It's probably hard to tell with surrounds because they only get bits and pieces of the content anyways, but here's what you see with the mains :
- when polarity is correct (left and right are the same) your brain sees the sounds distributed properly between the speakers, with many sounds clearly coming from the midpoint between the speakers
- when polarity is reversed you hear a weird "phasey" kind of sound (you know the sound a phase shifter (not a flanger) makes on a voice or instrument ?) and the sounds seem to move more to the outside, ie there is sound on the left and on the right but nothing in the middle
If you're not a musical instrument junkie and aren't familiar with phase shifters let me know what you do watch/listen to and I'll try to give you an example
