ELECTRODYNAMIC TRANSDUCER STRUCTURE

Abstract: An electrodynamic transducer (100) includes a magnet assembly (101) providing an air gap (118), a diaphragm (114) in the shape of a body at least partly defined by rotation of a segment of a two dimensional curve about an axis (126). The diaphragm (114) has a long edge (116), a short edge (128) and an apex, said short edge (128) and said apex lying in the air gap. A voice coil (120) is applied directly to a region of the diaphragm, which region lies in the air gap (118). A spider (124) positions the region of the diaphragm (114) to which the voice coil (120) is applied in the air gap (118). The spider (124) is coupled to the diaphragm (114) and the magnet structure (101). This electrodynamic transducer structure permits the implementation of designs which avoid the need for a voice coil form and eliminates excessive moving masses or excessive flexibilities.

Description: ELECTRODYNAMIC TRANSDUCER STRUCTURE This invention relates to electrodynamic transducer structures and particularly to a structure which integrates the voice coil with the diaphragm of such a transducer. This permits the implementation of designs which avoid the need for a voice coil form. Different types of electrodynamic transducers are known. The following listed patents, while illustrative of the available art, by no means constitute an exhaustive listing of this art: Hanlet U.S. Patent 3,012,107; Tibbetts U.S. Patent 3,164,686; Sawafuji U.S. Patent 4,228,327; Willy U.S. Patent 3,979,566; Wiik U.S. Patent 4,160,133; Delbuck U.S. Patent 4,590,332; and Parker U.S. Patent 3,937,904. Nor is any representation intended hereby that no more pertinent art exists. The transducers of the listed patents typically include voice coils wound on voice coil forms with the forms in turn attached to their respective diaphragm, or include voice coils applied to flat diaphragms. The former of these technologies results in moving masses which include the voice coil form mass and the mass, e.g., adhesive mass, associated with whatever technique is used to attach the voice coil form to the diaphragm. The latter of these technologies results in diaphragms which may have excessive flexibilities, or, if designed for reduced flexibilities, excessive masses, for optimum performance, particularly at low frequencies. It is an object of the present invention to provide an electrodynamic transducer design which addresses these weaknesses in prior art designs by applying the voice coil directly to the diaphragm. According to one aspect of the invention, an electrodynamic transducer consists essentially of a magnet assembly providing an air gap, and a diaphragm in the shape of a body at least partly defined by rotation of a segment of a two dimensional curve about an axis. The diaphragm has an edge and an apex. One of the edge and apex lies in the air gap. A voice coil is applied to a region of the diaphragm. Spider means positions the region of the diaphragm to which the voice coil is applied in the air gap. The spider means is coupled to the diaphragm and the magnet structure. Illustratively according to this embodiment, the curve is an exponential curve, a circle, an ellipse, a parabola, or a hyperbola. According to another aspect of the invention, an electrodynamic transducer consists essentially of a magnet assembly providing an air gap, and a diaphragm having a long edge and a short edge. One edge lies adjacent the air gap. A voice coil is applied to the diaphragm adjacent said one edge. Spider means positions the voice..coil in the air gap. The spider means is coupled to the diaphragm and the magnet structure. According to yet another aspect of the invention, an electrodynamic transducer consists essentially of a frame and magnet structure including a ring for supporting an edge of the transducer's diaphragm and an air gap across which a magnetic field is maintained, and a diaphragm having a long edge and a short edge. One edge lies adjacent the air gap and the other edge is coupled to the ring. A voice coil is applied to the diaphragm adjacent said one edge. According to a still further aspect of the invention, an electrodynamic transducer consists essentially of a frame and magnet structure including a ring for supporting an edge of the transducer's diaphragm and an air gap across which a magnetic field is maintained, and a diaphragm having a long edge and a short edge. One edge lies adjacent the air gap and the other edge is coupled to the ring. A voice coil is applied to the diaphragm adjacent said one edge. A spider positions the voice coil in the air gap. The spider is coupled to the diaphragm and the frame and magnet structure. Illustratively according to several aspects of the invention, the one edge lying adjacent the air gap is generally circular. The one edge is the short edge. The other edge coupled to the ring may be generally elliptical, and said other edge is the long edge. The invention may best be understood by referring to the following description and accompanying drawings which illustrate the invention. In the drawings: Fig. 1 illustrates a sectional side elevational view of a transducer constructed according to the present invention; Fig. 2 illustrates a sectional side elevational view of another transducer constructed according to the present invention; Fig. 3 illustrates a sectional side elevational view of another transducer constructed according to the present invention; Fig. 4 illustrates a sectional side elevational 5 view of another transducer constructed according to the present invention; Fig. 5 illustrates a sectional side elevational view of another transducer constructed according to the present invention; and 10 Fig. 6 illustrates a sectional side elevational view of another transducer constructed according to the present invention. In each of the views, the last two digits of the respective elements' reference numbers are identical 15 with the reference numbers of the corresponding elements of the other views. The first digit of each element's reference number is the Figure number. In the embodiment of the invention illustrated in Fig. 1, a transducer 100 includes a permanent magnet 20 assembly 101 to which is secured a frame 112 having a generally somewhat conical, open framework. The shape of the opening 113 formed by the ring 115 of the frame 112 is circular. Opening 113 can be other than circular, such as, for example, elliptical. The -•- transducer diaphragm 114 flares outwardly toward the ring 115 and its outer circular edge 116 is secured to ring 115 by means of a compliant suspension 117. The inner extent of diaphragm 114 extends directly into the air gap 118 formed by the permanent magnet assembly 101 30 and a voice coil 120 is applied directly to a region of the surface of diaphragm 114 which lies within the air gap 118, thereby avoiding the need for a voice coil form. Voice coil 120 surrounds the center pole 122 of the permanent magnet assembly 101. A centering spider 124 is provided, with the centering spider 124 being attached, for example, by a suitable adhesive, at its radially inner extent to diaphragm 114 adjacent the voice coil 120 location. The radially outer region of spider 124 is attached, again, illustratively, by a suitable adhesive, to frame 112. The flare of diaphragm 114 is defined, at least in the region in which it extends into air gap 118, by rotation of a sector of a circle x 2 + y2 = r2 about axis 126 of diaphragm 114. In this equation, y is the vertical coordinate of a point on a surface of diaphragm 114, x is the corresponding horizontal coordinate on the surface, and r is an appropriate constant. Since diaphragm 114 can experience a transition in shape between its inner circular edge 128 which lies within air gap 118 and its outer edge 116 which, as previously noted, can be elliptical or some other desired shape, diaphragm 114 may not be a body of rotation about axis 126 for its full extent between edges 128 and 116. It should also be noted that the illustrated section of the air gap 118 conforms generally to the section of the diaphragm 114 in the region of its inner circular edge 128. In this case, the section of air gap 118 is generally defined by arcs of two circles having the same centers as the circle x2 + y2 = r2 which defines diaphragm 114. A conventional dust cap reduces the likelihood of contamination entering the air gap 118 from the front of transducer 100. In the embodiment of the invention illustrated in Fig. 2, a transducer 200 includes a permanent magnet assembly 201 to which is secured a frame 212 having a generally somewhat conical, open framework. The shape of the opening 213 formed by the ring 215 of the frame 212 is circular. Opening 213 can be other than circular, such as, for example, elliptical. The transducer diaphragm 214 flares outwardly toward the ring 215 and its outer circular edge 216 is secured to ring 215 by means of a compliant suspension 217. The inner extent of diaphragm 214 extends directly into the air gap 218 formed by the permanent magnet assembly 201 and a voice coil 220 is applied directly to a region of the surface of diaphragm 214 which lies within the air gap 218, thereby avoiding the need for a voice coil form. Voice coil 220 surrounds the center pole 222 of the permanent magnet assembly 201. A centering spider 224 is provided, with the centering spider 224 being attached, for example, by a suitable adhesive, at its radially inner extent to diaphragm 214 adjacent the voice coil 220 location. The radially outer region of spider 224 is attached, again, illustratively, by a suitable adhesive, to permanent magnet assembly 201. The flare of diaphragm 214 is defined, at least in the region in which it extends into air gap 218, by rotation of a sector of an ellipse x 2/a 2 + y 2/b 2 = 1 about axis 226 of diaphragm 214. In this equation, y is the vertical coordinate of a point on a surface of diaphragm 214, x is the corresponding horizontal coordinate on the surface, and a and b are appropriate constants. Since diaphragm 214 can experience a transition in shape between its inner circular edge 228 which lies within air gap 218 and its outer edge 216 which, as previously noted, can be elliptical or some other desired shape, diaphragm 214 may not be a body of rotation about axis 226 for its full extent between edges 228 and 216. It should also be noted that the illustrated section of the air gap 218 conforms generally to the section of the diaphragm 214 in the region of its inner circular edge 228. In this case, the section of air gap 218 is defined by two generally elliptical arcs. A conventional dust cap reduces the likelihood of contamination entering the air gap 218 from the front of transducer 200. In the embodiment of the invention illustrated in Fig. 3, a transducer 300 includes a permanent magnet assembly 301 to which is secured a frame 312 having a generally somewhat conical, open framework. The shape of the opening 313 formed by the ring 315 of the frame 312 is circular. Opening 313 can be other than circular, such as, for example, elliptical. The transducer diaphragm 314 flares outwardly toward the ring 315 and its outer circular edge 316 is secured to ring 315 by means of a compliant suspension 317. The inner extent of diaphragm 314 extends directly into the air gap 318 formed by the permanent magnet assembly 301 and a voice coil 320 is applied directly to a region of the surface of diaphragm 314 which lies within the air gap 318, thereby avoiding the need for a voice coil form. Voice coil 320 surrounds the center pole 322 of the permanent magnet assembly 301. The centering spider is omitted in this embodiment. The compliant suspension 317 provides sufficient support to the diaphragm 314 to ensure that the voice coil 320 is centered in the air gap 318 when no current is flowing in the voice coil 320. The flare of diaphragm 314 is defined, at least in the region in which it extends into air gap 318, by rotation of a segment of a parabola y = x 2 about axis 326 of diaphragm 314. In this equation, y is the vertical coordinate of a point on a surface of diaphragm 314, and x is the corresponding horizontal coordinate on the surface. Since diaphragm 314 can experience a transition in shape between its inner circular edge 328 which lies within air gap 318 and its outer edge 316 which, as previously noted, can be elliptical or some other desired shape, diaphragm 314 may not be a body of rotation about axis 326 for its full extent between edges 328 and 316. The illustrated section of the air gap 318 conforms generally to the section of the diaphragm 314 in the region of its inner circular edge 328. In this case, the section of air gap 318 is defined between two generally parabolic arcs. A conventional dust cap reduces the likelihood of contamination entering the air gap 318 from the front of transducer 300. In the embodiment of the invention illustrated in Fig. 4, a transducer 400 includes a permanent magnet and frame assembly 401. In the embodiment of Fig. 4, the generally somewhat conical, open framework of the previous embodiments has been omitted. The transducer diaphragm 414 flares outwardly toward its outer circular edge 416. Outer edge 416 can be other than circular, such as, for example elliptical. The inner extent of diaphragm 414 extends directly into the air gap 418 formed by the permanent magnet and frame assembly 401 and a voice coil 420 is applied directly to a region of the surface of diaphragm 414 which lies within the air gap 418, thereby avoiding the need for a voice coil form. Voice coil 420 surrounds the center pole 422 of the permanent magnet and frame assembly 401. A centering spider 424 is provided, with the centering spider 424 being attached, for example, by a suitable adhesive, at its radially inner extent to diaphragm 414 adjacent the voice coil 420 location. The radially outer region of spider 424 is attached, again, illustratively, by a suitable adhesive, to permanent magnet and frame assembly 401. The flare of diaphragm 414 is defined, at least in the region in which it extends into air gap 418, by rotation of a segment of an exponential curve y = ε about axis 426 of diaphragm 414. In this equation, y is the vertical coordinate of a point on a surface of diaphragm 414, x is the corresponding horizontal coordinate on the surface, ε is the base of the " natural logarithms, and α is an appropriate constant. Since diaphragm 414 can experience a transition in shape between its inner circular edge 428 which lies within air gap 418 and its outer edge 416 which, as previously noted, can be elliptical or some other desired shape, diaphragm 414 may not be a body of rotation about axis 426 for its full extent between edges 428 and 416. It should also be noted that the illustrated section of the air gap 418 conforms generally to the section of the diaphragm 414 in the region of its inner circular edge 428. In this case, the section of air gap 418 is defined between two generally exponentially curved arcs. A conventional dust cap reduces the likelihood of contamination entering the air gap 418 from the front of transducer 400. In the embodiment of the invention illustrated in Fig. 5, a transducer 500 includes a permanent magnet and frame assembly 501. As with the embodiment of Fig. 4, the generally somewhat conical, open framework of the embodiments of Figs. 1-3 has been omitted. The transducer diaphragm 514 flares outwardly toward its outer circular edge 516. Outer edge 516 can be other than circular, such as, for example, elliptical. The inner extent of diaphragm 514 extends directly into the air gap 518 formed by the permanent magnet and frame assembly 501 and a voice coil 520 is applied directly to a region of the surface of diaphragm 514 which lies within the air gap 518, thereby avoiding the need for a voice-coil form. Voice coil 520 surrounds the center poϊe 522 of the permanent magnet and frame assembly 501. A centering spider 524 is provided, with the centering spider 524 being attached, for example, by a suitable adhesive, at its radially inner extent to diaphragm 514 adjacent the voice coil 520 location. The radially outer region of spider 524 is attached, again, illustratively, by a suitable adhesive, to permanent magnet and frame assembly 501. The flare of diaphragm 514 is defined, at least in the region in which it extends into air gap 518, by rotation of a segment of a hyperbola x /a y 2/b2 = 1 about axis 526 of diaphragm 514. In this equation, y is the vertical coordinate of a point on a surface of diaphragm 514, x is the corresponding horizontal coordinate on the surface, and a and b are appropriate constants. Since diaphragm 514 can experience a transition in shape between its inner circular edge 528 which lies within air gap 518 and its outer edge 516 which, as previously noted, can be elliptical or some other desired shape, diaphragm 514 may not be a body of rotation about axis 526 for its full extent between edges 528 and 516. It should also be noted that the illustrated section of the air gap 518 conforms generally to the section of the diaphragm 514 in the region of its inner circular edge 528. In this case, the section of air gap 518 is defined between two generally hyperbolically curved arcs. A conventional dust cap reduces the likelihood of contamination entering the air gap 518 from the front of transducer 500. in the embodiment of the invention illustrated in Fig. 6, a transducer 600 includes a permanent magnet assembly 601 to which is secured a frame 612 having a generally somewhat conical framework. The shape of the opening 613 formed by the ring 615 of the frame 612 is circular. Opening 613 can be other than circular, such as, for example, elliptical. The transducer diaphragm 614 flares outwardly toward the ring 615 and its outer circular edge 616 is secured to ring 615 by means of a compliant suspension 617. The inner extent of diaphragm 614 extends directly into the air gap 618 formed by the permanent magnet assembly 601 and a voice coil 620 is applied directly to a region of the surface of diaphragm 614 which lies within the air gap 618, thereby avoiding the need for a voice coil form. Voice coil 620 surrounds the center pole 622 of the permanent magnet assembly 601. A centering spider 624 is provided, with the centering spider 624 being attached, for example, by a suitable adhesive, at its radially inner extent to diaphragm 614 adjacent the voice coil 620 location. The radially outer region of spider 624 is attached, again, illustratively, by a suitable adhesive, to permanent magnet assembly 601. The flare of diaphragm 614 is defined, at least in the region in which it extends into air gap 618, by rotation of a segment of a line y = ax about axis 626 of diaphragm 614. In this equation, y is the vertical coordinate of a point on a surface of diaphragm 614, x is the corresponding horizontal coordinate on the surface, and a is an appropriate constant. As used in this description, and in the claims appended hereto, the term "segment of a two dimensional curve" is intended to encompass a straight line segment. Since diaphragm 614 can experience a transition in shape between its inner circular edge 628 which lies within air gap 618 and its outer edge 616 which, as previously noted, can be elliptical or some other desired shape, diaphragm 614 may not be a body of rotation about axis 626 for its full extent between edges 628 and 616. It should also be noted that the illustrated section of the air gap 618 conforms generally to the section of the diaphragm 614 in the region of its inner circular edge 628. In this case, the section of air gap 618 is generally defined between two parallel line segments having the same slope. The air gap 618 is protected against contamination in this embodiment by the mounting of a high frequency piezoelectric crystal-driven diaphragm of the type described in, for example, U.S. Patent 4,497,981. Any suitable technique can be used for integrating the voice coil and diaphragm. For example, the voice coil can be wound without the aid of a voice coil form to the designed geometry of the apex of the diaphragm, and inserted into the die in which the diaphragm is to be formed prior to forming the diaphragm. As with current voice coil geometry, the voice coil could be one or multiple layers in thickness. As another example, the voice coil could be etched on a metal-coated plastic film, for example of polypropylene or polyimide coated with aluminum. The plastic film can be on the order of .25-10 mils in thickness. The metallized coating can have a wide range of thicknesses and shapes depending upon the design parameters of the speaker. The plastic film can be formed to the design apex geometry of the diaphragm and either molded to or attached to the diaphragm's inner or outer surface. This thin film method can be used for multi-layer voice coil arrangements as well. For example, the film can be metallized on both sides and plated-through holes provided to connect the etched conductors on one side to those on the other side. Alternatively, plastic films metallized on one side can be stacked or laminated together to provide multi-layer coils for increased BL product.

Claims: What is claimed is: 1. An electrodynamic transducer consisting essentially of a magnet assembly providing an air gap, a diaphragm in the shape of a body at least partly defined by rotation of a segment of a two dimensional curve about an axis, the diaphragm having an edge and an apex, one of said edge and said apex lying in the air gap, a voice coil applied to a region of the diaphragm, and spider means for positioning the region of the diaphragm to which the voice coil is applied in the air gap, the spider means coupled to the diaphragm and the magnet structure. 2. The transducer of claim 1 wherein the curve is an exponential curve. 3. The transducer of claim 1 wherein the curve is a circle. 4. The transducer of claim 1 wherein the curve is an ellipse. 5. The transducer of claim 1 wherein the curve is a parabola. 6. The transducer of claim 1 wherein the curve is a hyperbola. 7. An electrodynamic transducer consisting essentially of a magnet assembly providing an air gap, a diaphragm having a long edge and a short edge, one edge lying adjacent the air gap, a voice coil applied to the diaphragm adjacent said one edge, and spider means for positioning the voice coil in the air gap, the spider means coupled to the diaphragm and the magnet structure. 8. The invention of claim 7 wherein said one edge lying adjacent the air gap is generally circular. 9. The invention of claim 8 wherein said one edge is the short edge. 10. The invention of claim 7 wherein the other edge is generally elliptical. 11. The invention of claim 10 wherein said other edge is the long edge. 12. An electrodynamic transducer consisting essentially of a frame and magnet structure, the structure including a ring for supporting an edge of the transducer's diaphragm and an air gap across which a magnetic field is maintained, a diaphragm having a long edge and a short edge, one edge lying adjacent the air gap and the other edge coupled to the ring, and a voice coil applied to the diaphragm adjacent said one edge. 13. The invention of claim 12 wherein said one edge lying adjacent the air gap is generally circular. 14. The invention of claim 13 wherein said one edge is the short edge. 15. The invention of claim 12 wherein said other edge coupled to the ring is generally elliptical. 16. The invention of claim 15 wherein said other edge is the long edge. 17. An electrodynamic transducer consisting essentially of a frame and magnet structure, the structure including a ring for supporting an edge of the transducer's diaphragm and an air gap across which a magnetic field is maintained, a diaphragm having a long edge and a short edge, one edge lying adjacent the air gap and the other edge coupled to the ring, a voice coil applied to the diaphragm adjacent said one edge, and a spider for positioning the voice coil in the air gap, the spider coupled to the diaphragm and the frame and magnet structure. 18. The invention of claim 17 wherein said one edge lying adjacent the air gap is generally circular. 19. The invention of claim 18 wherein said one edge is the short edge. 20. The invention of claim 17 wherein said other edge coupled to the ring is generally elliptical. 21. The invention of claim 20 wherein said other edge is the long edge.

Inventors: HOUSE WILLIAM NEAL, HOUSE, WILLIAM, NEAL
Applicants: HARMAN INT IND, HARMAN INTERNATIONAL INDUSTRIES, INC. INCORPORATED
Application year: 1989
Main classification: H04R7
IPC codes: H04R7, H04R9