To create a directional diagram, a loudspeaker is set up in an anechoic room and mounted on a turntable, then it is rotated to various positions and the volume levels at certain frequencies, or even the entire frequency response range, measured. The diagram shows the pattern made by the sound energy as it spreads in the various directions. We differentiate between omnidirectional (all-round), pencil beam (highly focussed), cardioid (kidney-shaped) and dipole or bidirectional characteristics (same distribution in front and behind) characteristics. The characteristics considered optimal for a given situation or application may differ considerably.