1. The problem statement, all variables and given/known data A sound wave with 40cm wavelength enters a tube at the source end. What must be the smallest radius r such that a minimum is heard at the detector end (picture attached)? 2. Relevant equations I am really lost in this problem, but I BELIEVE constructive/destructive wave interference: f = (2n+1)V/(2dX) where n is an integer, V is the wave speed, dX is the difference in travel distances between the two waves, and f is the frequency at which destructive interference occurs at a given point. 3. The attempt at a solution I have honestly been stumped by this question. I have a physics exam very soon and so I need to know how to solve these sorts of problems. I am not looking for anyone to help me find the answer; I was just wondering if someone could help me get started off? Thus far, can conceptually see that if r is the same size as the bump, then the wave will flow through as if it were an open ended pipe, but beyond that I do not know what is going on. Could someone please throw me on the right track?