Abstract:
An edge-driven diaphragm loudspeaker driver is configured such that the suspension system of the driver is connected to the voice coil rather than to the diaphragm. Thus, the diaphragm in the loudspeaker is free of suspension systems connected to or extending from the diaphragm. By attaching the surround suspension to the voice coil rather than to the diaphragm, the diaphragm is isolated from the influence of spurious high frequency vibrations in the suspension system, thereby increasing the performance of the loudspeaker at high frequencies. The loudspeaker driver configuration also provides for a longer excursion range for the voice coil/diaphragm assembly, which allows for the driver components to be more accurately aligned during manufacturing, thereby enabling the loudspeaker driver to operate as a full range unit by producing low output frequencies.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority of U.S. provisional application Serial No. 60/093,600 filed Jul. 21, 1998 and U.S. application Ser. No. 09/346,954, filed Jul. 1, 1999, both incorporated by reference into this application. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of Invention  
           [0003]    The invention relates to the field of loudspeakers and more particularly to the configuration of a loudspeaker driver suspension system.  
           [0004]    2. Related Art  
           [0005]    The general construction of a loudspeaker driver consists of a diaphragm, voice coil, magnetic motor, frame and suspension system. The magnetic motor is generally attached to the frame. The voice coil and diaphragm are then mounted to the frame via the suspension system, which may include one or more suspension members. The voice coil of the driver typically consists of a voice coil former having a wire wound about the lower portion of the voice coil former. Often times, although not necessary, the voice coil former is encased in a wrapper. The suspension system of the driver acts to provide the stiffness of the driver and also provide air sealing for the driver. The configuration of the voice coil and diaphragm in the frame via the suspension system depends generally upon the design and size of the diaphragm relative to the voice coil.  
           [0006]    Loudspeakers are generally of two common construction types. The first construction type is a conventional dual-suspension driver construction where the diaphragm of the driver is formed as a cone and is substantially greater in diameter than the voice coil. In this type of construction, two suspension members are generally utilized. A “surround” suspension member is connected to the diaphragm at its outer edge and extends outward from the diaphragm to connect the diaphragm to the frame. Similarly, a “spider” suspension is connected to the voice coil and extends from the voice coil to the frame, connecting the voice coil to the frame.  
           [0007]    The second type of driver construction is an edge-driven-diaphragm driver. In this construction, the diaphragm and the voice coil are of substantially equal diameter. The outer edge of the diaphragm is then attached to the diaphragm to form a diaphragm assembly. This assembly is then attached to the voice coil. The surround suspension assembly extends outward to connect the assembly to the frame. This edge-driven-diaphragm driver construction is often found in smaller speaker assemblies, such as tweeters, and sometimes in mid-range speakers.  
           [0008]    One common problem with smaller sized loudspeakers is as the size of the loudspeakers becomes smaller, achieving acceptable low frequency response becomes more difficult. This is because the loudspeaker is required to displace a larger volume of air to achieve the lower frequencies, and the suspension stiffness must be reduced to maintain a low resonance corresponding to the lighter mass of the smaller driver. The volume of air that a loudspeaker can displace is dependent upon the area of the diaphragm and the range of motion allowed by the suspension, i.e., amount of vibrational excursion, or volume displacement, of the loudspeaker. Additionally, higher suspension stiffness acts to reduce the motion of the diaphragm for a given input, so a minimum of stiffness is desired. Since smaller loudspeakers have a smaller diaphragm and stiffer suspension, the volume displacement, and thus the performance, is limited by the ability to manufacture loudspeakers with very low stiffness and high excursion capabilities.  
           [0009]    To operate efficiently, the suspension system in smaller loudspeakers, such as those found in edge-driven diaphragm speakers, must allow a required maximum amplitude of vibration while constraining the vibrational movement essentially to a straight-line path to avoid the voice coil contacting the surrounding structure. Thus, the surround suspension member is required to constrain the diaphragm against any tilting, rocking or other extraneous vibration while allowing maximum possible amplitude of desired vibration. A general problem with the current construction of edge-driven speakers is the difficulty of precisely aligning the components during manufacturing, as the magnetic air gap is shielded by the diaphragm. This forces the removal of all alignment gauges prior to the placement of the diaphragm/coil assembly, and thus causes uncertainty in location of the voice coil relative to the motor. This is commonly known as a “blind” assembly.  
           [0010]    An additional general problem with the current construction of loudspeakers is that spurious vibration of portions of the surround suspension members occur at high audio frequencies. These spurious vibrations may be transmitted to the diaphragm through the suspension, thereby degrading the high frequency performance of the speakers. Furthermore, with the current loudspeaker construction, the maximum amplitude of vibration is limited in smaller sized loudspeakers, preventing low frequency responses from the smaller diameter speakers.  
           [0011]    A need therefore exists for a loudspeaker construction that minimizes the effect of the spurious vibration of the suspension system on the diaphragm and that increases the amount of excursion of the voice coil/diaphragm assembly to provide low frequency response in smaller diameter loudspeaker systems.  
         SUMMARY  
         [0012]    The loudspeaker driver of the invention is designed so that the suspension system of the driver is connected to the voice coil former rather than to the diaphragm. In particular, the edge-driven voice coil/diaphragm assembly is supported by a single surround suspension member attached to the tubular voice coil former in a location spaced at a predetermined distance from the point at which the voice coil former attaches to the diaphragm. Thus, the diaphragm in the driver construction is free of suspension systems connected to or extending from the diaphragm. By attaching the surround suspension to the voice coil former rather than to the diaphragm, the diaphragm is isolated from the influence of spurious high frequency vibrations in the suspension system. Thus, the performance of the loudspeaker driver at high frequencies is improved.  
           [0013]    Additionally, by attaching the suspension to the voice coil former rather than the diaphragm, the loudspeaker driver configuration provides for a longer excursion range for the voice coil/diaphragm assembly. By attaching the diaphragm to the voice coil former, the driver components can be more accurately aligned during manufacture, which enables the driver to operate a higher excursion rate. Thus, the loudspeaker driver is able to operate as a full range unit, producing acoustic output at frequencies generally lower than those produced by typical loudspeaker constructions of a similar size and shape.  
           [0014]    The driver construction may be utilized in edge-driven diaphragm drivers utilizing both concave and convex domed diaphragms. When limited by size constraints, as with miniature loudspeakers for use in laptop computers, the concave diaphragm is preferred because a more compact driver configuration can be achieved.  
           [0015]    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  
       [0016]    The invention can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views.  
         [0017]    [0017]FIG. 1 is a front view of a loudspeaker driver.  
         [0018]    [0018]FIG. 2 is a side view of the loudspeaker driver illustrated in FIG. 1.  
         [0019]    [0019]FIG. 3 is an enlarged rear perspective view of the loudspeaker driver illustrated in FIG. 1.  
         [0020]    [0020]FIG. 4 is a side view of the cross-section of the loudspeaker driver illustrated in FIG. 1 taken along line A—A.  
         [0021]    [0021]FIG. 5 is an enlarged view of the encircled portion of the loudspeaker driver illustrated in FIG. 4. 
     
    
     DETAILED DESCRIPTION  
       [0022]    [0022]FIG. 1 is a front view of an edge-driven diaphragm loudspeaker driver  100  of the invention. The loudspeaker driver  100  has a frame  102  defining a circular perimeter. A pair of hookup wires  104  are shown extending outwardly from the frame  102 . Also illustrated is the diaphragm  106  and a surround member  108  positioned within the frame  102  of the loudspeaker driver  100 . The construction of the diaphragm  106  and the surround member  108  within the frame  102  are further explained below.  
         [0023]    [0023]FIG. 2 is a side view of the loudspeaker driver  100  of FIG. 1 and illustrates the surround suspension member  108  extending upwardly from the frame  102  of the loudspeaker driver  100 . FIG. 2 also illustrates the frame  102  of the loudspeaker driver  100  formed from a mounting ring  200 , a polar array of buttress blocks  202  and a pot  204 . The pot  204  of the frame  102  is a cupped shaped member that is engaged by the mounting ring  200 , through the use of the buttress blocks  202 . The mounting ring  202  is formed with the buttress blocks  202  extending downwardly, bearing against the walls of the pot  204 . The mounting ring  200  is typically molded from plastic and is configured with clusters of articulated fastening members  206  by which the loudspeaker driver  100  can be mounted to an associated baffle (not shown) in a housing of the loudspeaker system. The pot  204  of the frame  102  is typically formed of metal or other like material, and may have a magnetic pole incorporated in the lower most portion of the pot  204 , as illustrated in the figures.  
         [0024]    [0024]FIG. 3 is a rear perspective view of the loudspeaker driver  100  of FIG. 1. FIG. 3 shows the frame  102  of the loudspeaker and in particular, the mounting ring  200  having buttress blocks  202  arrayed about the underside of the mounting ring  200 . The buttress blocks  202  then connect to the pot  204  of the frame  102 . Also illustrated are the two hookup wires  104  extending outwardly from the loudspeaker driver  100 . In operation, the hookup wires  104  may be connected through integrated flat conductors (not shown) to the loudspeaker driver voice coil, shown in FIG. 4. Typically, a total of six buttress blocks  202  are arranged in a polar array around the underside of the mounting ring  200 . Each buttress block  102  is fitted closely against the wall of the pot  204  through the use of fasteners, adhesives or other securing mechanism. While the invention discloses the use of six buttress blocks  202 , one skilled in the art may use various numbers of blocks  202 , depending upon the size and shape of the loudspeaker driver  100 . Additionally, the design of the frame  102  may also be altered by one skilled in the art.  
         [0025]    In addition to the buttress blocks  202 , the mounting ring  200  is designed with fastening members  206  for attaching the frame  102  to baffles on the interior sides of an acoustic enclosure or housing (not shown), such as a bass-reflex system or an acoustic suspension system. The fastening members  206  include a flag-shaped lock tab  302  and a rotation stop post  304 , which serve to provide a snap-in attachment to the housing baffle. This snap-in fastening system can be implemented with metal springs or resilient plastic locking members. Various alternative configurations for attaching the loudspeaker driver frame  102  to the loudspeaker housing may be used and are known by those skilled in the art. Additionally, other mechanisms may be used for attaching the loudspeaker driver  100  to the housing. For example, the loudspeaker driver  100  could utilize a twist-lock mounting arrangement, involving the rotation of the speaker basket. Such a twist-lock mounting arrangement could be incorporated in conjunction with or as an alternative to the snap-in mounting described above. The loudspeaker driver may also be mounted to the housing with conventional screw hardware or other method known in the art.  
         [0026]    The mounting ring  200  is also formed with a stepped mounting strip  306  located between each pair of adjacent buttress  202  to further facilitate the mounting of the loudspeaker driver  100  in the loudspeaker housing. In the illustrated loudspeaker driver configuration, when the loudspeaker driver  100  is mounted against the rear baffle of the loudspeaker housing, the outer flange  308  of the surround suspension member  108  serves as a gasket, eliminating the need to provide a separate mounting gasket.  
         [0027]    Additionally, as illustrated by FIG. 3, a plurality of apertures  310  are created between the walls  312  of the pot  204 , the buttresses  202  and the mounting ring  200  to allow acoustic venting. By providing venting, the sound pressure from the rear of the diaphragm  106  can communicate to the interior of the housing of the loudspeaker system  100 , which is typically a bass-reflex or an acoustic suspension system.  
         [0028]    [0028]FIG. 4 is a central cross-section view of FIG. 1 taken along line a-a. FIG. 4 shows the pot  204  of the frame  102  supporting a cylindrical permanent magnet  400 . Positioned above the permanent magnet  400  is a top plate  402 . The permanent magnet  400  may be of any known magnet material commonly utilized in loudspeakers. The top plate  402  is typically made of a magnetically soft iron or steel but may be made from any other material suited to function as a top plate.  
         [0029]    As seen in FIG. 4, the diameter of both the permanent magnet  400  and top plate  402  is less than the diameter of the pot  204  and the frame  102 . Thus, a space  410  is formed between the interior side  404  of the pot  204  and the exterior sides  406  and  408  of the permanent magnet  400  and the top plate  402 , respectively. This space  410  is known as the “magnetic air gap.” A voice coil  411 , comprised of a former  412  wound with a voice coil wire  414  is then positioned within the magnetic air gap  410  and extends upwardly to join to the diaphragm  106  at its outer perimeter  416 . The voice coil former  412  and connecting diaphragm  106  are then supported in place by a surround suspension member  108  that is connected to the voice coil former  412 , as further described below. The voice coil  411  may also include a wrapper (not shown) that encases the voice coil former  412 . Thus, when reference is made to connecting or attaching the suspension member or any other speaker component to the voice coil former  412 , the attachment may be made either directly to the wrapper of the voice coil former  412  or directly to the voice coil former  412  when the former  412  is absent a wrapper. One skilled in the art will recognize that other configurations of the pot  204 , permanent magnet  400 , top plate  402  and voice coil  411  may be utilized without departing from the scope of the invention.  
         [0030]    In this embodiment, the diaphragm  106  is seen to have a concave shape; however, one skilled in the art will recognize the edge-driven diaphragm driver configuration can be used with a diaphragm  106  of other shapes, such as a convex diaphragm. The concave shape of diaphragm  106  is used to reduce the height of the loudspeaker driver  100  to provide an overall lower profile package that is often desired for use in smaller applications, such as loudspeakers designed for use in lap top computers. The diaphragm  106  may be made from any suitable material that provides rigidity, such as titanium, aluminum or other metal, or non-metal material, such as plastic or impregnated/reinforced paper, or various impregnated textiles.  
         [0031]    [0031]FIG. 5 is an enlarged view of the encircled region of FIG. 4 and provides a more detailed illustration of the configuration of the suspension member  108  relative to the voice coil  411  and diaphragm  106 . As described above, a voice coil  411 , which generally consists of a voice coil former  412 , wound with a voice coil wire  414 , is positioned in the magnetic air gap  410  between interior side  404  of the pot  204  of the frame  102  and the exterior sides  406  and  408  of the permanent magnet  400  and top plate  402 , respectively.  
         [0032]    The voice coil  411  then extends upward, in a direction parallel to the sides  406  and  408  of the permanent magnet  400  and top plate  402  and out of the magnetic air gap  410 . In this embodiment, the voice coil former  412  extends upward, to a point slightly above the mounting ring  200  of the frame  104 , to connect with the diaphragm  106  of the loudspeaker driver  100 . The voice coil former  412  attaches to the diaphragm  106  at its upper end  500 . The upper end  500  of the voice coil former  412  attaches to the underside of the outer perimeter edge  502  of the diaphragm  106  via an adhesive or other mechanism known in the art for mounting the diaphragm  106  to the voice coil former  412 . In this embodiment, the outer perimeter edge  502  is formed as a flat narrow flange; however, alternative perimeter edge  502  configurations may be used to attach the diaphragm  106  to the voice coil former  412 . For example, the diaphragm  106  may be formed with an annular downward-facing channel that could flank the upper end  500  of voice coil former  412  to facilitate locating and fastening operations.  
         [0033]    As illustrated by FIG. 5, the surround suspension member  108  is attached to the voice coil former  412  to support the voice coil  411  and diaphragm  106  and to maintain the alignment of the voice coil  411  in the magnetic air gap  410 . The surround suspension member  108  includes an inner edge  502 , which may include a short flange  504 , as shown. The inner edge  502  of the surround suspension member  108  is attached to the voice coil former  412  at a location beneath the point at which the diaphragm  106  attaches to the upper end  500  of the voice coil former  412 . The outer edge  506  of the surround suspension member  108  is attached to the mounting ring  200  via an outer flange  508  of the surround suspension member  108 . The mounting ring  200  includes an annular flat forward-facing suspension-attachment surface  510  for receiving the outer flange  508  of the surround suspension member  108 .  
         [0034]    The surround suspension member  108  is configured and arranged to provide a degree of constraint to the maximum excursions of the voice coil/diaphragm assembly in both the upward direction, which is not constrained otherwise, and in the lower direction, where the suspension acts to cushion the voice c oil  411  from the pot  204 . While the current configuration shows the suspension member having an arc subtending an angle of 180 degrees or slightly less, the invention could be practiced utilizing known alternate configurations of surround suspension member  108 , e.g., a series of concentric corrugations.  
         [0035]    In one embodiment of the loudspeaker driver  100 , the loudspeaker driver  100  may be approximately 31 mm in overall diameter by 14 mm in depth. The diaphragm  106  may be concave to a maximum depth of 2.6 mm. The exterior perimeter of the voice coil  411  and the concave portion of the diaphragm  106  are approximately 19 mm in diameter. The voice coil  411  is approximately 2.9 mm in length and the magnetic air gap space  410  is approximately 1.47 mm. The pot  204  is approximately 1.75 mm thick, the permanent magnet  400  is approximately 3.77 mm thick and the top plate  402  is approximately 1.4 mm thick.  
         [0036]    With the above set of loudspeaker driver dimensions, the voice coil former  412  is made to extend upwardly 4.3 mm beyond the voice coil  411 . The location designated for attachment of the surround suspension member  108  along the voice coil  411  is chosen to be 1.6 mm from the upper edge  500  of the voice coil former  500 , which in a speaker system of these dimensions would make the top of the arc of the surround suspension member  108  flush with the inner edge  502  of the diaphragm  106 . Proper selection of material of the surround suspension member  108  and its fastening location along the free region of voice coil former  412  act to cushion and isolate the diaphragm  106  and ensure that the voice coil  411  is constrained coaxially in the magnetic air gap  410  while it vibrates longitudinally. Thus, the voice coil  411  movement is maintained to a straight line and made free of rocking or other extraneous movement.  
         [0037]    Further, the clearance allowed for the excursion of the voice coil/diaphragm assembly in an assembly of the above dimensions is approximately 2.55 mm at two potential bottoming locations: (i) between the lower extremity of the voice coil former  412  and the floor of pot  204 ; and (ii) between the lower extremity of diaphragm  106  and top plate  402 . Thus, a maximum symmetrical excursion range of 5.1 mm peak-to-peak is provided.  
         [0038]    As a size efficiency factor, the excursion can be compared to the total thickness of the loudspeaker. For a hypothetical cylindrical loudspeaker of given diameter with a cone of equal diameter and a peak-to-peak excursion equal to the loudspeaker thickness, this factor would be 100%. That is, the volume of displaced air would equal the volume of the loudspeaker itself. In a loudspeaker driver  100  of the dimensions given above, this factor would be 5.1 mm/12 mm or 42.5%, compared to a percentage typically of less than 10% for conventional loudspeakers.  
         [0039]    The above loudspeaker dimensions are given by way of example only. One skilled in the art will recognize that the above configuration can be incorporated into speaker systems of various sizes and shapes and is not limited to the dimension described above, but may vary based upon the desired application.  
         [0040]    While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of this invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.