise that is picked up cancels itself out when hot and cold are recombined. This would be much harder to accomplish if the hot and cold were out of phase, because phase, being a temporal relationship, would require a time delay to put one signal 180 degrees out of phase with another, and to add to the difficulty, the amount of delay needed changes with frequency.

As a side point, reversing polarity is almost universally referred to as reversing phase, although this is incorrect, it is accepted because we usually know what is being referred to.

 

[no. 5]

When you are listening to sound it is important that the speakers are in phase otherwise the sound from one speaker could cancel the sound from the other speakers.

Well polarity really...

Because phase is a temporal relationship, speakers canceling each other at some frequencies is unavoidable in the right circumstances. Stereo speakers, for example, will always cause some amount of a null around 2kHz for the person seated in the sweet spot, simply because the distances between ears and speakers introduce some amount of time delay. It's not always that bad, but it is unavoidable.