A nice experiment shows the relation of phase to physical position. Set the speakers to monaural and play an 80 Hz tone into the two speakers, then reverse the phase to reduce the sound to virtually nothing. Uncoil the wire from the back of one speaker and move the speaker 12 or 15 feet across the front of the room; the loud bass tone returns! The waves from the two speakers are no longer out of phase. Can easily be combined with H2-26.