Abstract:
In an electro-dynamic loudspeaker, vent holes are optimized to provide improved the magnetic flux characteristics while maintaining sufficient ventilation. In addition, ported and unported enclosures may be utilized with the electro-dynamic loudspeakers to enhance low frequency performance.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application Nos. 60/380,001, filed May 2, 2002, 60/378,188, filed May 6, 2002, and 60/391,134, filed Jun. 24, 2002. These patent applications are incorporated reference.  
       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 “Acoustically Enhanced Electro-Dynamic Loudspeakers,” filed May 2, 2003; U.S. patent application Ser. No. ______, entitled “Directivity Control Of 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, to frequency response enhancements for electro-dynamic loudspeakers.  
           [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 that carries magnetic flux may improve efficiency over a non-ferrous frame. The frame presents design challenges because it should be 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 should be capable of bonding with the diaphragm film.  
           [0014]    The undriven portions of the diaphragm film may be dampened to help reduce distortion and smooth frequency response. Damping controls film edges by reducing unproductive vibration.  
           [0015]    Furthermore, the control directivity of sound is important for a good system design and acoustical interaction in the listening environment. The electro-dynamic loudspeakers exhibit defined acoustical directivity relative to frequency, to shape, and also to distance from the source. In addition, other frequency response enhancements can also be made to the current electro-dynamic loudspeaker designs.  
           [0016]    The dimensional flexibility obtained with an electro-dynamic loudspeaker permits various locations in automotive and non-automotive vehicles to house electro-dynamic loudspeakers. Different locations offer various advantages over other locations. The thin depth of the electro-dynamic loudspeaker allows it to fit where conventional loudspeakers would not. As the final assembly may be mounted on a vehicle, it should be rigid during shipping and handling and should not allow the diaphragm or frame to deform during installation.  
         SUMMARY  
         [0017]    The invention provides frequency response enhancements for electro-dynamic loudspeakers including optimizing vent hole sizes provided in the frame for balancing the magnetic flux versus acoustic performance. Specifically, an electro-dynamic loudspeaker includes a frame having a recess portion and a plurality of vent holes in the recessed portion. The vent holes are arranged in a plurality of columns with the vent holes in each column being separated by a plurality of webs, where a combined length of the vent holes in a longitudinal length of the columns and a combined length of the webs in a longitudinal length of the columns define a total length of the columns of vent holes. The combined length of the webs in a longitudinal length of the columns should be greater than 20 percent of the total length of the columns of vent holes. The vent holes allow air disposed between the diaphragm and frame of the electro-dynamic loudspeaker to enter and exit the electro-dynamic loudspeaker as the diaphragm vibrates. Some resistance to the airflow is provided by a layer of dampening material such as felt that resists the flow of air through it. A magnetic flux is provided between the adjacent columns of magnets where the webs disposed between the vent holes enhance the magnetic flux between the columns of magnets. The vent holes are also maintained of sufficient size to allow proper venting of the electro-dynamic loudspeaker.  
           [0018]    The electro-dynamic loudspeaker may be mounted to an enclosure defining an enclosed space behind the frame of the electro-dynamic loudspeaker. The enclosure can be provided with or without ports and optimizes low frequency performance for the electro-dynamic loudspeaker.  
           [0019]    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  
       [0020]    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  
         [0021]    [0021]FIG. 1 is a perspective view of an example electro-dynamic loudspeaker.  
         [0022]    [0022]FIG. 2 is an exploded perspective view of the electro-dynamic loudspeaker shown in FIG. 1.  
         [0023]    [0023]FIG. 3 is a cross-sectional view of the electro-dynamic loudspeaker taken along line  3 - 3  of FIG. 1.  
         [0024]    [0024]FIG. 4 is an enlarged cross-sectional view of the encircled area of FIG. 3.  
         [0025]    [0025]FIG. 5 is a plan view of an example conductor attached to the film.  
         [0026]    [0026]FIG. 6 is a plan view of an example frame for an electro-dynamic loudspeaker.  
         [0027]    [0027]FIG. 7 is a schematic cross-sectional view of an example electro-dynamic loudspeaker mounted in an enclosure.  
         [0028]    [0028]FIG. 8 is a schematic cross-sectional view of an example electro-dynamic loudspeaker mounted to a ported enclosure. 
     
    
     DETAILED DESCRIPTION  
       [0029]    [0029]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.  
         [0030]    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.  
         [0031]    [0031]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.  
         [0032]    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 .  
         [0033]    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 .  
         [0034]    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 .  
         [0035]    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 .  
         [0036]    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.  
         [0037]    [0037]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 .  
         [0038]    [0038]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.  
         [0039]    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 .  
         [0040]    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.  
         [0041]    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 .  
         [0042]    [0042]FIG. 6 provides a plan view of frame  102 . The frame  102  includes a plurality of apertures or vent holes  422  which are arranged in columns which are aligned between the magnets  202 . The columns include interior columns of vent holes  600   a,    600   b,    600   c,    600   d  and a pair of outer edge columns  602   a,    602   b.  The inner columns  600   a,    600   b,    600   c,    600   d  each have a length L1, and the outer columns  602   a,    602   b  of vent holes have a length L2. Each of the vent holes  422  of the inner columns  600   a,    600   b,    600   c,    600   d  are separated by a web portion  604  having a web length W1. The outer columns of vent holes  602   a,    602   b  are each separated by a web portion  606  having a width W2. Each of the vent holes  422  of the inner vent hole columns  600   a,    600   b,    600   c,    600   d  has a length X1 while the vent holes of the outer columns  602   a,    602   b  have a length X2. The vent holes  422  are provided in order to allow air disposed between the diaphragm  104  and the frame  102  to escape the recessed portion of the frame  102  as the diaphragm  104  vibrates. A layer of felt material  236  may be disposed on the back surface of the frame  102  to provide a dampening function by slightly inhibiting air travel through the vent holes  422 . The web portions  604  and  606  provided between the vent holes  422  provide enhanced flux lines to be formed between the magnets  202  of the different columns.  
         [0043]    An optimal web  604  size for balancing the flux density with the air flow resistance may be determined based on the amount of metal in the web areas and the size of the holes  422 . The webs  604  having a width W and the vent holes  422  having a width X1 combine to form a column of total longitudinal length L1. The length of the webs in the column may be optimized such that the combined web lengths W in the length L1 of one of the columns  600   a,    600   b,    600   c,    600   d  should be greater than about 20 percent and should be less than about 45 percent of the total length L1. In one example shown, the length L1 of a column  600   a,    600   b,    600   c,  or  600   d  is approximately 147 millimeters while the width X1 of the vent holes  422  is 7.25 millimeters and the web length W1 is 5.45 millimeters. Thus, the combined lengths of the webs W1 is approximately 60 millimeters (11 * 5.45 mm) yielding a combined web length of approximately 41 percent of the total column length L1. The webs have an approximate thickness of about 1.2 millimeters. The increased web distance provides around a six percent increase in the magnetic flux due to the increased magnetic path and therefore lower energy magnets may be utilized. The outer columns  602   a,    602   b  with vent holes  422  have narrower webs  606  provided between the vent holes  422 . The web of one of the outer columns  602   a,    602   b  makes up less than 20 percent of the total length of the outer columns  602   a  or  602   b.  Because the webs  606  are not provided between columns of magnets, the narrow webs have no impact on the flux lines and therefore, can be maintained with a narrower length. In one example, the total length L2 of the outer columns  602   a  and  602   b  is approximately 150 millimeters with the vent holes  422  having a length X2 equal to approximately 10.25 millimeters and the web  606  length W2 between each of the vent holes  422  is approximately 2.45 millimeters. Accordingly, the total distance of the webs  606  (2.45 mm * 11=26.95 mm) provided between the vent holes of the outer columns  602   a  and  602   b  is approximately 18 percent (26.95/150=18%) of the total length L2 of one of the outer columns. Similar effects may be obtained by using thicker steel in the frame but are more costly, heavier, and more difficult to form.  
         [0044]    In FIG. 7, the electro-dynamic loudspeaker  100  according to the invention is mounted to an enclosure  700  that is un ported. The enclosure  700  optimizes the low frequency performance of the electro-dynamic loudspeaker  100 . The materials, size, and shape of the enclosure are each application specific.  
         [0045]    With reference to FIG. 8, the electro-dynamic loudspeaker  100  is provided with a ported enclosure  800  including a port  802 . The port  802  provides a means for the rear output of the electro-dynamic loudspeaker to contribute to the total output of the system. However, the enclosure  800  only contributes over a very narrow range of frequencies. In fact, the enclosure  800  significantly reduces distortion and increases power handling at very low frequencies. Enclosures, ported and unported, can be used to extend low frequency response or reduce distortion at resonance.  
         [0046]    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.