Electromagnetic microphone including at least one acoustic resistance

Claim 2

An electrodynamic microphone comprising, a magnet system including a central core enclosed within a magnetic member having a top plate made of a sintered magnetic material and arranged to define an air gap with said core, a diaphragm having a movably mounted coil secured thereto and positioned so that the coil is disposed within said air gap of the magnet system, said diaphragm being mounted to define an air volume space with the top portion of the magnet system, said top plate having an upper surface and a lower surface with a plurality of narrow grooves formed in at least one surface and dimensioned so as to function as an acoustic resistance and being in communication with said air volume space behind the diaphragm, and a cover plate covering a portion of said grooves.

Claim 3

An electrodynamic microphone as claimed in claim 1 wherein said grooves are formed in the upper surface of the top plate so as to form an acoustic communication path between the air volume behind the diaphragm and the external atmosphere, and the cover plate comprises a ring which covers said grooves and is made of a non-magnetic material and to which the diaphragm is secured along its edge.

Claim 4

An electrodynamic microphone as claimed in claim 1 wherein the grooves are formed in the lower surface of the top plate, and the cover plate forms a part of a centering member made of a non-magnetic material.

Claim 5

An electrodynamic microphone as claimed in claim 1 wherein said grooves are disposed radially about the central core in the upper surface of the top plate so as to form a plurality of acoustic communication paths between said air volume space and the external atmosphere.

Claim 6

An electrodynamic microphone as claimed in claim 1 wherein said core and magnetic member are disposed so as to form together an annular air chamber and wherein said grooves are radially disposed about the central core in the lower surface of the top plate so as to form a plurality of acoustic communication paths between said air volume space and the air chamber.

Claim 7

An electrodynamic microphone as claimed in claim 1 wherein said central core comprises a cylindrical axially magnetized permanent magnet and said magnetic member comprises a sintered pot core.

Claim 8

An electrodynamic microphone as claimed in claim 1 wherein said core and magnetic member are disposed so as to form together an annular air chamber and said grooves are radially disposed in both the upper and lower surfaces of the top plate with the grooves in the upper surface angularly offset from the grooves in the lower surface, The grooves in the upper surface forming a plurality of acoustic communication paths between the air volume space and the external atmosphere and the grooves in the lower surface forming a second plurality of acoustic communication paths between the air volume space and said annular air chamber.

Claim 9

An electrodynamic microphone as claimed in claim 1 wherein said grooves are symmetrically disposed around the top plate through an angle of 360*, said grooves having a width of approximately 1 millimeter and a depth of approximately 150 micrometers.

Claim 10

An electrodynamic microphone comprising, a magnetic circuit including a cylindrical central magnetic core enclosed by a magnetic pot core having an annular top plate made of a sintered magnetic material and arranged to define an air gap with said central core, at least one element of said magnetic circuit being permanently magnetized to produce a magnetic field in the air gap, a vibratory system including a diaphragm having a movably mounted coil secured thereto and positioned so that the coil is disposed within said air gap, said diaphragm being positioned to define an air volume space with the top part of the magnetic circuit, said top plate including a plurality of narrow grooves dimensioned to function as an acoustic resistance in communication with the air volume space behind the diaphragm, and a cover plate covering a portion of said grooves to form therewith a plurality of tubular ducts.

Claim 11

An electrodynamic microphone comprising, a magnetic circuit including a cylindrical central magnetic core enclosed by a magnetic pot core having an annular top plate made of a sintered magnetic material and arranged to define an air gap with said central core, at least one element of said magnetic circuit being permanently magnetized to produce a magnetic field in the air gap, a vibratory system including a diaphragm having a movably mounted coil secured thereto and positioned so that the coil is disposed within said air gap, said diaphragm being positioned to define an air volume space with the top part of the magnetic circuit, said top plate including a plurality of narrow grooves dimensioned to function as an acoustic resistance in communication with the air volume space behind the diaphragm, and a cover plate covering a portion of said grooves to form therewith a plurality of tubular ducts.

Claim 12

An electrodynamic microphone as claimed in claim 9 wherein said cover plate comprises a non-magnetic ring adjacent the upper surface of the top plate and the grooves are radially disposed in the upper surface of said top plate.