Electret diaphragm microphone with means to corrugate the diaphragm when in an overstressed condition

摘要

A condenser microphone comprises two electrodes spaced from each other by a small distance, of which one electrode is a diaphragm responsive to sound waves and the other electrode is formed with raised pin-like portions or projections projecting into the interspace between the electrodes, toward the diaphragm. The raised portions extend through only a part of the interspace so that a free space is left permitting unimpeded oscillation of the diaphragm in response to normal sound waves. The raised portions act as stops determining the maximum amplitude so that if the sound waves are abnormally strong, the diaphragm is deflected only up to contact with the end faces of the raised portions thus remaining spaced from the main surface of the opposite electrode. The electrostatic attractive forces are thereby limited and do not prevent the diaphragm from further free oscillation. To further reduce the electrostatic forces in the extreme position of the diaphragm, the end faces of the raised portions against which the diaphragm may apply are concave or electrically non-conductive. The electrodes preferably comprise an electretic material.