Why is it that in a room, if you're close to any of the walls the lower frequencies of a sound become louder? Ofcourse, there's an interference pattern in the room. You can hear this by walking around and you'll notice that at some points the bass is weaker and at some points it's stronger (the nodes and antinodes are easier to pinpoint in the longer wavelengths). But shouldn't there be nodes at the walls and hence the level would drop there? Instead, there's a remarkable increase in bass level if you get within, say, 0.5 meters from a wall.