Abstract:
A two ply, synthetic drumhead for use in hand drums is created by using a laser to precisely remove excess material in the form of V-shaped notches from the peripheral portion of each layer disc of drumhead material prior to bonding and forming the drumhead sheet. After removal of the excess material, each layer disc has a peripheral edge consisting of equal size finger-like projections alternating with V-shaped notches. The layers are positioned so that the notches of one layer are covered by the projections of the other layer, producing a finished drumhead having a uniform exterior appearance and feel. The drumhead is tuned to duplicate the sound of a natural skin drumhead by positioning a damping element between the layer discs prior to bonding and assembly.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to the field of musical drums and is more particularly directed to a drumhead and a method for producing the drumhead. The drumhead is specifically adapted to be used in conjunction with hand drums. 
     Hand drums refer to musical drums that are usually played with the hand instead of with sticks, e.g., conga, bongo, djembe and bata drums. Hand drums have a generally cylindrical drum shell, typically constructed of wood, which has an open top and bottom. Shells for hand drums, such as conga drums, frequently have a shape which is larger around the middle and tapered toward the top and bottom openings. The top opening is usually covered with an animal skin drunhead tightened and tuned to a desired musical tone. Traditionally, such animal skins were tightened over the top of the wooden drum shell by the use of rawhide binding strips, twine or rope, producing a drum and head assembly not easily tuned or modified. While natural skin drumheads produce beautiful musical tones, they are also very sensitive to atmospheric changes such as heat and humidity. Large changes in temperature or humidity can dramatically change the musical tone of a natural skin head and render drums so equipped unplayable. 
     To address these disadvantages, musical instrument makers have developed synthetic drumheads closely approximating the musical characteristics of traditional skin drumheads. Synthetic drumheads are constructed from sheets of synthetic material joined to a drum hoop and formed to fit over the open top of a drum shell. The drum hoop is sized to pass over the open top end of a drum shell and be drawn toward the bottom of the drum shell by a counterhoop and tensioning mechanisms. Using such an arrangement makes changing drumheads and tuning of hand drums relatively quick and easy. 
     Manufacturing a synthetic drumhead which duplicates the sound quality of a natural skin drumhead requires the use of relatively thick layers of synthetic material. To construct a hand drumhead, these flat sheets of synthetic material must be formed into a shape having a planar central portion surrounded by a conical portion which terminates in a circular edge. Skin drumheads assume this configuration naturally when stretched over the open end of a drum shell. In contrast, when a flat disc of synthetic material is formed into a drumhead having a conical peripheral portion, a significant amount of excess material is produced which will overlap in folds creating a rough and irregular exterior surface on the conical portion of the drumhead. 
     It is known in the art to cut the peripheral edge portion of a synthetic drumhead into a series of slots which will allow the excess material to overlap without folding, somewhat alleviating the irregular surface problem. However, the overlapping material produces an uneven surface and the slots cut in the peripheral edge of the drumhead must be covered to produce a professional appearing drumhead. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a unique method for producing a synthetic hand drumhead by removing excess material from the periphery of the drumhead in the form of precisely cut V-shaped notches, leaving a peripheral edge made up of a series of finger-like projections of equal size. The removed material allows the synthetic drumhead material to lay flat without overlapping when it is formed into the shape of a drumhead. The notches are preferably cut with a numerically controlled laser, which can simultaneously cut a plurality of sheets of drumhead material. 
     During the forming process for the preferred embodiment of the drumhead, identically cut discs of drumhead material are bonded to each other with the finger-like projections of the first layer covering the V-shaped notches of the second layer. This configuration of layers produces a conical peripheral portion of a drumhead having a uniform appearance and feel which appeals to hand drum players. 
     In a preferred embodiment, the drumhead may be tuned by adding a damping element between the discs of drumhead material prior to forming, resulting in a drumhead which more closely duplicates the sound of a natural skin head. In a further preferred embodiment, the outwardly facing or planar surface of the drumhead is texturized to give the normally smooth synthetic material a more natural appearing and feeling surface texture. 
     An object of the present invention is to provide a method for cutting the disk-shaped layers of a hand drumhead from sheets of synthetic material which allows the efficient production of professional quality synthetic hand drumheads. 
     Another object of the invention is to provide a synthetic hand drumhead having a uniform outwardly facing surface and professional appearance. 
     A further object of the invention is to provide a method for manufacturing a synthetic hand drumhead of superior appearance and musical quality. 
     A yet further object of the invention is to provide a new and improved synthetic hand drumhead which closely approximates the feel and sound quality of a natural skin hand drumhead. 
     These and other objects, features and advantages of the invention will become readily apparent to those skilled in the art upon reading the description of the preferred embodiments, in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will be evident to one of ordinary skill in the art from the following detailed description, made with reference to the accompanying drawings, in which: 
     FIG. 1 is a top plan view of a disc of drumhead material prepared according to one aspect of the claimed invention; 
     FIGS. 1A,  1 B and  1 C are enlarged views of the disc of FIG. 1, illustrating various possible configurations; 
     FIG. 2 is a top plan view of the disc of FIG. 1 with a damping element centrally positioned thereon; 
     FIG. 3 is a schematic view, partly in phantom, of two discs of FIG. 1 (partially illustrated) positioned according to an aspect of the present invention; 
     FIG. 4 is a perspective view of a drumhead in accordance with the present invention; 
     FIG. 5 is a cross-sectional view, partly in phantom, of a drum shell (partially illustrated), a drumhead consisting of a drumhead sheet and drum hoop and a counter-hoop in an installed configuration; 
     FIG. 6 is a schematic cross-sectional view of a drum hoop according to the present invention; 
     FIG. 7 is a top plan view of the drum hoop of FIG. 6; and 
     FIG. 8 is a plan view of several discs of FIG. 1 being produced according to the method of the claimed invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in more detail and initially to FIG. 1, a disc of drumhead material  12  is shown having a peripheral edge  18  cut into a series of V-shaped notches  16 , leaving equal sized finger-like projections  14 . In the context of this application, the term Vshaped is used to describe the general shape of the material removed from the peripheral edge  18  of the drumhead layer discs. Notches having a pointed apex  17 A, a rounded apex  17 B or a square apex  17 C are illustrated in FIGS. 1A,  1 B and  1 C, respectively. The angled sides  19  of the notches  16 ,  16 A are preferably straight, but may be curved as indicated by the dashed lines in FIG.  1 C. V-shaped notches  16 ,  16 A may take any of the forms illustrated in FIGS. 1A,  1 B or  1 C without departing from the spirit and scope of the invention. 
     FIG. 2 illustrates another disc of drumhead material  12  with a damping element centrally positioned on the disc. The discs  12  of FIGS. 1 and 2 are preferably cut from flat sheets of drumhead material by a programmable machine tool using a laser cutting head. The use of an automated tool (not illustrated) and a laser cutting instrument result in discs of uniformly identical size having exactly the desired amount and shape of material removed from their peripheral edge. 
     FIG. 3 illustrates the positioning of two discs  12  (partially illustrated) prior to forming and bonding. The finger-like projections  14  of the top disc cover the V-shaped notches  16 A of the bottom disc and the finger-like projections  14 A of the bottom disc are beneath the V-shaped notches  16  of the top disc. 
     FIG. 4 illustrates a finished drumhead  10  according to the present invention. The layered flat discs of FIG. 3 are bonded together over a form having a substantially planar central portion  28  surrounded by a conical connecting surface  26  which connects the planar central portion  28  of the drumhead  10  with the drum hoop  30 . The conical connecting portion  26  terminates in a circular edge which is secured within the drum hoop  30  by use of a resin or epoxy  33 . In a preferred embodiment, each finger-like projection has a hole  20  cut near the peripheral edge. These holes  20  allow the resin or epoxy  33  to pass through before hardening, producing a stronger bond between the drum hoop  30  and the finger-like projections  14  which make up the connecting surface  26  of the drumhead  10 . 
     FIG. 5 illustrates a hand drumhead  10  constructed in accordance with the present invention installed over a drum shell  40  (partially illustrated). A counter hoop  42  engages the drum hoop  30  and pulls the drum hoop  30  toward the opposite end of the drum shell (not illustrated) creating tension in the planar central portion  28  of the drum head sheet  24 . The conical connecting surface  26  connects the planar central portion  28  of the drumhead sheet  24  with the circular edge  34  which is secured in the annular interior space  32  of the drumhead  30 . 
     FIGS. 6 and 7 illustrate the configuration of a drum hoop  30  appropriate for use in conjunction with the present invention. The drum hoop  30  is constructed of an extruded rigid material, preferably aluminum. FIG. 6 illustrates the generally U-shaped cross-section of the drum hoop  30  defining an interior space  32 . FIG. 7 illustrates the drum hoop of FIG. 6 as seen from above. Upper inner edge  36  and upper outer edge  38  define an opening to the annular interior space  32 . 
     With reference to FIGS. 5 and 8, according to a preferred method, a sheet of material  48  which will form each layer of a drumhead sheet is selected according to its thickness, musical properties and other characteristics. Preferred materials for use in conjunction with the method of the present invention are polyester sheet materials having a thickness in the range of 0.015 to 0.025 inches. The layer discs used to form the drumhead may be cut from film having the same thickness or different thicknesses. Different combinations of layer thicknesses will produce drumheads having different musical characteristics. 
     The dimensions of the drumhead to be constructed are determined and used to calculate the diameter of a disc of layer material which will be necessary to produce a finished drumhead of that size. The diameter of the bearing area  44  of the drum shell  40  determines the diameter of the planar central portion  28  of the finished drumhead  10 . A drum hoop  30  must be selected which will pass over the open end of the drum shell  40  far enough to create tension in the planar central portion  28  of the drumhead sheet  24 . The diameter of the drum hoop selected determines the diameter of the circular edge  34  of the finished drumhead. 
     With these measurements, the amount of material to be removed from the peripheral edge portion  18  of each layer disc  12  in the form of V-shaped notches  16  may be determined. The amount of material to be removed varies dependent on the difference between the diameter of the unformed layer disc  12  and the diameter of the circular edge  34  of the formed head. The greater the difference between these two dimensions, the more material must be removed to create a smooth conical connecting surface  26 . In a typical drumhead, approximately 30% of the material in the peripheral portion of the layer disc  12  is removed. 
     Once the dimensions and layout of the layer disc  12  have been determined, a machine tool (not illustrated) is preferably programmed to execute cutting the disc and its complex peripheral edge pattern from the selected sheet of drumhead material. The sheet of drumhead material  48  is placed on a vacuum table  52  and held in place by suction transmitted to the surface of the table through vacuum holes  54 . The programmable tool is then programmed to cut the maximum possible number of layer discs  12  given the size and shape of the sheet  48 . Locations for layer discs  12  are designated as target areas  58  on the sheet  48 . 
     A CO 2  laser cutting head  50  using a 0.010 inch beam  56  set at 100 watts of power is preferably used in conjunction with the programmable machine tool to produce a layer disc  12  of precise shape having a peripheral edge  18  in the correct configuration without rough edges or excess material. With reference to FIG. 1B, the programmable machine tool is directed to move the laser beam from point w laterally to point x, radially inwardly from point x to point y, radially outwardly from point y to point z and laterally to point x 1  repeatedly around the peripheral edge of the target area  58  until a layer disc  12  is produced. 
     An example of a programmable machine tool which may be used to cut the layer discs is the REBEL model manufactured by Vytek, Inc. of 2 Omega Way, Littleton, Mass. Such a machine tool is preferably equipped with a laser cutting device which produces a fine beam in the range of 0.005 to 0.010 inches in diameter. The fine beam reduces heat buildup during cutting which can lead to burning of the layer material. 
     In a preferred embodiment, two such layer discs are cut for each finished drumhead. The layer discs are then placed one on top of the other, in an offset configuration, so that the V-shaped notches  16  of one layer are above or beneath the finger-like projections  16  of the other layer. In this fashion no notch  16  passes completely through to the interior surface  8  of the drumhead sheet  24  and nowhere is there extra material folded, overlapping or otherwise gathered. The layer discs so positioned are then bonded using heat and pressure in a mold (not illustrated) having a substantially planar central surface and a conical peripheral surface. The hot, bonded layer discs are then placed in a second, chilled mold of the same configuration. The chilled mold “sets” the bonded layer discs into the desired shape for the finished drumhead. 
     Once set, the two layers remain in the shape of the finished drumhead having a planar central surface  28  and a conical connecting surface  26  substantially formed from the alternating V-shaped notches and finger-like projections bonded in staggered fashion one over the other. The resulting formed drumhead sheet  24  terminates in a circular edge  34  which may be inserted into the annular interior space  32  defined by the drum hoop  30  and secured within that space by a resin  33 . 
     In a preferred embodiment, each layer disc finger-like projection  14  has a single hole  20  formed near peripheral edge  18  by the laser cutting tool. The holes  20  allow the epoxy or resin to more securely engage the circular edge  34  of the drumhead sheet  24 . 
     In another preferred embodiment, the drumhead  10  is rotated beneath several nozzles, (not illustrated) each propelling a high speed stream of very fine abrasive particles at the outwardly facing surface  6  of the drunhead  10 . This process gives the normally smooth synthetic material a uniformly texturized surface having the friction and feel so important in drums which are played by the hand. 
     In an alternative embodiment, an acoustical damping element  22  may be inserted between the layer discs  12  of the drumhead  10 . The damping element  22  alters the vibration characteristics of the finished drumhead to more closely duplicate the tonal qualities of a natural skin drumhead. 
     Other modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. This description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and method may be varied substantially without departing from the spirit of the invention and the exclusive use of all modifications which come within the scope of the appended claims is reserved.