To be a total stickler for terminology, speakers CANNOT have their polarity reversed, since they are driven by AC, which has no + or - poles! Only DC has a + or - polarity. Speakers can have only an absolute phase inversion [both speakers have the wires reversed on the + and - terminals], out of phase [only ONE speaker wire will have the + and - terminals reversed...very bad indeed!], or have a phase shift. A phase shift occurs when different frequency ranges are shifted [delayed] by milliseconds. This can be due to crossovers, physical driver alignment, speaker wires, or the amplifier powering the speakers. Sort of like a prism splitting white light into the various frequencies of colored light...in effect, a rainbow. Again, not good. But phase shift is pretty much a fact of audiophile life. The amount of phase shifting will determine the coherency [or not] of the sound.
FYI, here's a neat trick to get raw drivers in phase when the terminals are not marked or marked incorrectly [it does happen!], or for car installations where multiple long concealed speaker wire runs can easily be installed out of phase. Take a "D" cell battery, and hold the speaker wires to the battery. Note whether the speaker cone moves out or in. I consider "out" to be the + terminal and "in" to be -, this being a good memory aid.
FYI, here's a neat trick to get raw drivers in phase when the terminals are not marked or marked incorrectly [it does happen!], or for car installations where multiple long concealed speaker wire runs can easily be installed out of phase. Take a "D" cell battery, and hold the speaker wires to the battery. Note whether the speaker cone moves out or in. I consider "out" to be the + terminal and "in" to be -, this being a good memory aid.