Abstract:
An electro-acoustic transducer for driving a large surface is used to convert electrical signals into sound. The transducer has a housing with a cast aluminum bottom and a molded plastic top. The top and bottom are fastened together by screws with a gasket in between the contacting surfaces to form a housing for a high power electromagnetic voice coil driver mechanism. The top has an opening to allow the voice coil to be centered in its gap by a centering gauge during assembly of the driver. A cap closes the opening once the voice coil is fixed in place in the housing. The op is hexagonal and flat with circular rings in the top surface to allow the top to flex in a controlled manner while supporting the bottom which remains stationary.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to improvements in transducers and more particularly pertains to new and improved electroacoustic drivers wherein the transducer attaches to a large surface and in response to electrical signals cause that surface to move and create sound waves.  
         [0003]     2. Description of Related Art  
         [0004]     Those concerned with the development of electroacoustic transducers for driving large surfaces have continually been concerned with need for providing sufficient power to drive the large surfaces, removing the heat generated by units that have sufficient power to drive large surfaces, and creating an electroacoustic transducer that will produce a high quality sound. The present invention fulfills these needs.  
       SUMMARY OF THE INVENTION  
       [0005]     The housing for the high power voice coil and driver mechanism of the transducer of the present invention is made of a rigid non-flexing bottom which supports a flat top designed to flex in a controlled manner as the result of its unique shape. A circular opening in the top allows the voice coil to be centered in its gap by a centering gauge during assembly of the driver mechanism. A cap closes the opening once the voice coil is fixed. The bottom of the housing is designed to remove large amounts of heat from the high power voice coil during operation.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The exact nature of the present invention as well as its objects and advantages will become readily apparent upon consideration of the following detailed description in conjunction with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:  
         [0007]      FIG. 1  is a top plan view of a preferred embodiment of the transducer of the present invention.  
         [0008]      FIG. 2  is a side plan view of the transducer of the present invention.  
         [0009]      FIG. 3  is a bottom plan view of the transducer of the present invention.  
         [0010]      FIG. 4  is an exploded view showing the parts of the transducer of the present invention.  
         [0011]      FIG. 5  is a cross-section taken along line  5 - 5  of  FIG. 1  showing the internal parts of the transducer of the present invention in its assembled form. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]     A preferred embodiment of the electroacoustic transducer  11  of the present invention, and specifically the novel features of the housing for the transducer of the present invention are illustrated in  FIGS. 1, 2  and  3 . The transducer  11  of the present invention is designed so that the top portion  15  ( FIGS. 1 and 2 ) moves, and the bottom portion  13  ( FIGS. 2 and 3 ) is rigid, and does not move. By allowing only the top portion to move, the transducer  11  behaves as a monopole transducer.  
         [0013]     A dipole transducer, on the other hand, one where both the top and bottom surfaces are designed to move, is susceptible to destructive cancellation of energy. Destructive cancellation is an acoustic phenomenon that occurs when sound waves operate out of phase with each other. This can happen when both surfaces, top and bottom, move away from each other. Each surface cancels the energy produced by the other.  
         [0014]     The transducer  11  of the present invention, by only allowing the top portion  15  of the transducer to move causes the overall energy radiated to be more efficient throughout the utilized band width. The bottom portion  13  is designed to be rigid and to efficiently dissipate heat generated by the transducer  11 . For that reason the bottom portion  13  is preferably made from metal, such as cast aluminum, for example.  
         [0015]     The top portion  15 , on the other hand, is designed to flex and move in a controlled manner. The top portion  15  has a unique hexagonal shape with six equal sides  20  that extend from the flat top to the base at an angle  30 . In addition to the sloping sides  30  for each of the six sides  20  of the hexagonally shaped top  15 , a perpendicular surface area  22  extends from the apex of each of the sides  20  at the top to the base. This particular hexagonal top and side configuration has been found to provide exceptional support for the weight of the transducer  11 , especially the weight contributed by the metal bottom portion  13 . The entire weight is carried by the top portion  15  when the transducer is mounted vertically to a surface by a bolt  45 , or similar fastener.  
         [0016]     The top portion  15  utilizes a plurality of circular rings  24 ,  26  which not only provide additional support for top portion  15 , but also provide hinge points for top portion  15  to move. A circular cap  17  is mounted over an aperture  46  ( FIG. 5 ) by being inserted into a circular groove  16  in top portion  15  ( FIG. 5 ). The mounting bolt  45  extends out of cap  17  (see also  FIG. 5 ). This bolt mounts the transducer  11  to a surface (not shown) to be driven by the transducer in a manner well known in the art. A plurality of support ribs  28  on cap  17  create additional rigidity and strength to the top portion  15  at the point where it mounts to the surface to be driven.  
         [0017]     The material used for the top portion  15  is preferably a material that can be molded or machined into the desired shape. The flexible properties of the material used for the top portion are chosen on the basis of the application of the transducer. For example, if the transducer  11  is to produce primarily low frequencies such as desired for subwoofer application, the material for the top portion  15  could be a material that has high flexibility such as a thermal plastic rubber, for example.  
         [0018]     The transducer of the present invention has been designed to achieve a high force factor. Force generated by the transducer  11  can be calculated from the formula: 
 
f=bli 
 
 where: 
        f=force     b=flux density of the magnetic gap     l=length of wire in magnetic gap     i=current input into the transducer        
 
         [0023]     To achieve a high force factor, the product of flux density of the magnetic gap times the length of the wire in the magnetic gap must be high. Accordingly, the diameter of the coil was chosen to be large. A large diameter coil permits a long length of wire to be in the magnetic gap. In addition to the large diameter conductive coil, the height of the wire windings on the coil is greater by using a thicker top plate that is 8 millimeters thick, for example. In addition to these features, to provide a high force factor, it is preferred that a neodymium magnetic material is used. This material has a very high magnetic strength and thereby provides a high flux density in the magnetic gap of the coil.  
         [0024]     The high power capability of transducer  11  requires that the resulting heat generated in the conductive coil be transferred to the surrounding metal parts. Adjusting the winding height of the voice coil to the height of the top plate and blackening all the metal parts helps to wick the heat from the voice coil to the surrounding metal parts. To increase heat dissipation, the outside portion  13  of the housing for transducer  11  is powder coated in black and has a plurality of cooling fins  32  extending radially from the center along the outside of the bottom portion  13 . Moreover, the voice coil  41  is designed with vent holes  44  ( FIGS. 4 and 5 ) to allow heat to flow away from the voice coil area out to the cooler metal or the plastic parts, and especially the aluminum bottom portion  13  and the magnetic metal assembly surrounding the voice coil  42  ( FIG. 5 ). It is also preferred that the material used for the voice coil is a material designed to handle high temperature and function to isolate the heat generated by the voice coil to the area of the voice coil. Materials such as Kapton or TIL (fiberglass) which are well known in the industry are well suited for this purpose. Other materials may also be used, such as aluminum, for example, for lower temperature applications which provide different acoustical damping characteristics.  
         [0025]     Referring now to  FIGS. 4 and 5 , the preferred structure for the transducer  11  of the present invention including all of its component parts is illustrated. The bottom portion  13  and the top portion  15  of the transducer housing are fastened together along their circumferential periphery to enclose the operative parts of the transducer as illustrated in  FIGS. 4 and 5 . A plurality of screws  53  pass through apertures in top portion  15  and thread into threaded apertures in bottom portion  13 . A gasket  31  is placed between the two connecting parts of top portion  15  and bottom portion  13 . The gasket functions to prevent buzzing noises between the two covers and is also a seal that prevents moisture from entering the housing of the transducer.  
         [0026]     A bottom plate  33  fastens to the inside of metal bottom portion  13  by a carriage bolt  27  that passes through an aperture in bottom portion  13  and threads into a threaded aperture in bottom plate  33 . Bottom plate  33  is made of an electromagnetic material. Bottom plate  33  has an aperture therein which accommodates a magnet  35  which is preferably in disk form. The magnet is preferably made out of neodymium magnetic material. A top plate  37  with a circular aperture  40  through its symmetrical center is fastened to the top of bottom plate  33 . The circular aperture  40  exposes the magnet  35  within the bottom plate  33 . The top plate  37  is fastened to the bottom plate  33  preferably by threaded screws and glue. A pole cap  39  is placed in the circular aperture of the top plate  37  on top of the magnet  35  within the bottom plate  33 . The pole cap  39  has a diameter which leaves a space between its outside circumference and the inner circumference of the aperture  40  in top plate  37 . This gap is sufficient to accommodate the voice coil wires  38  wound on voice coil form  41  at its second end. The voice coil has venting holes  44  along its first end. The voice coil wires  38  wound on coil form  41  are located within the circular aperture  40  of top plate  37 .  
         [0027]     The top portion  15  of the transducer housing has a circular aperture  46  ( FIGS. 4 and 5 ) through its symmetrical center. This aperture allows for centering of the voice coil  41  during assembly by use of a centering gauge (not shown). The centering gauge is inserted in place to align the voice coil in the gap between the pole cap  39  and the circular aperture  40  in top plate  37 . The first or upper end of voice coil  41  is glued to the inside surface  42  of the aperture  46  ( FIG. 5 ) in the top portion  15  of the transducer housing. A spider  43  is glued to the mid-section of voice coil  41  and to top plate  37 . When the adhesives have cured, the voice coil centering gauge is removed and the cap  17  is glued into the groove  16  of the top portion  15  of the transducer housing. A carriage bolt  45  extends through an aperture in cap  17  through a washer  47  on the other side and is fastened down by a hex nut  49 . A flexible cover  51  slips over hex nut  49 . A rubber boot  19  fits over the connected circumferential perimeter of the top and bottom portions of the housing to further seal out moisture and other impurities from the internal workings of the transducer.  
         [0028]     Electrical connection to the sealed transducer is obtained by way of cable  23  which has a plug-in connector  25  at one end. The cable  23  passes through a cable grip mechanism  29  that is held to the metal bottom portion  13  of the transducer housing by a nut  21 . The wires in cable  23  are connected to the wires  48  of the voice coil.  
         [0029]     The carriage bolt  45  secured to the cap  17  provides the means for fastening the transducer to a surface to be driven. For example, the transducer can be attached to a flat surface by making a hole through the material and threading a ⅜″ nut on the other end, thereby securely sandwiching the flat material between the nut and the transducer. If thicker material is to be driven by the transducer, a threaded insert may be embedded into the material so that the carriage bolt  45  can be threaded into it.