Acoustic transducer with improved electrode spacing

Abstract

An acoustic transducer with an improved electret assembly mounting for providing spacings between the fixed and movable electrodes, and having as one feature the lowering of the undesired capacitance therebetween.

We claim: .[.1. An acoustical transducer, comprising in combination, a case having a top, bottom and side walls; and electret assembly including a diaphragm having peripheral portions and a central vibratable plate portion forming a movable electrode, a diaphragm support ring having an opening thereon mounted in said case, the peripheral portions of said diaphragm being mountable to said support ring, a backplate mounted within the opening of said support ring to form a spacing between the backplate and the support ring, said backplate having a surface comprising a fixed electrode and cooperating with the diaphragm movable electrode to develop a signal, an acoustical chamber formed between the electret assembly and the bottom of said case, a second chamber formed between said assembly and the top of said case, said spacing between the backplate and the support ring lowering the capacitance between said electrodes, and said spacing 
     
        enabling air movement between said chambers..]. .[.2.  An acoustical transducer, comprising in combination, a case having a top, bottom and side walls; an electret assembly including a diaphragm having peripheral portions and a central vibratable plate portion having a conductive material thereon, a diaphragm support ring having an opening thereon mounted in said case, the peripheral portions of said diaphragm being mountable to said support ring, a backplate mounted within the opening of said support ring to form at least one spacing between the backplate and the support ring, an electret material, said backplate having a surface on which is electret material is positioned, said electret material cooperating with the diaphragm to develop a signal, support posts on the interior surface of the bottom of the case, protrusions on the surface of the backplate and aligned with said support posts for supporting the electret assembly in the case in spaced relation to the bottom of the case, an acoustical chamber formed between the electret assembly and the interior surface of the bottom of said case, a second chamber formed between said assembly and the top of said case, the spacing between the backplate and electret material and the support ring lowering the capacitance therebetween and hence the undesired capacitance affecting the electret assembly, and the spacing also providing a channel for air between the diaphragm and the electret material to escape into the second chamber of said casing..]. .[.3. An acoustical transducer as in claim 2 wherein said spacing extends substantially around said backplate..]. .[.4. An acoustical transducer as in claim 2 wherein said diaphragm includes a flange on its periphery, said flange conforming to the wall surface of the support ring, and means for adhering said flange to said ring..]. .[.5. An acoustical transducer as in claim 2 wherein the support ring includes shoulders or projections extending into said opening, and said backplate is affixed to said shoulders to provide said at least one spacing between the backplate and said ring..]. .[.6. An acoustical transducer as in claim 2 wherein said backplate includes wings or projections extending outwardly from the edges of said backplate for affixing said backplate to said 
     
     
        support ring to form said at least one spacing..]. .Iadd.7.  An acoustical transducer comprising, in combination: a case; a diaphragm having peripheral mounting portions and a central vibrating plate portion forming a movable electrode, the peripheral mounting portions of said diaphragm being sealed in said casing to define separate first and second acoustic chambers on opposite sides thereof; backplate support means having an opening; a backplate in said second acoustic chamber confronting said diaphragm in close but spaced relation thereto, said backplate being mounted within said opening of said support means and secured thereto at spaced points and being unsecured thereto and spaced from the support means and casing between said spaced points of securement, said spacing between the backplate and support member and casing between said spaced points of securement extending substantially around the entire periphery of said backplate so as to substantially lower the capacitance between said backplate and the peripheral mounting portions of said diaphragm, the side of said backplate facing away from said diaphragm being spaced from a confronting side of said case to define a relatively large space communicating with the space between said backplate and diaphragm and constituting the major portion of the volume of said acoustic chamber on one side of said diaphragm, said backplate having a layer of electret material thereon and cooperating with said diaphragm to generate a signal therebetween upon movement of said diaphragm relative to said backplate or the diaphragm being moved relative to the backplate when a signal is applied therebetween; and a pair of electric terminals respectively coupled to said backplate and diaphragm for coupling a signal to or from the same. .Iaddend. .Iadd.8. An acoustical transducer as in claim 7 wherein there are support posts on the interior surface thereof upon which posts said diaphragm seats and protrusions on the surface of said backplate contacting said diaphragm outwardly of said central portion thereof and aligned with said support posts for supporting said diaphragm in an initial given spaced relation to the backplate. .Iaddend. .Iadd.9. An acoustical transducer as in claims 7 or 8 wherein said support means is a ring surrounding said opening therein, said diaphragm includes a flange on its periphery, said flange conforming to said peripheral surfaces of said support ring, and including means for adhering said flange to said ring. .Iaddend. .Iadd.10. An acoustical transducer as in claims 7 or 8 wherein said support means is a ring surrounding said opening therein, said support ring includes shoulders extending into said opening, and said backplate is affixed to said shoulders to provide said spacing between said backplate and said ring. .Iaddend. .Iadd.11. An acoustical transducer as in claims 7 or 8 wherein said support means is a ring surrounding said opening therein, said backplate includes projections extending outwardly from the edges of said backplate for affixing said backplate to said support ring and to form said spacing between said support ring and backplate. .Iaddend. .Iadd.12. An acoustical transducer as in claims 7 or 8 including port means for communicating sound between the outside of said case and said first acoustic chamber. .Iaddend. .Iadd.13. An acoustical transducer comprising, in combination: a case; a diaphragm having peripheral mounting portions and a central vibrating plate portion forming a movable electrode, the peripheral mounting portions of said diaphragm being sealed in said casing to define separate first and second acoustic chambers on opposite sides thereof; backplate support means having an opening; a backplate in said second acoustic chamber confronting said diaphragm in close but spaced relation thereto, said backplate being mounted within said opening of said support means and secured thereto at spaced points and being unsecured thereto and spaced from the support means and casing between said spaced points of securement, the side of said backplate facing away from said diaphragm being spaced from a confronting side of said case to define a relatively large space communicating with the space between said backplate and diaphragm and constituting the major portion of the volume of said acoustic chamber on one side of said diaphragm, said spacing between said backplate and support means and casing effecting communications between the space between said diaphragm and backplate and said relatively large space on the opposite side of said backplate to reduce back pressure on said diaphragm in said second acoustical chamber; said backplate having a layer of electret material thereon and said cooperating with said diaphragm either to generate a signal therebetween upon movement of said diaphragm relative to said backplate or the diaphragm being moved relative to the backplate when a signal is applied therebetween; and a pair of electric terminals respectively coupled to said backplate and diaphragm for coupling a signal to or from the backplate and diaphragm. .Iadd.14. The transducer of claim 7 wherein said case has support posts on the interior surface thereof upon which posts said diaphragm seats, and protrusions on the surface of the backplate contacting said diaphragm outwardly of the central portion thereof and aligned with said support posts for supporting the diaphragm in an initial given spaced relation to the backplate. 
     
     
        .Iaddend. .Iadd.15.  An acoustical transducer as in claims 7 or 8 wherein said support means is a support ring surrounding said opening therein, said diaphragm includes a flange on its periphery, said flange conforming to the wall surface of the support ring, and means for adhering said flange to said ring. .Iaddend. .Iadd.16. An acoustical transducer as in claims 7 or 8 wherein said support means is a ring surrounding said opening therein, said support ring includes shoulders or projections extending into said opening of said ring, and said backplate is affixed to said shoulders to provide said spacing between the backplate and said ring. .Iaddend. .Iadd.17. An acoustical transducer as in claims 7 or 8 wherein said support means is a ring surrounding said opening therein, said backplate includes projections extending outwardly from the edges of said backplate for affixing said backplate to said support ring and to form said spacing between said support ring and backplate. .Iaddend. .Iadd.18. An acoustical transducer as in claims 7 or 8 including port means for communicating sound between the outside of said case and said first acoustic chamber. .Iaddend.