Abstract:
A cone suspension is for mounting a speaker cone to a housing. The cone suspension has an inner periphery supporting the speaker cone, an outer periphery mounted to the housing, and a resilient central portion extending between the inner periphery and the outer periphery. In cross section, the resilient central portion is separated from a base plane extending between the inner periphery and the outer periphery, and has a central apex spaced from the inner periphery and the outer periphery and spaced from the base plane by a selected height. The inner periphery and the outer periphery are separated by a selected width. The selected height is substantially greater than ½ of the selected width.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention is related to a loudspeaker cone suspension geometry for reducing non-linear distortion in loudspeakers.  
         BACKGROUND OF THE INVENTION  
         [0002]    The construction and operation of an electro-dynamic loudspeaker is well known in the art. It is well known that such loudspeakers exhibit non-linear distortion for various reasons, including: the displacement dependent compliance of cone suspensions and displacement dependent motor parameters, such as force factor “Bl” or voice coil inductance. The inventor has discovered that shape of a cone suspension contributes to distortion in the output of the loudspeaker.  
           [0003]    There is a need for a speaker cone suspension (surround) which is capable of reducing non-linear distortion, particularly in low frequency, high power sub-woofers having large cone displacements.  
         SUMMARY OF THE INVENTION  
         [0004]    In one aspect, the present invention provides a cone suspension with a semi-elliptical cross-section. The cone suspension creates less distortion in the sound produced by the loudspeaker in response to an audio signal that is used to displace the loudspeaker&#39;s speaker cone.  
           [0005]    In additional embodiment, cone suspensions with paraboloic and triangular cross-sections are provided.  
           [0006]    In another embodiment, one or more rib elements is added to the cone suspension to decrease its rigidity thereby reducing the formation of wrinkles in the suspension when the speaker cone is displaced. Such wrinkles contribute to distortion in the output of the loudspeaker and reducing them correspondingly reduces the distortion. Such rib elements may be provided on a cone suspension with a semi-circular, semi-elliptical, triangular or semi-parabolic cross section, or with another shape.  
           [0007]    An object of an aspect of the present invention is to provide an improved loudspeaker.  
           [0008]    In accordance with this aspect of the present invention, there is provided a loudspeaker comprising a housing; a speaker cone for displacing a volume of air; and, a cone suspension mounting the speaker cone to the housing. The cone suspension has an inner periphery supporting the speaker cone, an outer periphery mounted to the housing, and, a resilient central portion extending between the inner periphery and the outer periphery. In cross section, the resilient central portion is separated from a base plane extending between the inner periphery and the outer periphery, and has a central apex spaced from the inner periphery and the outer periphery and spaced from the base plane by a selected height. The inner periphery and the outer periphery are separated by a selected width. The selected height is substantially greater than ½ of the selected width.  
           [0009]    An object of a second aspect of the present invention is to provide an improved a cone suspension for a loudspeaker  
           [0010]    In accordance with this second aspect of the present invention, there is provided a cone suspension for mounting a speaker cone to a housing. The cone suspension has an inner periphery supporting the speaker cone, an outer periphery mounted to the housing, and a resilient central portion extending between the inner periphery and the outer periphery. In cross section, the resilient central portion is separated from a base plane extending between the inner periphery and the outer periphery, and has a central apex spaced from the inner periphery and the outer periphery and spaced from the base plane by a selected height. The inner periphery and the outer periphery are separated by a selected width. The selected height is substantially greater than ½ of the selected width.  
           [0011]    Further aspects of the present invention are illustrated and described in the following description and the attached drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, which show preferred embodiments of the present invention, and in which:  
         [0013]    [0013]FIG. 1 illustrates a graph of displaced air volume as a function of speaker cone displacement, for an ideal case speaker cone suspension, a speaker cone suspension with a semi-circular cross-section and a speaker cone suspension with a semi-elliptical shaped cross-section;  
         [0014]    [0014]FIG. 2 a  illustrates a series of graphs which shows the expansion/contraction, surface point deviation and linearity characteristics of a speaker cone suspension with a semi-circular cross-section;  
         [0015]    [0015]FIG. 2 b  illustrates a cross-sectional view of a speaker cone and speaker cone suspension with a semi-circular cross-section;  
         [0016]    [0016]FIG. 3 a  illustrates a series of graphs which show the expansion/contraction, surface point deviation and linearity characteristics of a first speaker cone suspension in accordance with the present invention;  
         [0017]    [0017]FIG. 3 b  illustrates a cross-sectional view of a speaker cone and the speaker cone suspension of FIG. 3 a;    
         [0018]    [0018]FIG. 4 illustrates a series of graphs which show the expansion/contraction, surface point deviation and linearity characteristics of a second speaker cone suspension in accordance with the present invention;  
         [0019]    [0019]FIG. 5 illustrates a series of graphs which show the expansion/contraction, surface point deviation and linearity characteristics of a third speaker cone suspension in accordance with the present invention;  
         [0020]    [0020]FIG. 6 a  illustrates a perspective view a fourth speaker cone suspension in accordance with the present invention;  
         [0021]    [0021]FIG. 6 b  illustrates a perspective view from the side for the speaker cone suspension shown in FIG. 6 a;    
         [0022]    [0022]FIG. 7 illustrates a cross-sectional view of a rib element of the speaker cone suspection of FIG. 6 a;    
         [0023]    [0023]FIG. 8 illustrates a cross-sectional view of a semi-elliptically shaped rib element on the surface of the speaker cone suspension of FIG. 6 a; and    
         [0024]    [0024]FIGS. 9 a,    9   b  and  9   c  illustrate alternative rib element structures according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    In loudspeakers, air is displaced by the movement of both the speaker cone and the speaker cone suspension, which is used to mount the speaker cone to the loudspeaker housing. In conventional speakers, the surface area of the speaker cone suspension is relatively small in comparison to the area of the cone. As the speaker is operated, cone movement results in the displacement of a main volume of air. This movement of the cone is also transferred to the cone suspension, which displaces a secondary volume of air. Consequently, the total amount of displaced air in an operational speaker is due the movement of both the cone suspension and the cone itself. In the case of conventional speakers, the secondary volume of air displaced by the cone suspension is relatively negligible in comparison to the main volume of air generated by the speaker cone. However, in high power, low frequency sub-woofer type speakers that have large cone displacements, the cone suspension area is increased to permit larger displacement of the speaker cone. This increase in cone suspension area results in a corresponding increase in the secondary volume of air displaced by the cone suspension during the operation of the speaker. Consequently, the secondary volume of air may no longer be negligible in comparison to the main volume of air displaced by the speaker cone. Any non-linearity in the displaced secondary volume of air will introduce undesirable non-linear distortion to the speaker&#39;s audio output.  
         [0026]    Reference is first made to FIG. 1. Graph  10  shows the relationship between the displacement of air volume V as a function of the displacement X of a speaker cone. It will be appreciated that the displacement of air volume V is due to the displacement of air created by both the speaker cone and the cone suspension. It will also be appreciated, that as the speaker cone moves, the cone suspension also moves by expanding and contracting in synchronous to the motion of the cone to which it is attached.  
         [0027]    Ideally, it is desirable to have a linear relationship between the displacement of air volume V and the displacement of the speaker cone X, as illustrated by line  12 . As the speaker cone is displaced, a linear increase in displaced volume of air is observed. In practice, however, this ideal is not achieved, particularly for large cone displacements X.  
         [0028]    Line  14  illustrates the displacement of air volume V as a function of the displacement of the speaker cone X, for a cone suspension having a semi-circular cross-section. Over a narrow region  18 , between points  22  and  23  there is a linear relationship between the displaced volume of air V and the speaker cone displacement X. Within this region  18 , a relatively small speaker cone displacement X from the rest position  20  i.e. X=0 the displaced volume of air (main volume and secondary volume) has a substantially linear relationship approximating to the ideal relationship  12 . As the speaker cone displacement X increases (in the direction of arrow A or A) beyond the boundary of region  18  the displaced volume of air V varies non-linearly.  
         [0029]    Line  16  illustrates the displacement of air volume V as a function of the displacement of the speaker cone X for a cone suspension having a semi-elliptical cross-section. Line  16  illustrates that a cone suspension with a semi-elliptical cross-section has a wider linear region  26  (between points  28  and  29 ) in which the relationship between the displaced volume of air V is substantially linear with the speaker cone displacement X. As illustrated in FIG. 1, the displaced volume of air as a function of the speaker cone displacement, defined by  16 , has a linear relationship, wherein linearity is maintained for much larger amounts of speaker cone displacement. As the speaker cone displacement increases (direction of Arrow A and A′) beyond the boundary of the linear region, defined by  28  and  29 , the generated volume of air varies non-linearly as a function of the speaker cone displacement.  
         [0030]    [0030]FIG. 1 illustrates that at some point, the displacement X of the speaker cone will produce a non-linear change in the volume of displace air V. This non-linearity produces distortion. FIG. 1 also illustrates that changing the cross-sectional geometry of the cone suspension can affect the linearity of the speaker and the amount of distortion produced by the speaker as a whole may be reduced. As previously mentioned, the non-linear secondary volume of air displaced by the cone suspension produces this distortion. Therefore, by changing the cone suspension cross-section, the linearity of the displaced volume of air V (which includes both the primary and second volumes of air) as a function of speaker cone movement is extended.  
         [0031]    [0031]FIG. 2 a  illustrates a series of analysis graphs  34 ,  36 ,  38  illustrating the mechanical movement properties of a speaker with a cone suspension that has a semi-circular cross-section. These graphs  34 ,  36 ,  38  are explained with the aid of FIG. 2 b  which shows a cross-sectional view of a speaker cone  42  and a cone suspension  40  with a semi-circular cross-section. The graphs  34 ,  36 ,  38  define the behavior and performance of the cone suspension  40  as a function of the speaker cone  42  displacement. Graph  34  shows how the physical points on the surface  40  (FIG. 2 b ) of the cone suspension cross-section  46  (FIG. 2 b ) are displaced as speaker cone  42  (FIG. 2 b ) moves in the direction of arrows B and C. Curve  50  of graph  34  shows the cone suspension cross-section  46  at rest position. Contour  52  intersects curve  50  at a center point  54  on the surface of the cone suspension  40  at this rest position. The center point  54  is also shown in FIG. 2 b  at  56 . Point  56  is part of a circular line connecting the midpoints of the cross-section of the cone suspension around its circumference. The center point  54  moves along contour  52  as the cone suspension moves from the rest position. For example, as the speaker cone  42  moves in the direction of arrow C by a given displacement, center point  54  moves along contour  52  to point  62  on curve  64 . Curve  64  illustrates that the cross-section of the cone suspension has contracted. Further displacement of cone  42  in the direction of arrow C will continue to contract the cross-section of the cone suspension  40 , as shown in curves  66  and  68  for example.  
         [0032]    Conversely, as the cone  42  moves in the direction of arrow B by a given displacement, center point  54  moves along contour  52  to point  72  on curve  74 . The cross-section of the cone suspension has expanded and will continue to do so as the cone  42  further moves in the direction of arrow B. The same explanation applies to other points  78 ,  80  on the surface of the cone suspension at rest position. These points  78 ,  80  will contract and expand along contours  84  and  86  respectively.  
         [0033]    Graph  36  illustrates the relative radial displacement of different points on the surface of the cone suspension  40  relative to their rest positions. Relative deviation of these points occur as the speaker cone  42  is displaced when driven by an audio source (e.g. audio amplifier). Graph  36  shows two deviation limits  90 ,  92  marked by 10% and −10%. A center horizontal line  94  located between the two deviation limits  90 ,  92  identifies a zero deviation position corresponding to the speaker cone  42  in the rest position. Vertical range line  96  corresponds to the point  56  (FIG. 2 b ) at the center of the surface of the cone suspension  40 . The intersection point  98  of the vertical range line  96  with the center horizontal line  94  indicates no deviation or movement of this point when the speaker cone  42  and corresponds to the cone  42  being in the rest position. Vertical range line  96  indicates the range of deviation of point  56  (FIG. 2 b ) when cone  42  is displaced by an audio source. As the speaker cone  42  moves in the direction of arrow B, point  56  (FIG. 2 b ) deviates towards the 10% deviation limit  90 . Similarly, as the speaker cone  42  moves in the direction of arrow C, point  56  (FIG. 2 b ) deviates towards the −10% deviation limit  92 . Therefore, vertical line  96  provides a measure of how much movement or deviation point  56  undergoes during the speaker cone  42  displacement. For point  56 , vertical line  96  shows a relatively symmetrical deviation of ±8% between the deviation limits  90 ,  92 . It will be appreciated that the same result applies to all points on the cone suspension  40  circumference, which are located at the center of the surface of the cone suspension  40  (see dotted line  56 , FIG. 2 b ). Vertical lines of graph  36  of FIG. 2 a  represent maximum deviation range in both directions achievable during cone movement through its range of excursion. Maximum deviation shown by graph  36  may not necessarily occur with maximum cone displacement.  
         [0034]    Vertical lines  100  and  102  correspond to points  78  and  80  on cone suspension  40 . As indicated by lines  100  and  102  respectively, points  78  and  80  do not undergo the same range of deviation during movement of speaker cone  42 . For example, vertical line  102  shows that point  80  deviates less in the direction of deviation limit  92 , which corresponds to the contraction of the cone suspension  40  as the speaker cone  42  moves in the direction of arrow C. Also, point  80  deviates less in the direction of deviation limit  90 , which corresponds to the expansion of cone suspension  40  as the speaker cone  42  moves in the direction of arrow B.  
         [0035]    These variations in the deviation of points on the surface of the cone suspension  40  are determined in order to predict the occurrence of wrinkles, which occur on the surface of the cone suspension  40 . These wrinkles produce audible distortion and must be accounted for in the cone suspension design process. As is described below, one embodiment of present invention provides a plurality of rib elements to the structure of the cone suspension for reducing wrinkles.  
         [0036]    Graph  38  illustrates the relationship between the deviation (or change) in displaced air volume (ΔV represents the deviation in displaced air volume—not the displaced air volume) indicated at  106 , and speaker cone displacement X, indicated at  108 . Curve  110  shows that the deviation in displaced air volume ΔV no longer remains zero as the speaker cone displacement increases. As the speaker cone displacement increases past points  112  and  114 , the deviation in displaced air volume ΔV is no longer zero. Consequently, only for a specific linear range  116  of speaker cone displacement X does the deviation in displaced air volume ΔV behave linearly. Outside the linear range  116  any non-linearity produces distortion at the speaker output. As previously indicated, the amount of introduced distortion depends on the ratio of the cone suspension area to the speaker cone area.  
         [0037]    Reference is next made to FIGS. 3 a  and  3   b.  FIG. 3 b  illustrates the cross-section of a first embodiment of a speaker cone suspension  170  made according to the present invention. Cone suspension  170  has a semi-elliptical cross-section with a height  172  that corresponds to half the value of the major axis for the full elliptical shape, which would have otherwise been formed by completing the semi-elliptical shape of the cone suspension  170 . The semi-elliptical cone suspension  170  also has a half width dimension  174  which corresponds to half the value the minor axis of the full elliptical shape which would have otherwise been formed by completing the present semi-elliptical shape.  
         [0038]    It has been found that the distortion produced by a speaker having a semi-elliptical cone suspension, such as cone suspension  170 , is less than that produced by a speaker with a semi-circular cone suspension when the height  172  exceeds half of width  174 . The benefit of reduced distortion has been found in semi-elliptical cone suspension where the ratio of the height to half the width is between 1.1 to 1.7. In one example, the inventor has found that semi-elliptical cone suspension with a ratio of 1.33 produces a notable reduction in distortion.  
         [0039]    [0039]FIG. 3 a  is set of analysis graphs  120 ,  122 ,  124  that illustrate the mechanical movement properties of cone suspension  170 . Graphs  120 ,  122 ,  124  define the behavior and performance of the cone suspension as a function of the speaker cone displacement. Graph  120  shows how the physical points on the surface of the semi-elliptical shaped cone suspension cross-section are displaced as the speaker cone is displaced. Curve  126  shows the cone suspension cross-section at rest position. Contour  128  intersects curve  126  at a center point  130  on the surface of the cone suspension at rest position. The center point  130  moves along contour  128  as the cone suspension  170  moves from the rest position illustrated by curve  126 . For example, as the speaker cone is displaced by a given amount in a direction away from the cone suspension, the cone suspension is contracted and the center point  130  moves along contour  128  to point  132  on curve  134 . Further cone displacement will continue to contract the cross-section of the cone suspension, as shown in curves  136  and  138  for example.  
         [0040]    Conversely, as the speaker cone is displaced by a given amount in a direction toward the cone suspension, center point  130  moves along contour  128  to point  140  on curve  142 . The cross-section of the cone suspension  170  has expanded and will continue to do so as the cone further moves in the direction the cone suspension. The same explanation applies to other points on the surface of the cone suspension at rest position.  
         [0041]    Graph  122  illustrates the relative deviation of different points on the surface of the semi-elliptical shaped cone suspension relative to the center of the speaker cone. Relative deviation of these points occurs as the speaker cone is displaced when driven by an audio source (e.g. audio amplifier).  
         [0042]    For a given range of speaker cone displacement,  146  indicates the deviation of point  130  at the center of the surface of the cone suspension. As the speaker cone moves (from rest position) in a direction towards the cone suspension, point  130  deviates towards the 10% deviation limit  148 . Similarly, as the speaker cone  42  moves in a direction away from the cone suspension, point  130  deviates towards the −10% deviation limit  150 . Therefore, vertical line  146  provides a measure of how much movement or deviation point  130  undergoes during the speaker cone displacement, as it moves towards and away from the cone suspension. For point  130 , vertical line  146  shows a relatively symmetrical deviation of ±10%. It will be appreciated that the same result applies to all points on the cone suspension circumference, which are located at the center of the surface of the cone suspension. Compared to the semi-circular cone suspension of FIG. 2 a,  the center points on the semi-elliptical shaped cone suspension (FIG. 3 a ) exhibit more deviation for a given amount of cone displacement.  
         [0043]    This also holds true for the physically adjacent points  140 ,  141  (graph  34 ) on either side of point  130 , wherein point  140  is represented by vertical line  152 , and point  141  is represented by vertical line  154 . The increased deviation for the semi-elliptical shaped cone suspension  170 , which is taller than semi-circular cone suspension  40  (assuming that the width of the cone suspensions  170  and  40  is the same) makes it more prone to the occurrence of wrinkles on its cone suspension surface.  
         [0044]    Graph  124  illustrates the relationship between the deviation (or change) in displaced air volume ΔV, indicated at  156 , and speaker cone displacement X, indicated at  158 . Curve  160  shows that the deviation in displaced air volume ΔV no longer remains zero as the speaker cone displacement increases. As indicated by curve  160 , when the speaker cone displacement increases past points  162  and  164 , the deviation in displaced air volume ΔV becomes non-zero. Consequently, for a range  166  of speaker cone displacement X the deviation in displaced air volume ΔV behaves linearly. Outside this range  166  any non-linearity translates to distortion at the speaker output. However, in comparison to the semi-circular cone suspension, the semi-elliptical suspension has a considerably wider linear range. This means that the deviation in displaced air volume ΔV remains linear for an increased range of speaker cone displacement X (i.e. range  166  is wider than range  116  (FIG. 2 a ) for cone suspension with the same width). Correspondingly, semi-elliptical cone suspension  170  suffers less non-linear distortion for increased amounts of speaker cone displacement and semicircular cone suspension  40 . The improved linear performance of the semi-elliptical cone suspension was illustrated by line  16  in FIG. 1, in contrast to the performance of the semi-circular cone suspension illustrated by line  14 .  
         [0045]    A second embodiment of the present invention is illustrated in FIG. 4. FIG. 4 illustrates the mechanical movement of a parabolic cone suspension, which illustrated in cross section by curve  186  of graph  180 . Graph  180  also illustrates how the physical points on the surface of the parabolic shaped cone suspension are displaced as the speaker cone is displaced. Curve  186  of graph  180  shows the cone suspension cross-section at rest position. Contour  190  intersects curve  186  at a center point  192  on the surface of the cone suspension at rest position. The center point  192  moves along contour  190  as the cone suspension moves from the rest position. For example, as the speaker cone is displaced by a given amount in a direction away from the cone suspension, the cone suspension contracts and center point  192  moves along contour  190  to point  194  on curve  196 . Further cone displacement will continue to contract the cross-section of the cone suspension, as shown in curves  198  and  200  for example.  
         [0046]    Conversely, as the speaker cone is displaced by a given amount in a direction toward the cone suspension, center point  192  moves along contour  190  to point  202  on curve  204 . Hence, the cross-section of the cone suspension has expanded and will continue to do so as the cone further moves in the direction the cone suspension. The same explanation applies to other points on the surface of the cone suspension at rest position.  
         [0047]    Graph  182  shows simulated measurements identifying the relative deviation of different points on the surface of the parabolic shaped cone suspension relative to the center of the speaker cone. Relative deviations of these points occur as the speaker cone is displaced when driven by an audio source (e.g. audio amplifier).  
         [0048]    For a given range of speaker cone displacement, vertical range line  206  indicates the deviation of the point  192  at the center of the surface of the cone suspension. As the speaker cone moves (from rest position) in a direction towards the cone suspension, point  192  deviates towards the 10% deviation limit  208 . Similarly, as the speaker cone moves in a direction away from the cone suspension, point  192  deviates towards the −10% deviation limit  210 . Therefore, vertical line  206  provides a measure of how much movement or deviation point  192  undergoes during the speaker cone displacement, as it moves towards and away from the cone suspension. For point  192 , vertical line  206  shows a relatively symmetrical deviation of ±10%. It will be appreciated that the same result applies to all points on the cone suspension circumference, which are located at the center of the surface of the cone suspension. Compared to the semi-circular cone suspension of FIG. 2 a,  the center points on the parabolic shaped cone suspension (FIG. 4) exhibit more deviation for a given amount of cone displacement.  
         [0049]    This also holds true for the physically adjacent points  214 ,  216  (graph  180 ) on either side of point  192 , wherein point  214  is represented by vertical line  218 , and point  216  is represented by vertical line  220 .  
         [0050]    Graph  184  illustrates the relationship between the deviation (or change) in displaced air volume ΔV, indicated at  222 , and speaker cone displacement X, indicated at  224 . Curve  226  shows that the deviation in displaced air volume ΔV no longer remains zero as the speaker cone displacement increases. As indicated by curve  226 , when the speaker cone displacement increases past points  230  and  232 , the deviation in displaced air volume ΔV becomes non-zero. Consequently, for a range  234  of speaker cone displacement X the deviation in displaced air volume ΔV behaves linearly. Hence, outside range  234 , any non-linearity translates to distortion at the speaker output. However, in comparison to the semi-circular cone suspension  40  (FIG. 2 a ), the parabolic shaped suspension has a considerably wider linear range. This means that the deviation in displaced air volume ΔV remains linear for an increased amount of speaker cone deviation. By comparing FIG. 2 a  and FIG. 4, it can be seen that range  234  is wider than range  116  for cone suspension with the same width, thus indicating that the parabolic cone suspension suffers less non-linear distortion for increased amounts of speaker cone displacement. Still, in contrast with the linear range, as indicated by  116 , of the semi-elliptical shaped cone suspension shown in FIG. 3 a,  the linear range, as indicated by  234 , of the parabolic cone suspension is slightly narrower.  
         [0051]    As with the semi-elliptical shaped cone suspension, the semi-parabolic cone suspension operates to reduce distortion when the ratio of the height of the cone suspension to half of its width is between 1.1 and 1.7.  
         [0052]    [0052]FIG. 5 illustrates a third embodiment of the present invention. FIG. 5 illustrates a cone suspension with a triangular cross-section at rest at curve  246  of graph  240 . Graphs  240 ,  242 ,  244  define the behavior and performance of the triangular cone suspension as a function of the speaker cone displacement. Graph  240  shows how the physical points on the surface of the triangular shaped cone suspension cross-section are displaced as the speaker cone is displaced. Curve  246  of graph  240  shows the triangular cone suspension cross-section at rest position. Contour  248  intersects curve  246  at a center point  250  on the surface of the cone suspension at rest position. The center point  250  moves along contour  248  as the cone suspension moves from the rest position. For example, as the speaker cone is displaced by a given amount in a direction away from the cone suspension, the center point  250  moves along contour  248  to point  252  on curve  254 . From curve  254 , it can be seen that the cross-section of the cone suspension has contracted. Further cone displacement will continue to contract the cross-section of the cone suspension, as shown in curves  256  and  258  for example. It will be appreciated that a triangular surround moves by pivoting about its sides whilst the sides of the surround remain substantially rigid (i.e. they do not distort).  
         [0053]    Conversely, as the speaker cone is displaced by a given amount in a direction toward the cone suspension, center point  250  moves along contour  248  to point  260  on curve  262 . Hence, the cross-section of the cone suspension has expanded and will continue to do so as the cone further moves in the direction the cone suspension. The same explanation applies to other points (e.g.  264 ) on the surface of the cone suspension at rest position.  
         [0054]    Graph  242  illustrates the relative deviation of different points on the surface of the triangular shaped cone suspension relative to the center of the speaker cone. Relative deviations of these points occur as the speaker cone is displaced when driven by an audio source (e.g. audio amplifier).  
         [0055]    For a given range of speaker cone displacement, vertical range line  266  indicates the deviation of the point  250  at the center of the surface of the cone suspension. As the speaker cone moves (from rest position) in a direction towards the cone suspension, point  250  deviates towards the 10% deviation limit  268 . Similarly, as the speaker cone moves in a direction away from the cone suspension, point  250  deviates towards the −10% deviation limit  270 . Therefore, vertical line  266  provides a measure of how much movement or deviation point  250  undergoes during the speaker cone displacement, as it moves towards and away from the cone suspension. For point  250 , vertical line  250  shows a relatively symmetrical deviation of approximately ±10%. It will be appreciated that the same result applies to all points on the cone suspension circumference, which are located at the center of the surface of the cone suspension. Compared to the semi-circular cone suspension of FIG. 2 a,  the center points on the triangular shaped cone suspension (FIG. 4) exhibit more deviation for a given amount of cone displacement.  
         [0056]    For the points  264 ,  272  (graph  240 ) located on either side of point  250 , less deviation is experienced, where this deviation continues to reduce as the points are located further away from center point  250 . For example, point  264  is represented by vertical line  276 , and point  272  is represented by vertical line  278 .  
         [0057]    Graph  244  illustrates the relationship between the deviation (or change) in displaced air volume ΔV, indicated at  280 , and speaker cone displacement X, indicated at  282 . Curve  284  shows that the deviation in displaced air volume ΔV no longer remains zero as the speaker cone displacement increases. As indicated by curve  284 , when the speaker cone displacement increases past points  286  and  288 , the deviation in displaced air volume ΔV becomes non-zero. Consequently, for a specific linear range of speaker cone displacement X the deviation in displaced air volume ΔV behaves linearly. Hence, outside range  290 , any non-linearity translates to distortion at the speaker output. However, in comparison to the semi-circular cone suspension, the triangular shaped suspension has a considerably wider linear range. This means that the deviation in displaced air volume ΔV remains linear for an increased amount of speaker cone deviation. By comparing FIG. 2 a  and FIG. 5, it can be seen that range  290  is wider than range  116 , thus indicating that the triangular cone suspension suffers less non-linear distortion for increased amounts of speaker cone displacement. In contrast to the linear range, as indicated by  116 , of the semi-elliptical shaped cone suspension shown in FIG. 3 a,  the linear range, as indicated by  290 , of the triangular cone suspension is approximately the same. However, the triangular cone suspension is not as practically robust as the elliptical shaped suspension cone. The fact that the triangular cone suspension pivots about its sides means that it should preferably, although not necessarily, be constructed from more rigid material than other cone suspensions. Although both the elliptical and triangular surround exhibit good linearity, the elliptical shaped cone suspension is more resilient to high internal speaker cabinet pressures, enabling the use of more lightweight and cost-effective materials in its construction.  
         [0058]    Reference is next made to  6   a,    6   b  and  7 , which illustrate a fourth embodiment of the present invention. FIGS. 6 a  and  6   b  illustrate an annular ring shaped cone suspension  300 , wherein the annular ring has a semi-elliptical shaped cross-section  304 . The annular ring also includes an inner edge annular flange  306  and an outer edge annular flange  308 . The inner edge annular flange  306  is adjacent to both the base  310  of the semi-elliptical shaped cross-section  304  and an inner edge  312  of the semi-elliptical shaped outer surface  302 . The inner edge annular flange  306  is attached to a speaker cone in a manner known in the art of speaker construction, where generated air volume (sound) from the speaker cone passes through a circular opening  305 .  
         [0059]    The outer edge annular flange  308  is adjacent to both the base  310  of the semi-elliptical shaped cross-section  304  and an outer edge  314  of the semi-elliptical shaped outer surface  302 . The outer edge annular flange  308  attaches to a speaker basket, which provides a stationary mechanical construction.  
         [0060]    A plurality of rib elements  316  are circumferentially distributed on the semi-elliptical shaped outer surface  302  of the annular ring shaped cone suspension  300 . The rib elements  316  can be either uniformly distributed on the semi-elliptical shaped outer surface  302  of the annular ring shaped cone suspension  300 , or non-uniformly distributed. FIG. 7 illustrates a rib element  320  in cross section between lines  7 ′ and  7 ′ (FIG. 6). Each of the plurality of rib elements  316  has a semi-elliptical shape. Each rib may be formed integrally with the suspension  300  or the cone suspension may be assembled from a number of rib elements  316  and a number of sections of the annular ring.  
         [0061]    Each rib element  316  extends between flanges  306  and  308 . In an alternative embodiment of the present invention, the rib elements may be formed between, and spaced apart from, flanges  306  and  308 .  
         [0062]    As illustrated in FIG. 6 a,  the rectangular shaped strip  320  of material extends over the central portion  318  of the semi-elliptical shaped outer surface  302 , and between the inner and outer edge  312 ,  314  of the semi-elliptical shaped outer surface  302 . The rectangular shaped strip of material  320  also extends between the inner and outer edge annular flange  306 ,  308 . The material used in constructing the rectangular shaped strip  320 , which forms a rib element  316 , can be of the same material as that used for constructing the annular ring  300 . Alternatively, the material used in constructing the rectangular shaped strip  320  can be of a different type of material as that of the annular ring  300 .  
         [0063]    [0063]FIG. 8 is a cross-sectional view of cone suspension  300  through line  8 ′ and  8 ′ (FIG. 6 b ). Each elliptical rib element  316  has a first end portion  322 , a second end portion  324  and a center portion  326  therebetween. The center portion  326  extends over the central portion  318  of the semi-elliptical shaped outer surface  302 , whilst the first and second end portion  322 ,  324  extend between the outer and inner edges  314 ,  312  of the semi-elliptical shaped outer surface  302  respectively. The center portion  326  has an increased cross-section relative to the first and second end portion  322 ,  324 , where the first and second end portions  322 ,  324  are adjacent the outer and inner edge annular flange  308 ,  306  of the semi-elliptical shaped outer surface  302 , respectively. In an alternative embodiment of the present invention, each rib element may have a constant cross-section through its length from its first end portion  322  to its second end portion  324 .  
         [0064]    As described above in relation to semi-circular cone suspension  40  and semi-elliptical cone suspension  170 , wrinkles may be formed in a cone suspension when the attached speaker cone is displaced from its rest position. A similar effect is observed in semi-parabolic cone suspensions (FIG. 4) and in cone suspensions with other shapes.  
         [0065]    The embodiment of FIGS. 6 a,    6   b,    7  and  8  reduces the formation of such wrinkles. Rib elements  316  operate to decrease the rigidity of the cone suspension, reducing the formation of wrinkles and decreasing the distortion produced by the speaker. Rib elements  316  have been illustrated and described in conjunction with a semi-elliptical cone suspension. Such rib elements may also be used with semi-circular, semi-parabolic and other cone suspensions to reduce the formation of wrinkles in those cone suspensions.  
         [0066]    The inventor has found that the use of rib elements  316  has the effect of reducing distortion whether rib elements  316  are distributed uniformly (i.e. regularly spaced) or non-uniformly. Preferably, the ribbed elements are spaced periodically to provide a consistent rigidity to the cone suspension.  
         [0067]    Preferably, the number, position and circumferential width of the rib elements  316  are selected based on the mechanical properties of the material from which the suspension is constructed. Specifically, the rib elements  316  must be able to accommodate for the rigidity of the suspension material, as well as for the degree to which it resists stretching. In addition, the number of ribs should be selected such that the two walls of each rib element  316  do not come into contact with one another when the cone suspension is contracted. In practice, however, this situation is unlikely to arise. By suitably selecting the number, position and circumferential, rib elements can absorb the contraction and expansion of the cone suspension and reduce the formation of wrinkles in the cone suspension.  
         [0068]    Preferably at least six ribbed elements are provided. More preferably 8 or more elements are provided. In one embodiment, the inventor has provided 12 periodically spaced rib elements. In another embodiment of the inventor has provided 24 periodically spaced rib elements on a semi-elliptical cone suspension. The addition of more ribs on a cone suspension allows shallower ribs to be used.  
         [0069]    Reference is made to FIGS. 9 a,    9   b  and  9   c.  Rib elements  316  have been described as having a semi-elliptical cross section. Alternatively, triangular rib elements  416   a,  rectangular rib elements  416   b  or semi-circular rib elements  416   c  may be used.  
         [0070]    The embodiments of the present invention provide a loudspeaker suspension for further reducing non-linear distortion. It should be understood that various modifications can be made to the preferred and alternative embodiments described and illustrated herein without departing from the spirit and scope of the invention. For example, in FIG. 2 b  the cone suspension  40  is shown as having a contour that bends away from the cone  42 . That is, the suspension  40  is convex in the direction C, and concave in the direction B. The cone suspension embodying the invention described above may, of course, be concave or convex in the direction B. Further, the cone suspension may be used either as part of a speaker including a magnet and a voice coil, or as part of passive radiator that does not include a magnet and voice coil.