Abstract:
An electro-dynamic loudspeaker is provided with dampening arrangements that contribute to improved acoustical properties for the electro-dynamic planar loudspeaker. The dampening arrangements include providing a frame having a curved sidewall surface for reducing standing waves. Another design provides for a ferrofluid being disposed between the diaphragm and magnets of the electro-dynamic loudspeaker in order to dampen the resonance frequency of the device. In addition, a diaphragm of an electro-dynamic loudspeaker is provided with a short turn of conductor disposed along a fringe zone at an edge of the diaphragm in order to electro-dynamically dampen the edge resonance of the film.

Description:
1. CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/380,001, filed May 2, 2002, No. 60/378,188, filed May 6, 2002, and No. 60/391,134, filed Jun. 24, 2002. These patent applications are incorporated by reference.  
       2. CROSS REFERENCE TO CO-PENDING APPLICATIONS  
       [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 “Directivity Control Of 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]    The invention relates to electro-dynamic loudspeakers, and more particularly, improvements for electro-dynamic loudspeakers and manufacturing methods thereof.  
           [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 frame of the electro-dynamic loudspeakers supports the magnets, the diaphragm, and the terminal. A ferrous steel frame has the advantage of carrying magnetic flux that can improve efficiency over a non-ferrous frame. However, frames constructed from non-ferrous or non-metallic materials provide other manufacturing advantages. The frame presents design challenges since it is preferably rigid enough to keep the diaphragm film tension uniform and capable of not deforming during handling, assembly, or over time. The frame also should be capable of withstanding environmental high temperatures, humidity, salt, spray, etc., and be capable of bonding with the diaphragm film.  
           [0014]    Other features affecting the acoustic characteristics of the electro-dynamic loudspeaker include damping of undriven portions of the diaphragm film in order to help reduce distortion and smooth frequency response. Damping is required to control film edges by reducing unproductive or counter productive vibration.  
           [0015]    Furthermore, the controlled directivity of sound is critical for a good system design and acoustical interaction in the listening environment. The electro-dynamic loudspeakers exhibit defined acoustical directivity relative to frequency and to their shape and also relative to the distance from the source. In addition, other frequency response enhancements can also be made to the current electro-dynamic loudspeaker designs.  
           [0016]    With the dimensional flexibility obtained with an electro-dynamic loudspeaker, various locations in automotive and non-automotive vehicles may be employed to house electro-dynamic loudspeakers. Different locations offer various advantages over other locations. The thin depth of the electro-dynamic loudspeaker allows them to fit where conventional loudspeakers would not. The final assembly may be mounted on a vehicle, and therefore, must be rigid during shipping and handling and should not allow the diaphragm or frame to deform during installation.  
         SUMMARY  
         [0017]    The invention provides several arrangements and methods for enhancing the acoustical properties of an electro-dynamic loudspeaker. According to one aspect of the invention, the electro-dynamic loudspeaker includes a frame defining a recessed portion having a pair of sidewalls interconnected by a pair of endwalls and at least one of the sidewalls including a plurality of curves along a length of the sidewall. The curves can be in the form of a sinusoidal curve or scallops or another shape that is non-parallel to the opposing sidewall. The curves that are placed in at least one sidewall are provided in order to reduce standing waves that contribute to distortion.  
           [0018]    The electro-dynamic loudspeaker includes a frame including a plurality of magnets mounted to the frame. A diaphragm is mounted to the frame and a ferrofluid is disposed between the diaphragm and the magnets and contacts a lower surface of the diaphragm. A ferrofluid is a stable colloidal suspension of sub-domain magnetic particles in a liquid carrier. The ferrofluid dampens the resonant frequency of the diaphragm in order to reduce distortion and smooth frequency response.  
           [0019]    An electro-dynamic loudspeaker is provided with a shorted turn of conductor disposed along a fringe zone at an edge of the diaphragm. The shorted turn electro-dynamically dampens the edge resonance of the diaphragm.  
           [0020]    A diaphragm of an electro-dynamic loudspeaker is made from a piezoelectric material, such as PVDF (polyvelydeneflouride) and is provided with a current carrying conductor and an undriven conductor applied to both sides of the film material. The undriven conductors are caused to move by the electromotive force on the circuit as the diaphragm vibrates, thus creating electric current through the undriven conductor. The electric current causes the piezoelectric material of the film to expand and contract in response to the electric current, and thereby dampens the film modes to reduce distortion and smooth frequency response. As an alternative, a PVDF strip can also be glued to a PEN (polyethylene naphthalate) film.  
           [0021]    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  
       [0022]    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  
         [0023]    [0023]FIG. 1 is a perspective view of a electro-dynamic loudspeaker as it would appear with the grille removed.  
         [0024]    [0024]FIG. 2 is an exploded perspective view of the electro-dynamic loudspeaker shown in FIG. 1 having a grille.  
         [0025]    [0025]FIG. 3 is a cross-sectional view of the electro-dynamic loudspeaker taken along line  3 - 3  of FIG. 1.  
         [0026]    [0026]FIG. 4 is an enlarged cross-sectional view of the encircled area of FIG. 3.  
         [0027]    [0027]FIG. 5 is a plan view of the film having an attached conductor.  
         [0028]    [0028]FIG. 6A is a perspective view of a frame having sinusoidal curved sidewalls.  
         [0029]    [0029]FIG. 6B is a partial plan view of a scalloped sidewall.  
         [0030]    [0030]FIG. 6C is a partial plan view of a jagged sidewall.  
         [0031]    [0031]FIG. 7 is a perspective view of a frame having an angled sidewall.  
         [0032]    [0032]FIG. 8 is a cross-sectional view illustrating a ferrofluid disposed on a surface of a magnet and in contact with the film.  
         [0033]    [0033]FIG. 8A is a detailed cross-sectional view of the ferrofluid on the magnet with the diaphragm in an upward direction.  
         [0034]    [0034]FIG. 8B is a detailed cross-sectional view of the ferrofluid on the magnet with the diaphragm in a downward direction.  
         [0035]    [0035]FIG. 9 is a perspective view of an electro-dynamic loudspeaker including an undriven conductor applied to both sides of the film for providing a dampener for the diaphragm film.  
         [0036]    [0036]FIG. 10 is a cross-sectional view taken along line  10 - 10  of FIG. 9.  
         [0037]    [0037]FIG. 11 is a plan view of an electro-dynamic loudspeaker having a shorted turn of conductor in the fringe zone at the edges of the film to electro-dynamically dampen the edge resonance.  
         [0038]    [0038]FIG. 12 is a cross-sectional view taken along line  12 - 12  of FIG. 11.  
     
    
     DETAILED DESCRIPTION  
       [0039]    [0039]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.  
         [0040]    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.  
         [0041]    [0041]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.  
         [0042]    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 .  
         [0043]    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 .  
         [0044]    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 .  
         [0045]    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 .  
         [0046]    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.  
         [0047]    [0047]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 .  
         [0048]    [0048]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.  
         [0049]    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 .  
         [0050]    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.  
         [0051]    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 .  
         [0052]    With reference to FIG. 6, an alternative frame  600  is provided which defines a recessed portion  602  having a pair of sidewalls  604 ,  606  interconnected by a pair of endwalls  608 ,  610 . As described above, the magnets of the electro-dynamic planar loudspeaker are mounted to the frame and a diaphragm is mounted to an upper attachment surface  612 . One or more of the sidewalls  604 ,  606  or end walls  608 ,  610  includes a plurality of curves along a length of the wall in order to reduce transverse standing waves across the diaphragm. The curved sidewall  604  or  606  can include a sinusoidal curve (FIG. 6A), scallops  614  (FIG. 6B), triangular peaks  616  (FIG. 6C), or any other configuration which reduces standing waves by varying a diameter of the frame along a longitudinal length thereof in order to reduce transverse standing waves across the diaphragm by minimizing the length of parallel wall lengths.  
         [0053]    With reference to FIG. 7, a frame  700  according to a second embodiment of the invention, has a recessed portion  702  having a pair of sidewalls  704 ,  706  connected to one another by a pair of endwalls  708 ,  710 . A plurality of magnets are mounted to the frame  700  and a diaphragm is mounted to an attachment surface  712  of the frame  700 . The sidewall  704  is non-parallel to the sidewall  706  in order to reduce transverse standing waves. In particular, sidewall  704  can be angled relative to the sidewall  706 . By varying the distance across the frame  700  along a longitudinal length thereof, the production of standing waves is thereby reduced.  
         [0054]    With reference to FIG. 8, another embodiment of the invention will now be described. In FIG. 8, an electro-dynamic loudspeaker  800  is provided including a frame  802  having a plurality of magnets  804  (one shown) mounted to the frame  802 . A diaphragm  806  is mounted to an attachment surface  808  of the frame  802  by an adhesive  810 . The diaphragm includes a conductor including a plurality of elongated traces  812  mounted thereto. A ferrofluid  814  is provided between the diaphragm  806  and magnets  804 . The ferrofluid  814  is in contact with the diaphragm  806  so that as the diaphragm  806  vibrates, the contact with the ferrofluid  814  dampens the vibration. As illustrated in FIG. 8A, as the film  806  moves upward, the ferrofluid  814  is “stretched” upward while maintaining contact with the film and as shown in FIG. 8B, as the film  806  moves downward, the ferrofluid  814  is compressed. The ferrofluid  814  is maintained on the surface of the magnet  804  by the magnetic field attracting the ferrous fluid. A wall structure  816  surrounds the magnets  804  in order to isolate the ferrofluid  814  on an upper surface of the magnets  804 . The ferrofluid  814  can be provided on all of or selective ones of the magnets  804 . In particular, putting ferrofluid only on the outermost magnets  804  may provide sufficient damping. The ferrofluid provides a mechanical dampener for dampening the resonance frequency of the film  806  instead of the use of felt or another dampener material on the back of the frame.  
         [0055]    With reference to FIGS. 9 and 10, an alternative damping arrangement is provided for an electro-dynamic loudspeaker  900 . As shown in FIG. 10, the electro-dynamic loudspeaker  900  includes a frame  1000  having a plurality of magnets  1002  mounted thereto as previously described. A film  1004  is mounted to the frame by an adhesive  1006 . A conductor  1008  is provided on the film  1004  in the same manner as is described above with reference to FIG. 1. The film  1004  is made from a piezoelectric material such as polyvelydeneflouride (PVDF) that is available under the trade name KYNAR. KYNAR exhibits a piezoelectric effect in that when electricity is applied to conductors attached on opposite sides, the material contracts or expands. A pair of undriven conductors  1010 ,  1012  (not part of the conductor  1008 ) are applied to both sides of the film  1004  along opposite edges of the film. The undriven upper and lower conductors  1010 ,  1012  are each connected together by a rivet  902  extending through the film  1004 . The undriven conductor is located in order to dampen the film modes. Specifically, as the film  906  vibrates, the undriven conductor  912 ,  914  is moved relative to the magnetic field generated by magnets  1002  and generates electric current therethrough which causes the film material to contract and expand as the current changes so that the conductors  1010 ,  1012  act to dampen film modes and behave like an edged treat. Due to the piezoelectric effect, the PVDF film has a resultant change in thickness based on the relationship dta=d33*Vt where: dta is the change in thickness; d33 is the piezoelectric moduli appropriate for the material; and Vt is an applied voltage. Conversely, Vt=dta/d33.  
         [0056]    With reference to FIGS. 11 and 12, an alternative dampening arrangement is provided for an electro-dynamic loudspeaker  1100 . The electro-dynamic loudspeaker  1100 , as shown in FIG. 12, includes a frame  1200  including a plurality of magnets  1202  mounted thereto. A diaphragm  1204  is mounted to the frame  1200  by an adhesive  1206 . A conductor  1208  is mounted to the diaphragm  1204  in the same manner as described with reference to FIG. 1. A shorted turn of conductor  1102  is separately provided in the fringe zone at the edges of the film  204 , as best illustrated in FIG. 11. The shorted turn  1102  electro-dynamically dampens the edge resonance of the film  1204  by providing a damping electromotive force.  
         [0057]    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.