To add to your example, this is one of the test I have done:
If I'm in a control room/living room, will stand in the 'sweet spot' and turn 90 degrees so my left ear is facing the back wall while my right is facing the speakers. As I walk through the 'sweet spot' all the center channel information
will bounce off the back wall and be heard by my left ear. My right ear will get the 'null'.
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If the L and R are 180 degrees out, if I walk into the middle of the speaker field, yeah, I can tell if it's out, especially with a tune I'm familiar with. Easier with headphones, of course.
>While on the subject, can anyone reading this claim they can hear an out-of-phase stereo audio, by just listening to the audio in STEREO?