Fig.68 Phase displacement leads to the shift of nodes and anti-nodes.

Fig.69 The observer has to move to implement the condition of frequency equality of the waves coming to him. In this case he registers the standing wave!

Fig.70 Frequency difference takes place (v₁>v₂). The speed of energy flow and the speed of the car are equal. The passengers in the car observe a standing wave, and for them the energy transfer doesn’t exist. The observers outside see a complex wave picture which is not a standing wave.

Fig.71 Frequency difference is absent. The flow of energy in the system of motionless observers is absent. In the system of moving observers relative to standing wave the energy flow exists. The of energy flow velocity equals in modulus the car velocity.  Could it be the source of de Broglie waves?