A big trick to get it working is actually “Stereo Dipole”, which is that the speakers are around 10 degrees apart and you are at least 2m away. The University of Southampton has a great site with good demos: http://resource.isvr.soton.ac.uk/FDAG/VAP/html/download.html
Sound Cancellation
Get your speakers (or a pair of headphones cranked up) and play around with these different sound files! One is a mono signal in both channels, the other file is the same track, except one ear has flipped polarity! Hold them apart from each other in front of you and then slowly bring them together / play with them.