Try a search on slot resonators on the Studio Building board.
As for phase, best way to learn this is to set up an experiment. Set up two mics right next to each other and sing, play an instrument, etc. from a distance of one foot. Now reverse phase on one of them. Now move one of the mics a foot apart, and move yourself a little closer to one mic. Listen with and without the phase switch flipped on one mic. Repeat the experiment at two feet and three feet separation between the mics.
What you will here in some cases is a loss in response at certain frequencies, sometimes subtle and sometimes drastic. Those are the setups with the phase problems. Flipping a phase switch doesn't always fix it although it may help. The correct solution is to change your mic placement to avoid the problem.
Having said that, grossly out of phase mics are a pretty good low-tech way of generating the "telephone effect" discussed on the other thread.
