You are not alone. No one understands phase. I think Scott Hinson wrote an article on this, but I have yet to read it. Phase is a very abstract term that means time. But it's not time measured in arbitrary units like seconds, but in waves. A wave can have any propagation time so saying 0.5ms delay doesn't tell you much. However if you say "the length of 2khz wave, which is at the same time half the length of 1khz" then you can start imagining what that delay is going to do to your frequency response simply knowing how waves combine. As I said it's an abstract term and consequently we can apply it to different situations. For example phase cancellation suggests that there are two sources. One makes positive pressure, the other makes negative pressure and they end up working hard and achieving nothing. These two things can be anything. For example two halves of a diaphragm. Grab a sheet of paper and hold it flat in one hand. Move it up and down slowly. The paper should flex a little but generally move with your hand. The suspended part of your diaphragm is in phase with your hand. Now as you speed up, it starts to bend. At certain very specific pace, the end of this sheet will flap up when your hand goes down and vice versa. It'll be out of phase. When your hand makes positive pressure the suspended paper makes negative pressure. When these pressure regions propagate, they expand into each other and to a large degree cancel. Here your hand is driver's motor and the far end is diaphragms edge or suspension. Other examples of a phase issue can be waves bouncing back and forth between the driver and the back enclosure, effectively impeding it's movement. It can be some part of the enclosure ringing also out of phase with the driver. In these cases the propagated sound coming back is the second source. Phase issues are deeply connected with resonances. A resonance can be out of phase with it's energy source. Engineers often use that to their advantage for example Helmholtz resonator is a phase reversing device that is used to extend bass in a bass reflex enclosure. The air in the port is out of phase with the back of a driver inside the enclosure, consequently in phase with it's front. We like when this happens :) The last phase issue that comes to my mind is quite tricky. It comes from driver being relatively big to the wave that it makes. It's called directivity because it works in such a way that depending on the angle from which you listen to the speaker, it's frequency response will change. It will change because there will be travel distance differences between various points on the driver. The far part of the driver makes pressure that has to travel more to reach you and by the time it reaches the pressure from the close part of the driver, they are out of phase (on some specific frequency or frequencies). This is especially a problem on expensive headphones with big drivers. In speakers we fix that with so called phase plugs - obstacles that force selected parts of the wave to take longer paths.