Crystal microphones utilize the piezoelectric effect. These microphones employ specific crystals, like quartz or Rochelle salt, which generate an electric voltage when subjected to mechanical pressure or vibrations. Sound waves impinging on the microphone's diaphragm induce pressure variations on the crystal, resulting in an electrical signal directly proportional to the sound's intensity.
This characteristic renders crystal microphones sensitive and appropriate for uses such as in telephones and certain recording equipment. In contrast to dynamic microphones that operate via electromagnetic induction, crystal microphones achieve a direct conversion of mechanical stress into electrical energy through the piezoelectric phenomenon.