Patent Publication Number: US-2022212068-A1

Title: Multi-material golf club head

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 16/042,979, titled Multi-Material Golf Club Head, filed on Jul. 23, 2018, which is incorporated herein in its entirety. To the extent appropriate, priority is claimed to the above application. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a new and improved golf club having a secondary barrier behind a striking face portion via a panel member. The panel member allows the golf club head to incorporate exotic materials at the rear aft portion of the golf club head without sacrificing performance. More specifically the secondary barrier preserves the acoustic characteristics of a metallic golf club head while allowing the rear aft portion of the golf club head to be made out of exotic materials that may generally degrade the acoustic characteristics of a golf club head. 
     BACKGROUND OF THE INVENTION 
     The utilization of lightweight materials in a golf club head is generally known. The utilization of lightweight materials in a golf club head removes mass from specific portions of the golf club head and allows it to be redistributed to more optimized areas. U.S. Pat. No. 6,612,938 to Murphy et al. illustrates one of the earlier attempts to use exotic materials in a golf club head such as plies of pre-preg material. 
     However, despite the potential gains in the discretionary mass gained by the utilization of such lightweight material, the utilization of such material usually comes with some drawbacks. More specifically, the utilization of such lightweight material may generally come with an undesirable acoustic characteristic, making the golf club undesirable to a golfer irrespective of performance. 
     U.S. Pat. No. 5,064,197 to Eddy back in 1991 provides one of the earlier attempts to adjust the acoustic characteristics of a golf club by providing a first forward chamber in the head opening to the club head face, wherein the forward chamber vibrates at a given primary frequency. 
     U.S. Pat. No. 8,651,975 to Soracco provided another example of an attempt to address the acoustic characteristics associated with golf clubs that utilizes exotic material. More specifically, Soracco provided a golf club head with sound tuning composite members forming at least a portion of the surface of the golf club head. 
     Finally, U.S. Pat. No. 8,849,635 to Hayase et al. went above and beyond the mere basic design of a golf club head for acoustic characteristics and even made an attempt to predict modal damping ratio of composite golf club heads. 
     Despite the above, none of the references provide a method to improve the performance of a golf club head by providing a way to improve the performance of a golf club head utilizing advanced materials all while providing a clean way to address the degradation of the acoustic characteristics of the golf club head. Hence, it can be seen from the above that a golf club design that is capable of achieving both of the goal of incorporating exotic lightweight materials in order to increase discretionary mass as well as achieving a desirable acoustic characteristic while minimizing the undesirable sound and feel of the golf club head. 
     BRIEF SUMMARY OF THE INVENTION 
     One aspect of the present invention is a golf club head comprising of a frontal acoustic chamber located at a front side of the golf club head and made out of a first material having a first volume, and a rear weight saving chamber located rearward of the frontal acoustic chamber at least partially made out of a second material having a second volume, wherein the frontal acoustic chamber and the rear weight saving chamber are separated by a panel member that bifurcates the golf club head by connecting to a crown portion and a sole portion, and wherein said second material has a lower density than said first material, and wherein the golf club head has a Front to Rear Volume Ratio of less than about 0.35, the Front to Rear Volume Ratio defined as the first volume of the frontal acoustic chamber divided by a second volume of the rear weight saving chamber. 
     In another aspect of the present invention is a golf club head comprising of a frontal acoustic chamber located at a front side of the golf club head and made out of a first material having a first volume, and a rear weight saving chamber located rearward of the frontal acoustic chamber at least partially made out of a second material having a second volume, wherein the frontal acoustic chamber and the rear weight saving chamber are separated by a panel member that bifurcates the golf club head by connecting to a crown portion and a sole portion, and wherein said second material has a lower density than said first material, and wherein the panel member is further comprised of an upper sub-panel member, a middle sub-panel member, and a lower sub-panel member, and all three panel members are all placed at different angles relative to a striking face. 
     In another aspect of the present invention is a golf club head comprising of a frontal acoustic chamber located at a front side of the golf club head and made out of a first material having a first volume, and a rear weight saving chamber located rearward of the frontal acoustic chamber at least partially made out of a second material having a second volume, wherein the frontal acoustic chamber and the rear weight saving chamber are separated by a panel member that bifurcates the golf club head by connecting to a crown portion and a sole portion, and wherein said second material has a lower density than said first material, wherein the panel member is curved away from the front side of the golf club head such that a center of the panel member is placed further away from a striking face than at a crown and a sole portion of the panel member. 
     In one aspect, the technology relates to a golf club head that includes a forward portion located at a front side of the golf club head and comprising a first material. The forward portion includes a striking face and a forward joint section having an exterior surface and an interior surface. The golf head also includes an aft portion located rearward of the forward portion and joined to the forward portion, the aft portion comprising a second material. The aft portion includes an aft joint section joined with the forward joint section, the aft joint section having an interior surface and an exterior surface, wherein the exterior surface of the aft joint section is in contact with the interior surface of the forward joint section; and an aft rib attached to an interior surface of the aft portion, the aft rib extending, from an interior surface of the aft joint section, in a direction away from the striking face. 
     In an example, the aft rib is a continuous aft rib extending from a first location on a first half of the interior surface of the aft joint section to a second location on a second half of the interior surface of the aft joint section. In another example at least one surface of the continuous aft rib is entirely in contact with the interior surface of the aft portion. In yet another example, the aft joint section and the forward joint section are joined together as a taper joint. In still another example, the aft rib and the aft portion are configured such that the exterior surface of the aft joint section exerts a force on the interior surface of the forward joint section when the golf club head strikes a golf ball. In an additional example, the aft joint section and the forward joint section are joined together via an adhesive. In still yet another example, the aft portion includes an opening towards the forward portion, and the aft joint section extends continuously around a circumference of the opening. 
     In another example, the first material is a metallic material and the second material is a composite material. In an additional example, the aft rib is made from a third material, the third material having a Young&#39;s Modulus value greater than a Young&#39;s Modulus value for the second material. In yet another example, at least a segment of the aft portion is made from a structure comprising: an inner layer; a middle layer in contact with the inner layer; and an outer layer in contact with the middle layer, wherein a distance between an interior surface of the inner layer and an exterior surface of the outer layer is at least 0.8 mm. In still another example, the structure has an areal density of less than 1000 g/m 2 . 
     In another aspect, the technology relates to a golf club head that includes a striking face, a sole, and a crown. The crown has an areal density of less than 1000 g/m 2  and is made from a structure comprising: an inner layer; a middle layer in contact with the inner layer; and an outer layer in contact with the middle layer, wherein a distance between an interior surface of the inner layer and an exterior surface of the outer layer is at least 0.8 mm. 
     In an example, the distance between the interior surface of the inner layer and the exterior surface of the outer layer is at least 2.5 mm. In another example, the inner layer has a thickness of less than about 0.2 mm; and the middle layer has a thickness of at least 0.6 mm. In yet another example, the crown has an areal density of less than 900 g/m 2 . In still another example, the outer layer has an areal density of less than about 400 g/m 2 ; the middle layer has an areal density of less than about 300 g/m 2 ; and the inner layer has an areal density of less than about 200 g/m 2 . In still yet another example, the inner layer and the outer layer comprise a carbon-fiber material; and the middle layer comprises a foamed material. In an additional example, the inner layer and the outer layer comprise a thermoplastic composite material. In another example, the crown is part of an aft portion joined to a forward portion, wherein the aft portion includes an aft joint section and the golf club head further comprises an aft rib attached to an interior surface of the aft joint section and an interior surface of the inner layer of the crown, the aft rib extending in a direction away from the striking face. 
     In another aspect, the technology relates to a golf club head that includes a forward portion located at a front portion of the golf club head and made from at least a first material. The forward portion includes a striking face and a forward joint section having an exterior surface and an interior surface. The golf club head also includes an aft portion located rearward of the forward portion and joined to the forward portion, the aft portion made from at least a second material. The aft portion includes an aft joint section joined with the forward joint section, the aft joint section having an interior surface and an exterior surface, wherein the exterior surface of the aft joint section is in contact with the interior surface of the forward joint section; and a crown section having an areal density of less than 2000 g/m 2 . The crown is made from a structure including an inner layer; a middle layer in contact with the inner layer; and an outer layer in contact with the middle layer, wherein a distance between an interior surface of the inner layer and an exterior surface of the outer layer is at least 0.8 mm. The aft portion also includes an aft rib attached to an interior surface of the aft joint section, the aft rib extending in a direction away from the striking face. 
     In another aspect, the technology relates to a golf club head that includes a striking face, a sole, and a crown, the crown having an areal density of less than 1000 g/m 2 . The crown is made from a structure comprising: an inner layer; a middle layer in contact with the inner layer; and an outer layer in contact with the middle layer, wherein an amount of deflection of the crown as a function of a mass of the crown is governed by the following equation when subjected to a pressure of 20 MPa on or near the geometric center: Deflection≤−0.3177 (Mass)+5.615. 
     In an example, the distance between an interior surface of the inner layer and an exterior surface of the outer layer is at least 0.8 mm. In another example, the distance between the interior surface of the inner layer and the exterior surface of the outer layer is at least 2.5 mm. In still another example, the crown has a D Score of at least 1.3. In yet another example, the middle layer comprises a foamed material. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the invention will be apparent from the following description of the invention as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
         FIG. 1  of the accompanying drawings shows a frontal perspective view of a golf club head in accordance with the present invention; 
         FIG. 2  of the accompanying drawings shows a rear perspective view of a golf club head in accordance with the present invention; 
         FIG. 3  of the accompanying drawings shows a partial rear perspective view of a golf club head in accordance with the present invention wherein the crown is removed to illustrate internal components; 
         FIG. 4  of the accompanying drawings shows an exploded perspective view of a golf club head in accordance with the present invention; 
         FIG. 5  of the accompanying drawings shows a cross-sectional view of a golf club head in accordance with the present invention; 
         FIG. 6  of the accompanying drawings shows a partial rear perspective view of a golf club head in accordance with an alternative embodiment of the present invention; 
         FIG. 7  of the accompanying drawings shows a partial rear perspective view of a golf club head in accordance with an alternative embodiment of the present invention; 
         FIG. 8  of the accompanying drawings shows a partial rear perspective view of a golf club head in accordance with an even further alternative embodiment of the present invention; 
         FIG. 9  of the accompanying drawings shows a cross-sectional view of a golf club head in accordance with a further alternative embodiment of the present invention; 
         FIG. 10  of the accompanying drawings shows a partial rear perspective view of a golf club head in accordance with an alternative embodiment of the present invention; 
         FIG. 11  of the accompanying drawings shows a cross-sectional view of a golf club head in accordance with an alternative embodiment of the present invention; 
         FIG. 12  of the accompanying drawings shows a partial rear perspective view of a golf club head in accordance with another alternative embodiment of the present invention; 
         FIG. 13  of the accompanying drawings shows a cross-sectional view of a golf club head in accordance with another alternative embodiment of the present invention; 
         FIG. 14  of the accompanying drawings shows a partial rear perspective view of a golf club head in accordance with another alternative embodiment of the present invention; 
         FIG. 15  of the accompanying drawings shows a cross-sectional view of a golf club head in accordance with another alternative embodiment of the present invention; 
         FIG. 16  of the accompanying drawings shows an exploded perspective of a golf club head in accordance with an even further alternative embodiment of the present invention; 
         FIG. 17  of the accompanying drawings shows a cross-sectional view of a golf club head in accordance with an even further alternative embodiment of the present invention; 
         FIG. 18  of the accompanying drawings shows a time sequence diagram representing the amplitude of the sound of a golf club head in accordance with an embodiment of the present invention; 
         FIG. 19  of the accompanying drawings shows a time sequence diagram representing the amplitude of the sound of an exemplary prior art golf club head; 
         FIG. 20  of the accompanying drawings shows a spectrogram of the frequency and power of the sound of a golf club head in accordance with an embodiment of the present invention; 
         FIG. 21  of the accompanying drawings shows a spectrogram of the frequency and power of the sound of a golf club head in accordance with a prior art golf club head; 
         FIG. 22A  of the accompanying drawings shows a cross-sectional view of a golf club head in accordance with an embodiment of the present invention; 
         FIG. 22B  of the accompanying drawings shows an enlarged view of a joint of the club head depicted in  FIG. 22A  in accordance with an embodiment of the present invention; 
         FIG. 22C  of the accompanying drawings shows a perspective view of an aft portion of another embodiment of a golf club head in accordance with an embodiment of the present invention; 
         FIGS. 22D-22F  of the accompanying drawings show cross-section views of example profiles of an aft rib in accordance with embodiments of the present invention. 
         FIG. 22G  of the accompanying drawings shows a perspective view of an aft portion of another embodiment of a golf club head in accordance with an embodiment of the present invention; 
         FIG. 23A  of the accompanying drawings shows an exploded perspective of a golf club head in accordance with an embodiment of the present invention; 
         FIG. 23B  of the accompanying drawings shows an enlarged cross-sectional view of a portion of a crown of the golf club head depicted in  FIG. 23A  in accordance with an embodiment of the present invention; 
         FIG. 24A  of the accompanying drawings shows a bottom view of a crown of a club head in accordance with an embodiment of the present invention; 
         FIG. 24B  of the accompanying drawings shows a cross-sectional side view of the crown depicted in  FIG. 24A  in accordance with an embodiment of the present invention; 
         FIG. 25A  of the accompanying drawings shows a bottom view of a crown of a club head in accordance with an embodiment of the present invention; 
         FIG. 25B  of the accompanying drawings shows a cross-sectional side view of the crown depicted in  FIG. 25A  in accordance with an embodiment of the present invention; 
         FIG. 26A  of the accompanying drawings shows a plurality of layers of a crown in accordance with an embodiment of the present invention; 
         FIG. 26B  of the accompanying drawings shows a plurality of layers of a crown in accordance with an embodiment of the present invention; 
         FIG. 27  of the accompanying drawings shows a plurality of configurations of a crown in accordance with an embodiment of the present invention; 
         FIG. 28  of the accompanying drawings shows a table of data representing characteristics of example crowns in accordance with embodiments of the present invention; 
         FIG. 29  of the accompanying drawings shows a table representing characteristics of example crowns in accordance with embodiments of the present invention; and 
         FIG. 30  of the accompanying drawings shows a plot of data for deflection versus mass of example crowns in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description describes the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     Various inventive features are described below and each can be used independently of one another or in combination with other features. However, any single inventive feature may not address any or all of the problems discussed above or may only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below. 
       FIG. 1  of the accompanying drawings shows a perspective view of a golf club head  100  in accordance with an exemplary embodiment of the present invention. The golf club head  100  shown in  FIG. 1  provides only a rough sketch of the externals components of the golf club head  100  without illustrating the internal workings of the golf club head  100 . More specifically, golf club head  100  will generally have a striking face  102  placed at a frontal portion of a chassis  101  the golf club head  100 , a sole portion  106  located at the bottom of an aft portion of the chassis  101 , and a crown portion  104  located at the top of an aft portion of the chassis  101 . The striking face  102 , together with the chassis  101 , which includes the frontal portion and the skirt portion, may generally be made out of a first material having a density of between about 4.0 g/cc and about 4.7 g/cc, more preferably between about 4.1 g/cc and about 4.6 g/cc, and most preferably about 4.4 g/cc. The first material in most cases may generally be a titanium metallic material such Titanium 8-1-1, ATI 425 Titanium, SP 700 Titanium, KS 120 Titanium, KS 100 Titanium, Ti 6-4, or any other type of titanium material having the density recited above without departing from the scope and content of the present invention. However, in alternative embodiments of the present invention, the first material may be steel in a fairway type of construction without departing from the scope and content of the present invention. The crown portion  104  and the sole portion  106  in accordance with this embodiment of the present invention may be made out of a second lightweight material having a lower density than the remainder of the golf club head in order to achieve the weight savings desired without departing from the scope and content of the present invention. The lightweight second material could be made out of aluminum type material with a density of between about 2.5 g/cc and about 2.9 g/cc, a magnesium material with a density of about 1.738 g/cc, a wooden material that may have a density as low as 0.6 g/cc, but most commonly a fiber reinforced plastic composite type material may be used having a density of between about 1.2 g/cc to about 1.8 g/cc. More information regarding composite materials with a low fiber areal mass in a golf club head may be found in U.S. Patent Publication 2015/0360094 to Deshmukh, the disclosure of which is incorporated by reference in its entirety. Although not visible from  FIG. 1 , the golf club head  100  in accordance with this embodiment of the present invention may be internally separated into a frontal acoustic chamber and a rear weight saving member, creating a dual chambered golf club head  100  that is capable of achieving improved performance characteristics by increasing the discretionary weight of the golf club all while preserving the acoustic signature of the golf club head  100 . 
       FIG. 2  of the accompanying drawings shows a rear perspective view of a golf club head  200  in accordance with an alternative embodiment of the present invention. Golf club head  200  may generally be comprised out of very similar components illustrated in  FIG. 1 , comprising of a metallic chassis  201 , a striking face  202 , a crown  204 , and a sole  206 . However, in this angle shown in  FIG. 2 , the internal components of the golf club head  200  can be shown more clearly if the crown  204  cover is removed for illustration purposes. 
       FIG. 3  of the accompanying drawings shows a perspective view of a golf club head  300  in accordance with an alternative embodiment of the present invention wherein the crowns cover is removed. The removal of the crown cover allows the internal components of the golf club head  300  to be shown more clearly. More specifically,  FIG. 3  of the accompanying drawings shows the rear weight saving chamber component of the golf club head  300 . The rear weight saving chamber shown here is created by a panel member  310  that separates the frontal acoustic chamber from the rear weight saving chamber. The panel member  310  in accordance with this embodiment of the present invention may generally be multi-facetted. More specifically, the panel member  310  shown in  FIG. 3  contains at least one facet or bend that separates the panel member  310  into different sub-components to further improve the acoustic signature of the golf club head  300 . The faceting of the panel member  310  shown in  FIG. 3  may create three different sub-panel members  310   a ,  310   b , and  310   c . The upper sub-panel member  310   a  may generally be connected to the crown portion of the golf club head  300 ; the middle sub-panel member  310   b  may generally be connected to the bottom of the upper sub-panel member  310   a ; and the bottom sub-panel member  310   c  may generally be connected to the bottom of the middle sub-panel member  310   b  and also connected to the sole portion of the golf club head  300 . 
     In addition to illustrating the panel member  310 ,  FIG. 3  of the accompanying drawing providing a cut open view of golf club head  300  also illustrates a plurality of circular pressure release holes  312   a  and  312   b  located in the middle sub-panel member  310   b  of the panel member  310 . The plurality of two or more pressure release holes  312   a  and  312   b  allows pressure built up in the frontal acoustic chamber during impact with a golf ball to travel towards the rear weight saving chamber to minimize any undesirable acoustic effects whenever the design of the golf club head  300  necessitates their utilization. In this exemplary embodiment of the present invention, the plurality of pressure release holes  312   a  and  312   b  may have an opening area of between about 15 mm to about 25 mm, more preferably between about 17 mm and about 23 mm, and most preferably about 20 mm. It should be noted here that although the present embodiment shows a plurality of two pressure release holes  312   a  and  312   b , the present invention can incorporate only one pressure release hole  312 , or more than two pressure release hole  312  without departing from the scope and content of the present invention. Moreover, although the present embodiment of the present invention shows that the pressure release holes  312   a  and  312   b  are located in the middle sub-panel member  310   b , they can be located at other portions of the panel member  310  to achieve similar goals without departing from the scope and content of the present invention. In fact, in alternative embodiments of the present invention, the golf club head  300  could be constructed without any pressure release holes  312   a  and  312   b  without departing from the scope and content of the present invention. (See  FIG. 7 ) 
     Finally  FIG. 3  of the accompanying drawings also shows a plurality of ribs  314   a  and  314   b , that connect to the bottom sub-panel member  310   c  and the sole to provide structural rigidity to the panel member  310  to further tune the acoustic signature of the golf club head  300  without departing from the scope and content of the present invention. It should be noted that although  FIG. 3  shows two ribs  314   a  and  314   b , the present invention only incorporates the ribs  314   a  and  314   b  when the acoustic signature of the golf club head  300  needs further tuning. In fact, in alternative embodiments of the present invention, one rib, three ribs, or any multiple ribs may be used as necessary without departing from the scope and content of the present invention. In fact, in extreme situations, the current design may not incorporate any ribs at all. (See  FIG. 6 ) 
       FIG. 4  of the accompanying drawings shows an exploded view of a golf club head  400  in accordance with an embodiment of the present invention. The exploded view of the golf club head  400  shown here in  FIG. 4  allows the relationship between the various components to be shown more clearly. More specifically,  FIG. 4  introduces the ability of the sole  406  of the golf club head to be detachable from the chassis  401  of the golf club head  400 . The sole  406  works in conjunction with the crown  404  to create the rear weight saving chamber previously discussed, which once again, is separated from the frontal acoustic chamber via a panel member  410 . This exploded frontal view with the striking face  402  removed, allows the frontal acoustic chamber to be shown more clearly, and the frontal view of the panel member  410  to be shown as well. Similar to the discussion above, the panel member  410  may be further divided into an upper sub-panel member (not shown in  FIG. 4 ), a middle sub-panel member  410   b , and a lower sub-panel member  410   c , all while incorporating the same pressure release hole  412   a  and  412   b  (not shown in  FIG. 4 ). 
     In order for the relationship between the frontal acoustic chamber and the rear weight saving chamber to be shown more clearly, a cross-sectional view of the golf club head  400  may be more helpful.  FIG. 5  of the accompanying drawings does exactly this by providing a cross-sectional view of a golf club head  500  in accordance with an exemplary embodiment of the present invention. Although previous discussion has hinted at the existence of a frontal acoustic chamber  520  and a rear weight saving chamber  522  within the internals of the golf club head  500 , the cross sectional view of the golf club head  500  identifies the here as frontal acoustic chamber  520  and rear weight saving chamber  522 , which are separated and bifurcates the golf club via a panel member  510 . The frontal acoustic chamber  520  shown here is comprised out of a frontal portion of a chassis of the golf club head  500  as well as the striking face  502  insert. The rear weight saving chamber  522  may generally be comprised of at least one composite panel that helps achieve the weight saving goals of the golf club head  500 . The word “composite” as used in this application may refer to the general term of any material that has two or more different materials combined together, however, in a preferred embodiment of the present invention, fiber reinforced plastic is the general material. In this specific embodiment shown in  FIG. 5 , the golf club head  500  incorporates two composite panels by incorporating a lightweight composite crown  504  and a lightweight composite sole  506  to maximize the weight savings; however, in alternative embodiments either one of the pieces may be used exclusively without the other component without departing from the scope and content of the present invention. 
     The cross-sectional view of the golf club head  500  shown in  FIG. 5 , in addition to showing the relationship between the frontal acoustic chamber  520  and the rear weight saving chamber  522 , also provides a perspective on their relative volumes to one another to create a very critical volume ratio. First and foremost, this cross-sectional view, is taken along a plane that runs front and back through the golf club head, taken down the center through the center of the face. The golf club head  500  may generally have a Front to Rear Volume Ratio of less than about 0.50, more preferably less than about 0.40, and most preferably less than about 0.35; wherein the Front to Rear Volume Ratio is defined by Equation (1) below: 
     
       
         
           
             
               
                 
                   
                     Front 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     to 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Rear 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Volume 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Ratio 
                   
                   = 
                   
                     
                       Volume 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       of 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Frontal 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Acoustic 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Chamber 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       520 
                     
                     
                       Volume 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       of 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Rear 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Weight 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Saving 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Chamber 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       522 
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     More specifically, the frontal acoustic chamber  520  may generally have a volume of less than about 230 cc, more preferably less than about 150 cc, and most preferably less than about 100 cc; while the rear weight saving chamber  522  may have a volume of greater than about 230 cc, more preferably greater than about 310 cc, and most preferably greater than about 360 cc. 
     In order to create the Front to Rear Volume Ratio identified above, the panel member  510  shown in this embodiment may generally have a thickness d 1  of between about 0.1 mm to about 2.0 mm, more preferably between about 0.25 mm to about 1.0 mm, and most preferably about 0.5 mm. The thickness of the panel member  510  is important and critical to the proper functioning of the golf club head  500 , as it creates the necessary barrier between the frontal acoustic chamber  520  and the rear weight saving chamber  522 . If the thickness d 1  of the panel member  510  is too thick, then the correlation between the vibration of the frontal acoustic chamber  520  and the rear weight saving chamber  522  might no longer be synchronized, eliminating the efficiency of the frontal acoustic chamber  520 . Alternatively, if the thickness d 1  is too thin, then the correlation between the two chambers might be too high, allowing the acoustic signature to be over damped by the composite material used by the rear weight saving chamber  522 . It should be noted here that although the thickness d 1  is shown here as constant throughout the panel member  510 , the thickness could be variable depending on the needs of the golf club head  500  without departing from the scope and content of the present invention. 
       FIG. 5  of the accompanying drawings also shows the placement of the panel member  510  relative to the frontal striking surface of the golf club head  500 . In this exemplary embodiment of the present invention, the top of the panel member  510  may generally be placed at a distance d 2  of between about 8 mm to about 36 mm, more preferably between about 9 mm to about 24 mm, and most preferably about 10 mm. The bottom of the panel member  510  may be placed at a distance d 3  of between about 13 mm to about 51 mm, more preferably between about 14 mm to about 45 mm, and most preferably about 15 mm. It should be noted here that distance d 3  here is intentionally greater than the distance d 2  in order to create the acoustic characteristics desired in the frontal acoustic chamber  520 . In order to achieve the acoustic signature, a specific ratio between the distance d 2  of the top and the distance d 3  of the bottom is maintained between about 0.45 and 0.70, more preferably between about 0.50 and about 0.60, and most preferably about 0.55; which is referred to as the Panel Offset Ratio. The Panel Offset Ratio is defined here by Equation (2) below: 
     
       
         
           
             
               
                 
                   
                     Panel 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Offset 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Ratio 
                   
                   = 
                   
                     
                       Distance 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       d 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       of 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       crown 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       offset 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       from 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       frontal 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       plane 
                     
                     
                       Distance 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       d 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       3 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       of 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       sole 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       offset 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       from 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       frontal 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       plane 
                     
                   
                 
               
               
                 
                   Eq 
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       FIG. 5  of the accompanying drawings also shows a specific geometry used to create the panel member  510  wherein the tri-facetted panel member  510  create a unique geometry wherein the center of the panel member  510  is further away from the striking face  502  to increase the volume of the frontal acoustic chamber  520 . Alternatively speaking, it can be said that the panel member has a unique geometry wherein the center of the panel member  510  being placed further away from the striking face  502  than at the crown  504  and sole  506  portion of the panel member  510 . 
       FIG. 5  of the accompanying drawings also shows more detail regarding the different facets created by the panel member  510  in creating the upper sub-panel member, the middle sub-panel member, and a lower sub-panel member. More specifically, a closer look at the panel member  510  in  FIG. 5  shows that the upper sub-panel member may form an angle θ with the middle sub-panel member of between about 10 degree to about 15 degrees, more preferably between about 12 degrees to about 14 degrees, and most preferably about 13 degrees. The lower sub-panel member and the middle sub-panel member form an angle β of between about 16 degrees to about 20 degrees, more preferably between about 17 degrees to about 19 degrees, and most preferably about 18 degrees. It should be noted here that similar to the intentional difference between distances d 2  and d 3 , the difference in the angle of the upper sub-panel member and the lower sub-panel member is intentional and critical in achieving the desired acoustic signature of the golf club head  500  as it alters the angle of the panel. 
     Finally,  FIG. 5  shows a different attachment methodology for the crown  504  composite panel and the sole  506  composite panel, as it relates to the chassis of the golf club head  500 . In this embodiment of the present invention, the crown  504  composite panel may generally be attached externally to the golf club head  500  via recesses created in the club head  500 , wherein the sole  506  composite panel is attached internally to the golf club head  500  via the opening created in the crown  504  section. This combination of different attachment mechanisms is beneficial to the current invention because it allows different unique constructions that would previously be difficult to achieve. In one example, the internal attachment of the sole  506  composite piece would allow an internal rib to be added wherein such an internal rib would not be physically possible if the attachment was external. Although the present invention shows the crown  504  composite piece being external and the sole  506  composite piece being internal, the two attachment methodologies could be reversed with the crown piece  504  being installed internally without departing from the scope and content of the present invention. 
       FIG. 6  of the accompanying drawings shows a golf club head  600  in accordance with an alternative embodiment of the present invention wherein the panel member  610  does not need any ribs. This alternative embodiment still incorporates a facetted panel member  610  that separates the panel member  610  in to three separate sub-components, and still utilizes pressure release holes  612   a  and  612   b  to achieve the acoustic properties desired. It should be noted that the necessity and placement of the ribs and pressure releases holes  612   a  and  612   b  may generally depend on the shape, contour, and choice of materials of the golf club head  600  and the acoustic signatures that it generates, and either of these components may exist independent of one another without departing from the scope and content of the present invention. In this current embodiment shown in  FIG. 6 , the golf club head  600  may exhibit sufficient structural stiffness in the panel member  610  in the bottom, but the acoustic attenuation within the frontal acoustic chamber builds up too much pressure and requires a relief via the pressure release holes  612   a  and  612   b.    
     In fact,  FIG. 7  of the accompanying drawings shows exactly one of the alternative embodiments of the present invention wherein the golf club head  700  incorporates a plurality of ribs  714   a  and  714   b  without the need for pressure release holes. This embodiment may be preferred when the acoustic signature of the golf club head is undesirable due to the lack of stiffness in the bottom portion of the panel member  710 . 
       FIG. 8  of the accompanying drawings shows a golf club head  800  in accordance with an alternative embodiment of the present invention wherein the panel member  810  that separates the frontal acoustic chamber and the rear weight saving chamber may be comprised out of one oversized pressure release hole  812  to help achieve differing acoustic frequencies that may be required for the golf club head  800 . In this embodiment of the present invention, the area of the oversized pressure release hole  812  may generally be greater than about 2,000 mm 2 , more preferably greater than about 2,200 mm 2 , and most preferably greater than about 2,400 mm 2 . The oversized pressure release hole  812  may be desired in situations wherein the acoustic properties of the golf club head  800  require such a design. 
     In order to illustrate the relationship between the frontal acoustic chamber and the rear weight saving chamber in this alternative embodiment of the present invention,  FIG. 9  is provided here showing a cross-sectional view of a golf club head  800  in accordance with an alternative embodiment of the present invention. In this cross-sectional view, it can be seen that the oversized pressure release hole  812  provides a large connection between the frontal acoustic chamber  820  and the rear weight saving chamber  822  not only for the acoustic properties as previously mentioned, but can also provide additional weight savings from the panel member  810  as well. 
       FIGS. 10 and 11  provide a rear opened view and a cross-sectional view of golf club heads  1000  in accordance with an alternative embodiment of the present invention wherein the oversized pressure release hole  1012  that is created on the panel member  1010  can be covered up by a lightweight panel  1016  to regain some of the acoustic characteristic and provide more separation between the frontal acoustic chamber  1020  and the rear weight saving chamber  1022 . The lightweight panel  1016  may be attached using different means of attachment such as gluing, screwing, swaging, just to name a few. One thing to recognize is that because the placement of the lightweight panel  1016  is away from the frontal contact region, the stresses of impact are smaller, allowing more simplistic attachment means to be used. 
       FIGS. 12 and 13  provide a rear opened view and a cross-sectional view of a golf club head  1200  in accordance with an alternative embodiment of the present invention wherein the panel member  1210  may take on a slightly different shape than previous embodiments. More specifically,  FIGS. 12 and 13  show a golf club head  1200  wherein the panel member  1210  is curved away from the frontal portion of the golf club head  1200  instead of being facetted into three different zones as shown in previous embodiments. Alternatively it can be said that the shape of the panel member  1210  is continuously curved with the center of the panel member  1210  being placed further away from the striking face  1202  than at the crown  1204  and sole  1206  portion of the panel member  1210 . Having a panel member  1210  that contains a continuous curvature is beneficial in certain embodiments wherein the acoustic signature of the frontal acoustic chamber  1220  requires more vibration, wherein the convergence points of the previous design would disrupts this vibration. In addition, the rear weight savings chamber  1222  may also benefit by minimizing the volume within that chamber. It should be noted although this embodiment of the present invention shown in  FIGS. 12 and 13  does not incorporate any ribs or pressure release holes, they can be incorporated into this design depending on the acoustic needs of the golf club head  1200  without departing from the scope and content of the present invention. 
       FIGS. 14 and 15  provides a rear opened view and a cross-sectional view of a golf club head  1400  in accordance with an even further alternative embodiment of the present invention wherein the panel member  1410  is a complete vertical wall. Having the panel member in the shape of a completely vertical wall is generally less desirable in creating the appropriate acoustic signature in the frontal acoustic chamber  1420 , as a completely vertical panel member  1410  can hinder the ability of the golf club head  1400  to generate the vibration needed to achieve a desirable sound. Conversely, the rear weight saving chamber  1422  is adjusted accordingly. However, in extreme situations wherein the profile of the golf club head  1400  requires such a design, this alternative embodiment of the present invention will provide a golf club head  1400  that can achieve the acoustic signature required. 
       FIGS. 16 and 17  provide an exploded perspective view and a cross-sectional view of a golf club head  1600  in accordance with an even further alternative embodiment of the present invention. In this alternative embodiment of the present invention, the golf club head  1600  is separated into two separate components, a forward metallic portion  1630  and an aft composite portion  1632 . It should be noted that the forward metallic portion  1630  and the aft composite portion  1632  refer to the external physical components that make up the golf club head  1600 , while the frontal acoustic chamber  1620  and the rear weight saving chamber  1622  refer to internal components within the golf club head  1600 . In this embodiment of the present invention, the external physical components of the golf club head  1600  are a striking face  1602 , a forward metallic portion  1630  having a frontal opening and forming a panel member  1610 , and an aft composite portion  1632 . The exploded view of the golf club head  1600  shown in  FIG. 16 , especially when compared to the exploded view of the golf club head  400  (shown in  FIG. 4 ) demonstrate the difference between the two embodiments of the present invention. More specifically, it can be seen here that the present embodiment shown in  FIG. 16  completely removes any metallic components from the rear portion of the golf club head  1600 , utilizing a completely composite material at the back half of the golf club head  1600  to further achieve weight savings. 
     In order to illustrate the relationship between the external physical components and the internal components,  FIG. 17  is provided with a cross-sectional view of the golf club head  1600 . In this cross-sectional view of the golf club head  1600 , it can be seen that the frontal acoustic chamber  1620 , similar to all previous embodiments, is completely formed by the forward metallic portion  1630 . However, the aft composite portion  1632  shown in this cross-sectional view illustrates that the entirety of the back of the golf club head  1600  is made out of a composite material, making the frontal acoustic chamber  1620  even more important in creating the proper acoustic signature. In this embodiment of the present invention, the aft composite portion  1632  is joined to the forward metallic portion  1630  via a lap joint wherein the aft composite portion  1632  is underneath the forward metallic portion  1630 . This type of unique construction of putting the composite material underneath the metallic material can be beneficial to the performance of the golf club head  1600 , as it lends itself well to the utilization of internal ribs to provide structural rigidity to a composite material that tends to need such a support. However, it should be noted here that although the golf club head shown in this embodiment of the present invention shows a lap joint, numerous other types of joints may be used as long as it is capable of connecting the forward metallic portion  1630  and the aft composite portion  1632  without departing from the scope and content of the present invention. 
     A lot of the aforementioned discussion relates to the utilization of the frontal acoustic chamber to create a desirable acoustic signature for a golf club head using different designs and embodiments. Hence, this invention would be remiss if it did not provide more information regarding what acoustic signature it achieves. 
       FIG. 18  of the accompanying drawing shows a time sequence diagram of the amplitude of the sound produced by the current inventive golf club head in accordance with an embodiment of the present invention. As the discussion previously indicated, the sound of the golf club head in accordance with the current inventive golf club head is one of the key factors in determining the performance of the golf club head. Before the discussion dives into the actual data, it is worthwhile to set forth the parameters of measurement of the present invention that will yield the results shown in  FIG. 18 . The time sequence diagram is created by gathering the audio profile using an audio recorder such as the TASCAM® DH-P2 Portable High Definition Stereo Audio recorder in conjunction with an A-weighting microphone. The recording is recorded at a distance of 39 inches away from the impact between the golf club head and the golf ball, which is determined as the distance that most closely simulates the distance to a golfer&#39;s ear as if he or she were hitting the golf club himself or herself. Data is sampled at 44.1 Hz to resolve the appropriate frequencies. 
     Moving onto the actual data shown in  FIG. 18 , we can see that on the x-axis, the time of the sound recording is shown in increments of 0.01 seconds; while on the other hand, on the y-axis shows the amplitude of the sound in millivolts. In the current sound recording shown in  FIG. 18 , it can be seen that the sound recording begins at a time  1844  right before impact with a golf ball and goes into a sinusoidal wave that reaches the peak amplitude A max  at a time point  1840 . Once the sound reaches the peak amplitude A max  at time point  1840 , the amplitude begins to resonate and begins decreasing until it dissipates completely. However, before it dissipates, it is worthwhile to note the point where the amplitude drops to beneath 10% of the peak amplitude A max  it is of particular interest, as it defines a time point  1842  where the sound amplitude becomes borderline negligible to the naked ear. Due to the inherent oscillating tendencies of sound shown here in  FIG. 18 , the determination of when the sound oscillation actually reaches down to 10% of the peak amplitude A max  can be difficult to discern visually. Hence, in order to help ease the determination, and in order to help pinpoint the oscillation variance inherent in these sound diagrams, the time where the amplitude is determined using a running average of the  5  most recent data points. In order to label this location of the 10% of the peak amplitude A max  it is said to occur at time point  1842  shown in  FIG. 18 . In the current exemplary embodiment of the present invention, the peak amplitude A max  is generally about 0.50 millivolts, occurring at a time point  1840  of about 0.007 seconds; while the diminished 10% peak amplitude A max  occurs at a time point  1842  of about 0.025 seconds. The time that occurs between these the time points  1840  and  1842  is critical to recognize because it helps define a Critical Time T critical . Critical Time T critical  provides a way to quantify the quality and desirability of the sound of the golf club head as it impacts a golf ball. In the present embodiment of the present invention, the Critical Time T critical  may be about 0.018 seconds. 
     A golf club head in accordance with the present invention may generally have a Critical Time T critical  of greater than about 0.01 seconds and less than about 0.02 second, more preferably greater than about 0.015 seconds and less than about 0.02 seconds, and most preferably greater than about 0.0175 and less than about 0.02 seconds without departing from the scope and content of the present invention. Alternatively speaking, it can be said that the time it takes for the sound amplitude to go from the peak amplitude A max  to an amplitude that is 10% of peak amplitude A max  is defined as the Critical Time T critical , and is generally greater than about 0.01 seconds and less than about 0.02 seconds, more preferably greater than about 0.015 seconds and less than about 0.02 seconds, and most preferably greater than about 0.0175 seconds and less than about 0.02 seconds. 
       FIG. 19  of the accompanying drawings provides an illustration of a time sequence diagram of a prior art golf club head that incorporates a composite crown technology that fails to recognize the importance of the sound component of a golf club head. As it can be seen from  FIG. 19 , not only the is peak amplitude A max  significantly lower than the current inventive golf club head by being close to about 0.25 millivolts, it loses amplitude really quickly yielding a Critical Time T critical  of less than about 0.01. In this exemplary prior art golf club head, the peak amplitude A max  occurs at a time of about 0.008 second, while the diminished 10% of peak amplitude A max  occurs at a time of about 0.015 second, yielding a Critical Time T critical  of about 0.007 seconds, which is significantly less than the inventive golf club head T critical  range of between about 0.01 seconds and 0.02 seconds. This prior art time sequence shown in  FIG. 19  generally yields an undesirable sound, which the present invention avoids by adjusting the thickness ranges of the different materials and their respective layers. 
       FIG. 20  provides more information regarding the acoustic signature of a golf club head that yields a desirable sound in accordance with the current inventive golf club head. Although the amplitude and duration of the sound is an important factor, it does not paint the entire picture about capturing the sound of a golf club head. More specifically, the third component in accurately capturing the sound of a golf club head is the frequency of the sound emitted by the golf club head during impact with a golf ball.  FIG. 20  provides exactly this information by presenting a spectrogram that provides a visual representation of the spectrum of frequency of sound as it varies over time. Although the spectrogram provided in  FIG. 20  contains a lot of information, the key feature to focus on is the dominant acoustic frequency  2046  occurring at a frequency that is above 3500 Hz. The dominant frequency is determined by the shading decided in the power/frequency chart  2048  on the right of the spectrogram itself shown in  FIG. 20 . 
     Similar to the discussion above regarding the amplitude of the current inventive golf club head, to truly appreciate the difference in the spectrogram of the acoustic signature of the current golf club head, a prior art golf club head that contains an undesirable acoustic signature is presented here in  FIG. 21 .  FIG. 21  of the accompanying drawings provides a spectrogram of a prior art golf club head that has composite material that produces an undesirable acoustic signature. Even a cursory examination of the spectrogram shown in  FIG. 21  shows a clear difference from the current inventive golf club head spectrogram shown in  FIG. 20 . More specifically, a closer examination of  FIG. 21  one can see that the dominant acoustic frequency  2146  occurs at a frequency that is significantly less than 3500 Hz, at a frequency of about 2100 Hz. This deficiency of frequency of 1100 Hz between this prior art golf club head and the current inventive golf club head, combined with the fast over damping of the amplitude of the golf club head explains the difference in a desirable acoustic signature and an undesirable acoustic signature previously discussed. 
     Finally, it is worth noting here that the panel member here may generally have its own resonant frequency of greater than 3300 Hz, which when combined with the other structures of the golf club head may yield the golf club head resonant frequency articulated above. 
       FIG. 22A  of the accompanying drawings shows a cross-sectional view of a golf club head  2200  in accordance with an embodiment of the present invention. Similar to the golf club  1600  described above with reference to  FIGS. 16 and 17 , the golf club head  2200  depicted in  FIG. 22A  includes a forward portion  2230  and an aft portion  2232 . In some examples, the forward portion  2230  may be made from a metallic material and the aft portion  2232  may be made from a non-metallic or composite material. In other examples, the forward portion  2230  may also be made at least partially of a composite material. The forward portion  2230  may be made from a material or combination of materials that has an effective density referred to as the first density, and the aft portion  2232  may be made from a material of combination of materials that has an effective density referred to as the second density. As discussed above, the second density may be lower than the first density. In some examples, if the aft portion  2232  includes additional structures, such as weights, those weights may be may be removed from the determination of the effective density of the aft portion  2232 . For example, any structures in the aft portion  2232  that have a density greater than three times the other materials of the aft portion  2232 , those structures may be excluded from the calculation or determination of the effective density of the aft portion  2232 . 
     The golf club head  2200  includes a striking face  2202 , a crown  2204 , and a sole  2206 . Each of those components is formed from portions of the forward portion  2230  and/or the aft portion  2232 . A cavity  2210  is formed between the crown  2204 , the striking face  2202 , and the sole  2206 . 
     The thickness of the aft portion  2232  in some examples may be less than 0.8 mm, and in some examples may be between 0.4 mm and 0.6 mm or less than about 0.5 mm. Due in part to the thin shell of the aft portion  2232 , a plurality of ribs  2214  are also included in the interior of the aft portion  2232 . For example, a crown aft rib  2214   a  may be attached to the interior surface of the aft portion  2232  at the crown  2204 , and a sole aft rib  2214   b  may be attached to the interior surface of the aft portion  2232  at the sole  2206 . The crown aft rib  2214   a  extends from the forward edge, or near the forward edge, of the aft portion  2232  and extend towards the rearmost point of the aft portion  2232 . For instance, he crown aft rib  2214   a  may extend from about 0-3 mm from the forward edge of the aft portion  2232 . In some examples, the crown aft rib  2214   a  may have length that is equal to the length of the aft portion  2232  measured a direction from the striking face  2202  to the rearmost point of the aft portion  2232 . The crown aft rib  2214   a  may also extend from the forward edge of the aft portion  2232  all the way to the rearmost point of the interior surface of the aft portion  2232 . In other examples, crown aft rib  2214   a  may have a length that is greater than about 80% or about 60% to 80% of the length of the aft portion  2232 . The sole aft rib  2214   b  also extends from the forward edge of the aft portion  2232  to the rearmost point of the aft portion  2232 . The length of the sole aft rib  2214   b  may be equal to the length of the aft portion  2232  measured a direction from the striking face  2202  to the rearmost point of the aft portion  2232 . In some examples, the sole aft rib  2214   b  may also extend from the forward edge of the aft portion  2232  all the way to the rearmost point of the interior surface of the aft portion  2232 . In other examples, the sole aft rib  2214   b  may have a length that is greater than about 80% or about 60% to 80% of the length of the aft portion  2232 . A weight  2208  may also be included in the aft portion  2232 . For example the weight  2208  may be positioned between the rearmost end of the sole aft rib  2214   b  and the rearmost point of the aft portion  2232 . 
     The crown aft rib  2214   a  and/or the sole aft rib  2214   b  may be made from the same material as the aft portion  2232 . In some examples, the crown aft rib  2214   a  and/or the sole aft rib  2214   b  may be made from a different material than the aft portion  2232 . For example, the crown aft rib  2214   a  and/or the sole aft rib  2214   b  may be made from a material having a Young&#39;s Modulus value greater than the Young&#39;s Modulus value for material of the aft portion  2232 . By having a stiffer material used for the crown aft rib  2214   a  and/or the sole aft rib  2214   b , additional support is provided the aft portion  2232 , resulting in a higher durability. 
     The forward portion  2230  and the aft portion  2232  are joined at a joint that is shown in further detail in  FIG. 22B .  FIG. 22B  of the accompanying drawings shows an enlarged view of a joint of the golf club head  2200  depicted in  FIG. 22A  in accordance with an embodiment of the present invention. The aft portion includes an opening towards the forward portion, and the joint extends continuously around the circumference of the opening. The forward portion  2230  and the aft portion  2232  are joined together via a taper joint. A taper joint is used to join the forward portion  2230  and the aft portion  2232  to improve the durability of the golf club head  2200 . As compared to a lap joint to connect the forward portion  2230  and the forward portion  2230  (which can be seen as the joint connecting the crown to the forward portion of golf club  1400  depicted in  FIG. 15 ), the taper joint provides for a reduced likelihood of a failure at the joint. For example, when the golf club head  2200  strikes a golf ball, the golf club head experiences a substantial amount of force and stress. In particular, a substantial amount of stress is applied to the joint, and the joint is often the most likely point for failure. With a standard lap joint, the stress and force experienced during a golf ball strike causes the outermost portion (the crown in  FIG. 15 ) to experience a peeling force that encourages the outermost portion to peel away from the inner portion (the forward portion in  FIG. 15 ). The use of the taper joint reduces the peeling force tendency. The inclusion of the ribs  2214  also strengthens the joint and reduce the likelihood of a failure at the joint. The use of the ribs  2214  and the taper joint also allows for the joint section (e.g., the area where the forward portion  2230  and the aft portion  2232  overlap) to be reduced. 
     As depicted in  FIG. 22B , at the taper joint, the forward portion  2230  includes a forward joint section that has a forward joint section exterior surface  2240  and a forward joint section interior surface  2242 . The forward joint section exterior surface  2240  is the surface of the forward portion  2230  that faces the exterior of the golf club head  2200 . The forward joint section interior surface  2242  is the surface of the forward portion  2230  that faces the interior of the golf club head  2200 . Similarly, at the taper joint, the aft portion  2232  includes an aft section joint that has an aft joint section exterior surface  2250  and a aft joint section interior surface  2252 . The aft joint section exterior surface  2250  is the surface of the aft portion  2232  that faces the exterior of the golf club head  2200 . The aft joint section interior surface  2252  is the surface of the aft portion  2232  that faces the interior of the golf club head  2200 . At the taper joint, the aft joint section exterior surface  2250  is in contact with the forward joint section interior surface  2242 . The aft joint section exterior surface  2250  may be attached to the forward joint section interior surface  2242  via an adhesive or other bonding application. The crown aft rib  2214   a  is attached to the aft joint section interior surface  2252  and extends in a direction away from the striking face  2202 , as also shown in  FIG. 22A . 
       FIG. 22C  of the accompanying drawings shows a perspective view of an aft portion  2232  of a golf club head in accordance with an embodiment of the present invention. In the embodiment depicted, two continuous aft ribs  2224  are attached to the interior surface of the aft portion  2232 . Each continuous aft rib  2224  extends from first location on a first half of the interior surface of the aft portion  2232  to a second location on a second half of the interior surface of the aft portion  2232 . For instance, the continuous aft rib  2224  may extend from the forward edge of the interior surface of the aft joint section at the crown to the forward edge of the aft joint section at the sole, as depicted in  FIG. 22C . In some examples, at least one surface of the continuous aft rib  2224  is entirely in contact with the interior surface of the aft portion  2232 . The continuous aft ribs  2224  may be made from the same material as the aft portion  2232 . In some examples, the continuous aft ribs  2224  may be made from a different material than the aft portion  2232 . For example, the continuous ribs  2224  may be made from a material having a Young&#39;s Modulus value greater than the Young&#39;s Modulus value for material of the aft portion  2232 . By having a stiffer material used for the continuous ribs  2224 , additional support is provided to the joint and the aft portion  2232 , resulting in a higher durability. In some examples, however, where the difference in stiffness is too large, such as the continuous ribs  2224  being made of a material that is significantly stiffer than the remainder of the aft portion  2232 , the continuous ribs  2224  may tear through the remainder of the aft portion  2232 . Accordingly, in some examples, the Young&#39;s Modulus value for the continuous ribs  2224  is no greater than the 120% of the Young&#39;s Modulus value for the material of the aft portion  2232 . In another example, where the aft portion  2232  is made from a fiber reinforced plastic, fiber may also be used in the continuous aft ribs  2224 . In one example, the fiber used in the aft portion  2232  may have a lower Young&#39;s Modulus value than the fiber used in the continuous aft ribs  2224 . 
       FIGS. 22D-22F  of the accompanying drawings show cross-section views of example profiles of an aft rib  2224  in accordance with embodiments of the present invention. In  FIG. 22D , a rectangular profile for the aft rib  2224  is shown. The rectangular profile for the aft rib  2224  can also be seen in  FIG. 22C . The rectangular profile of the aft rib  2224  has a height (H) and a width (W). In some examples, the width (W) may be about 0.5 mm and the height may be about 2 mm. In other examples, the width may be about the same width as the thickness of the outer shell of the aft portion  2232 . The height (H) of the rib may be greater than or equal to the width (W) of the rib  2224 . In  FIG. 22E , a round profile for the rib  2224  is shown. The round profile has a radius (R). In some examples, the radius (R) is approximately equal to the thickness of the outer shell of the aft portion  2232 . In other examples, the radius (R) may be about 0.5 mm. In  FIG. 22F , a trapezoidal profile for the rib  2224  is shown. The trapezoidal profile has a first width (W 1 ) for the wide base, a height (H), and a second width (W 2 ) for the short base. The wide base is the portion of the profile attached to the interior surface of the aft portion  2232 . In some examples, the first width (W 1 ) may be about 0.5 mm or about equal to the thickness of the outer shell of the aft portion. The second width (W 2 ) is less than the first width (W 1 ), and may be about 0.3 mm. In some examples the second width (W 2 ) is less than or equal to about 80% or 60% of the first width (W 1 ). The height (H) may be greater than or equal to first width (W 1 ). In some examples, the height may be about four times greater than the first width (W 1 ). By using a round profile or a trapezoidal profile, additional weight savings for a golf club head may be achieved as the total volume of the rib may be reduced. 
       FIG. 22G  of the accompanying drawings shows a perspective view of an aft portion  2232  of a golf club head in accordance with an embodiment of the present invention. In the embodiment depicted, a panel  2226  and/or a brace  2228  may be used rather than the continuous aft ribs  2224  depicted above in  FIG. 22C . In some examples, the panel  2226  and/or the brace  2228  may be used in addition to the continuous aft ribs  2224 . The panel  2226  and/or the brace  2228  may be made of the same materials as the continuous aft ribs  2224 . The panel  2226  is a generally planar piece of material. The brace  2228  is similar with the exception that some material has been removed, which may provide for weight savings in the golf club head. The width of the panel  2226  and/or the brace  2228  may be any of the widths discussed above with reference to the continuous aft ribs  2224 . 
       FIG. 23A  of the accompanying drawings shows an exploded perspective of a golf club head  2300  in accordance with an embodiment of the present invention. Golf club head  2300  may be similar to golf club head  400  discussed above and depicted in  FIG. 4 . For example, golf club head  2300  includes a crown  2304  and a sole  2306  that are detachable from the chassis  2301 . The golf club head also includes a striking face  2302 . The crown  2304  and/or the sole  2306  may be formed from a “sandwich-type” structure and include multiple layers to allow for the crown  2304  and/or the sole  2306  to have high stiffness and durability characteristics, while still maintaining a low mass. 
       FIG. 23B  of the accompanying drawings shows an enlarged cross-sectional view of a portion of a crown  2304  of the golf club head  2300  depicted in  FIG. 23A  in accordance with an embodiment of the present invention. The sandwich-type structure that makes up the crown can be more clearly seen in  FIG. 23B . The sandwich-type structure of the crown  2304  includes an outer layer  2350 , a middle layer  2352 , and an inner layer  2354 . The exterior surface of the outer layer faces the exterior of the crown  2304  and the golf club head  2300 . The middle layer  2352  is in contact with the outer layer  2350  and the inner layer  2354 . The interior surface of the inner layer  2354  faces the interior or cavity of the golf club head  2300 . The total thickness (T) of the crown is the sum of the thicknesses of each of the layers, and the thickness (T) may be measured from the interior surface of the inner layer to the exterior surface of the outer layer. For instance, the total thickness (T) of the crown is generally equal to sum of the thickness of the outer layer  2350 , the thickness of the middle layer  2352 , and the thickness of the inner layer  2354 . As will discussed further below, the total thickness (T) of the crown  2304  is generally thicker than what was previously pursued by those having skill in the art. To reduce mass, the generally accepted view was to reduce the thickness of the crown  2304 . The present inventors, however, have gone against that traditional wisdom to create a thicker crown that still has low mass properties while maintaining high stiffness and durability. For instance, in examples of the present technology, the crown  2304  may have an areal density of less than 1000 grams per square meter (g/m 2 ) yet have a thickness (T) that is greater than or equal to 0.8 mm. In some examples, the thickness (T) of the crown  2304  may be at least 2.5 mm and the areal density may be less than 900 g/m 2 . In golf club heads where the thickness (T) of the crown varies, the maximum or average thickness may be used. In the above examples, the maximum thickness of the crown  2304  may be 2.5 mm. 
     To achieve such results for the crown  2304 , the layers making up the crown  2304  may be manufactured to have particular specifications. In examples, the middle layer  2352  is the thickest of the three layers. For example, the inner layer  2354  may have a thickness of less than about 0.2 mm and the middle layer  2352  may have a thickness of at least 0.6 mm. The outer layer  2350  may have a thickness that is about the same as the thickness of the inner layer  2354 . The areal densities of each of the layers also have an effect on the total areal density for the crown  2304 . As an example, the outer layer  2350  may have an areal density of less than about 400 g/m 2 . The middle layer  2352  may have an areal density of less than about 300 g/m 2 . The inner layer  2354  may have an areal density of less than about 200 g/m 2 . In some examples, the inner layer  2354  and the outer layer  2350  may be made from a carbon-fiber material, a thermoplastic composite material, a thermoset material, a solid or foamed polymer, a metal, or a super wood. The middle layer  2352  may be made from a foamed material, such as a foamed polymer, graphite, or aluminum. The middle layer  2352  may also include balsa wood, graphitic foams, liquid crystalline polymer foams, or microcellular carbon. 
     By using such a sandwich-type structure for at least a portion of the crown  2304 , high stiffness-to-mass ratios can be achieved. Through the selection of the different layers, additional acoustic and stiffness customizations are also provided. For instance, different geometries and types of materials may be used to target different sounds or frequencies that are emitted from the golf club head when the golf club head strikes a golf ball. Similarly, because different materials can be utilized, additional shaping options are also provided. As an example, the present technology allows for crowns to take on many different shapes without being limited by curvature to achieve various levels of desired stiffness. Such shaping flexibility may yield volume savings or aerodynamic improvements. While a crown has been generally discussed herein, the materials, properties, and measurements may be equally used for a sole of the golf club head. Such sandwich-type structures may also be used for the skirt, internal structures, track or flat weight structures, and elongated or aerodynamic ferrules. 
     The crown and/or sole may be made from a variety of different manufacturing techniques. The inner, middle, and outer layers may be formed concurrently or separately and then subsequently attached. In one example, pre-fabricated sandwich structures are thermo-formed. In such an example, a thermo-formable sandwich construction method may be performed to create panels of the sandwich structure. Construction may include generating a foamed core between an inner and outer carbon-fiber skin. The foamed core may be a thermoplastic foam material that matches and/or is thermally compatible with the matric material in the composite inner and outer layers. The constructed panels may then be heated via infrared or other techniques. The panels may then be formed in a mold to the desired shape for the crown and/or the sole, potentially including variable thickness as well. For example, a FITS (Foamed In-situ Thermoform Sandwich) system panel may be utilized, such as a panel from FITS Technology of Driebergen, The Netherlands. Such panels may be based on a polyetherimide (PEI) thermoplastic polymer system for the matrix and/or foam material. The inner layer and outer layer in such panels may be a thermoplastic composite skin, such as the TenCate Cetex® thermoplastic composites available from Toray Advanced Composites of Morgan Hill, Calif. Such constructions may result in crowns having a maximum thickness of 3.2 mm or greater and areal densities (g/m 2 ) that are equal to, or less than, simpler composite constructions having thickness of 0.6 mm. As another example, a thermoplastic honeycomb panel may also be utilized, such as the honeycomb panels from EconCore of Leuven, Belgium. In such an example, a honeycomb middle layer may be utilized, such as a ThermHex® honeycomb core from ThermHex Waben GmbH, of Halle (Saale), Germany. The outer layer and the inner layer may be made from materials such as Tepex® materials available from Bond-Laminates GmbH of Brilon, Germany. Other thermoformable sandwich constructions are also available, such as sandwich construction made from materials from Topkey Corporation of Taiwan. 
     In another example, custom foam sandwich structures may be directly constructed. For example, a foamed polymer core may be created from heating a gas-saturated polymer sheet in a process published by Martini et al. That process is described in M. Itoh and A. Kabumoto, Effects of Crystallization on Cell Morphology in Microcellular Polyphenylene Sulfide,  Furukawa Rev.,  2005, vol. 28, 32-38, which is incorporated by reference herein in its entirety. In summary, the process includes saturating, in a pressure chamber, a thin polymer sheet with carbon dioxide or nitrogen gas under high pressure at room temperature for a determined period of time. If the pressure is higher, a shorter time is needed to achieve saturation. The gas pressure in the pressure chamber is then rapidly reduced and the polymer sheet is heated above its glass transition temperature to initiate foaming. Different temperatures may be used depending on the desired foam properties. The foaming process may be done before or after joining the polymer sheet to other thermoplastic composite skins as the inner layer and the outer layer. Such joining may be achieved via ultrasonic welding. 
     A ribbed sandwich construction may also be utilized to create the sandwich-type structure of the crown. The ribbed structure may be used to further stiffen the sandwich-type structure. The ribbed sandwich structure may also utilize a honeycomb or hex-pattern core, such as the ThermHex® honeycomb core discussed above. The honeycomb structure may use an engineered thermoplastic polymer, such as a polyphenylene sulfide (PPS), a polyether ether ketone (PEEK), a polyamide (PA), or similar polymer. The honeycomb hex pattern making up the middle layer may have a height or thickness of 0.5 mm to more than 3 mm. The honeycomb middle layer may be joined to the inner surface of the outer layer via injection molding. In an example, the injection molding process includes first heating the outer layer in the mold, and then the injection molding of the honeycomb middle layer happens afterward. Such a hybrid molding process is available from Bond-Laminates. The inner layer and outer layer may be a thermoset material, but they may also include thermoplastic matrix material. In some examples, the inner layer may also have cutouts to save mass, as discussed in further detail below with reference to  FIGS. 26A-B . The inner layer may be joined to the outer layer and the middle layer via ultrasonic welding. In other examples, the inner layer may be omitted entirely where no additional stiffness provided by the inner layer is required or desired. 
     In another example, an injection molded foam may be used in manufacturing a sandwich structure. For instance, a foaming agent may be incorporated into the molten polymer of an injection molding process. The foaming of the polymer and the generation of the skins (e.g., the inner layer and the outer layer) may be produced as part of the molding process. Such an injection molding process may include a hybrid molding process as discussed above where the thermoforming of the outer layer and the injection molding of the middle layer happens in the same mold. The foamed polymer middle layer may also be formed from the MuCell® injection molding process. Core back features may be utilized in some examples to further lower polymer density. 
       FIG. 24A  of the accompanying drawings shows a bottom view of a crown  2404  of a club head in accordance with an embodiment of the present invention.  FIG. 24B  of the accompanying drawings shows a cross-sectional side view of the crown depicted in  FIG. 24A  in accordance with an embodiment of the present invention.  FIGS. 24A-24B  are discussed concurrently. In the example crown  2404 , a circular section of the crown  2404  is made from a sandwich-type structure. In the circular section, the sandwich-type structure includes an outer layer  2450 , a middle layer  2452 , and an inner layer  2454 . The portion of the crown  2404  that is made from the sandwich-type structure may be at least 70% or more of the crown  2404 . In some examples, the portion of the crown  2404  made from the sandwich-type structure may be at least 80% or 90% of the crown  2404 . 
       FIG. 25A  of the accompanying drawings shows a bottom view of a crown of a club head in accordance with an embodiment of the present invention.  FIG. 25B  of the accompanying drawings shows a cross-sectional side view of the crown depicted in  FIG. 25A  in accordance with an embodiment of the present invention.  FIGS. 25A-25B  are discussed concurrently. The example crown  2504 , a circular portion of the crown  2504  is made from a sandwich-type structure. The sandwich-type structure of the crown  2504 , however, has a ribbed pattern. In the sandwich-type structure, the maximum thickness of the crown  2504  occurs at the peaks of the ribs where the thickness is the sum of the thicknesses of the outer layer  2450 , the middle layer  2552 , and the inner layer  2454 . The minimum thickness of the crown  2504  occurs at the valleys of the ribs where middle layer  2552  is omitted. At such valleys, the thickness of the crown  2504  is the sum of the thicknesses of the outer layer  2550  and the inner layer  2554 . In other examples, at such valleys, the middle layer  2552  is minimized, but not omitted. The ribs may be evenly spaced throughout the sandwich-type structure. 
       FIG. 26A  of the accompanying drawings shows a plurality of layers of a crown  2604  in accordance with an embodiment of the present invention. In particular,  FIG. 26A  shows multiple stages of generating the sandwich-type structure for the crown  2604 . At the first stage, a first layer  2650  has a middle layer  2652  attached. In the example depicted, the middle layer  2652  is a honeycomb or hex structure. The honeycomb structure of the middle layer  2652  may be any of the honeycomb structures and/or formed from the processes discussed above. At the second stage, the inner layer  2654  is attached to the middle layer  2652  and, in some examples, the first layer  2650 . As discussed above, the inner layer  2654  may be attached using a variety of methods, such as ultrasonic welding. The inner layer  2654  has had portions removed to reduce the overall mass of the inner layer  2654 . Such an inner layer  2654  with portions removed may be referred to as a partial inner layer. In the example shown in  FIG. 26A , portions of inner layer  2654  have been removed in a radial pattern. At the third stage, the final assembled sandwich structure of the crown  2604  is shown.  FIG. 26B  of the accompanying drawings shows a plurality of layers of a crown  2604  in accordance with an embodiment of the present invention.  FIG. 26B  is substantially the same as  FIG. 26A  with the exception of the inner layer  2654 . The inner layer  2654  in  FIG. 26B  is also a partial inner layer, but portions have been removed in a checkerboard pattern rather than a radial pattern. 
       FIG. 27  of the accompanying drawings shows a bottom views of a plurality of configurations of a crown in accordance with an embodiment of the present invention. More specifically, four different configurations of middle layers of the sandwich structure are shown in  FIG. 27 . Instead of a honeycomb structure, the middle layer may be formed as the structures depicted in  FIG. 27 , among other structures. For example, a first crown  2704 A has a middle layer  2752 A formed on an outer layer  2750 A. The middle layer  25752 A is formed as a grate or a series of intersecting ribs that protrude from the outer layer  2750 A towards the interior of the golf club head. As another example, a second crown  2704 B has a middle layer  2752 B formed on an outer layer  2750 B. The middle layer  2752 B is formed as a series of parallel ribs that protrude from the outer layer  2750 B towards the interior of the golf club head. As another example, a third crown  2704 C has a middle layer  2752 C formed on an outer layer  2750 C. The middle layer  2752 C is formed as a plurality of protruding ribs extending radially away from the center of the outer layer  2750 C. As another example, a fourth crown  2704 D has a middle layer  2752 D formed on an outer layer  2750 D. The middle layer  2752 D is formed as plurality of protruding ribs extending radially away from the center of the outer layer  2750 D as well as a plurality of protruding ribs in the form of concentric circles that intersect with radially extending ribs. 
       FIG. 28  of the accompanying drawings shows a table of data representing characteristics of example crowns in accordance with embodiments of the present invention. More specifically, the table in  FIG. 28  provides data for five different crowns: a crown made from titanium only, a crown made from a composite only, and three example crowns according to the present technology. The density (p), thickness (t), areal density (AW), area (A), and mass for each layer and for the total crown are provided for each crown in the table. The crowns had the same general shape as the example crowns discussed above. The titanium and composite crowns are provided for a baseline against the present examples. As can be seen from the table, the titanium crown has a density of 4.45 g/cm 3 , a thickness of 0.4 mm, an areal density of 960 g/m 2  an area of 9000 mm 2 , and a mass of 16 g. Because there is only one layer for the titanium crown, those values are also the total values. The composite crown has a density of 1.6 g/cm 3 , a thickness of 0.6 mm, an areal density of 960 (g/m 2 ) an area of 9000 mm 2 , and a mass of 8.6 g. Because there is only one layer for the composite crown, those values are also the total values for the crown. 
     The first example golf club (Example 1) had a crown with three layers. The outer layer was a PEI laminate skin that had a density of 1.91 g/cm 3 , a thickness of 0.2 mm, an areal density of 382 g/m 2 , an area of 9000 mm 2 , and a mass of 3.4 g. The middle layer was an in-situ PEI foam that had a density of 0.1 g/cm 3 , a thickness of 2.9 mm, an areal density of 290 g/m 2 , an area of 9000 mm 2 , and a mass of 2.6 g. The inner layer was a PEI laminate skin that had a density of 1.91 g/cm 3 , a thickness of 0.1 mm, an areal density of 191 g/m 2 , an area of 9000 mm 2 , and a mass of 1.7 g. Accordingly, the crown of Example 1 had a total area of 9000 mm 2 , a total mass of 7.767 g, a total thickness of 3.2 mm and a total areal density of 863 g/m 2 . 
     The second example golf club (Example 2) also had a crown with three layers. The outer layer was a PPS skin that had a density of 1.6 g/cm 3 , a thickness of 0.25 mm, an areal density of 400 g/m 2 , an area of 9000 mm 2 , and a mass of 3.6 g. The middle layer was a PPS honeycomb that had a density of 1.0 g/cm 3 , a thickness of 1.5 mm, an areal density of 240 g/m 2 , an area of 9000 mm 2 , and a mass of 2.2 g. The inner layer was a partial layer that was a PPS skin that had a density of 1.6 g/cm 3 , a thickness of 0.25 mm, an areal density of 200 g/m 2 , an area of 9000 mm 2 , and a mass of 1.8 g. Thus, the crown of Example 2 had a total area of 9000 mm 2 , a total mass of 7.56 g, a thickness total of 2 mm, and a total areal density of 840 g/m 2 . 
     The third example golf club (Example 3) also had a crown with three layers. The outer layer was a PPS skin that had a density of 1.6 g/cm 3 , a thickness of 0.25 mm, an areal density of 400 g/m 2 , an area of 9000 mm 2 , and a mass of 3.6 g. The middle layer was a PPS foam that had a density of 0.35 g/cm 3 , a thickness of 1 mm, an areal density of 350 g/m 2 , an area of 9000 mm 2 , and a mass of 3.2 g. The inner layer was a partial layer that was a PPS skin that had a density of 1.6 g/cm 3 , a thickness of 0.25 mm, an areal density of 200 g/m 2 , an area of 9000 mm 2 , and a mass of 1.8 g. Thus, the crown of Example 3 had a total area of 9000 mm 2 , a total mass of 8.55 g, a total thickness of 1.5 mm, and a total areal density of 950 g/m 2 . 
     As can be seen, the examples of the present technology are able to achieve lower areal densities despite having greater thicknesses. As the examples of the present technology may be formed or molded into a substantial number of different shapes that still preserve the stiffness and durability of the crown, the examples provide for an improved golf club having a lower total mass. The reduction in mass allows for higher swing speeds by a golfer and/or the ability to place discretionary weights in other areas of the golf club head. In addition, the different layers from the respective examples in the table may be combined with layers of other examples to form additional examples. 
       FIG. 29  of the accompanying drawings shows a table representing characteristics of example crowns in accordance with embodiments of the present invention. The crowns had the same general shape as the example crowns discussed above. For each example crown, the mass and a deflection are provided. The deflection is the amount the crown deflects when a 20 MPa pressure is applied to the substantially geometric center of the crown. The pressure is applied downward on the crown or in direction towards the sole or bottom of the golf club head if the crown is attached to the golf club head. An amount of increase in mass versus the baseline crown and an amount of change in deflection is also shown in the table. In general, a decrease in mass (indicated by a negative percentage) is desired with a decrease in deflection (indicated by a percentage less than 100%). The deflection score, or D Score, is a measure that accounts for such a change in mass as well as a change in deflection properties. The D Score is equal to 100% minus the mass increase vs baseline value plus 100% minus the deflection vs baseline value. The D Score, however, is represented in a decimal form rather than a percentage form (e.g., 0.31 rather than 31%). A representative equation for the D Score is thus: 
       DS=(100%−Δ M )+(100%−Δ D )
 
     where DS is the D Score, ΔM is the percentage change from the baseline mass of 5.21, and ΔD is the percentage change from the baseline deflection of 3.96. A D score of greater than 1 is indicative of an improved more efficient crown in that it has combined change in mass and change in deflection that is better than the baseline. Higher D Scores indicate higher efficiencies of the crown. Accordingly, in some examples, golf clubs having a D score of at least 1.3, 1.4, 1.5, or even 1.6 are utilized to more fully take advantage of the improvements of the present technology. 
     The baseline crown is a composite crown having a 0.5 mm thickness. The Example 1 crown is a titanium crown having a 0.4 mm thickness. The Example 2 crown is a crown having a polycarbonate foam middle layer, a 0.25 mm-thick outer layer, and no inner layer. The Example 3 crown is a crown having a polycarbonate foam middle layer with composite outer and inner layers each having a 0.25 mm thickness. The difference in deflection values from Examples 2 and 3 demonstrate the additional stiffness of the crown that results from adding an inner layer. The Example 4 crown is a crown that has a polycarbonate honeycomb middle layer with no outer layer or inner layer. The Example 4 crown shows how high deflection results from a lack of either an outer layer or an inner layer. The Example 5 crown is a crown having a honeycomb middle layer with an outer layer having a 0.25 mm thickness. The Example 6 crown is a honeycomb middle layer, but with larger hex patterns than Example 5, with an outer layer having a 0.25 mm thickness. The Example 7 crown is a crown with a honeycomb middle layer with composite outer and inner layers each having a 0.125 mm thickness. The Example 8 crown is a crown with a honeycomb middle layer with composite outer and inner layers each having a 0.25 mm thickness. The Example 9 crown is a crown that has a honeycomb middle layer with a composite outer layer with a 0.25 mm thickness and an inner layer in the shape of a circle having an area of about 50% of the area of the middle layer. The Example 10 crown is a crown that has a honeycomb middle layer with a composite outer layer with a 0.25 mm thickness and an inner layer in the shape of a plus sign centered on the middle layer. The Example 11 crown is a crown that has a honeycomb middle layer with a composite outer layer with a 0.25 mm thickness and an inner layer in the shape of a ring centered on the middle layer. 
       FIG. 30  of the accompanying drawings shows a plot of data for deflection versus mass of example crowns in accordance with embodiments of the present invention. More specifically, the plot includes a plurality of data points for example golf clubs in the table shown in  FIG. 29  with several additional data points. An efficiency line is displayed on the plot. The efficiency line is represented by the following equation: 
       Deflection=−0.3177(Mass)+5.615
 
     where deflection is the deflection in millimeters of the crown when a 20 MPa pressure is applied to the geometric center of the crown and the mass is the mass of the crown in grams. It has been found the crowns having mass and deflection properties below the efficiency line provide a combined improved mass and deflection properties, thus providing for a lighter, more durable golf club head. Accordingly, improved crowns have been identified where an amount of deflection of the crown as a function of a mass of the crown is governed by the following equation when subjected to a pressure of 20 MPa: Deflection≤−0.3177 (Mass)+5.615. Again while the above properties and data have been discussed for crowns, similar properties may also apply to other regions of a golf club head, such as the sole or weight support areas. 
     Other than in the operating example, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages such as those for amounts of materials, moment of inertias, center of gravity locations, loft, draft angles, various performance ratios, and others in the aforementioned portions of the specification may be read as if prefaced by the word “about” even though the term “about” may not expressly appear in the value, amount, or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the above specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Furthermore, when numerical ranges of varying scope are set forth herein, it is contemplated that any combination of these values inclusive of the recited values may be used. 
     It should be understood, of course, that the foregoing relates to exemplary embodiments of the present invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.