You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD 
       [0001]    This application relates generally to doors, and in particular, doors that are designed to be sound insulating. 
       BACKGROUND 
       [0002]    In the provision of so-called soundproof (or sound insulating) structures, it has been the general practice to use one type of construction for fixed walls and another type of construction for doors. However, difficulties have resulted from the doors being far less effective in sound insulation than the fixed walls so that regardless of the sound insulation properties of the wall, much of the efficiency is destroyed by sound transmission through the door. 
         [0003]    Another difficulty encountered in connection with sound-insulating door construction results from the fact that some structures, while relatively efficient at preventing the transmission of sound at some frequencies have a poor efficiency at certain particular frequencies. 
         [0004]    For many years, the general assumption has been that the control of sound through a barrier, such as a door, is accomplished by absorption. However, doors configured only to absorb sound waves have been found to still allow a significant amount of sound to pass therethrough. More specifically, because sound tends to travel linearly, the sound waves slow down, but still pass through the absorption material and escape through the door. 
       SUMMARY 
       [0005]    According to an embodiment of the present invention, a door is provided including a first panel having a plurality of stiffeners thereon; a second panel facing the first panel, the second panel having a plurality of stiffeners thereon facing the stiffeners on the first panel; a first baffle between the first panel and the second panel, the first baffle having a plurality of openings of a first size; and a second baffle adjacent to the first baffle and between the first panel and the second panel, the second baffle having a plurality of openings of a second size different than the first size. 
         [0006]    In one embodiment, the openings on the first baffle are arranged in columns extending across a lateral axis of the first baffle. The openings on the first baffle may be substantially rectangular and a longitudinal axis of the openings may be substantially perpendicular to a longitudinal axis of the first baffle. Moreover, the openings on the second baffle may be arranged in columns extending across a lateral axis of the second baffle. 
         [0007]    Similarly, in one embodiment, the openings on the second baffle are substantially rectangular and wherein a longitudinal axis of the openings is substantially perpendicular to a longitudinal axis of the second baffle. 
         [0008]    Further, in one embodiment, each of the stiffeners on the first panel and on the second panels includes a pair of feet contacting a surface of the first panel or the second panel, a top spaced from the surface of a respective one of the first panel and the second panel, and a pair of inclined connectors, each of the inclined connectors extending between the top and one of the pair of feet. The stiffeners may be elongate and extend diagonally with respect to a longitudinal axis of the first panel and the second panel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic exploded view of an embodiment of a door of the present invention. 
           [0010]      FIG. 2  is cross-sectional view of the door of  FIG. 1 . 
           [0011]      FIG. 3  is a front view of a first panel of the door of  FIG. 2 . 
           [0012]      FIG. 4  is a front view of a second panel of the door of  FIG. 2 . 
           [0013]      FIG. 5  is a cross-sectional view of a stiffener of the door of  FIG. 1 . 
           [0014]      FIG. 6  is a front view of a short slot baffle of the door of  FIG. 1 . 
           [0015]      FIG. 7  is a front view of a long slot baffle of the door of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    According to embodiments of the present invention, a door  10  is provided having improved sound insulation properties. In general, the door  10  includes a pair of baffles located between a pair of door panels and having a configuration of openings or slots intended to “deaden” sound waves passing through the door, thereby providing effective and efficient sound insulation. 
         [0017]    With reference now to  FIGS. 1 and 2 , the door  10  includes a first panel  20  and a second panel  22  spaced from and opposite to the first panel. The door  10  also includes edges extending between a periphery of the first panel  20  and the second panel  22 . The first panel  20  and the second panel  22  form the exterior panels of the door  10  and may also be referred to as the door skin. In embodiments, the first panel  20  and the second panel  22  are made from galvannealed sheet steel ranging from 18 gauge to 14 gauge and may be flat or embossed. However, it will be appreciated that the first and second panels  20 ,  22  may be made from any suitably rigid material and are not limited to those disclosed specifically herein. 
         [0018]    In one embodiment, each of the first panel  20  and the second panel  22  is substantially rectangular and has an external surface  26  and an internal surface  28 , wherein the internal surfaces of the panels face each other. In use, a longitudinal axis of the first and second panels  20 ,  22  extends vertically and a lateral axis extends horizontally. However it will be appreciated that a shape of the door  10  is not limited to the rectangle described herein, but rather that the door may have any suitable shape. 
         [0019]    One or both of the panels  20 ,  22  may include stiffeners  30  attached thereto to maximize the structural integrity of the door  10  and to further provide sound insulation. In one embodiment, the stiffeners  30  are elongate members that extend along a portion of the interior surface  28  of one of the panels  20 ,  22 . 
         [0020]    With reference now also to  FIG. 3 , the first panel  20  includes thirteen stiffeners  30  that are oriented such that a longitudinal axis of each stiffener  30  extends generally diagonally on the internal surface  28  with respect to the longitudinal axis of the panel. Additionally, all of the stiffeners  30  on the first panel  20  are oriented to extend substantially parallel to each other. Due to their diagonal orientation, the stiffeners  30  disperse sound to the outer more rigid rails of the door  10  rather than moving the sound vertically to the top and bottom edges of the door where it can more easily escape. In one embodiment, the stiffeners  30  are angled at about  45  degrees from the horizontal, but it will be understood that the stiffeners could be oriented at other angles as well. Additionally, it will be appreciated that although the stiffeners  30  have been described as being diagonally oriented in one embodiment, the stiffeners  30  may also be oriented vertically or horizontally within the scope and spirit of the invention. 
         [0021]    With reference now to  FIG. 5 , a cross-sectional view of the stiffener  30  is shown. The stiffener  30  includes a pair of feet  32 , a top  34 , and a pair of inclined connectors  36  extending between each foot and the top. In one embodiment, the feet  32  are substantially flat and substantially parallel to the internal surface  28  of the first panel  20  and the second panel  22 . Accordingly, the feet  32  provide a sufficient surface for coupling the stiffeners  30  to each panel  20 ,  22 , such as by welding or by a fastener, for example, an adhesive, a nut and bolt, a rivet, or a screw. However, it will be appreciated that the stiffeners  30  can be attached to the panels  20 ,  22  by any structure able to sufficiently secure them to the panels. 
         [0022]    The inclined connectors  34  extend from a respective foot  32  at an oblique angle. Although the specific angle is not critical, in one embodiment, the inclined connectors  36  extend at between about 110 degrees and about 125 degrees. The top  34  extends between the pair of inclined connectors  36  in a direction substantially parallel to the feet  32 . Accordingly, the stiffener  30  has a cross-sectional “mesa” or flat-top pyramid shape. In one embodiment, a height of the stiffener  30  is less than a thickness of the respective panel  20 ,  22  to which it is attached and its corresponding edge such that a height of a stiffener on one of the panels does not overlap with the height of a stiffener on the other panel. Specifically in one embodiment, the stiffener  30  has a height of between about 0.25 inch and about 0.75 inch, but it will be appreciated that the height is not limited thereto. 
         [0023]    The stiffener  30  may be made from a single integral piece of galvannealed sheet steel, for example, between 12 gauge and 20 gauge sheet steel, but it will be appreciated that the stiffener  30  may be made from any sufficiently rigid material and may be made from separate components coupled together rather than being integral. 
         [0024]    With reference now to  FIG. 4 , the second panel  22  also includes a plurality of stiffeners  30  having substantially the same configuration as those described with respect to the first panel  20  ( FIG. 3 ). As shown in the figure, the stiffeners  30  on the second panel  22  are also on the interior surface  28  and are oriented such that their longitudinal axis extends diagonally with respect to the longitudinal axis of the panel. However, the stiffeners  30  on the second panel  22  are oriented opposite to the stiffeners on the first panel  20  such that when the interior surfaces  28  of the first panel and the second panel  22  face each other, the stiffeners extend substantially parallel to each other. Additionally, the stiffeners  30  on the second panel  22  are spaced to occupy a space between adjacent stiffeners  30  on the first panel ( FIG. 2 ) such that the stiffeners on the first second panels  20 ,  22  alternate along the door  10 . 
         [0025]    With reference now to  FIGS. 6 and 7 , the door  10  includes a pair of baffles  40 ,  42  located between the first panel  20  and the second panel  22  ( FIG. 2 ). More specifically, the baffles  40 ,  42  are sized to have substantially the same size as the panels  20 ,  22  and serve to deaden sound waves within the door  10 . In one embodiment, the door  10  includes a short slot baffle  40  and a long slot baffle  42 . 
         [0026]    As shown in  FIG. 6 , the short slot baffle  40  includes a generally rigid and planar rectangular body  44  having a longitudinal axis extending in a first direction, for example, in a vertical direction when the door  10  is installed. Additionally, the short slot baffle  40  includes a plurality of openings or slots  46  arranged in columns  48  that extend in a second direction along a lateral axis substantially perpendicular to the longitudinal axis of the body  44 . Further, a longitudinal axis of each of the slots  46  extends parallel to the columns  48  of slots and therefore substantially perpendicular to the longitudinal axis of the body  44 . In one embodiment, a length of the slots  46  is between about 1.4 inches and about 1.6 inches and a width of the slots is between about 0.04 inch and about 0.14 inch. Further, in one embodiment, adjacent slots  46  in the same column  48  are spaced between about 0.2 inch and about 0.3 inch apart and the distance between a centerline of adjacent slots in adjacent columns is also between about 0.2 inch and about 0.3 inch apart. As shown in  FIG. 6 , the slots  46  in adjacent columns  48  are staggered such that a slot in a first column overlaps the space between adjacent slots in a second column adjacent to the first column. 
         [0027]    As shown in  FIG. 7 , the long slot baffle  42  is similar to the short slot baffle  40  and includes a generally rigid and planar rectangular body  50  having a longitudinal axis extending in a first direction, for example, in a vertical direction when the door  10  is installed. Additionally, the long slot baffle  42  includes a plurality of openings or slots  52  arranged in columns  54  that extend in a second direction along a lateral axis substantially perpendicular to the longitudinal axis of the body  50 . Further, a longitudinal axis of each of the slots  52  extends parallel to the columns  54  of slots and therefore substantially perpendicular to the longitudinal axis of the body  50 . In one embodiment, a length of the slots  52  is between about 3.9 inches and about 4.1 inches and a width of the slots is between about 0.2 inch and about 0.3 inch. Further, in one embodiment, adjacent slots  52  in the same column  54  are spaced between about 0.2 inch and about 0.3 inch apart and the distance between a centerline of adjacent slots in adjacent columns is between about 0.4 inch and about 0.6 inch apart. As shown in  FIG. 7 , the slots  52  in adjacent columns  54  are staggered such that a slot in a first column overlaps the space between adjacent slots in a second column adjacent to the first column. 
         [0028]    The slotted baffles  40 ,  42  improve sound insulation by confusing the sound. More specifically, each slot is tuned to a certain general frequency which bounces the sound within and through the baffling system, thereby significantly minimizing the ability for sound waves to escape from the door. 
         [0029]    An insulation material  60 , such as a fiber glass matting, is located between the first panel  20  and the second panel  22  including, in one embodiment, between the baffles  40 ,  42 , for sound insulation purposes. 
         [0030]    One embodiment of assembly of the door  10  will now be described. The first and second panels  20 ,  22  are formed from two faces that are punched into a pan assembly form. Each pan assembly receives the stiffeners  30  which may be taped or otherwise secured to the pan assemblies. After the stiffeners  30  are attached, the fiberglass matting  60  is inserted between the two panels  20 ,  22  and one, two, or more baffles  40 ,  42  are inserted between the panels. Additional fiberglass matting  60  may also be inserted between adjacent baffles. The halves are then joined and seam welded continuously to seal them together. 
         [0031]    While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.

Summary:
A door includes a first panel having a plurality of stiffeners thereon; a second panel facing the first panel, the second panel having a plurality of stiffeners thereon facing the stiffeners on the first panel; a first baffle between the first panel and the second panel, the first baffle having a plurality of openings of a first size; and a second baffle adjacent to the first baffle and between the first panel and the second panel, the second baffle having a plurality of openings of a second size different than the first size.