I have always wondered what the purpose of the phase switches that are on most powered subwoofers.

They usually have two positions, 0 degrees and 180 degrees. Am I correct in assuming the 180 degree switch simply is setting it up out of phase(like swapping the positive and negative leads to the speaker)?

What would be the purpose of this? Does it actually allow it to blend better with some systems?

I have always listened to a sub I have setup in both positions, but have always found the change is sound very minimal if any, so I have always set them to 0. Let me know if I am totally off track with my perception.