Abstract: A partition wall is held in contact with a back electrode on the opposite side from a diaphragm, and a fine acoustic path is formed in at least one of the contact surfaces of the partition wall and the back electrode. The acoustic path communicates with a sound hole made in the back electrode and a sound hole made in the partition wall. The velocity component of sound reaching the back of the diaphragm is controlled by the fine acoustic path.

Abstract: An electret diaphragm is housed in a case, a back electrode is disposed opposite the back of the electret diaphragm, a damper cloth is disposed in contact with the back of the back electrode, and a terminal plate is placed behind the damper cloth and connected with the back electrode. The back electrode, the damper cloth and the terminal plate are held by a tubular back electrode holder. The back of the back electrode holder is closed by a printed circuit board to define a rear compartment in the back electrode holder, and an impedance converter is disposed in the rear compartment. A sound hole is made for intercommunication of the rear compartment with the outside to achieve unidirectional directivity.

Abstract: An electret microphone in which an electret diaphragm, a back electrode plate disposed opposite thereto and a tubular back electrode holder for holding the back electrode plate are housed in a capsule, an impedance conversion element is housed in a hole made in the peripheral wall of the back electrode holder, and an input terminal of the impedance conversion element is connected to the back electrode plate and an output terminal is led out of the capsule through a notch formed in its peripheral wall.

Abstract: In an electret microphone in which an impedance conversion element housing chamber for an impedance conversion element is provided on the side opposite from an electret diaphragm with respect to a back electrode in a capsule, an isolating metal plate is disposed in the impedance conversion element housing chamber in spaced relation to the back electrode to define between the isolating metal plate and the back electrode an air compartment which is pneumatically isolated from the impedance conversion element chamber.