Abstract:
A loudspeaker having a cylindrical sound-producing membrane includes an acoustic lens which radially surrounds the membrane. The membrane is composed of wire mesh formed into a cylinder. The cylindrical membrane is positioned on the magnet structure by an inner supporting cylindrical core column. Sound from the membrane is fractionally redirected by the lens which is centered along the axis of the membrane. The lens includes a plurality of radially disposed petals that reflect a portion of the sound. The base of the lens supports and mounts the loudspeaker magnet and driver assembly.

Description:
FIELD OF THE INVENTION 
     The present invention relates to high fidelity loudspeakers. More specifically it relates to high frequency tweeter loudspeakers which have sound dispersion structures. 
     BACKGROUND OF THE INVENTION 
     My previous U.S. Pat. No. 3,939,942, which is hereby incorporated by reference as though fully set forth herein, introduces a loudspeaker having a cylindrical sound-producing surface. The surface comprises a matrix of helically oriented fibers suspended in an elastomeric impregnate. The soft textile bundles of the membrane have restricted motion due to a large surface area that develops at the crossover points in the fine bundles such as fiberglass cloth which are then bonded by the sealant. While the device described in the &#39;942 patent permits ease of manufacture, flexibility of the end product is greatly sacrificed. Consequently, relative to other technologies of the modern era this device is less efficient than desired. 
     Relevant prior technologies are disclosed in the following U.S. Pat. No 1,862,552 to Schlenker; U.S. Pat. No. 6,061,461 to Paddock; U.S. Pat. No. 4,138,733 to Falkenberg; U.S. Pat. No. 4,761,817 to Christie; U.S. Pat. No. 4,164,613 to Garner; U.S. Pat. No. 8,418,802 to Sterling; and U.S. Pat. No. 3,735,336 to Long. 
     SUMMARY OF THE INVENTION 
     The present invention greatly improves upon the device described in my previous &#39;942 patent. The sound-producing diaphragm of the present invention comprises an array of formed wires which constitutes a cylindrical mesh membrane. The shape of the membrane is supported by the retained shape of the wires which are interwoven and then further formed into a closed cylindrical shape. Formation of the cylinder by bonding two virtually identical seamed halves of mesh sections provides balance in a preferred version. Overlay pieces may be employed to bond the edges of the identical section halves together along two radially symmetrical helical seams. The cylindrical membrane is positioned on the magnet structure by a core support column which extends from the magnet structure up through the center of the membrane cylinder. A voice coil is attached to the membrane cylinder around its bottom circular edge using a former at the driving end of the membrane adjacent the magnet structure. A former typically constitutes a thin strip of aluminum foil formed into a short cylinder. The opposite stationary retained top end of the mesh membrane is attached to a termination collar held by the top of the core column. The retainers typically constitute a terminus and associated washer. 
     The use of wires in contrast to the prior art are individually self-supporting because of their retained shape memory within the group without impregnation. Furthermore they do not deform during impregnation at the wire crossovers like fiberglass and similar carbon fiber or Kevlar products with hundreds or thousands of strands. This relatively enhanced deformability of the sealed wire mesh membrane permits miniaturization. 
     Sound from this membrane is fractionally redirected by a lens surrounding the axis of the cylinder thus maintaining virtually constant dispersion over the useable frequency range. The lens includes a plurality of radially disposed petals which reflect a portion of the sound to achieve better sound dispersion. The base of the lens structure also supports and mounts the driver assembly. Other features such as electrical terminal mounting holes are also contained in the lens structure. 
     The resulting mechanism of the present invention is best described as a motion transformer with a fixed area of vibratory action than as a transmission line where low frequencies are found near the terminal end and high frequencies concentrate near the driving source. The wire mesh has a relatively frequency independent central zone of maximum output equidistant between the voice coil and the terminal mounted end. 
     Thus the present device has many differences from the device disclosed in my previous patent U.S. Pat. No. 3,939,942. Other advantages and differences will follow from the foregoing explanation and the following drawings and description of the invention. The preferred embodiment of the invention will provide one of skill in the art with a full understanding of what has been invented. It will thereby be appreciated that the object of the invention to devise a high frequency loudspeaker with various advantages over the prior art has been achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a dual axis perspective cutaway view. 
         FIG. 2  is a perspective assembly view. 
         FIGS. 3 and 4  are diagrams showing the basic operation of the sound producing mesh cylinder. 
         FIGS. 5 through 7  are perspective views of different cylinder mesh weaves. 
         FIG. 8  is a perspective view diagrammatically showing sound dispersion patterns of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a cutaway view of the preferred embodiment of the loudspeaker invention and  FIG. 2  is an assembly view thereof. Line  8  represents a cylindrical longitudinal axis of the device in the direction of motion of the voice coil  17 . The axis line&#39;s arrow indicates the upward axial direction. As seen in these Figures the components of the device are radially symmetrical about the axis  8 . Accordingly this drawing will give clear meaning to the terms; “axial”, “axially”, “upwardly”, “top”, “bottom”, used herein. 
     Referring now to  FIGS. 1 and 2 , an acoustic lens  11  has a base  7  which unifies the loudspeaker assembly. A radial array of axially extending diffuser petals  10  is attached to the lens base to increase the sound dispersion at the highest frequencies. The sound-producing diaphragm  15  is a wire mesh membrane covered with a sealant and formed into a cylinder which is located about the longitudinal axis  8 . A core column  19  is the main structural support for the membrane and extends coaxially up through the center of the membrane. The membrane is located coaxially about the support column and is suspended from its top end by an intermediate termination collar  14  attached to the top of the support column. The termination collar  14  is preferably composed of rubber and is capped by a washer  13 . The base  7  of the lens  11  also holds a magnet structure which surrounds the bottom of the membrane  15 . The magnet structure is an assembly united by an adhesive and is comprised of a magnet  24 , a magnetic focusing structure  25 , and a top plate  23 . The circular bottom edge of the membrane is positioned by the core column  19  in a gap between magnet  24  and magnetic focusing structure  25 . A former  16  composed of a thin cylinder of aluminum foil is affixed between the voice coil  17  and the membrane  15 . 
     With continued reference to  FIGS. 1 and 2 , the lens  11  includes means at the base  7  for mounting the magnet and core column  19  structures described above. The bottom of core column  19  is affixed to the magnet assembly top plate  23  and is hollow, preferably including slots  30 . It is surrounded on either side by acoustic damping means comprising two cylindrical felt layers  20  and  21 . The outer felt layer  20  dampens the sound-producing membrane while the felt plug  21  inside the column absorbs the inwardly directed sound. The slots  30  provide a path for air pressure changes to be conducted through the felt layer  20  on the surface of the core column to the felt plug  21  in the interior which also acts to resistively dissipate acoustic energy. Gasket  22  retains the lead out wires from the voice coil and positions the magnet structure within the lens  11 . An acoustic shim  12  creates a narrow annulus at the base of the membrane. A second magnet  18  is held in a countersink at the end of the core column in part to collect magnetic dust, attracting it away from the voice coil  17 . Optional plug  26  and dust shielding magnet  18  complete the assembly. The petals  10  are equally spaced apart about 360 radial degrees. In the example shown the spaces or gaps between the individual petals are approximately one-half the width of each of the petals which are all substantially identical. The particular dimensions and proportions shown are to be only considered as exemplary and may vary. Shown here is an array of sixteen petals as exemplary of one embodiment of the invention however the individual petals have an arcuate longitudinal cross-section such that they flare outwardly toward their free ends. Unless otherwise specified all components whether indicated as “affixed”, “attached” or otherwise are united by a suitable adhesive 
       FIGS. 3 and 4  illustrate the basic operation of the sound-producing membrane of the invention. It is believed the highest frequency motion  27  is transmitted directly in the cylinder wall mesh as shown. This is because the assembly including the mesh sealant provides a shorter path of less resistance than bending the wires. Viscous properties in the sealant provide a lower resistance path. The viscous sealant thus becomes less flexible at higher frequencies but offers little change in the modulus of elasticity of the assembly statically. At low frequencies axial force  28  is converted to radial motion  29  by the bending of the wires in the mesh. It is further believed compressive and tensile forces on the assembly  27  can place stress in tension and compression depending on the direction of actuation along each wire (through the center line of the wire undulations) and along the curvature of the individual wires which regulate the deformation of the cylindrical membrane in accordance with the bending deformations which are also the result of motion  27 . These compressive and tensile forces can be characterized by a resonance near the top of the band at high frequencies which enhances efficiency. Because of the angle of the wire array the internal volume increases as the cylindrical form is compressed and decreases as it is stretched. The bending motion compliance provides a resonant frequency typically an order of magnitude lower than the high frequency effect described above. The lower resonant frequency is typically predominantly a function of the internal acoustic compliance of the assembly. The force  27  acts on the bias ply of the wire mesh typically at 45 degrees to each wire. 
       FIGS. 5 through 7  depict various weaves of the wires which comprise the cylindrical membrane. In  FIG. 5  we see a plain weave of formed wires that retains the shape of the assembly due to the residual retained shape of the wires. If the cylinder is formed from portions of a flat sheet the wire shape memory will flare the ends of the cylindrical shape which bends each wire unless the ends of each wire are affixed to the voice coil assembly and terminal assembly. Alternatively there may be variations in the weave where strands of a first degree of stiffness in one direction can be straight or almost straight crossed by woven strands of a second degree of stiffness in the other direction with a greater bend as seen in  FIG. 6 . The large wire can be composed of a few strands of smaller wire combined with the large wire in the asymmetrical weave. Undulating and straight variations are shown on  FIG. 7 . The undulations can vary and the shape of this bundle can vary by rearranging the strands. This can occur many times in a weave. This mesh is referred to as “Organza” in the fabric industry. These wires are typically a plastic such as polyester. In one direction in the organza the formed bundle can vary between in line or triangular. The use of an asymmetrical weave is believed to add a rotary reactive force on the voice coil. This can enhance the stability of the voice coil motion. The reduced or eliminated wire form undulation in one direction provides a more direct path for axial tension and compression in the wire. This can provide a desired modification in vibratory operation of the mesh. The other direction should be formed to accommodate the thicker wire and provide minimum thickness in the weave. 
     In one method of construction a flat section of wire mesh is cut into two trapezoidal sections. One section is bonded to a second identical section by being adhered to identical intermediate bonding strips which lie across the helical seams between the sections. The mesh has little dimensional stability prior to bonding the halves together so a rigid cylinder form is used. When wrapped around the cylinder form the final bond creates the cylindrical membrane. This method of producing the invention preferably incorporates the use of sacrificial liners to facilitate handling the mesh during manufacturing. The adhesive properties of the sealant require the use of non-adhesive liners such as wax paper. Dual liners can be used for part of the process. Once the sealed mesh is sandwiched between the liners the mesh is cut and then formed around the cylinder. Only after the assembly is complete and the now cylindrical mesh attached at both helical side seams and to the termination collar and former is it desirable to fully remove the liners. The final assembly has a flexible but stable shape due to the aggregate effect of individual shape memory of each wire and in the case of a formed originally flat construction the end attachments of each wire. Plastic wire which has functional elastic qualities within the bounds of its rigidity has been used. Metal wire performance is also advantageous. The wires flex together with very low sealant binding forces. While forming the wires directly into a cylinder shape by weaving could avoid assembling the cylinder from identical halves as described above, it does not appear to be presently practical. 
       FIG. 8  shows how the lens alters the sound dispersion pattern of the membrane at high frequencies where the sound becomes directional. The output level and directionality without the lens is represented by pattern  34 . The radial line of pattern  34  shows the original directional signal strength. The arc of pattern  34  shows the dispersion in a simplified sectional way. By employing the lens, high frequency sound emanating from the membrane radially outwardly and orthogonal to the membrane&#39;s axis either travels directly between the diffuser petals to the surrounding environment beyond a backside of the petals or is reflected by a front side of the petals. The output represented by  34  is there by fractionally dispersed by the lens into two attenuated patterns  35  and  36 . The diagrammatic shell cut-away  36  represents the sound passing radially through the slots in the lens. The  35  shell cut-away represents the sound reflected by these lens petals axially. The combination approximates radiation into a hemisphere. The lens is shown mounted on a surface in a preferred manner. With a diameter of the cylindrical membrane of one inch a frequency range of approximately 2 to 20 kHz or more is obtained. Efficiency corresponds roughly to a conventional dome tweeter with the same electro motor. The net size above the mounting surface is slightly greater than a conventional dome tweeter but the dispersion is greater. 
     The foregoing is to be considered illustrative only of the principles and possible embodiments of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. Accordingly, suitable modifications and equivalents may be resorted to, all falling within the scope of the invention which shall be determined only by the following claims and their legal equivalents.