Put your index and middle finger on your neck. Then try it as soft as you can. You not only hear a sound, but you can feel a movement inside your throat. That means they move quickly back and forth. As your vocal cords vibrate they produce sound.
Sound waves are compressional waves.
Use a toy slinky. Stretch it out between two students. One student should grab several coils on the slinky. Then let go. You will see the group of coils go across to the other student.