Abstract:
A loudspeaker and method of assembling same is disclosed in which the motor structure and frame are interconnected, the voice coil is initially secured within the magnetic gap of the motor by the lower suspension and then the diaphragm and surround are installed by first affixing the surround to a flange at the upper end of the frame so that the outer diameter of the surround is concentric to its inner diameter, and then inserting the lower end of the diaphragm within a pool of adhesive carried by a well structure mounted to the exterior surface of the voice coil such that the diaphragm is allowed to move in both a lateral direction and a vertical direction within the well structure while the adhesive cures, thus maintaining the original shape of the surround and substantially preventing misalignment of the voice coil within the magnetic gap of the motor during operation of the loudspeaker.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to loudspeakers, and, more particularly, to a method of assembling a loudspeaker in which deformation of the surround and tolerance stack-up which can create dynamic misalignment of the voice coil relative to the magnetic gap are substantially eliminated.  
         BACKGROUND OF THE INVENTION  
         [0002]    Loudspeakers generally comprise a frame, a motor structure, a diaphragm, a lower suspension or spider and an upper suspension or surround. In one common type of speaker, the motor structure includes a permanent magnet mounted between a top plate and a back plate, a pole piece centrally mounted on the back plate and a voice coil axially movable with respect to the pole piece. The voice coil includes a hollow, cylindrical-shaped former having an outer surface which receives a winding of wire.  
           [0003]    One end of the diaphragm is connected to the surround, which, in turn, is mounted to the upper end of the frame. The lower suspension or spider is connected at one end to a seat formed in the frame at a point between its upper and lower ends. The free ends of the diaphragm and spider are mounted to the voice coil and support it within the magnetic gap between the pole piece and top plate of the motor structure, with the former of the voice coil concentrically disposed about the pole piece. In some speaker designs, a dust cap is mounted to the diaphragm in position to overlie the voice coil and pole piece to protect them from contaminants.  
           [0004]    In the course of operation of a speaker of the type described above, electrical energy is supplied to the voice coil causing it to axially move relative to the pole piece and within the magnetic gap formed between the top plate and pole piece. The diaphragm, spider and surround move with the excursion of the voice coil and are intended to collectively maintain the voice coil concentric to the pole piece within the magnetic gap. Nevertheless, a pervasive problem associated with speaker operation involves misalignment of the voice coil which can create noise, distortion and/or speaker failure.  
           [0005]    Problems with voice coil misalignment can be attributed to different factors, some involving techniques for manufacturing speaker components and others relating to the method of assembling the speaker components. Currently, it is typical for a manufacturer of loudspeakers to purchase the surround and diaphragm as a pre-assembled unit from an outside vendor. Often the same vendor manufactures both parts, and it is presumed that such vendor can more efficiently interconnect the diaphragm and surround at its facility than can the speaker manufacturer. Unfortunately, it is not uncommon for the combined diaphragm-surround assembly to be shipped to the speaker manufacturer in such a way that the surround becomes deformed.  
           [0006]    In a conventional speaker assembly operation, the frame and motor structure are initially interconnected, and then the voice coil is secured within the magnetic gap of the motor by the lower suspension or spider. With the voice coil in position, the diaphragm-surround assembly is attached by first gluing the apex of the diaphragm along the outer surface of the former of the voice coil and then gluing the surround onto a flange at the upper end of the frame. The surround is allowed to “float” or move atop the flange as the glue dries.  
           [0007]    One problem created by this assembly operation is due to tolerance “stack-up,” or accumulation, in the components assembled prior to affixing the surround. As noted above, the motor, frame, spider and voice coil are all interconnected before attaching the diaphragm-surround assembly, and the dimensional variations of these elements within design tolerances may result in a lack of concentricity between the voice coil, and frame at the completion of the final assembly step. Further, the deformation of the surround may also result in a lack of concentricity between the outside diameter of the surround and its inside diameter.  
           [0008]    In theory, by allowing the surround to float or move along the flange at the upper end of the frame while its glue dries, problems with lack of concentricity due to tolerance stack-up and/or deformation of the surround are overcome. It has been found that this is not adequate in some applications, particularly high excursion speaker designs. The cross-sectional shape of the surround is a carefully engineered parameter in the overall speaker design, and substantially affects the excursion response of the loudspeaker particularly when the excursions are high. Once the surround has been deformed, it is unlikely to return to its original profile or shape, or cannot do so because of a lack of concentricity with the flange at the upper end of the frame. As a result, when a deformed surround is attached to the frame, one side or area of the surround is typically stretched or extended to some extent whereas another area is compressed. In response to movement of the voice coil in either direction, the area of the surround which was stretched during assembly reaches its limit of extension or compression before other areas of the surround. When one area of the surround extends to a greater or lesser extent than another area of the surround, it tends to tilt or twist with the movement of the voice coil, especially at high excursions. This, in turn, causes the diaphragm and voice coil to twist or tilt in the same fashion and can be characterized as dynamic misalignment. When the voice coil becomes misaligned with the magnetic gap of the motor structure by such tilting or twisting motion, the result is the creation of noise, distortion and potential speaker failure due to direct parts contact.  
           [0009]    In addition to the misalignment of the voice coil noted above, current assembly techniques may create an initial offset in a vertical direction. The connection between the diaphragm and voice coil is typically quite tight to maintain concentricity, and to ensure that a good bond is created in order to avoid a failure at the diaphragm-voice coil interface. Conventionally, the apex of the diaphragm is placed along the exterior of the voice coil against the spider or some other vertical reference point on the former of the voice coil, irrespective of the position of the surround. But since the surround and diaphragm are typically interconnected and assembled as a unit, as noted above, it is not uncommon for the surround to be displaced in a vertically upward or downward direction due to tolerance stack-up within the already assembly components, e.g. the motor structure, frame, spider and voice coil. As a result of such vertical displacement, the surround can be initially extended or depressed and will not assume its desired vertical profile after the assembly operation is completed.  
         SUMMARY OF THE INVENTION  
         [0010]    It is therefore among the objectives of this invention to provide a loudspeaker, and a method of assembling same, in which dynamic misalignment of the voice coil with the magnetic gap of the motor structure is substantially eliminated, and the incidence of noise and distortion is reduced.  
           [0011]    These objectives are accomplished in a method of assembling a loudspeaker in which the motor structure and frame are interconnected, the voice coil is initially secured within the magnetic gap of the motor by the lower suspension and then the diaphragm and surround are installed by first affixing the surround to a flange at the upper end of the frame so that its outer diameter of the surround is concentric to its inner diameter, and then inserting the lower end of the diaphragm within a pool of adhesive carried by a well structure mounted to the exterior surface of the voice coil such that the diaphragm is allowed to move in both a lateral direction and a vertical direction within the well structure while the adhesive cures.  
           [0012]    This invention is predicated on the concept of accommodating both deformation of the surround and tolerance stack-up within elements of the loudspeaker while permitting the surround to assume as close to its original, design shape and position within the speaker as possible. With respect to the shape of the surround, in the presently preferred embodiment a ring is formed in the flange at the upper end of the frame having a diameter which is equal to the original outside diameter of the surround. Because the inner diameter of the surround is constrained by its connection to the diaphragm, affixing the outer diameter of the surround to the frame in a position against the ring tends to cause the surround to assume its original shape with its inner and outer diameters concentric to one another.  
           [0013]    Tolerance stack-up is accommodated by the manner in which the diaphragm is secured to the voice coil. In one presently preferred embodiment, a diaphragm structure is provided which comprises an upper diaphragm mounted to the surround and a lower diaphragm having the general cross-sectional shape of a “W” with an outer section connected to the surround and an inner section mounted to the upper diaphragm. A protrusion is formed at the juncture of the inner and outer sections of the lower diaphragm. A sleeve formed with an adhesive trough or well is attached to the outer surface of the former of the voice coil in position so that the protrusion of the lower diaphragm can be inserted within the interior of the well. The well has a bottom wall connected to a pair of opposed side walls which are spaced from one another in a lateral direction and extend generally vertically upwardly from the bottom wall. Upon assembly of the diaphragm and surround, the surround is affixed by adhesive against the ring on the flange at the upper end of the frame and then the protrusion of the lower diaphragm is inserted within a pool of adhesive located within the well of the sleeve carried by the voice coil. The protrusion of the lower diaphragm is allowed to move both in a lateral direction and in a vertical direction within the well before the adhesive cures to account for tolerance stack-up within the components of the speaker in each of the lateral and vertical directions.  
           [0014]    In an alternative embodiment, a standard diaphragm is employed having an upper end connected to the surround and a lower end insertable within the well structure of a sleeve mounted to the voice coil. The same lateral and vertical adjustment of the position of the lower end of the diaphragm within the well is provided as described above, and therefore problems of lack of concentricity between the surround, diaphragm and voice coil created by tolerance stack-up are substantially eliminated. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0015]    The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings, wherein:  
         [0016]    [0016]FIG. 1 is an elevational view, in partial cross section, of a speaker having one embodiment of the upper and lower diaphragm construction of this invention;  
         [0017]    [0017]FIG. 2 is an enlarged view of the connection between the lower diaphragm, lower suspension and the voice coil depicted in FIG. 1; and  
         [0018]    [0018]FIG. 3 is a partial view of a loudspeaker as depicted in FIG. 1, except of an alternative embodiment of the connection between a single diaphragm and the voice coil. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    Referring now to FIGS. 1 and 3, a loudspeaker  10  is illustrated which is identical in each embodiment except for the inclusion of a different diaphragm construction as described in detail below The elements of speaker  10  common to the embodiments of FIGS. 1 and 3 include a motor structure  12 , a frame  14  mounted to the motor structure  12 , a lower suspension or spider  18  and an upper suspension or surround  20 . Conventionally, the motor structure  12  includes a top plate  22  and a back plate  24  which are spaced from one another and mount a permanent magnet  26  therebetween. A vented pole piece  30  is integrally formed with and extends upwardly from the back plate  24  into a central bore  28  formed in both the magnet  26  and top plate  22 . A magnetic gap is formed between the top plate  22  and the pole piece  30 , as shown. A voice coil  32  is also provided which includes a hollow, cylindrical-shaped former  34  having an inner surface  35  and an outer surface  37  which receives a wire winding  36 . The former  34  is concentrically disposed about the pole piece  30 , and the voice coil  32  is axially movable within the magnetic gap during operation of the speaker  10 .  
         [0020]    For purposes of the present discussion, the terms “top” or “upper” refer to a location or direction toward the uppermost part of the loudspeaker  10  in the orientation as it is depicted in the FIGS., whereas the terms “bottom” or “lower” refer to the opposite direction. Additionally, the terms “inner” or “inwardly” refer to a direction toward the center of the loudspeaker  10  as shown in the drawings, while the terms “outer” or “outwardly” refer to a direction radially outwardly from the center of the loudspeaker  10 .  
         [0021]    With reference initially to FIGS. 1 and 2, in one presently preferred embodiment the voice coil  32  is held in place with respect to the pole piece  30  by the spider  18 , the surround  20  and a two piece diaphragm construction which includes an upper diaphragm  40  and a lower diaphragm  42 . The upper diaphragm  40  is generally circular in shape, and slightly tapered or arcuate in cross section from its outer edge  44  toward the center thereof The outer edge  44  of the upper diaphragm  40  is mounted by adhesive to the upper surface of the inner edge  48  of the surround  20 . As described in more detail below, the opposite, outer edge  50  of the surround  20  is connected to a flange  51  at the upper end  52  of the frame  14 .  
         [0022]    The lower diaphragm  42  is in the general shape of a “W” in cross section, including a tapered outer section  54  integrally formed with an inner section  56 . The outer section  54  of the lower diaphragm  42  is connected at one end by adhesive to the lower surface of the inner edge  48  of the surround  20 , and it tapers inwardly to form a protrusion  58  at the juncture with the inner section  56 . As depicted in FIGS. 1 and 2, the inner section  56  of the lower diaphragm  42  has a substantially frusto-conical cross section defined by a generally planar top wall  60  and a tapered side wall  62 . The tapered side wall  62  of the inner section  56  meets with the outer section  54  to form protrusion  58 , and the top wall  60  of the inner section  56  is affixed by adhesive to the underside of the upper diaphragm  40 .  
         [0023]    The lower diaphragm  42  is mounted to the voice coil  32  by a sleeve  64  in position so that the inner section  56  of the lower diaphragm  42  overlies the hollow former  34  of the voice coil  32 . In the presently preferred embodiment, the sleeve  64  is essentially a cylindrical-shaped member, formed of light weight but relatively stiff plastic or the like, which is mounted by adhesive to the outer surface  37  of the former  34 . The upper end of the sleeve  64  includes an annular trough or well  66  having a bottom wall  68  and opposed side walls  70  and  72 . The lower end of the sleeve  64  is formed with a generally horizontally extending platform  74 . The spider  18  is adhesively mounted between a seat  15  formed in the frame  14  and the platform  74  at the lower end of sleeve  64 . The protrusion  58  formed at the juncture of the outer section  54  and inner section  56  of the lower diaphragm  42  is received within and adhesively mounted to the well  66  at the top of the sleeve  64 , as described more fully below.  
         [0024]    With reference to FIG. 3, an alternative embodiment of this invention is shown which includes a single diaphragm  90  having an upper end  92  connected to the inner edge  48  of the surround  20 , and a lower end  94 . The outer edge  50  of the surround  20  abuts an annular ring  96  formed in or connected to the flange  51  at the upper end  52  of the frame  14 , as described more fully below. Preferably, a sleeve  98  formed with an adhesive trough or well  100  is mounted to the outer surface  37  of the former  35  of voice coil  32  so that the well  100  is located in a position to receive the lower end  94  of the diaphragm  90 . The well  100  is formed with a bottom wall  102  connected to a pair of side walls  104  and  106  which are laterally spaced from one another and extend generally vertically outwardly from the bottom wall  102 .  
         [0025]    Method of Assembly  
         [0026]    The method of assembly of the speaker  10  is essentially the same for each of the embodiments depicted in the FIGS. Initially, the frame  14  and motor structure  12  are interconnected in the orientation shown in FIG. 1. In particular, the lower end of the frame  14  rests on the top plate  22  of the motor structure  12  and is secured in place by screws, rivets or similar fasteners (not shown). The sleeve  64  of FIGS. 1 and 2, or the sleeve  98  of FIG. 3, is glued or otherwise permanently connected to the outer surface  37  of the former  35  of voice coil  32  so that the adhesive well  66  of sleeve  64  and the adhesive well  100  of sleeve  98  are positioned as shown.  
         [0027]    The next step in the assembly operation is to secure the voice coil  32  in position within the magnetic gap of the motor structure  12  concentric to the pole piece  30 . In the embodiment of the speaker  10  depicted in FIGS. 1 and 2, the inner end of the spider  18  is secured by adhesive to the bottom surface of the platform  74  of sleeve  64 . Alternatively, the inner end of the spider  18  is mounted by adhesive to the bottom wall  102  of the adhesive well  100  formed in the sleeve  98  of the speaker  10  depicted in FIG. 3. With the inner end of the spider  18  secured to the voice coil  32 , a gauge or fixture (not shown) is inserted along the inner surface  35  of the voice coil former  34 . The gauge is intended to contact the pole piece  30  of the motor structure  12  and center the voice coil  32  with respect to the pole piece  30  and within the magnetic gap between the pole piece  30  and top plate  22 . The voice coil  32  is moved vertically downwardly into position relative to the pole piece  30 , until the outer edge of the spider  18  rests within the seat  15  formed in the frame  12 , when it is adhesively connected. Even if the voice coil  32  and spider  18  are somewhat non-concentric relative to the frame  14 , concentricity between the voice coil  32  and pole piece  30  is ensured by the gauge and the seat  15  of the frame  14  is sufficiently wide to allow the outer edge of the spider  18  to adhesively connect thereto regardless of a lack of precise concentricity.  
         [0028]    As described above, it has been found that difficulties often arise during the final stages of speaker assembly when the diaphragm and surround are mounted in place. In particular, deformation of the surround  20  resulting from problems with shipment or otherwise, and tolerance stack-up within the already assembled motor structure  12 , frame  14 , voice coil  32  and spider  18 , both can contribute to a lack of concentricity between elements of the speaker  10 . These problems are addressed by method of assembly and construction of the connections between the surround  20  and frame  14 , and between the diaphragm  42  or  90  and the voice coil  32 .  
         [0029]    With reference to FIGS. 1 and 2, the upper end  52  of the frame  14  has a flange  51  formed with a vertically upwardly extending ring  53 . The ring  53  has a diameter which is equal to the outside diameter of the outer edge  50  of surround  20 , according to the original design of the surround  20 . Similarly, the flange  51  at the upper end  52  of frame  14  in the embodiment of the speaker  10  illustrated in FIG. 3 has an annular ring  96  whose diameter is equal to the outside diameter of the outer edge  50  of the surround  20 . In each embodiment, the surround  20  is glued to the flange  51  so that the outside diameter of its outer edge  50  abuts either the ring  53  of FIGS. 1 and 2 or the ring  96  of FIG. 3. This forces the surround  20  to assume its original shape, at least along the outside diameter.  
         [0030]    Although not required in accordance with the teachings of this invention, it is preferable to mount the diaphragms  42 ,  40  and the diaphragm  90 , to the surround  20  before either are connected to other elements of the speaker  10 . This mounting step can be done by the supplier of the diaphragms  40 ,  42  or  90  and the surround  20 , or by the speaker manufacturer. Fixtures or other assembly devices are employed to make certain that the connection between the surround  20  and the diaphragms  40  and  42  of FIGS. 1 and 2, and between the surround  20  and the diaphragm  90  of FIG. 3, are precise and do not change the original inner diameter shape and dimension of the surround  20 . In either case, the inside diameter of the inner edge  48  of surround  20  is maintained in its original shape by the rigid material forming the diaphragms  42 ,  90 . As such, once the surround  20  is forced to assume its original outside diameter as described above, it is believed that any deformities in the original shape of the surround  20  which may have been present at the time of assembly are substantially eliminated.  
         [0031]    With the surround  20  in position against the ring  53  or the ring  96  atop the flange  51  at the upper end  52  of frame  14 , the diaphragms  42  or  90  are then secured to the voice coil  32 . In the embodiment of FIGS. 1 and 2, the protrusion  58  formed at the juncture of the outer section  54  and inner section  56  of inner diaphragm  42  is received within a pool of adhesive  112  within the well  66  of the sleeve  64 . Similarly, the lower end  94  of diaphragm  90  is placed into a pool of adhesive  114  within the well  100  of the sleeve  98  in the embodiment of FIG. 3. In either case, the lateral spacing between the side walls  70 ,  72  of well  66  and between the side walls  104 ,  106  of well  100  allow for movement of the diaphragms  42  and  90 , respectively, in the lateral direction. Further, since the side walls  70 ,  72  of well  66  and side walls  104 ,  106  of well  100  extend vertically upwardly from their respective bottom walls  68  and  102 , vertical movement of the diaphragms  42  and  90  is permitted within the wells  66  and  100 . Consequently, before the adhesive within the adhesive pools  112  and  114  cures, the lower end of each of the diaphragms  42  and  90  is allowed to move in both the lateral direction and the vertical direction to account for tolerance stack-up in the previously assembled elements of the speaker  10 , e.g. the motor structure  12 , frame  14 , voice coil  32  and spider  18 . This ensures that the surround  20  assumes as close to its original shape and position within the speaker  10  as possible.  
         [0032]    While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof.  
         [0033]    For example, the rings  53  and  96  shown as being integrally formed in the flange  51  at the upper end  52  of the frame  14 . It should be understood that a separate annular element or guide could be releasably or permanently mounted to the flange, such as a gasket or the like, to provide a surface against which the outer edge  50  of the surround  20  could rest in order to assure its original outside diameter. Alternatively, a ring or other element could be located along the flange  51  at the upper end  52  of the frame  14  in position to engage the outer portion of the interior of surround  20 , designated by the reference number  116  in FIG. 3 for example, instead of contacting the outer edge  50 . This would also serve to force the surround  20  to assume the original shape and dimension of its outside diameter.  
         [0034]    Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.