Speaker to the transmitter causes compression in the diaphragm. Runs the current of gases through the solids. The air molecules change as they go through the movement of the receiver diaphragm. The pump manipulates the air molecules. There is a gradual elimination of the air molecules.
Transmitters are similar.
There is no sound transmitter in a vacuum. Cylinder goes up while turning the wheel is turned. The same with the pump. The gases are sucked out. List as many physical principles as you can that can be taught by using a vacuum pump as an example.