So I know that for constructive interference to occur, in phase waves must be separated by a distance 2 pi. What I'm confused about, though, is what if the point they interfere at is separated by a distance 2 pi, but isn't where their crests meet? Like what if one speaker is one wavelength behind the other, but they both start off at zero amplitude, so wouldn't that point where they meet still be zero? Thanks for the help.