Abstract:
A speaker driver surround has tapered thickness to provide improved linearity of the force versus displacement response. The tapered thickness surround provides for a larger emissive piston area, thus increasing the acoustic efficiency of the transducer. The surround has an integral gasket with a groove to accept grill to cover the speaker cone.

Description:
RELATED APPLICATIONS 
   This application claims priority to U.S. provisional patent application Ser. No. 60/438,488 filed Jan. 7, 2003 entitled “Tapered Thickness Surround For High Excursion Speaker Driver”. 

   BACKGROUND 
   A surround is a flexible annular ring connecting between the basket and the cone and provides a movable support for the speaker driver cone. Surrounds are commonly made from compressed foam or molded elastomer. As the driver cone is displaced by the force of the voice coil along the axis of travel, the surround is stretched from its resting position. The force required to move the cone and surround changes as a function of displacement distance in a non-linear fashion. This causes audio distortion. This non-linear effect is particularly evident in high excursion drivers because the non-linearity of the force/displacement relationship increases at high displacements. 
   The surround and gasket are normally two separate parts. 
   SUMMARY OF THE INVENTION 
   A surround has varied thickness to create a more linear force to displacement relationship. The thickness of the surround is varied from the base of the surround to the apex. The surround has a different thickness on the inside diameter base and the outside diameter base to result in a more linear and symmetric force versus displacement curve in both up and down directions. 
   The surround and gasket are one integral part. The combined component eliminates tolerance and alignment problems between conventional surrounds and gaskets. Integrating the surround and the gasket allows the surround to be offset with respect to the attaching surface on the basket upwards to provide increased clearance. The surround has a groove to accommodate the grill with an interference fit. 
   The surround is narrow yet capable of high excursion. The narrow width of the surround also allows an increase in the cone surface, which is the primary emissive surface, thus making the driver more efficient. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a cross section view of a surround according to the present invention. 
       FIG. 2  shows a surround with a grill installed into the integrated gasket. 
       FIG. 3  shows a detailed view of a grill installed into the integrated gasket. 
       FIG. 4  shows a front view of a surround according to the present invention. 
       FIG. 5  shows a cross section view with dimensions of the thickness profile of an embodiment of the surround. 
       FIG. 6  shows a honeycomb pattern of a grill for use with the present invention. 
       FIG. 7  shows a dimensioned drawing an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a cross section view of a surround  100  according to the present invention, a cone mounting region  110  allows the surround to be attached at the inside edge to a cone, which moves in response to force applied by a voice coil. The cone mounting region  110  is adjacent to an inner rising region  120 . An arch region  130  is a curved segment that connects the inner rising region  130  to an outer rising region  140 . The outer rising region  140  is adjacent to a gasket  150  that mounts the surround  100  to the driver basket, not shown. The inner and outer rising regions  120  and  140  along with the arch region  130  allow the surround to extend above and below the resting position as the cone is displaced by the voice coil. These three regions will experience a change in shape as the surround moves. Base  122  is thicker than apex  124 . Both the inner and outer rising regions  120  and  140  have a thicker base and thinner apex with an approximately linear taper thickness in between. 
   A groove  160  with a rectangular shape is used to attach a grill to the front of the driver. Friction or glue holds the grill in the groove. 
   To achieve linearity of applied force throughout the range of cone travel, a height offset is created between the inner base and outer base edge. Height offset  170  is shown in  FIG. 5 . This aids linear travel, which is symmetrical in both directions of travel from the resting position. The height offset should be approx. 7.5–21% of the outer edge thickness. In an exemplary embodiment, with a base thickness of 0.15 inches a height displacement of 0.02 inches is used. 
   The outer base thickness can be approximately 15–45% larger than the apex thickness. The outer base thickness can be approximately 1–5% smaller than the inner base thickness. 
     FIG. 2  shows a cross section of a grill  210  inserted in the groove  160  of surround  100  and spanning the opening in front of the cone  220 .  FIG. 3  shows a detail of the surround and the gasket inserted in the groove. 
     FIG. 4  shows a view of the surround  100  as seen from the front of the driver. The inner diameter is adapted to the driver cone. The outer diameter is adapted to the driver basket. The grill determines the location of the groove. Holes  102  allow screws to pass through the surround  100  for mounting to a speaker basket. 
     FIG. 5  shows dimensions of a representative surround. Inner rising region has a thickness at the base of 0.15 inches, tapering to 0.12 inches at the apex. Arch region maintains the thickness at 0.12 inches to the transition to the outer rising region that tapers to 0.17 inches at the base. Inner rising region has an angle of 12 degrees from vertical and outer rising region has an angle 14 degree from vertical. Arch region has an inner radius of curvature of 0.33 inches. Arch region traverses an angle of approximately 154 degrees and is approximately 0.8 inches wide at the rising regions apex. 
   Other thicknesses can be used for the tapered surround. For example, the surround can have a thickness of 0.06 inches, tapering to 0.04 inches. Alternatively, thicker or thinner dimensions can be used. The tapering ratio can be for the inner region can be different from the outer region. 
   Alternatives to the construction of a surround according to the present invention can use a symmetric profile, as in the previous example, or a non-symmetric profile of thickness and height. 
   The preferred technique for fabricating the surround is injection molding using EPDM (ethylene propylene diene monomer) or SANTOPRENE or SARLINK elastomer. Desirable properties of the elastomer are: 
   Tensile Strength: 3,000 
   Elongation, max. 6× 
   Hardness, Shore A 30–90 
   Other elastomers suitable for use are butadiene rubber, butyl rubber, chlorinated polyethylene, chloroprene/neoprene, chlorinated sulfonate polyethylene, epichlorohydrin, fluorocarbon, fluorosilicone, natural rubber, neoprene, nitrile butadiene, polyacrylate, polyisoprene, silicone, styrene butadiene, and urethane. 
   Other fabrication techniques and material commonly used for constructing flexible items can be employed. Another example of a surround construction technique is foam compression molding, where polyester or polyether foam is compressed by a mold to form the surround. Another example of a construction technique is molding using expanding foam rubber such as closed cell urethane foam. 
   It is desirable to keep the surround as narrow as possible to allow for maximum cone area while achieving maximum travel for cone movement. Increased cone area increases air volume displacement for a given amount of excursion. The shape of the surround was designed using finite element analysis and testing to maximize linearity and increase the excursion while remaining only one inch wide.