A number of you missed some of the similarities and differences between gravitational, electrical, and magnetic phenomena. All of them take place between separated bodies with no obvious physical contact between them. All three effects fall off with the inverse-square of the distance between the bodies. Gravity is only attractive whereas the other two can be either attractive or repulsive. Sound is a vibration in matter - moving molecules, whereas EM waves can, and do, occur in vacuum.
Effect has nothing to do with distance, everything to do with velocity, of sound source.
Same phenomenon occurs for all waves, e.g., also for EM waves. So there is no interference in general. If there were some instants when conditions for interference existed, and the leads were interchanged, constructive interference would become destructive and vuce-versa. Thus you see the flash long before you hear it. Since the wavelength is twice the distance between nodes, the wavelength is 2 meters.