The single element unidirectional microphone exhibiting the Limaçon directional patternm+ (1 −m) cos θ was an accidental discovery during an effort to develop a bidirectional piezoelectric microphone, affirming the research director's lament that the best inventions are those leading into unexpected directions. Refined through equivalent circuit analysis and embodied in many configurations this principle over the years has been employed in many important and interesting microphone applications in Public Address, Broadcasting, Recording, and others. The theory and some of the most important configurations and applications of this principle are described.