Abstract:
The present invention comprises an improved center pole having a distortion reduction cap and an improved method of coupling the cap to a speaker center pole. The speaker assembly comprises a distortion reduction cap and a cylindrical center pole having a gripping surface formed on an outer cylindrical surface of the center pole and a frustoconical recess on a top surface of the center pole. The cap is coupled to the center pole through the application of pressure on the cap to conform the cap to the center pole and to non-rotatably couple the cap onto the center pole by deforming a portion of the cap against the gripping surface. The distortion reduction cap is coupled to the center pole in a manner forming a corresponding fiustoconical portion mating with the frustoconical recess on the top surface of the center pole in a manner providing an air tight seal.

Description:
TECHNICAL FIELD  
       [0001]    This application is a continuation of copending application Ser. No. 09/277,639 filed on Mar. 26, 1999 which is a continuation-in-part of application Ser. No. 08/908,564 filed on Aug. 8, 1997, now abandoned. Copending application Ser. No. 09/277,639 and application Ser. No. 08/908,564 are hereby incorporated by reference. The present invention relates to improved audio speaker acoustics and more specifically to the elimination of distortion from a speaker through the use of an improved distortion reduction cap and center pole configuration and method of coupling the two.  
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Normal magnetic material has a magnetic hysteresis loop characteristic and the relation of magnetizing force and magnetic flux density is nonlinear. As a result, when magnetic flux of a voice coil passes through a center pole and a plate near an air gap, the magnetic reaction in the voice coil results in a distorted output signal from the speaker.  
           [0003]    A conventional speaker of the type contemplated by the present invention is illustrated in FIG. 1. The unit shown in FIG. 1 has a pole yolk  12  with an inverted T-cross section which has around its bottom an annular magnet  14  that is magnetized in the direction of its thickness. A top plate  18  rests on magnet  14  to form a magnetic gap with the peripheral wall of center pole  16  of pole yolk  12 . A voice coil  28  wound around a bobbin  30  is inserted into the magnetic gap. Bobbin  30  is supported on a frame  26  by a damper  24  that permits vibratory movement of bobbin  30 . A diaphragm  22  with a dust cover  20  is connected to bobbin  30 . The outer periphery of diaphragm  22  is supported by an edge portion  32  that is fixed to frame  26  by a gasket  34 . In order to make effective use of the magnetic flux in the gap, voice coil  28  is wound around bobbin  30  a length in the longitudinal direction of the coil which is greater than the magnetic gap link. Center pole  16  of pole yolk  12  is fitted with a cap  36  provided to reduce the distortion that is introduced into the coil current by the inductance of voice coil  28 . The operation of the speaker shown in FIG. 1 is as follows. When a current flows through voice coil  28 , either an upward or downward driving force acts on coil  28  depending upon the direction of the current flow. Since voice coil  28  is mobile, the driving force acting on voice coil  28  is transmitted to diaphragm  22  through bobbin  30 . As a result, diaphragm  22  pushes the air in front of it, creating sound waves.  
           [0004]    Various methods of eliminating the distortion described above have been attempted, such as covering a center pole with a copper cap as described in FIG. 1, and putting a copper ring around the center pole. The copper ring requires a higher level of manufacturing technique and tends to disturb the magnetic flux distribution in the speaker&#39;s air gap thus interfering with the output signal. The application of a copper cap covering the center pole of a speaker has been more successful but also has several drawbacks.  
           [0005]    The pole/cap configuration and processes used in the prior art for coupling the cap have not resulted in an easily manufactured assembly which performs well, particularly in high volume production environments. FIG. 2 is directed to one prior art method for coupling the cap described briefly in FIG. 1, to a speaker center pole to reduce the distortion introduced into the speakers voice coil due to inductance are shown. FIGS. 2 a  and  2   b  demonstrate different methods of coupling a distortion reduction cap to center pole  16  of pole yolk  12 . In both methods the cap must be formed on cap die press  40 . FIG. 2 a  shows the prior art method of coupling distortion reduction cap  46  with adhesives at  42 . Once cap  46  is formed by cap die press  40 , applicator  48  applies an adhesive, such as glue, within cap  46  which in turn is coupled onto center pole  16  of pole yolk  12  to form partial speaker assembly  50 . Use of an adhesive requires additional manufacturing steps to provide the correct amount of adhesive to ensure that center pole  16  receives an even coating to securely couple cap  46 . Distortion reduction cap  46  must also be properly coupled to center pole  16  to ensure no air gaps are formed between cap  46  and center pole  16 . Such gaps reduce the effectiveness of cap  46 .  
           [0006]    In order for distortion reduction cap  46  to provide maximum reduction in distortion there must not only be no air gaps between cap  46  and center pole  16  but cap  46  must also remain absolutely stationary. Adhesives used in the prior art are problematic because when subjected to varying temperatures and environmental conditions they can loosen and allow cap  46  to vibrate and move again creating air gaps which effect the distortion reduction performance of cap  46 . FIG. 2 b , at  44 , shows an alternate method found in the prior art for coupling a distortion reduction cap to a speaker center pole. The process begins with cap  52  being formed on cap die press  40 . Distortion reduction cap  52  is shown in cross-section and is identical to cap  46  with the exception of an annular inwardly extending lip  54 . Instead of using an adhesive to maintain the coupling between cap  52  and center pole  16  of yolk  12 , the coupling is instead maintained by forcing the lower portion of cap  52  into axial inwardly formed groove  56  within center pole  16 . The portion of cap  52  forced within groove  56  becomes annular inwardly extending lip  54 . This method is inadequate as it does not prevent cap  52  from rotating upon center pole  16  once retained in place, and may result in air gaps between cap  52  and center pole  16 . Vibration from sound waves and due to imperfect road conditions, if the speakers are used in automobiles, may cause such rotation which allows air gaps between cap  52  and center pole  16  to again reduce the effectiveness of distortion reduction cap  52 .  
           [0007]    Although not previously discussed, larger conventional type speakers of the type contemplated by the present invention use a center pole which includes a through hole through the center axis of the center pole. Another method for reducing distortion is to keep dust and debris from entering this chamber and affecting the diaphragm. A dust screen is typically attached to the pole yolk with an adhesive. Adhesives used in the prior art are problematic because when subjected to varying temperatures and environmental conditions they can loosen providing gaps around the edges of the screen or disengaging the screen altogether which will allow dust and other contaminants into the speaker affecting the diaphragm and resulting in increased distortion.  
           [0008]    Therefore, in light of the foregoing deficiencies in the prior art, the applicant&#39;s invention is herein presented.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention comprises an improved center pole speaker assembly having a distortion reduction cap and an improved method of coupling the cap to a speaker center pole. These and other advantages are provided by a speaker assembly comprising a distortion reduction cap and a cylindrical center pole having a gripping surface formed on an outer cylindrical surface of the center pole and a frustoconical recess on a top surface of the center pole. The distortion reduction cap is coupled to the center pole through the application of pressure on the cap to conform the cap to the center pole and to non-rotatably couple the cap onto the center pole by deforming a portion of the cap against the gripping surface. The distortion reduction cap is coupled to the center pole in a manner forming a corresponding frustoconical portion mating with the frustoconical recess on the top surface of the center pole.  
           [0010]    The present invention also provides a method of coupling a distortion reduction cap to a speaker center pole to reduce audio distortion comprising the following steps. Forming a distortion reduction cap. Forming a gripping surface on a center pole having a frustoconical recess on a top surface of the center pole wherein the gripping surface extends radially outwardly from the center pole. Positioning the distortion reduction cap over the center pole. Applying pressure on the distortion reduction cap to conform the distortion reduction cap to the center pole and non-rotatably couple the distortion reduction cap onto the center pole by deforming a portion of the distortion reduction cap against the gripping surface and deforming a portion of the distortion reduction cap forming a corresponding frustoconical portion of the distortion reduction cap mating with the frustoconical recess on the top surface of the column.  
           [0011]    These along with other advantages of the present invention will become more readily apparent from a reading of the detailed description taken in conjunction with the drawings and the claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a elevational view in partial cross section of a typical acoustic speaker;  
         [0013]    [0013]FIG. 2 illustrates the steps required in two prior art methods of coupling a cap with a speaker center pole;  
         [0014]    [0014]FIG. 3 illustrates the steps required in one of the preferred embodiments of the present invention for coupling a distortion reduction cap to a speaker center pole;  
         [0015]    [0015]FIG. 3A is a partial elevational view also in partial cross-section showing a pole/cap relationship which may be accomplished via the steps illustrated in FIG. 3;  
         [0016]    [0016]FIG. 3B illustrates various gripping surface configurations which may be applied to the center pole to secure a cap thereon;  
         [0017]    [0017]FIG. 4 illustrates the steps required in a second preferred embodiment of the present invention for coupling a distortion reduction cap to a speaker center pole;  
         [0018]    [0018]FIG. 4A is a partial elevational view also in partial cross-section showing a pole/cap relationship which may be accomplished via the steps illustrated in FIG. 4;  
         [0019]    [0019]FIG. 5 is an elevational view in partial cross-section illustrating a distortion reduction cap applicator tool which may be applied to coupling a distortion cap to a speaker center pole;  
         [0020]    [0020]FIG. 5A diagrammatically illustrates the steps of pole/cap coupling using the tool shown in FIG. 5;  
         [0021]    [0021]FIG. 6 is an elevational view in partial cross-section illustrating a distortion reduction cap applicator tool with frustoconical extension which may be applied to coupling a distortion cap to a speaker center pole; and  
         [0022]    [0022]FIG. 6A diagrammatically illustrates the steps of pole/cap coupling using the tool shown in FIG. 6;  
         [0023]    [0023]FIG. 7 is an elevational view in cross section of a center pole assembly of the present invention showing the specific features of the through hole; and  
         [0024]    [0024]FIG. 7A diagrammatically illustrates the steps for securing a screen within a speaker center pole through hole with the ring retainer.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    [0025]FIGS. 3, 3A and  3 B show the preferred embodiment of the present invention which consists of both improved distortion reduction cap  88  and the method of applying cap  88 . The process of manufacturing the pole/cap assembly of the invention in a first step forms distortion reduction cap  88  in cap die press  82 . Cap  88  is shown in both perspective and cross-section after exiting cap die press  82  at  81 . In the preferred embodiment, cap  88  is comprised of planar surface  110 , preferably circular in shape, having side wall  112  coupled to the periphery of planar surface  110  and extending from and perpendicular to planar surface  110 .  
         [0026]    Side wall  112  includes an axial flare or enlarged diameter portion  90  formed along or near the lower edge of side wall  112  opposite planar surface  110  and is essentially formed at a diagonal angle. If axial flare  90  is formed near the lower edge of side wall  112  as opposed to along the lower edge, side wall  112  will have two different inner diameters separated by axial flare  90  where the portion of side wall  112  furthest from planar surface  110  will be larger than the diameter for the portion of side wall  112  closest to planar surface  110 . Planar surface  110  may also include aperture  114  disposed through its center to provide improved sound and manufacturing characteristics. Axial flare  90  will eventually mate with an axial or outwardly extending grip pattern  92  which is formed on center pole  16  of pole yolk  12  by pattern roller  84 .  
         [0027]    The combination of center pole  16  and pole yolk  12  will also be referred to as center pole assembly  80 . Center pole assembly  80  is made up of a circular planar surface having a column extending outward which forms center pole  16 . Formed on and around center pole  16  is an axial griping surface  92  which may comprise an outwardly extending surface having one of several different patterns such as vertically oriented score lines or splines  94 , diagonal lines score  96  and  98 , or a cross-hatch pattern of score lines  100 , any of which may be formed on center pole  16  by a pattern roller  84  as these are illustrated in FIG. 3B. In the preferred embodiment either diagonal pattern  96  or  98  is used to provide the most effective gripping action to maintain cap  88  on center pole  16  by interference fit. Cross-hatch pattern  100  is also very effective but increases the amount of metal shavings which must be removed from center pole assembly  80  which would otherwise interfere with the intended reduction of distortion. The axial gripping surface  92  may be slightly raised from the side wall surface of center pole  16  in which cap  88  is eventually coupled. During coupling, axial flare  90  is stretched over raised axial gripping surface  92  forming stretched latching portion  102  as shown in FIG. 3A.  
         [0028]    After cap  88  is formed and center pole assembly  80  has received axial gripping surface  92 , cap  88  is placed on center pole  16  of center pole assembly  80  and inserted within cap applicator press  86 . The end result after operation of cap applicator press  86  is shown in more detail in FIG. 3A where cap  88  is coupled to center pole  16  with axial flare  90  stretched against and over axial gripping surface  92  with stretched latching portions  102  formed against center pole  16  to effectively grip the axial gripping surface  92 . The portion of cap  88  which is pressed against axial gripping surface  92  is forced to conform to the pattern so that the material cap  88  is fabricated from grips pattern  92 . FIG. 3A shows center pole  16  and cap  88  having axial flare  90  wherein the arrows “A” show the forces applied to cap  88  and axial flare  90  by cap applicator press  86  when being mounted to center pole  16 . Stretched latching portions  102  of cap  88  provide additional gripping of cap  88  to axial gripping surface  92  but also eliminates gaps which would otherwise be caused if axial flare  90  had simply been stretched downward vertically without being pressed horizontally against center pole  16 . Again, any such air gaps reduce the effectiveness of the distortion reduction properties of cap  88 .  
         [0029]    While the dimensions and materials used for cap  88  and center pole assembly  80  can vary depending on the size of the speaker which assembly  80  is to be used in and/or the specific electromagnetic effect desired, several dimensions and materials will now be described to ensure that one of ordinary skill in the art can practice the preferred embodiment of the invention as disclosed. In the preferred embodiment center pole assembly  80  is comprised of 1008 low carbon steel plated with zinc dichromate. Cap  88  is formed from copper sheets having a uniform thickness of approximately 0.03 mm. As shown in FIG. 3A the typical height  104  of cap  88  is approximately 10 mm with stretched latching portion  102  exceeding the width of axial gripping surface  92  at  108  by approximately 1-2 mm. The width of axial gripping surface  92  is approximately 2-4 mm. Axial gripping surface  92  is typically raised from the sidewall of center pole  16  by approximately 0.1-0.2 mm. To further reduce air gaps between cap  88  and center pole  16 , the outer diameter of center pole  16  is sized to be extremely close to the inner diameter of cap  88  to provide a secure and tight fit which becomes permanent once axial flare  90  has been stretched over and pressed against axial gripping surface  92 . Various high frequency response characteristics are obtainable by changing the intrinsic resistance and thickness of distortion reduction cap  88  and therefore cap  88  can be fabricated from a number of materials including but not limited to copper, anoxic copper, gold, silver, aluminum and various composites formed from these and other materials.  
         [0030]    Referring to FIGS. 4 and 4A, an alternate embodiment of the center pole assembly having a cap mounted thereto is shown with the process for coupling the cap to the center pole assembly. In an identical manner to that described in FIG. 3, cap  126  is formed on cap die press  120  and shown having an axial flare  134 . Cap  126  is once again placed on center pole  16  of pole yolk  12  wherein center pole  16  and pole yolk  12  are also referred to as center pole assembly  118 . The difference between the center pole assembly shown in FIG. 3 and center pole assembly  118  is that punch hole roller  122  places several indentations or scores  132  in an axial fashion about circumference of center pole  16 . FIG. 4A shows that in the preferred embodiment indentations  132  are triangular in shape and face downward, although many other shapes would be suitable. The profile of triangular indentations  132  shown at  138  demonstrates that indentations  132  form a ridge near the top of center pole  16  which then flares diagonally towards the surface of center pole  16  near the downwardly directed point of each triangular indentation  132 . Once cap  126  is placed onto center pole assembly  118 , the combination is then inserted within cap applicator press  124  which permanently couples cap  126  onto center pole assembly  118 . Arrows “A” show the direction of the forces applied to cap  126  and axial flare  134  which stretch axial flare  134  both downward vertically and inward horizontally such that stretched latching portions  136  cover and are forced to conform within triangular indentations  132  as shown, which prevent vertical upward and horizontal side movement of cap  26 .  
         [0031]    Referring to FIGS. 5 and 5A, the actual coupling of the cap to the center pole of the center pole assembly will be described in more detail. In order to properly stretch axial flare  152  of cap  150  over axial gripping surface  92  or over and within indentations  132 , shown in FIGS. 3A and 4A the cap applicator press must be equipped with cap applicator tool  160 . As illustrated in FIG. 5, tool  160  is comprised of housing  162  having an ejection piston  164  disposed through spring  166  and the top of housing  162  to provide a means for ejecting center pole assembly  80  once cap  150  is coupled to center pole  16 . Coupled to the bottom of applicator housing  162  is mold  168  having aperture  170  disposed through its center for receiving center pole  16  and cap  150 . Once cap  150  is positioned upon center pole  16  having axial gripping surface  92  or indentations  132 , center pole assembly  80  or  118  is then positioned beneath cap applicator tool  160  and aligned with aperture  170 . While not shown, a press or similar device then pushes center pole assembly  80  thereby forcing center pole  16  and cap  150  within aperture  170 . It is also contemplated that center pole assembly  80  is kept stationary while tool  160  is forced down upon cap  150  and center pole  16  to provide the effect. As cap  150  and center pole  16  travel within aperture  170 , spring loaded ejection piston  164  is forced upward causing compression of spring  166 . Once the pressure applied to force center pole assembly  80  into aperture  170  of cap applicator tool  160  is removed, the force being placed on ejection piston  164  by spring  166  causes ejection piston  164  to move downward to eject center pole assembly  80  from aperture  70 . The steps of pole/cap coupling are diagrammatically illustrated in FIG. 5A, using the tool of FIG. 5.  
         [0032]    [0032]FIG. 5 shows in cross-section the aperture in which cap  150  and center pole  16  are inserted within to seal and stretch cap  150  onto center pole  16  of assembly  80  or  118  respectively. Initially, aperture  170  has a diameter  142  which is larger than the outer diameter of cap  150 . As aperture  170  continues within mold  168 , a conical section is provided wherein the diameter begins to narrow, which in the preferred embodiment is at an angle of between 15° and 20° in relation to diameter  140 . After the conical portion, aperture  170  becomes constant having a diameter small enough to cause cap  150  to be stretched over and pressed against center pole  16  of center pole assembly  80 . By having the initial diameter  142  of aperture  170  greater than the outer diameter of cap  150  the initial alignment of center pole  16  and cap applicator tool  160  can be less accurate because axial angle  172  provides a mechanism for correcting the alignment and centering of cap  150  just prior to cap  150  and center pole  16  being driven within smaller diameter  140  to complete the coupling of cap  50  and center pole  16 .  
         [0033]    Referring to FIGS. 6 and 6A, an alternate preferred embodiment of the invention is shown. The coupling of the cap  250  is the same as in the previous embodiment except that the cap applicator tool  260  has a modified ejector piston  264  that has a frustoconical portion  265  extending downward from the center of the mating surface of the ejection piston  264 . The cap  250  is the same as the cap  150  of the previous embodiment but will be attached differently as follows. The coupling of the cap  250  to the center pole  216  of the center pole assembly  280  takes place in the same fashion as described in the previous embodiment except that the frustoconical portion  265  of the ejection piston  264  forces the center of the top surface  210  of the cap  250  to be stretched downward along the corresponding frustoconical indentation  267  of the center pole  216 . The cap  250  and center pole  216  are then ejected by the piston  264  in the same fashion as the previous embodiment. The resulting cap coupling has a better surface contact with the center pole  216  as more surface contact is available for the cap to contact with the center pole. The stretching of the top surface  210  of the cap  250  in combination with the stretching of the cap  250  over the center pole results in a much tighter and secure fit than with previous methods and also results in less chance of air gaps. Although not shown in the previous embodiments, the frustoconical indentation  267  is a standard feature on many of the center pole  216  designs. Accordingly, this embodiment requires only a modification of the original ejection piston  164  and is easily incorporated into the manufacturing environment in such that high volume production can be maintained. The tighter fit also makes the cap  250  more stationary and less susceptible to vibration or coming loose.  
         [0034]    Although not discussed, larger speakers have center pole assemblies with through holes extending through the longitudinal axis of the center pole. It is important that dust and other contaminants are kept from traveling up this passage where they can affect the diaphragm thus resulting in increased distortion and detrimentally affect the speaker performance. Referring now to FIGS. 7 and 7A, another alternate embodiment of the invention is shown. The cross-sectional view of the center pole  316  of pole yolk  312  shows a through hole  313 . Although it may be alternately comprised of a single diameter, the through hole  313  is preferably comprised of a first diameter  315  and a second larger diameter  317  such that a horizontal ledge  323  is formed on which a dust screen  390  can be supported within the through hole  313 . The first diameter  315  is herein shown as, but not limited to, an as-cast portion tapering in to the first diameter  315  near the bottom of the center pole  316 . The second diameter  317  is herein shown as, but not limited to, a counterbore having a second diameter  317  at the top of the center pole  316  which is slightly larger than that of the first diameter  315 . An annular groove  321  is preferably cut into the through hole  313  at the horizontal ledge  323 . The purpose of the annular groove  321  is to provide a feature that can house a retaining ring  391  and also to provide a wider horizontal ledge  323  to support the dust screen  390  in the through hole  313 . The groove  321  is preferably shaped crossectionally as an acute angle, having a horizontal annular flat surface  323  or ledge of a diameter larger than the second diameter  317  and an angled sidewall  325  tapering upward from the apex  327  formed by the flat surface and the angled sidewall until it intersects with the second diameter of the through hole  313 .  
         [0035]    As shown in FIG. 7A, a dust screen  390  having a diameter substantially equal to that of the horizontal ledge  323  of the annular groove  321 , is inserted down the through hole  313  to the horizontal ledge  323  of the annular groove  321  where it is able to reshape to its original size on the ledge. Although not shown, the dust screen  390  can be forced down the smaller through hole  313  using a press  364 . Simple presses of this type are known and one of ordinary skill in the art would be able to seat the dust screen  390  on the horizontal ledge  323  using a press. The dust screen  390  is held in place on the horizontal ledge  323  by a screen retaining ring  391 . The retaining ring  391  is preferably an annular ring of a which has a opening between its annular ends  393  which allows it to be compressed to a smaller diameter allowing the ring to be pressed through the through hole  313  to the annular groove  321 . The retaining ring  393  in its uncompressed state is preferably of a larger diameter than the annular groove  321  such that the ring will be compressibly retained in a manner preventing rotation or any movement of the ring or of the retained dust screen  390 . The insertion of the retaining ring  391  into the through hole  313  is preferably completed using press  364  (also used for seating the dust screen  390 ) which will force the retaining ring down the hole only until it reaches the annular groove. At that point the angled walls  325  of the annular groove  321  will enable the retaining ring  391  to seat itself into the annular groove. The retaining ring  391  attempts to return to its uncompressed condition when it encounters the acutely angled sidewall  325  of the annular groove  321  which results in a downward movement of the retaining ring until the ring abuts the dust screen  390  on the horizontal ledge  323  of the annular groove. As the retaining ring  391  is still in a compressed state, the retaining ring presses against the acutely angled sidewall  325  of the annular groove  321  which results in a downward force which securely retains the dust screen  390  in position on the horizontal ledge  323 . The embodiment is not limited to this particular configuration, as it includes any configuration using a press fit retainer and dust screen.  
         [0036]    The dust screen  390  prevents dust and other contamination from entering the through hole  313  of the center pole assembly  380  and thus preventing contamination of the diaphragm which may result in distortion of the speaker. The dust screen is held securely in place by the retaining ring  391  in a manner not affected by temperature or vibration. While the insertion of the dust screen  390  and ring retainer  391  is accomplished in a separate operation independent from the cap coupling operation, it is contemplated that the two could be combined to be accomplished at the same time by a modifying the ejector pistons  164 ,  264  of the previous embodiments to include a cylindrical extension which would fit into the through hole in a manner forcing the dust screen  390  and retaining ring  391  into the annular groove  321 .  
         [0037]    While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.