Does the amplitude of a wave changes when the source is moving? I am mainly interested in waves in a medium (e.g. sound, water...) No text about Doppler effect I have found mentions anything about the amplitude so I guess it does not change. However in the case if the speed of the source is equal to the wave, I think, if there where N wavefronts emitted the amplitude should be N-times larger than that of one amplitude (see http://upload.wikimedia.org/wikipedia/commons/2/25/Mach_cone.svg" [Broken] (the case Ma=1)). If the speed of the source is slightly below the wave speed, the amplitude should be slightly lower than N-times and so on... So I get the feeling that the amplitude does indeed change. What's correct, what's wrong? Why? It would be great if someone has a detailed explanation!