To get this out of the way: I know how a kundt's tube generally works and how you can use it to determine the speed of sound. For anyone who hasn't heard of it, you take a tube and "feed" it a resonant frequency.(very similar to a rubens tube) The nodes of the resulting standing wave in the tube can be seen if you put dust in it. The dust forms odd stripes I am concerned with in this thread. (Alternatively you can put styrofoam balls in there) The movement of the styrofoam balls is puzzling. The dust particles probably move the same way when accreting into the stripes, they are just too small to see. In the antinodes (of the air-displacement), the points where the air is moving back and forth the most, the styrofoam balls form "walls". If you have never seen this before, here is a link PRO TIP: Turn the volume down. I thought about it for a while but I can't come up with a plausible explaination. So I am asking you all, why does it form the stripes/walls ?