Patent Publication Number: US-2004042632-A1

Title: Directivity control of electro-dynamic loudspeakers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS.  
     [0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/380,001, filed on May 2, 2002; U.S. Provisional Patent Application No. 60/378,188, filed on May 6, 2002; and U.S. Provisional Patent Application No. 60/391,134, filed on Jun. 24, 2002. The disclosures of the above applications are incorporated by reference.  
     [0002] This application incorporates by reference the disclosures of each of the following co-pending applications which have been filed concurrently with this application: U.S. patent application Ser. No. ______, entitled “Mounting Bracket System,” filed May 2, 2003; U.S. patent application Ser. No. ______, entitled “Film Tensioning System,” filed May 2, 2003; U.S. patent application Ser. No. ______, entitled “Film Attaching System,” filed May 2, 2003; U.S. patent application Ser. No. ______, entitled “Electrical Connectors For Electro-Dynamic Loudspeakers,” filed May 2, 2003; U.S. patent application Ser. No. ______, entitled “Electro-Dynamic Loudspeaker Mounting System,” filed May 2, 2003; U.S. patent Application Ser. No. ______, entitled “Conductors For Electro-Dynamic Loudspeakers,” filed May 2, 2003; U.S. patent application Ser. No. ______, entitled “Frame Structure,” filed May 2, 2003; U.S. patent application Ser. No. ______, entitled “Acoustically Enhanced Electro-Dynamic Loudspeakers,” filed May 2, 2003; U.S. patent application Ser. No. ______, entitled “Frequency Response Enhancements For Electro-Dynamic Loudspeakers,” filed May 2, 2003; and U.S. patent application Ser. No. ______, entitled “Magnet Arrangement For Loudspeaker,” filed May 2, 2003. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0003] 1. Field of Invention  
       [0004] This invention relates to electro-dynamic loudspeakers, and more particularly, to electro-dynamic loudspeakers that control and/or enhance the acoustical directivity pattern of the loudspeaker.  
       [0005] 2. Related Art  
       [0006] The general construction of an electro-dynamic loudspeaker includes a diaphragm, in the form of a thin film, attached in tension to a frame. An electrical circuit, in the form of electrically conductive traces, is applied to the surface of the diaphragm. Magnetic sources, typically in the form of permanent magnets, are mounted adjacent to the diaphragm or within the frame, creating a magnetic field. When current is flowing in the electrical circuit, the diaphragm vibrates in response to the interaction between the current and the magnetic field. The vibration of the diaphragm produces the sound generated by the electro-dynamic loudspeaker.  
       [0007] Many design and manufacturing challenges present themselves in the manufacturing of electro-dynamic loudspeakers. First, the diaphragm, that is formed by a thin film, needs to be permanently attached, in tension, to the frame. Correct tension is required to optimize the resonance frequency of the diaphragm. Optimizing diaphragm resonance extends the bandwidth and reduces sound distortion of the loudspeaker.  
       [0008] The diaphragm is driven by the motive force created when current passes through the conductor applied to the diaphragm within the magnetic field. The conductor on the electro-dynamic loudspeaker is attached directly to the diaphragm. Because the conductor is placed directly onto the thin diaphragm, the conductor should be constructed of a material having a low mass and should also be securely attached to the film at high power (large current) and high temperatures.  
       [0009] Accordingly, designing conductors for electro-dynamic loudspeaker applications presents various challenges such as selecting the speaker with the desired audible output for a given location that will fit within the size and location constraints of the desired applications environment. Electro-dynamic loudspeakers exhibit a defined acoustical directivity pattern relative to each speaker&#39;s physical shape and the frequency of the audible output produced by each loudspeaker. Consequently, when an audio system is designed, loudspeakers possessing a desired directivity pattern over a given frequency range are selected to achieve the intended performance of the system. Different loudspeaker directivity patterns may be desirable for various loudspeaker applications. For example, for use in a consumer audio system for a home listening environment, a wide directivity may be preferred. In the application of a loudspeaker, a narrow directivity may be desirable to direct sound, e.g., voice, in a predetermined direction.  
       [0010] Often, space limitations in the listening environment prohibit the use of a loudspeaker in an audio system that possesses the preferred directivity pattern for the system&#39;s design. For example, the amount of space and the particular locations available in a listening environment for locating and/or mounting the loudspeakers of the audio system may prohibit the use of a particular loudspeaker that exhibits the intended directivity pattern. Also, due to space and location constraints, it may not be possible to position or oriented the desired loudspeaker in a manner consistent with the loudspeaker&#39;s directivity pattern. Consequently, size and space constraints of a particular environment may make it difficult to achieve the desired performance from the audio system. An example of a listening environment having such constraints is the interior passenger compartment of an automobile or other vehicle.  
       [0011] While the electric circuitry of electro-dynamic loudspeakers may present design challenges, electro-dynamic loudspeakers are very desirable loudspeakers because they are designed to have a very shallow depth. With this dimensional flexibility, electro-dynamic loudspeakers may be positioned at locations where conventional loudspeakers would not traditionally fit. This dimensional flexibility is particularly advantageous in automotive applications where positioning a loudspeaker at a location that a conventional loudspeaker would not otherwise fit could offer various advantages. Further, because the final loudspeaker assembly may be mounted on a vehicle, it is important that the assembly be rigid during shipping and handling so that the diaphragm or frame does not deform during installation.  
       [0012] While conventional electro-dynamic loudspeakers are shallow in depth and may therefore be preferred over conventional loudspeakers for use in environments requiring thin loudspeakers, electro-dynamic loudspeakers have a generally rectangular planar radiator that is generally relatively large in height and width to achieve acceptable operating wavelength sensitivity, power handling, maximum sound pressure level capability and low-frequency bandwidth. Unfortunately, the large rectangular size results in a high-frequency beam width angle or coverage that may be too narrow for its intended application. The high-frequency horizontal and vertical coverage of a rectangular planar radiator is directly related to its width and height in an inverse relationship. As such, large radiator dimensions exhibit narrow high-frequency coverage and vice versa.  
       [0013] The acoustical directivity of the audible output of a loudspeaker is critical to the design and performance of an audio system and to the creation of a positive acoustical interaction with the listeners in a listening environment. Because electro-dynamic loudspeaker designs are desirable for use in environments with space and location constraints, a need therefore exists to provide an electro-dynamic loudspeaker that is able to better control and/or enhance the directivity pattern of the loudspeaker.  
       SUMMARY  
       [0014] The electro-dynamic loudspeaker of the invention controls the acoustical directivity of a loudspeaker (i.e., beam steering) by amplitude shading of the thin film diaphragm of the electro-dynamic loudspeaker or by varying the shape of the loudspeaker. Amplitude shading of the diaphragm may be achieved in a number of different ways. For example, amplitude shading may be achieved by spacing the magnets away from thin film diaphragm in specific predetermined zones of the diaphragm to reduce the sensitivity of the diaphragm.  
       [0015] Alternatively, amplitude shading may be accomplished by manipulating the dc resistance (DCR) of the conductor traces on the diaphragm of the loudspeaker. For example, the loudspeaker diaphragm can include a plurality of traces forming individual circuits in separate “zones” of the diaphragm. In selected zones, the traces may be in series or in parallel, electrically, in order to result in different DCR in the traces. The variable sensitivity of the traces affects the acoustical directivity of the loudspeaker by amplitude shading of the diaphragm.  
       [0016] In addition to the relationship of the traces electrically, the DCR of the traces may be manipulated in other ways to achieve the same effect. For example, multiple traces on the diaphragm may each possess different physical dimensions, including different lengths, different widths, different thicknesses, and cross-sectional areas. Also, the traces may be formed from different materials (including for example, copper or aluminum alloys, etc.). Such variation in physical characteristics and/or properties results in the traces having different DCR, hence, the acoustical directivity of the loudspeaker may be modified. Further, acoustical directivity control of the loudspeaker via amplitude shading may be accomplished by magnetizing the plurality of magnets in the loudspeaker so that the flux densities of the different magnets vary in a predetermined relationship relative to the diaphragm of the loudspeaker.  
       [0017] Similarly, the shape of the loudspeaker may also be varied to achieve a predetermined or preferred acoustical directivity performance of the loudspeaker. Manipulation of the acoustical directivity of the loudspeaker may be achieved, by varying the length-to-width aspect ratio of the planar loudspeaker, such as for example, as much as a ratio of 10:1. Such a high-aspect ratio planar loudspeaker may be suitable for installation in a structural pillar of a vehicle, such as an automobile.  
       [0018] Additionally, the loudspeaker may take on a non-rectangular, polygonal shape, such as a trapezoid, parallelogram, triangle, pentagon or hexagon. The shaped panel reduces off axis acoustical lobes, so that the acoustical output from the loudspeaker, particularly when amplified, provides better directional performance and control. The loudspeaker may also be configured in other shapes, including annular shapes like ellipses and circles, to obtain the desired acoustical directivity control of the loudspeaker.  
       [0019] In addition to varying the shape of the loudspeaker, amplitude shading of the diaphragm of the loudspeaker may be achieved by the non-uniform application of damping material over the driven zone of the diaphragm. For example, damping material may be applied in unequal and/or excessive amounts on the surface, or on selected portions of the surface, of the driven portion of the diaphragm to effectively vary the mass of the diaphragm across its surface and achieve directivity control.  
       [0020] Other systems, methods, features and advantages of the invention 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 accompanying claims. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0021] The invention can 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 reference numerals designate corresponding parts throughout the different views.  
     [0022]FIG. 1 is a perspective view of a electro-dynamic loudspeaker as it would appear with the grille removed.  
     [0023]FIG. 2 is an exploded perspective view of the electro-dynamic loudspeaker shown in FIG. 1 having a grille.  
     [0024]FIG. 3 is a cross-sectional view of the electro-dynamic loudspeaker taken along line  3 - 3  of FIG. 1.  
     [0025]FIG. 4 is an enlarged cross-sectional view of the encircled area of FIG. 3.  
     [0026]FIG. 5 is a cross-sectional view taken along the line  5 - 5  of FIG. 1 showing an example of an electro-dynamic loudspeaker.  
     [0027]FIG. 6 is a cross-sectional view taken along the line  5 - 5  of FIG. 1 showing an alternative example of an electro-dynamic loudspeaker.  
     [0028]FIG. 7 is a cross-sectional view taken along the line  5 - 5  of FIG. 1 showing another example of an electro-dynamic loudspeaker.  
     [0029]FIG. 8 is schematic view showing a conductive trace on a diaphragm of an electro-dynamic loudspeaker.  
     [0030]FIG. 9 is a cross-sectional view taken along the line  9 - 9  of FIG. 8 showing the dimensional cross-section of a portion of the conductive trace.  
     [0031]FIG. 10 is a cross-sectional view taken along the line  10 - 10  of FIG. 8 showing the dimensional cross-section of the conductive trace.  
     [0032]FIG. 11 is a cross-sectional view taken along the line  11 - 11  of FIG. 8 showing the dimensional cross-section of another portion of the conductive trace.  
     [0033]FIG. 12 is a schematic view showing an alternative example of a conductive trace on a diaphragm of an electro-dynamic loudspeaker.  
     [0034]FIG. 13 is a cross-sectional view taken along the line  5 - 5  of FIG. 1 showing another example of an electro-dynamic loudspeaker.  
     [0035]FIG. 14 is a plan view of an electro-dynamic loudspeaker having a high aspect ratio of its length relative to its width.  
     [0036]FIG. 15 is a polar response graph depicting the natural horizontal directivity of a direct radiating electro-dynamic loudspeaker at a variety of frequencies.  
     [0037]FIG. 16 is a horizontal polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 1 kHz.  
     [0038]FIG. 17 is a horizontal polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 1.6 kHz.  
     [0039]FIG. 18 is a horizontal polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 3.15 kHz.  
     [0040]FIG. 19 is a horizontal polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 5 kHz.  
     [0041]FIG. 20 is a horizontal polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 8 kHz.  
     [0042]FIG. 21 is a horizontal polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 12.5 kHz.  
     [0043]FIG. 22 is a horizontal polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 16 kHz.  
     [0044]FIG. 23 is a vertical polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 1 kHz.  
     [0045]FIG. 24 is a vertical polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 1.6 kHz.  
     [0046]FIG. 25 is a vertical polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 3.15 kHz.  
     [0047]FIG. 26 is a vertical polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 5 kHz.  
     [0048]FIG. 27 is a vertical polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 8 kHz.  
     [0049]FIG. 28 is a vertical polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 12.5 kHz.  
     [0050]FIG. 29 is a vertical polar response plot comparing the output of an electro-dynamic loudspeaker of FIG. 14 with a conventional single tweeter loudspeaker at 16 kHz.  
     [0051]FIG. 30 is a plan view of an electro-dynamic loudspeaker having a non-rectangular polygonal shape. 
    
    
     DETAILED DESCRIPTION  
     [0052]FIG. 1 is a perspective view of an electro-dynamic loudspeaker  100  of the invention. As shown in FIG. 1, the electro-dynamic loudspeaker is a generally planar loudspeaker having a frame  102  with a diaphragm  104  attached in tension to the frame  102 . A conductor  106  is positioned on the diaphragm  104 . The conductor  106  is shaped in serpentine fashion having a plurality of substantially linear sections (or traces)  108  longitudinally extending along the diaphragm interconnected by radii  110  to form a single current path. Permanent magnets  202  (shown in FIG. 2) are positioned on the frame  102  underneath the diaphragm  104 , creating a magnetic field.  
     [0053] Linear sections  108  are positioned within the flux fields generated by permanent magnets  202 . The linear sections  108  carry current in a first direction  112  and are positioned within magnetic flux fields having similar directional polarization. Linear sections  108  of conductor  106  having current flowing in a second direction  114 , that is opposite the first direction  112 , are placed within magnetic flux fields having an opposite directional polarization. Positioning the linear sections  108  in this manner assures that a driving force is generated by the interaction between the magnetic fields developed by magnets  202  and the magnetic fields developed by current flowing in conductor  106 . As such, an electrical input signal traveling through the conductor  106  causes the diaphragm  104  to move, thereby producing an acoustical output.  
     [0054]FIG. 2 is an exploded perspective view of the electro-dynamic loudspeaker  100  shown in FIG. 1. As illustrated in FIG. 2, the flat panel loudspeaker  100  includes a frame  102 , a plurality of high energy magnets  202 , a diaphragm  104 , an acoustical dampener  236  and a grille  228 . Frame  102  provides a structure for fixing magnets  202  in a predetermined relationship to one another. In the depicted embodiment, magnets  202  are positioned to define five rows of magnets  202  with three magnets  202  in each row. The rows are arranged with alternating polarity such that fields of magnetic flux are created between each row. Once the flux fields have been defined, diaphragm  104  is fixed to frame  102  along its periphery.  
     [0055] A conductor  106  is coupled to the diaphragm  104 . The conductor  106  is generally formed as an aluminum foil bonded to the diaphragm  104 . The conductor  106  can, however, be formed from other conductive materials. The conductor  106  has a first end  204  and a second end  206  positioned adjacent to one another at one end of the diaphragm  104 .  
     [0056] As shown in FIG. 2, frame  102  is a generally dish-shaped member preferably constructed from a substantially planar contiguous steel sheet. The frame  102  includes a base plate  208  surrounded by a wall  210 . The wall  210  terminates at a radially extending flange  212 . The frame  102  further includes apertures  214  and  216  extending through flange  212  to provide clearance and mounting provisions for a conductor assembly  230 .  
     [0057] Conductor assembly  230  includes a terminal board  218 , a first terminal  220  and a second terminal  222 . Terminal board  218  includes a mounting aperture  224  and is preferably constructed from an electrically insulating material such as plastic, fiberglass or other insulating material. A pair of rivets or other connectors (not shown) pass through apertures  214  to electrically couple first terminal  220  to first end  204  and second terminal  222  to second end  206  of conductor  106 . A fastener such as a rivet  226  extends through apertures  224  and  216  to couple conductor assembly  230  to frame  102 .  
     [0058] A grille  228  functions to protect diaphragm  104  from contact with objects inside the listening environment while also providing a method for mounting loudspeaker  100 . The grille  228  has a substantially planar body  238  having a plurality of apertures  232  extending through the central portion of the planar body  238 . A rim  234  extends downward, substantially orthogonally from body  238 , along its perimeter and is designed to engage the frame  102  to couple the grille  228  to the frame  102 .  
     [0059] An acoustical dampener  236  is mounted on the underside of the base plate  208  of the frame  102 . Dampener  236  serves to dissipate acoustical energy generated by diaphragm  104  thereby minimizing undesirable amplitude peaks during operation. The dampener  236  may be made of felt, or a similar gas permeable material.  
     [0060]FIG. 3 is a cross-sectional view of the electro-dynamic loudspeaker taken along line  3 - 3  of FIG. 1. FIG. 3 shows the frame  102  having the diaphragm  104  attached in tension to the frame  102  and the permanent magnets  202  positioned on the frame  102  underneath the diaphragm  104 . Linear sections  108  of the conductor  106  are also shown positioned on top of the diaphragm  104 .  
     [0061]FIG. 4 is an enlarged cross-sectional view of the encircled area of FIG. 3. As illustrated by FIG. 4, the diaphragm  104  is comprised of a thin film  400  having a first side  402  and a second side  404 . First side  402  is coupled to frame  102 . Generally, the diaphragm  104  is secured to the frame  102  by an adhesive  406  that is curable by exposure to radiation. However, the diaphragm  104  may secured to the frame  102  by other mechanism, such as those known in the art.  
     [0062] To provide a movable membrane capable of producing sound, the diaphragm  104  is mounted to the frame  102  in a state of tension and spaced apart a predetermined distance from magnets  202 . The magnitude of tension of the diaphragm  104  depends on the speaker&#39;s physical dimensions, materials used to construct the diaphragm  104  and the strength of the magnetic field generated by magnets  202 . Magnets  202  are generally constructed from a highly energizable material such as neodymium iron boron (NdFeB), but may be made of other magnetic materials. The thin diaphragm film  400  is generally a polyethylenenaphthalate sheet having a thickness of approximately 0.001 inches; however, the diaphragm film  400  may be formed from materials such as polyester (e.g., known by the tradename “Mylar”), polyamide (e.g., known by the tradename “Kapton”) and polycarbonate (e.g., known by the tradename “Lexan”), and other materials known by those skilled in the art for forming diaphragms  104 .  
     [0063] The conductor  106  is coupled to the second side  404  of the diaphragm film  400 . The conductor  106  is generally formed as an aluminum foil bonded to diaphragm film  400 , but may be formed of other conductive material known by those skilled in the art.  
     [0064] The frame  102  includes a base plate  208  surrounded by a wall  210  extending generally orthogonally upward from the plate  208 . The wall  210  terminates at a radially extending flange  212  that defines a substantially planar mounting surface  414 . A lip  416  extends downwardly from flange  212  in a direction substantially parallel to wall  210 . Base plate  208  includes a first surface  418 , a second surface  420  and a plurality of apertures  422  extending through the base plate  208 . The apertures  422  are positioned and sized to provide air passageways between the first side  402  of diaphragm  104  and first surface  418  of frame  102 . An acoustical dampener  236  is mounted to second surface  420  of frame base plate  208 .  
     [0065] To control the acoustical directivity of the loudspeaker  100 , various structural aspects of the loudspeaker  100  may be modified to produce amplitude shading of the thin film diaphragm of the loudspeaker. Amplitude shading can be accomplished by (i) varying magnetic flux density at the conductor traces (FIGS.  5 - 7 ); (ii) varying the resistance of the diaphragm traces (FIGS.  8 - 12 ); and/or (iii) varying mass over the driven portion of the diaphragm (FIG. 13). Alternatively, acoustical directivity can be controlled though varying the size of the loudspeaker, as illustrated in FIGS.  14 - 30 .  
     [0066] FIGS.  5 - 7  illustrate various examples of amplitude shading of the thin film diaphragm of the loudspeaker by varying the magnetic flux density at the conductor traces  108 . FIG. 5 is a cross-sectional view taken along the line  5 - 5  of FIG. 1. In FIG. 5, amplitude shading of the diaphragm  104  of the loudspeaker  500  is achieved by varying the spacing the of the magnets  202  away from the thin film diaphragm  104  at different distances  502 ,  504 ,  506  in specific and predetermined zones  508 ,  510 ,  512  of the diaphragm  104  over the length “l” of the loudspeaker  500 . In this regard, the magnets  202  may be spaced from the diaphragm  104  at a distance of between about 0.1 mm to more than about 1 mm.  
     [0067] As shown, the magnets  202  are spaced variably closer to the diaphragm  104  across the length “L” of the loudspeaker. This arrangement may be accomplished through the structure of the frame  102  of the loudspeaker  500  that locates same sized magnets  202  at different distances  502 ,  504 ,  506  from the diaphragm  104 .  
     [0068] Alternately, as shown in FIG. 6, is a cross-sectional view taken along the line  5 - 5  of FIG. 1, the frame  102  of the loudspeaker  600  may remain unchanged and magnets  602 ,  604 ,  606  having different physical dimensions may be used to vary their respective positions relative to the diaphragm  104 . In either embodiment (FIG. 5 or FIG. 6), the result of the modified magnet spacing arrangement is that the flux density of the magnetic field at the location of the traces  108  (and hence the strength of the magnetic field) varies across the length “l” of the loudspeaker  500  and  600 . In this regard, the flux density at the location of the traces  108  for each magnet  202  is greater as the distance between the magnet  202  and the diaphragm  104  decreases. Consequently, the sensitivity of the diaphragm  104  changes across its driven zone, resulting in amplitude shading of the diaphragm  104  and a controllable acoustical directivity of the loudspeakers  500  and  600 .  
     [0069]FIG. 7 is a cross-sectional view, illustrating another example amplitude shading to alter the natural acoustical directivity of a loudspeaker  700  by magnetizing the plurality of magnets  702 ,  704 ,  706  in the loudspeaker  700  to different energy densities. Energy densities of magnets are measured in units of Gauss-Oersteds (GOe). For example, the magnet  702  may be magnetized to the strength of half of that of magnet  704  that, in turn, may have half of the energy density of magnet  706 .  
     [0070] In this case the magnetic flux, measured in units called Tesla (T), that is generated by each of the different magnets  702 ,  704 ,  706  will vary across the length “1” of the loudspeaker  700  at the location of the conductive traces  108 , due not to the magnets  702 ,  704 ,  706  physical spacing from the diaphragm  104 , but instead to their individual magnetic strength as ultimately determined by their material compositions. This predetermined and controllable relationship between the magnets&#39;  702 ,  704 ,  706  flux densities at the location of the conductive traces  108  over several zones  708 ,  710 ,  712  on the diaphragm  104  of the loudspeaker  700  creates amplitude shading that can produce a controlled directivity response for the loudspeaker  700 .  
     [0071] Although the magnets of the various example embodiments of FIGS.  5 - 7  are define by five rows of magnets  202  with three magnets  202  in each row, the number of magnets in a row and the number of rows may vary depending upon the application. Despite the number of magnets  202  used a particular application, amplitude shading can still be accomplished to vary, control or enhance the acoustic directivity of the loudspeaker by varying the spacing between the magnets  202  and the diaphragm, by varying the size of the magnets  202  and by varying the energy densities of the magnets  202  across the diaphragm  104  of the loudspeaker  100 .  
     [0072] FIGS.  8 - 12  illustrate various examples of amplitude shading of the thin film diaphragm of the loudspeaker by varying the resistance of the conductive traces  108  of the diaphragm  104 . FIG. 8 is schematic view showing a conductive trace on a diaphragm of an electro-dynamic loudspeaker  800 . In FIG. 8, amplitude shading is accomplished by manipulating the dc resistance (DCR) of the plurality of traces  801 ,  803 ,  805  on the diaphragm  804  of the loudspeaker  800 . For example, the diaphragm  804  may comprise a conductor  820  including a plurality of traces  801 ,  803 ,  805 , respectively forming individual circuits  806 ,  808 ,  810  located in separate zones  812 ,  814 ,  816  of the diaphragm  804 . In selected zones, the traces  801 ,  803  and  805  may be electrically in series (as shown in FIG. 8) or in parallel (see FIG. 12) to achieve the result of a different DCR in the traces  801 ,  803 ,  805  across the diaphragm  804 . The variable sensitivity of the traces  801 ,  803 ,  805  affects the acoustical directivity of the loudspeaker  800  by amplitude shading of the diaphragm  804 .  
     [0073] In addition to the relationship of the traces electrically (e.g., series or parallel), the DCR of the traces may be manipulated in other ways to achieve the same effect. For example, as shown in the cross-sections of FIGS.  9 - 11 , the multiple traces  801 ,  803  and  805  on the diaphragm  804  may each possess different physical dimensions, including different widths w 9 , w 10 , w 11 , different thicknesses t 9 , t 10 , t 11  (heights), and cross-sectional areas a 9 , a 10 , a 11 .  
     [0074]FIG. 9 is a cross-sectional view taken along the line  9 - 9  of FIG. 8 showing the dimensional cross-section of the conductive trace  803  along circuit  808  of the conductor  820 . FIG. 10 is a cross-sectional view taken along the line  10 - 10  of FIG. 8 showing the dimensional cross-section of the conductive trace  801  along circuit  806  of the conductor  820 . As seen in FIG. 10, the widths w 10 , thicknesses t 10  (height), and cross-sectional area a 10  of the conductive trace  803  in circuit  804  are larger than the widths w 9 , thicknesses t 9 , and cross-sectional area a 9  of the conductive trace  803  of circuit  808  (FIG. 9).  
     [0075] Similarly, FIG. 11 is a cross-sectional view taken along the line  11 - 11  of FIG. 8 showing the dimensional cross-section of the conductive trace  805  along circuit  810  of the conductor  820 . As seen in FIG. 11, the widths w 11 , thicknesses t 11  (height), and cross-sectional area all of the conductive trace  805  in circuit  810  are smaller than the widths w 9 , thicknesses t 9 , and cross-sectional area a 9  of the conductive trace  803  of circuit  808  (FIG. 9), as well as the widths w 10 , thicknesses t 10  (height), and cross-sectional area a 10  of the conductive trace  803  in circuit  804  (FIG. 10).  
     [0076]FIG. 12 is a schematic view showing an alternative example of a conductive trace on a diaphragm of an electro-dynamic loudspeaker. As shown in FIG. 12, the electrical traces  1201 ,  1203  and  1205  are in parallel. Further, the traces of a loudspeaker  1200  may also have different lengths, resulting in their respective DCRs to be different. Similar to that described above, the loudspeaker  1200  has, for example, three traces  1201 ,  1203 ,  1205  across the diaphragm  1204 . The respective traces  1201 ,  1203 ,  1205  form individual circuits  1206 ,  1208 ,  1210  connected electrically in parallel and located in separate zones  1212 ,  1214 ,  1216  of the diaphragm  1204 . The lengths of the traces  1201 ,  1203 ,  1205  may, however, vary as desired.  
     [0077] While the example embodiment, illustrates three traces  1201 ,  1203  and  1205  forming three circuits  1206 ,  1208  and  1210 , the number of traces and number of circuits formed by the traces may vary depending upon the application. Additionally, the traces  108  of the loudspeakers  100  may be formed from a number of different materials, including, but not limited to copper, aluminum alloys or other conductive materials possessing different DCR values. Such variation in physical characteristics and/or properties of a plurality of traces  108  on the diaphragm  104  enable the acoustical directivity of the loudspeaker  100  to be modified accordingly by amplitude shading.  
     [0078]FIG. 13 is a cross-sectional view taken along the line  5 - 5  of FIG. 1 showing another example of an electro-dynamic loudspeaker. In FIG. 13, amplitude shading of the diaphragm  104  of the loudspeaker  1300  may be achieved by the non-uniform application of a damping material  1302  on the second side  404  of the diaphragm  104 . For example, damping material  1302  may be applied in unequal and/or excessive amounts to the surface  404 , or only on selected portions of the surface  404 , over the driven portion of the diaphragm  104 , that may be separated into zones  1304 ,  1306 ,  1308 . In this regard, damping material  1302  may be applied to a thickness that may vary from a minimum of about 0.1 mm to 3 mm or more depending upon the damping material&#39;s physical properties and/or characteristics. Such application of damping material  1302  effectively varies the mass of the diaphragm  104  across the driven zones  1304 ,  1306 ,  1308  and achieves directivity control by amplitude shading. The damping material may be made from, for example, a liquid urethane oligomer acrylic monomer blend, such as Dymax 4-20539, that cures into a flexible solid, or other material known by those skilled in the art that may be used as a dampener on thin-film diaphragms.  
     [0079] As illustrated by FIGS.  14 - 30 , the acoustical directivity of an electro-dynamic loudspeaker can also be controlled by varying the size and configuration of the loudspeaker. FIG. 14 illustrates one example of a modification that can be made to the size of the loudspeaker to vary acoustical directivity.  
     [0080]FIG. 14 is a plan view of an electro-dynamic loudspeaker  1400  having a high aspect ratio of its length relative to its width. As illustrated by the polar response curves shown in FIGS.  15 - 29 , by varying the length-to-width aspect ratio of the planar loudspeaker  1400 , for example, by a ratio of about 10:1, the planar loudspeaker  1400  may exhibit directivity characteristics that differ greatly from a conventional loudspeaker. By way of example, the length of the loudspeaker  1400  may range from on the order of about 200 mm to about 400 mm, and the width may range from on the order of about 20 mm to about 65 mm. Such a high-aspect ratio planar loudspeaker  1400  may be particularly suitable for installation onto a structural pillar of a vehicle, such as an automobile.  
     [0081] The characteristic of directivity of a loudspeaker is the measure of the magnitude of the sound pressure level (SPL) of the audible output from the loudspeaker, in decibels (dB), as it varies throughout the listening environment. It is well-known that the SPL of the audible output of a loudspeaker can vary at any given location in the listening environment depending on the direction (angle) and the distance from the loudspeaker of that particular location and the frequency of the audible output from the loudspeaker. The directivity pattern of a loudspeaker may be plotted on a graph called a polar response curve. The curve is expressed in dB at an angle of incidence with the loudspeaker, where the on-axis angle is 0 degrees.  
     [0082] By way of example, FIG. 15 illustrates a polar response curve for a loudspeaker whose audible output is at a very low frequency relative to the size of the loudspeaker. The polar response for a loudspeaker at this low frequency is shown to be generally omni-directional. As the frequency of the audible output from a loudspeaker increases relative to the size of the loudspeaker, the polar response curve for the loudspeaker becomes increasingly directional. The increasing directivity of a loudspeaker at higher frequencies gives rise to off-axis lobes and null areas in the polar response curves, and is a phenomenon referred to as “fingering” or “lobing.” 
     [0083] FIGS.  16 - 22  show the horizontal polar response plots H of a high-aspect ratio electro-dynamic loudspeaker shown in FIG. 14 at a variety of frequencies verses the horizontal polar response plots H c  of a conventional single tweeter loudspeaker. FIG. 16 represents the horizontal polar response plot comparison of the loudspeakers at 1 kHz. FIG. 17 is the horizontal polar response plot comparison at 1.6 kHz. FIG. 18 is the horizontal polar response comparison at 3.15 kHz. FIG. 19 is the horizontal polar response plot comparison at 5 kHz. FIG. 20 is the plot at 8 kHz, while FIGS. 21 and 22 are the plots at 12.5 kHz and 16 kHz, respectively.  
     [0084] Similarly, FIGS.  23 - 29  depict the vertical polar response plots V of a high-aspect ratio electro-dynamic loudspeaker shown in FIG. 14 and those of a conventional single tweeter loudspeaker V c  at a variety of frequencies. FIG. 23 represents the vertical polar response plot of the comparing of the loudspeakers at 1 kHz. FIG. 24 is the vertical polar response plot comparison at 1.6 kHz. FIG. 25 is the vertical polar response comparison at 3.15 kHz. FIG. 26 is the vertical polar response plot comparison at 5 kHz. FIG. 27 is the plot at 8 kHz, while FIGS. 28 and 29 are the plots at 12.5 kHz and 16 kHz, respectively.  
     [0085] In addition to varying aspect ratio of the loudspeaker to control acoustical directivity, the shape of the loudspeaker  3000 , as shown in FIG. 30, may be modified to achieve a predetermined or preferred acoustical directivity performance. FIG. 30 shows a plan view of an electro-dynamic loudspeaker  3000  having a non-rectangular polygonal shape. As illustrated by FIG. 30, the loudspeaker  3000  may take on a non-rectangular, polygonal shape, such as a trapezoid. The shaped panel reduces off-axis acoustical lobes, so that the acoustical output from the loudspeaker, particularly when amplified, provides better directional performance and control. It is contemplated that the loudspeaker may also be configured in the shape of other polygons or other non-traditional configurations to achieve the same result.  
     [0086] While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that other embodiments and implementations are possible that are within the scope of this invention. Accordingly, the invention is not restricted except in light of the attached claims and their equivalents.