Abstract:
A transducer membrane enhances sound reproduction. Curved portions of the membrane periphery contribute to the enhanced sound reproduction. The transducer membrane may add or improve sound reproduction capability in cell phones, gaming systems, personal data assistants, or other devices.

Description:
BACKGROUND OF THE INVENTION 
     1. Priority Claim 
     This application claims the benefit of priority from PCT Application No. PCT/EP2006/001438, filed Feb. 16, 2006, and European Patent Application No. EP 05450034.3, filed Feb. 18, 2005. 
     2. Technical Field 
     This application relates to a transducer membrane, and more particularly to a transducer membrane that reduces acoustic distortions. 
     3. Related Art 
     Audio speakers act as transducers that convert electrical energy in an audio signal to acoustic energy. Small audio speakers may be incorporated into mobile telephones, speaker phones, headphones, personal data assistants, portable gaming systems, and other devices. In some applications, the transducer includes a transducer membrane that deforms to produce sound. When the deformations are nonlinear, however, the deformations may produce acoustic distortions noticeable by a listener. Therefore, a need exits for an improved transducer that reduces acoustic distortions resulting from nonlinear deformation in a transducer membrane. 
     SUMMARY 
     A transducer membrane provides enhanced sound reproduction. Curved portions of the membrane periphery contribute to the enhanced sound reproduction. The transducer membrane may add or improve sound reproduction capability in cell phones, gaming systems, personal data assistants, or other devices. 
     The transducer membrane has a construction that linearizes deformations in the transducer membrane, thereby reducing acoustical distortions. The transducer membrane may include a dome. An intermediate membrane may be formed around or coupled to some/or all of the dome. A periphery surrounding the intermediate membrane defines a non-circular footprint of the transducer membrane. The periphery includes a first periphery corner and a second periphery corner. A first periphery segment includes a deformation linearizing curvature disposed between the first periphery corner and the second periphery corner. A second periphery segment includes a symmetrical curvature with respect to the first periphery segment. 
     Other systems, methods, features and advantages will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The technology may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a perspective view of a transducer membrane. 
         FIG. 2  is a top plan view of the transducer membrane of  FIG. 1 . 
         FIG. 3  is a side view of the transducer membrane of  FIG. 2  along line A-A. 
         FIG. 4  is a side view of the transducer membrane of  FIG. 2  along line B-B. 
         FIG. 5  is a top plan view of a non-circular transducer membrane footprint. 
         FIG. 6  is a top plan view of a second non-circular transducer membrane footprint. 
         FIG. 7  is a top plan view of a second transducer membrane. 
         FIG. 8  is a transducer membrane in a frame. 
         FIG. 9  is a flow diagram for fabricating a transducer membrane. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a perspective view of a transducer membrane  100 . The transducer membrane  100  includes a dome  102  that may be positioned near the center of the transducer membrane  100 . Alternatively, the dome  102  may be positioned in other locations of the transducer membrane  100 . An intermediate membrane  104  may be formed around or coupled to some/or all of the dome  102 , and may be delineated by a groove or ring  106 . A periphery may surround the intermediate membrane  104 , and may extend around the intermediate membrane  104  to define a non-circular footprint of the transducer membrane  100 . The periphery may include periphery segments  108  and  110 . Periphery segments  108 , as shown in  FIG. 1 , are symmetrically curved, in the footprint plane, with respect to one another. The periphery may also include periphery corners  112 . The periphery corners  112  may be a location along the periphery where two periphery segments meet or end. In some applications, the periphery corners  112  may be open. In other implementations, the periphery corners  112  may be closed with transducer material that forms a continuous or discontinuous extension of the periphery segments to transition from one segment to the next. The transducer material closing the periphery corners  112  may be a membrane or a membrane like material that may include ridges and/or grooves. The ridges and/or grooves may reduce acoustic short-circuit artifacts, and may be included, for example, when an acoustical short circuit is noticeable in the emitted sound field. The decision to close the periphery corners  112  may depend on the extent to which an acoustical short circuit is noticeable in an emitted sound field. 
     The dome  102  may have a circular, elliptical, or polygonal footprint. A coil may be coupled to an underside of the dome  102 . In some applications, the coil may be glued to the dome  102 . Alternatively, the coil may be attached to the dome  102  with a fastener, clamp, or other coupling. 
     The coil may carry signal current supplied by sound reproduction circuitry. The interaction of the signal current in the coil and a surrounding magnetic field may impart a reciprocating motion in the transducer membrane  100  near a center portion to produce acoustic energy. The center portion of the membrane  100  may move like a rigid piston and may cause deformations in the intermediate membrane  104  and/or periphery. 
     The periphery segments  108  and  110  may be formed along an outer portion of the transducer membrane  100 . The periphery segments  108  and  110  may include an adhesive edge  114 . Adhesive may be applied to the adhesive edge  114  and may secure the outer edge of a periphery segment  108  or  110  to another structure, such as a loudspeaker frame. Alternatively, the membrane  100  may be secured in place by other manners, such as by a fastener, a clamp, or other coupling. 
     The periphery segments  108  and  110  may have a cross-sectional curvature or may have no curvature. The curvature may give a periphery segment  108  or  110  a height between about zero (e.g., flat) and about half of the width of the corresponding periphery segment. Alternatively, the curvature height may be larger than the width of the corresponding periphery segment. The cross-sectional curvature of one or more of the periphery segments  108  and/or  110  may be substantially semicircular, substantially elliptical, helix shaped, or otherwise curved. In some applications, the cross-sectional curvature of the periphery segments  108  and/or  110  may be in a direction opposite a cross-sectional curvature of the dome  102 . 
     At least two periphery segments may be symmetrically curved with respect to one another in the footprint plane. In  FIG. 1 , the periphery segments  108  are symmetrically curved with respect to each other in the footprint plane, while the periphery segments  110  are approximately straight. Periphery segments  108  are also symmetrically curved with respect to the dome  102 . In  FIG. 1 , periphery segments  108  are convexly curved with respect to the dome  102 . Alternatively, periphery segments  108  may be concavely curved with respect to the dome  102 . In yet other implementations, more than two periphery segments may be curved in the footprint plane. 
     The intermediate membrane  104  may run along all or part of the periphery. In  FIG. 1 , the intermediate membrane  104  runs along the inside of periphery segments  108  and  110  and between the ring  106 . The intermediate membrane  104  may also taper away as it reaches a border region where a periphery segment reaches, meets, joins, merges, or connects with the dome  102  or the ring  106 . 
       FIG. 2  is a top plan view of the transducer membrane of  FIG. 1 . In  FIG. 2 , the periphery segment  108  has a length L and the periphery segment  110  has a length S. The length L may range between about 7 mm and about 100 mm, and more particularly may be between about 30 mm and about 70 mm. In some implementations, a ratio of periphery segment lengths (e.g., L/S) may range between about 1 and about 2. In other implementations, the ratio of periphery lengths may be less than 1 or may be greater than 2, such as about 5. 
       FIG. 2  also shows a radius of curvature, R, of a periphery segment (e.g.,  108 ). The radius of curvature may be measured from about the middle of the periphery segment. In some implementations, a periphery segment with curvature may have a radius of curvature that ranges between about half the length of the periphery segment (e.g., about 0.5 L) and about twenty times the length of the periphery segment (e.g., about 20 L). It is to be noted that in some implementations, periphery segment  110  may be curved in the footprint plane, and periphery segment  108  may be linear. In yet other implementations, periphery segments  108  and  110  may be curved in the footprint plane. 
       FIG. 3  is a side view of the transducer membrane  100  of  FIG. 2  along line A-A. The intermediate membrane  104  may have a height H, measured from the footprint plane  116 . The footprint plane  116  may be the plane in which the outmost edges of the periphery segments lie or the plane in which the coil is coupled, fastened, clamped or otherwise attached to the underside of the transducer membrane  100 . In implementations in which the transducer membrane footprint  116  is generally rectangular, the height, H, of the intermediate membrane  104  may range between about 0 mm and about half of the length of a periphery segment (e.g., periphery segment  110 ). In other implementations, the intermediate membrane  104  may have larger heights. 
       FIG. 4  is a side view of the transducer membrane  100  of  FIG. 2  along line B-B. In  FIG. 4 , periphery segments  108  may approach the dome  102  and may almost reach, meet, join, merge, or connect with the dome  102  or the groove/ring  106 . In other implementations, more or less space may exist between periphery segment  108  and the dome  102  or the grove/ring  106 . 
     The intermediate membrane  104  and the periphery portions  108  and  110  may have thicknesses that are about equal. The thicknesses may depend on a resonance frequency. In one implementation, the periphery portion  108  and  110  may have thicknesses that range between about 20 μm and about 80 μm. In other implementations smaller or larger material thicknesses may be employed. 
     The transducer membrane  100  may be formed from polycarbonate materials, such as Macrofol or Pokalon. Alternatively, the transducer membrane  100  may consist of polyester (Mylar), polyimide (Kapton), or polypropylene (Daplen). Composite materials are also suitable, including carbonate, polycarbonate, and polyurethane. In some implementations, metals such as beryllium, copper, titanium, or aluminum may be employed. 
     The coil and the transducer membrane  100  may form the mass in a spring-mass system. Each part of the transducer membrane  100 , including the dome  102 , the intermediate membrane  104 , and/or the periphery segments (e.g.,  108  and  110 ), may act as mechanical springs in the spring-mass system. Individually, each of these different parts of the transducer membrane  100  may act as a non-linear spring interacting at its border with a neighboring spring or springs. When a periphery includes periphery segments having curvature (e.g.,  108 ) the interactions between a periphery segment and the intermediate membrane  104  may be modeled and analyzed as two series connected springs. When a static or harmonic force is applied through the coil the membrane is deflected. In the case of a harmonic force, a frequency below the resonance frequency is chosen to drive the transducer membrane  100 . Below the resonance frequency, the behavior of the spring-mass system is determined by the spring properties. 
     The spring properties may be established by setting the curvature, in the footprint plane  116 , of symmetrical periphery segments. The curvature influences the deformation behavior of the intermediate membrane  104  and both the curved and linear periphery segments. The deformation behavior may be established to impart evenly increasing deformation from an edge of the transducer membrane  100  toward the center of the transducer membrane  100 . In other words, the distribution of deformation over several parts of the transducer membrane  100  produces a substantially uniform deformation in the transducer membrane  100 . The substantially uniform deformation linearizes mechanical compliance of the transducer membrane  100 . Linearizing mechanical compliance of the transducer membrane  100  helps to reduce, and may minimize or substantially minimize, acoustical distortions, such as harmonic distortions and/or intermodulation distortions, in the transducer membrane  100 . 
       FIG. 5  is a top plan view of a non-circular transducer membrane footprint  500 . In  FIG. 5 , the transducer membrane footprint  500  is generally rectangular. In  FIG. 5 , the transducer membrane footprint  500  includes two planes of symmetry, axis A  502  and axis B  504 . One half of the transducer membrane footprint  500  is a mirror image of its other half when viewed with respect to axis A  502  or axis B  504 . That is, the lengths, angles, and curvatures of the transducer membrane  500  on one side of axis A  502  or axis B  504  generally mirror the corresponding portion on the other side of axis A  502  or axis B  504 . 
       FIG. 6  is a top plan view of a second non-circular transducer membrane footprint  600 . In  FIG. 6 , the transducer membrane footprint  600  generally resembles a hexagonal shape including curved and straight edges. In  FIG. 6 , the transducer membrane footprint  600  includes three planes of symmetry, axis A  602 , axis B  604 , and axis C  606 . The transducer membrane footprint  600  is symmetrical about axis A  602 , in that the portion of the transducer membrane footprint  600  on one side of axis A  602  generally mirrors the portion of the transducer membrane footprint  600  on the other side of axis A  602 . The transducer membrane footprint  600  is symmetrical about axis B  604 , in that the portion of the transducer membrane footprint  600  on one side of axis B  604  generally mirrors the portion of the transducer membrane footprint  600  on the other side of axis B  604 . The transducer membrane footprint  600  is symmetrical about axis C  606 , in that the portion of the transducer membrane footprint  600  on one side of axis C  606  generally mirrors the portion of the transducer membrane footprint  600  on the other side of axis C  606 . 
     A transducer membrane footprint may include other non-circular regular or irregular polygonal shapes that include at least one axis of symmetry. As examples, the shapes may be square, rectangle, pentagon, triangle, trapezoid, parallelogram, rhombus, deltoid, octagon, hexagon, or other shapes. 
       FIG. 7  is a top plan view of a second transducer membrane  700 . Transducer membrane  700  has a generally hexagonal footprint as shown in  FIG. 6 . The transducer membrane  700  includes a dome  702  that may be positioned near the center, or in other locations, of the transducer membrane  700 . An intermediate membrane  704  may be formed around or coupled to some/or all of the dome  702 , and may be delineated by a grove or ring  706 . A periphery may surround the intermediate membrane  704  to define a non-circular footprint around the intermediate membrane  704 . The periphery may include periphery segments  708  and  710 . The periphery segments  708  and  710  may include an adhesive edge  714 . Periphery segments  708 , as shown in  FIG. 7 , are symmetrically curved, in the footprint plane, with respect to one another. The periphery may also include periphery comers  712 . The periphery corners may be at a location along the periphery where two periphery segments meet or end. In some applications, the periphery corners  712  may be open. In other implementations, the periphery corners  712  may be closed with transducer material that forms a continuous or discontinuous extension of the periphery segments to transition from one segment to the next. The transducer material closing the periphery corners  712  may be a membrane or a membrane like material that may include ridges and/or grooves. The ridges and/or grooves may reduce acoustic short-circuit artifacts, and may be included, for example, when an acoustical short-circuit is noticeable in the emitted sound filed. The decision to close the periphery corners  712  may depend on the extent to which an acoustical short circuit is noticeable in an emitted sound field. 
     The transducer membrane  700  shown in  FIG. 3  has three planes of symmetry, axis A  716 , axis B  718 , and axis C  720 . Independent of the selected plane of symmetry, at least two of the periphery segments  708  that are curved are symmetrical to one another. The remaining third periphery segment  708  has symmetrical curvature around the axis through the third periphery segment (sometimes described as having curvature symmetrical to itself). 
       FIG. 8  is a transducer membrane in a frame. In  FIG. 8 , the transducer membrane  800  has a generally rectangular shape. The transducer membrane  800  includes a dome  802  that is positioned near a center of the transducer membrane  800 . An intermediate membrane  804  is formed around or coupled to some/or all of the dome  802 , and is delineated by a groove or ring  806 . The periphery surrounding the intermediate membrane  804  extends around the intermediate membrane  804  to define a generally rectangular transducer membrane footprint. The periphery includes periphery segments  808  and  810 . As shown in  FIG. 8 , periphery segments  808  are curved in the transducer membrane footprint plane and are symmetrical to one another. With respect to the dome  802 , periphery segments  808  are convexly curved. In  FIG. 8 , the transducer membrane  800  is fixed at edges  814  to the frame  816 . Edges  814  may be fixed to the frame  816  through the use of adhesive, a fastener, clamp, or other coupling. In  FIG. 8 , periphery corners  812  are open, and frame protrusions  818  nearly fill the periphery corners  812  on a base surface as well as along the edges of the periphery segments so that the transducer membrane  800  is almost touching the frame protrusions  818 . Additionally, the frame protrusions  818  are configured such that the transducer membrane  800  along the periphery corners  812  does not further separate from the frame protrusions  818  during the reproduction of sound. These frame protrusions  818  may reduce acoustic short circuits during the reproduction of sound. 
       FIG. 9  is a flow diagram for fabricating a transducer membrane. The transducer membrane may be formed from a single sheet of membrane material using a heat molding process. In yet other fabrications, the transducer membrane may be formed in other manners. 
     A designer or processor determines the membrane periphery properties and shape ( 902 ). The properties may include membrane material, thickness, variation in thickness, curvature, height, width, periphery segment size and shape, transducer membrane footprint size and shape, or other properties. The intermediate membrane properties and shape are also determined ( 904 ). The properties may include intermediate membrane material, thickness, variation in thickness, curvature, height, width, shape, or other properties. 
     A dome is formed in the transducer membrane ( 906 ). A ring or groove may be formed in the transducer membrane around the dome ( 908 ). The dome may be centrally located, or may be located in other positions of the transducer membrane. 
     The intermediate membranes are formed around the dome or the ring or groove ( 910 ). A periphery defining a non-circular footprint of the transducer membrane is formed around the intermediate membrane ( 912 ). The periphery includes periphery segments positioned between periphery corner locations. At least two periphery segments are curved in the transducer membrane plane symmetrically along one or more axes with respect to one another and/or the dome. The curvature in the transducer membrane plane of a periphery segment may be convex and/or concave with respect to the dome. In some implementations, the radius of curvature of a periphery segment ranges between about one half to about twenty times the length of the periphery segment. 
     A small section of the periphery segments may be formed to act as an adhesive edge. Adhesive may be added to the adhesive edge of the periphery segments ( 914 ). The adhesive edge may facilitate installation of the transducer membrane in a device employing sound reproduction circuitry. Alternatively, other fasteners may be employed to install the transducer membrane. 
     The transducer membrane with symmetrical curvature linearizes transducer membrane deformations, thereby reducing acoustical distortions. These reductions may enhance sound reproductions in an emitted sound field, and improve a listener&#39;s experience. 
     While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.