Unidirectional electret microphone
First Claim
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1. A unidirectional electret microphone comprising:
- a tubular case having at one end thereof a front end plate formed integrally therewith, said front end plate having a front sound hole therein;
a diaphragm disposed in the case in parallel relation to said front end plate;
a back electrode disposed in the case in parallel relation to said diaphragm, said back electrode having at least one sound hole therein, and one of said back electrode and said diaphragm being formed as an electret;
a partition wall in said case, said partition wall having its front surface in contact with the rear surface of said back electrode, the said partition wall having at least one sound hole therein disposed in opposing relation to said rear surface of said back electrode;
a rear sound hole in the case at the back of the partition wall; and
at least one of the surfaces of the back electrode and the partition wall which contact one another being formed to define at least one air path of small predetermined dimensions, said air path being positioned in said surface to acoustically couple the sound hole of said back electrode and the sound hole of said partition wall to one another.
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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.
104 Citations
14 Claims
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1. A unidirectional electret microphone comprising:
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a tubular case having at one end thereof a front end plate formed integrally therewith, said front end plate having a front sound hole therein; a diaphragm disposed in the case in parallel relation to said front end plate; a back electrode disposed in the case in parallel relation to said diaphragm, said back electrode having at least one sound hole therein, and one of said back electrode and said diaphragm being formed as an electret; a partition wall in said case, said partition wall having its front surface in contact with the rear surface of said back electrode, the said partition wall having at least one sound hole therein disposed in opposing relation to said rear surface of said back electrode; a rear sound hole in the case at the back of the partition wall; and at least one of the surfaces of the back electrode and the partition wall which contact one another being formed to define at least one air path of small predetermined dimensions, said air path being positioned in said surface to acoustically couple the sound hole of said back electrode and the sound hole of said partition wall to one another. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A unidirectional electret microphone comprising:
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a tubular case having at one end a front end plate formed integrally therewith, said front end plate having a front sound hole therein; a diaphragm disposed in said case adjacent to said front end plate in parallel relation thereto; a back electrode disposed in said case in parallel relation to said diaphragm, said back electrode having at least one sound hole therein; one of said back electrode and said diaphragm being formed as an electret; an elastic plate disposed in contact with a rear surface of said back electrode, said elastic plate having a through hole therein opposing the rear surface of said back electrode; a partition wall disposed in contact with said elastic plate so as to sandwich said elastic plate between said partition wall and said back electrode, said partition wall having a sound hole therein in communication with said through hole of said elastic plate; at least one groove in the rear surface of said back electrode defining an air path which acoustically couples the sound hole of said back electrode to the sound hole of said partition wall via the through hole of said elastic plate; and a rear sound hole on said case at the back of said partition wall.
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14. A unidirectional electret microphone comprising:
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a tubular case having at one end a front end plate formed integrally therewith, said front end plate having a front sound hole therein; a diaphragm disposed in said case adjacent and parallel to said front end plate; a back electrode disposed in said case in parallel relation to said diaphragm, said back electrode having a sound hole therein; one of said back electrode and said diaphragm being formed as an electret; a cylindrical electrode holder comprising a block of an insulating material in said case, said block being disposed behind the said back electrode in contact therewith for fixedly holding the back electrode; an impedance converter element disposed in a compartment formed in said electrode holder block at a rear end portion thereof, said impedance converter element having an input terminal which is electrically connected to said back electrode through a hole in said electrode holder block; and a through hole in said electrode holder block which forms an air path through said block that acoustically connects the sound hole of said back electrode to a rear open space of the microphone.
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Specification