Vibration is ubiquitous.  At some level everything moves periodically across an equilibrium point. Vibration can be desirable; as in the motion of a tuning fork, the reed in a woodwind instrument or harmonica, a mobile phone, or the cone of a loudspeaker. In many cases however vibration is undesirable indicating imbalances in the rotating parts, uneven friction, or the meshing of gear teeth. Careful acoustical designs reduces unwanted vibration and “sound pollution” in classrooms and campuses overall.