the word Phase describes a relationship it can be applied to anything really
Weseixas, Phase and polarity have very definite meanings in electronics. Just because phase has different meanings in different contexts does not mean you can use it however you want in a scientific discipline like electronics and be correct. In electronics phase has a single meaning. To say things are in phase means they happen at the same time. Out of phase means the time relationship between two signals has changed. One is occurring later in time with respect to the other. A polarity inversion means what was negative is now positive and vice versa.
When you put an audio signal through a crossover there is a phase shift at the crossover point. Some frequencies are shifted in time. No polarity change of anything. Phase dispersive as Almarg described it.
Like I said before, even though it is very common to call a polarity inversion at a speaker out of phase this is technically incorrect. There has been no timing change, we have only inverted the polarity. It is common because for a single frequency a polarity inversion and out of phase 180 degrees gets the same result (see below) but just because it is common usage does not mean it is scientifically correct. We're also not dealing with a single frequency in audio.
We say that the sun rises in the east and moves across the sky. Is this scientifically correct even though everyone says it. No, the earth rotates, the earth is moving, not the sun.
At the end of the day does it really make any difference if we say speakers are out of phase? In that context no, since everyone does it so we all know they mean the leads were reversed. The problem arises if you try to expand your knowledge of electronics and continue to confuse the two terms.
Please see the link below which says exactly what I just said. Notice the author points out that polarity switches on audio equipment are sometimes incorrectly labeled phase switches. This is exactly the same error committed when we describe switching speaker leads as out of phase.
Almarg said, "A polarity inversion is the same thing as a 180 degree non-dispersive phase shift."
It may appear that way on a scope for a single frequency but if you have a complex waveform consisting of more than one frequency you get different results. Two scenarios
(1) Take 2 signals of equal amplitude and the same frequency that are in phase...
...polarity invert one and sum the result you get complete cancellation.
...phase shift one signal by 180 degrees and sum the result you get complete cancellation.
Same result but for a different reason.
(2) Take 2 equal signals consisting of a mix of 20 hertz and 100 Hz all the same amplitude in phase....
.... polarity invert one and sum the result you get complete cancellation.
.... phase shift one signal by 180 degrees...well... here is where you run into a problem. You can't phase shift them both by 180 degrees because the periods are different. a 180 degree shift of 20 Hz is 25 milliseconds and a 180 degree shift for 100 Hz is 5 milliseconds. You can't phase shift them both by 180 degrees.
Conclusion... phase shift and polarity inversion are always 2 different things even though under special circumstances you get the same result. Sorry I got a bit long winded. Phase/polarity confusion is a pet peeve of mine.
http://www.musiciansfriend.com/document?doc_id=91427
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