Pressure gradient electret microphone
First Claim
1. A directional condenser microphone comprising a hollow casing having an opening extending from the exterior to the interior thereof, an electrically conducting diaphragm disposed in a flat plane confronting the opening in the casing, means for mounting said diaphragm on the casing and acoustically sealing the diaphragm about the perimeter of the opening, an electrically conducting back plate mounted in the casing and electrically insulated from the diaphragm, said back plate having a flat surface disposed parallel to and confronting the side of the diaphragm opposite the opening, means including the back plate and diaphragm forming a cavity between the diaphragm and back plate, and channel defining means including the cavity forming means and casing defining a plurality of channels, each of said channels having a first port at one end and a second port at the other end, the first port of each channel communicating with the cavity and being located adjacent to the perimeter of the back plate, and the first ports of the plurality of channels being spaced from each other, the portion of each of said channels adjacent to the first port being acoustically isolated from each other, the second port of each channel being located on the exterior of the casing, said second ports being spaced from the plane of the diaphragm by approximately the same distance, said cavity being acoustically coupled to the sound field exterior of the casing only through the diaphragm and the channels.
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Accused Products
Abstract
A pressure gradient electret microphone provided with a plurality of channels extending between ports located in a ring of plastic material disposed about the periphery of a cylindrical back plate. Each of the channels expanding in horn fashion from the port at the diaphragm chamber to ports in the casing, and the ports in the casing being provided with an electrically conducting shield connected to the electrically conducting casing. In one embodiment of the invention, a line extends from the forward side of the diaphragm, and the line is provided with an aperture adjacent to the diaphragm coupling the diaphragm to the surrounding sound field at frequencies below the critical frequency of the line.
45 Citations
9 Claims
- 1. A directional condenser microphone comprising a hollow casing having an opening extending from the exterior to the interior thereof, an electrically conducting diaphragm disposed in a flat plane confronting the opening in the casing, means for mounting said diaphragm on the casing and acoustically sealing the diaphragm about the perimeter of the opening, an electrically conducting back plate mounted in the casing and electrically insulated from the diaphragm, said back plate having a flat surface disposed parallel to and confronting the side of the diaphragm opposite the opening, means including the back plate and diaphragm forming a cavity between the diaphragm and back plate, and channel defining means including the cavity forming means and casing defining a plurality of channels, each of said channels having a first port at one end and a second port at the other end, the first port of each channel communicating with the cavity and being located adjacent to the perimeter of the back plate, and the first ports of the plurality of channels being spaced from each other, the portion of each of said channels adjacent to the first port being acoustically isolated from each other, the second port of each channel being located on the exterior of the casing, said second ports being spaced from the plane of the diaphragm by approximately the same distance, said cavity being acoustically coupled to the sound field exterior of the casing only through the diaphragm and the channels.
Specification