Sound waves

As rbj says, your question is not quite accurate. A better way to ask would be "Where does the sound wave energy go at constructive interference nodes?" Just like with standing waves on a string, where you get some parts of the string swinging up and down with maximum amplitude ("antinodes"), and some locations where the string is not moving up and down at all ("nodes"). For the string, the answer to the question "How do the left-propagating and right-propagating waves move through the non-moving nodes?" is that the *tension* in the string at the nodes is what propagates the waves. The string does not need to be moving up and down there in order to propagate the energy that results in the up-down movement of the rest of the string.

String waves are "transverse", meaning that the motion of the string is perpendicular to the direction of propagation of the wave on the string. Sound waves are longitudinal, meaning that the oscillating motion of the air molecules is parallel with the direction of the sound wave travel. So, when you get a node in the superposition of two equal-frequency sound waves from separated sources, I would guess that the energy is tranferred through the nodes still with oscillating air pressure waves, but the local addition sums to zero (so you hear nothing). The waves still exist and pass by each other, since sound waves do not interact with each other in linear media like air. It's just that the sum of them is zero at the point where you are listening....