Abstract:
A sound transducer ( 10 ) for imparting acoustical energy directly to a solid surface ( 12 ) while achieving the sound quality and frequency response found only in conventional diaphragm speakers. The sound transducer ( 10 ) comprises a pair of symmetrical magnet assemblies ( 16, 18 ), a pair of symmetrical voice coils ( 66, 68 ), and an actuator ( 22 ). The magnet assemblies ( 16, 18 ) each present an area of concentrated magnetic flux ( 60, 62 ). The symmetrical voice coils ( 66, 68 ) are positioned in the vicinity of the areas of concentrated magnetic flux and are operable to receive an alternating audio signal which causes the voice coils to move relative to the magnet assemblies. The actuator ( 22 ) moves with the voice coils and includes a foot ( 70 ) for coupling with a solid surface to impart movement to the solid surface and thereby produce sound when the voice coils receive the audio signal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to audio systems and speakers. More particularly, the invention relates to an improved sound transducer for imparting acoustical energy directly to a solid surface such as a wall or pane of glass.  
         [0003]     2. Description of the Prior Art  
         [0004]     High performance audio systems and speakers continue to grow in popularity as more and more consumers install home theater systems in their homes, offices and other personal spaces. Such home theater systems typically consist of a high definition TV, projection TV, plasma screen, or other monitor; one or more video sources such as a DVD player or a VCR; a surround-sound receiver; and a plurality of speakers coupled with and driven by the surround-sound receiver.  
         [0005]     High performance surround-sound receivers typically have five or seven separate audio channels for driving five or more speakers. The speakers are strategically positioned around a listening area to accurately produce the audio portion of a movie or other program. A pair of speakers may, for example, be positioned behind a typical listening area, another pair of speakers may be positioned in front of the listening area, and another pair of speakers may be positioned to the sides of the listening area.  
         [0006]     Speakers convert electrical energy representative of music or other sounds to acoustical energy. Conventional speakers include a voice coil which moves relative to a permanent magnet when it receives an alternating audio signal. The voice coil then vibrates a paper diaphragm or cone to provide sound waves. The cone moves because of a dynamic interaction between two magnet fields, one coming from the permanent magnet and the other created by the signal voltage applied to the voice coil. The permanent magnet&#39;s field does not change direction; it remains highly concentrated and constant near the voice coil. An alternating audio signal applied to the voice coil creates an alternating magnetic field emanating from the voice coil. The alternating magnetic field of the voice coil interacts with the stationary magnetic field of the permanent magnet to move the voice coil. Specifically, the voice coil and the attached cone move forward and backward in accordance with the varying polarity of the signal applied to the voice coil. The oscillations of the diaphragm closely follow the variations in the applied electrical signal to set up sound waves.  
         [0007]     Because conventional speakers rely upon the movement of a diaphragm or cone, they must be mounted so that the diaphragm is at least partially exposed to the listening area in which the sound is directed. Mounting numerous speakers in a listening area without interfering with windows, doors, columns, and other structural components of a room can be challenging. One way to overcome this challenge is to hang some or all of the speakers from the room&#39;s ceiling with swiveling brackets so they may be oriented to project sound in desired directions. However, some people find this mounting arrangement unsightly, especially when numerous speakers of varying sizes must be hung from the ceiling. Another installation method flush mounts the speakers in walls, ceilings and other surfaces so that the speakers do not project as far into a room. However, this method is considered unattractive by some people as well, because the speakers and their associated grills take up valuable wall and ceiling space and remain visible, thus detracting from the appearance of the room.  
         [0008]     Magnetostrictive speakers, such as the SolidDrive™ speakers sold by Induction Dynamics® have been developed to alleviate some of the problems associated with speaker installation. Such speakers convert audio signals to powerful vibrations that can be transferred into solid surfaces such as walls, ceilings, windows, tables, office desks, etc., thus delivering sound from the entire surfaces. This permits the speakers to be positioned entirely behind these surfaces and therefore completely hidden from view. For example, such speakers are often mounted behind walls so that there are absolutely no visible speakers or wires. Although magnetostrictive speakers can be hidden and therefore solve many of the installation problems discussed above, they do not reproduce sound as accurately as conventional speakers and often exhibit non-uniform and less predictable frequency responses.  
         [0009]     Sound transducers which use conventional voice coil technology to impart acoustical energy to solid surfaces have also been developed. However, these prior art sound transducers are generally not powerful enough to move a rigid wall or other solid surface sufficiently to create a desirable level and quality of sound. Moreover, such prior art transducers do not produce a uniform frequency response due to their construction.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention solves the above-described problems and provides a distinct advance in the art of audio systems and speakers used in home theater systems and other high performance audio applications. More particularly, the present invention provides a sound transducer for imparting acoustical energy directly to a solid surface while achieving the sound quality and frequency response found only in conventional diaphragm speakers.  
         [0011]     One embodiment of the sound transducer comprises a pair of symmetrical magnet assemblies, a pair of symmetrical voice coils, and an actuator. The magnet assemblies each present an area of concentrated magnetic flux. The symmetrical voice coils are positioned in the vicinity of the areas of concentrated magnetic flux and are operable to receive an alternating audio signal which causes the voice coils to move relative to the magnet assemblies. The actuator moves with the voice coils and includes a foot for coupling with a solid surface to impart movement to the solid surface and thereby produce sound when the voice coils receive the audio signal.  
         [0012]     The symmetrical magnet assemblies and voice coils drive the actuator with more power than prior art sound transducers and therefore reproduce more sound. Moreover, the symmetrical design provides a more consistent and uniform frequency response. The actuator foot is larger than actuators of prior art sound transducers and therefore transfers more acoustical energy without damaging the solid surface to further enhance the sound production and frequency response of the sound transducer.  
         [0013]     The sound transducer may also include a pair of symmetrical suspension springs for creating more uniform and consistent movement of the actuator and therefore more uniform and consistent sound reproduction and frequency response.  
         [0014]     These and other important aspects of the present invention are described more fully in the detailed description below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0015]     Preferred embodiments of the present invention are described in detail below with reference to the attached drawing figures, wherein:  
         [0016]      FIG. 1  is a perspective view of a sound transducer constructed in accordance with an embodiment of the present invention and shown coupled with a wall or other solid surface.  
         [0017]      FIG. 2  is a vertical sectional view of the sound transducer shown in  FIG. 1 .  
         [0018]      FIG. 3  is a vertical sectional view of a sound transducer constructed in accordance with another embodiment of the invention. 
     
    
       [0019]     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     A sound transducer  10  constructed in accordance with a preferred embodiment of the present invention is shown in  FIG. 1  attached to a solid surface  12  such as a wall of a room or other listening area. As explained in more detail below, the sound transducer  10  imparts acoustical energy directly to the solid surface  12  to vibrate the solid surface  12  in accordance with an applied audio signal to thereby produce sound.  
         [0021]     The solid surface  12  may be constructed of any material or combination of materials such as drywall, glass, fiberglass, wood, or even metal; however, extremely thick materials such as concrete are not preferred because they do not transfer acoustical energy well enough to produce much usable sound. The sound transducer  10  is preferably mounted to an area of the solid surface  12  that is not directly attached to another more rigid surface. For example, when attached to a wall consisting of drywall supported by wooden studs, the sound transducer  10  is preferably attached near the mid-point of two adjacent studs so that the portion of drywall to which the sound transducer is attached moves more freely.  
         [0022]     One embodiment of the sound transducer  10  is shown in  FIG. 2  and broadly includes an outer housing  14 ; a pair of symmetrical magnet assemblies  16 ,  18 ; a voice coil assembly  20 ; an actuator  22 ; and a shaft  24  for coupling the actuator  22  to the voice coil assembly  20 . Each of these components is described in detail below.  
         [0023]     The outer housing  14  is preferably a hollow cylinder presenting a side wall  26 , an end wall  28  enclosing one end of the side wall and an open end  30 . The housing  14  is preferably made of a heavy, non-magnetic material such as zinc and in one embodiment has a side wall thickness of approximately 3/16 inch, a height of approximately two inches, and a diameter of approximately two inches. The particular dimensions of the housing, however, can be varied as a matter of design choice and are provided only for purposes of disclosing a best mode of the invention.  
         [0024]     A section of the side wall  26  adjacent the open end  30  has a reduced thickness to form a shelf  32  for receiving and supporting a circular cover plate  34  for removably closing the open end  30 . The cover plate  34  is also preferably formed of a heavy, non-magnetic material such as zinc and has a central bore or hole through which one end of the shaft  24  extends. The cover plate  34  is held in place by a snap-ring  36  positioned in an annular groove  38  adjacent the outer end  30  of the side wall  26 . Another groove  40  is formed in the shelf  32  for receiving an O-ring  42  or other type of seal.  
         [0025]     The magnet assemblies  16 ,  18  are positioned within opposite ends of the housing  14  and are substantially identical and therefore symmetrical. As described in more detail below, use of two symmetrical magnet assemblies  16 ,  18  increases the power of the sound transducer  10  and provides a more uniform frequency response.  
         [0026]     Each of the magnet assemblies  16 ,  18  includes a permanent magnet  44 ,  46  sandwiched between a top plate  48 ,  50  and a bottom plate  52 ,  54 . The permanent magnets  44 ,  46  are preferably ring-shaped so as to present a central opening or bore. The permanent magnets  44 ,  46  are preferably formed of Neodymium material, and in one embodiment, are capable of producing a flux density between 8,000 and 14, 000 Gauss and more specifically between 10,000 and 12,000 Gauss.  
         [0027]     The top plates  48 ,  50  and the bottom plates  52 ,  54  cover the top and bottom faces of the permanent magnets  44 ,  46  to concentrate the magnetic flux of the permanent magnets. The top and bottom plates are also preferably ring-shaped so as to present a central opening or bore aligned with the bore of the permanent magnets and are preferably formed of a magnetic material such as iron or carbon steel. A ring-shaped magnetic pole piece  56 ,  58  is integrally formed with or attached to each of the bottom plates  52 ,  54  to further concentrate the magnetic flux of the permanent magnets  44 ,  46 . The magnetic pole pieces  56 ,  58  are preferably formed of low-carbon steel material.  
         [0028]     An area of concentrated magnetic flux  60 ,  62  is defined by the inner wall of each permanent magnet  44 ,  46 , the inner wall of each top plate  48 ,  50 , and the outer wall of each magnetic pole piece  56 ,  58 . This area of concentrated magnetic flux  60 ,  62  receives the voice coils as described below.  
         [0029]     The housing  14 , magnet assemblies  16 ,  18 , and the other enclosed components must be sufficiently heavy to provide inertia for the actuator to work against because the housing is preferably only supported through the actuator foot. If the housing  14  and the enclosed components were too light, the actuator would simply vibrate the housing rather than the solid surface. In one embodiment, the housing and the components contained therein weigh approximately 1-2 pounds and preferably approximately 1.75 pounds. To further increase the weight of the housing and enclosed components, a ring-shaped ballast  63  may be positioned between the two magnet assemblies  16 ,  18 .  
         [0030]     The voice coil assembly  20  includes a voice coil former  64  and two symmetrical voice coils  66 ,  68  wound on opposite ends of the voice coil former  64 . The voice coil former  64  is preferably a hollow cylinder formed of aluminum. The voice coils  66 ,  68  are preferably insulated with a high-temperature coating.  
         [0031]     The voice coil former  64  extends between the two magnet assemblies  16 ,  18  and within the central bores of the top plates and permanent magnets to position the voice coils  66 ,  68  within the areas of concentrated magnetic flux  60 ,  62 . As explained in more detail below, the voice coil assembly  20  moves relative to the magnet assemblies  16 ,  18  in a direction parallel to an axis extending through the central bores of the permanent magnets  44 ,  46 .  
         [0032]     Each of the voice coils  66 ,  68  consists of a length of wire or other electrically conductive material wound on opposite ends of the voice coil former  64  and electrically coupled to one or more input terminals. The input terminals are in turn connected to a source of audio signals such as those provided by a stereo radio receiver. Both voice coils  66 ,  68  include the same amount of wire and are connected to the same audio source so as to be symmetrical. Thus, the voice coils  66 ,  68  assist each other in moving the voice coil former  64  and the attached actuator  22 .  
         [0033]     The actuator  22  includes an enlarged foot  70  that extends from the open end  30  of the housing  14  and a stud or pin  72  which extends into the housing through the central opening in the cover plate  34 . The foot  70  is glued or otherwise attached to the solid surface  12  as illustrated in  FIG. 1  to transfer acoustical energy to the solid surface as explained in more detail below. The foot  70  presents a large surface area for two primary purposes: 1) to transfer a maximum amount of acoustical energy to the solid surface  12  without damaging the surface; and 2) to provide enough area for a sufficient amount of glue or other adhesive to suspend the sound transducer  10  from the solid surface  12 . The particular shape, size, and surface area of the foot can vary depending on the size and strength of the magnet assemblies  16 ,  18  and the voice coil assembly  20  as well as the weight of the housing  14  and enclosed components. The illustrated foot  70  has a diameter of two inches, which is approximately equal to the diameter of the housing  14 . Thus, this embodiment of the foot presents a surface area slightly greater than three square inches.  
         [0034]     The actuator stud  72  extends from one side of the foot  70  and indirectly couples the foot to the voice coil assembly  20  through the shaft  24 . The actuator stud may be glued in the shaft, threaded into the shaft, or held in place by other conventional means.  
         [0035]     The elongated shaft  24  may be partially hollow and is preferably formed of strong, non-oxidizing material such as stainless steel. The shaft  24  extends through the opening in the cover plate  34  and is positioned inside the central bores of the magnet assemblies  16 ,  18 . The shaft  24  can move in a direction along an axis extending through the center of the housing and is supported against movement in other directions by a pair of bearing tubes  74 ,  76  each positioned inside of one of the pole pieces. The bearing tubes are preferably formed of Teflon or other material exhibiting low friction. The bearing tubes  74 ,  76  are each held in place on one end by a shelf or ridge  78 ,  80  formed between the bottom plates  52 ,  54  and the pole pieces  56 ,  58  and on the other end by a non-magnetic washer  82 ,  84 .  
         [0036]     The voice coil assembly  20  is attached to the shaft  24  by a ring-shaped coupler  86  that extends between the outer wall of the shaft  24  and the inner wall of the voice coil former  64 . The coupler  86  is preferably formed of aluminum or other heat conductive material so as to transfer heat generated by the voice coils  66 ,  68  away from the voice coil former  64  and to the shaft  24  and ambient air in the center of the housing.  
         [0037]     A pair of symmetrical suspension springs  88 ,  90  suspend the voice coils  66 ,  68  in the areas of concentrated magnetic flux  60 ,  62  when no audio signal is applied to the voice coils and resist movement of the voice coils relative to the magnet assemblies  16 ,  18  when an audio signal is applied to the voice coils. Each suspension spring  88 ,  90  is supported between the voice coil coupler  86  and one of the washers  82 ,  84 . When the various components of the sound transducer are positioned within the housing  14  and the cover plate  34  is attached to the open end  30  of the housing, the suspension springs  88 ,  90  are slightly compressed so as to securely hold in place the magnet assemblies  16 ,  18  while permitting the voice coil assembly  20 , the shaft  24 , the voice coil coupler  86 , and the actuator  22  to move against the applied force of the springs  88 ,  90 . A number of non-magnetic spacers  92 ,  94 ,  96 ,  98 ,  100 ,  102  may also be positioned within the housing  14  as shown to isolate the magnet assemblies  16 ,  18  from the housing and to firmly support them within the housing. The spacers are not required, however, as the magnet assemblies  16 ,  18  may be formed so as to tightly fit within the housing.  
         [0038]     In operation, the actuator foot  70  is glued or otherwise attached to a solid surface  12  as shown in  FIG. 1  so that the housing  14  and all its contained components are suspended from the solid surface  12 . The permanent magnets  44 ,  46  of the magnet assemblies  16 ,  18  magnetize the top plates  48 ,  50 , the bottom plates  52 ,  54 , and the pole pieces  56 ,  58  to produce a constant magnetic field which is concentrated in the areas  60 ,  62 . When an audio signal is applied to the voice coils  66 ,  68 , an alternating magnetic field emanates from the voice coils to interact with the fixed magnetic field in the areas of concentrated magnetic flux  60 ,  62 . This causes the voice coil assembly  20  to move or vibrate in accordance with the applied audio signal. The movement of the voice coil assembly  20  is transferred through the voice coupler  86  and to the shaft  24 , which in turn transfers the acoustical energy to the solid surface  12  through the actuator foot  70 .  
         [0039]     Because two symmetrical magnet assemblies  16 ,  18  and voice coils  66 ,  68  are used, the sound transducer  10  generates considerably more power than prior art sound transducers. This force is then transferred to the solid surface  12  by the large surface areas of the actuator foot  70 . The symmetrical suspension springs  66 ,  68  resist the movement of the voice coil assembly  20  and bias it back to its rest state shown in  FIG. 2  to provide a uniform frequency response.  
         [0040]     Another embodiment of a sound transducer  10   a  is shown in  FIG. 3 . The sound transducer  10   a  of this embodiment also includes an outer housing  14   a;  a pair of symmetrical magnet assemblies  16   a,    18   a;  a voice coil assembly  20   a ; and an actuator  22   a.  These components are substantially similar to the components described above in connection with the embodiment illustrated in  FIG. 2  except for the following differences.  
         [0041]     The magnet assemblies  16   a,    18   a  are configured so as to present an area of concentrated magnetic flux  60   a ,  62   a  that is between the outer wall of the permanent magnets  44   a ,  46   a  and the inner wall of the pole pieces  56   a ,  58   a , rather than between the inner wall of the permanent magnets and the outer wall of the pole pieces as with the  FIG. 2  embodiment. Also, the voice coil former  64   a  of the embodiment of  FIG. 3  has a greater diameter so that it is spaced from the outer periphery of the permanent magnets rather than within the central bore of the permanent magnets with the  FIG. 2  embodiment. By placing the permanent magnets  44   a ,  46   a  inside the voice coil former  64   a  and the pole pieces  56   a ,  58   a  outside the voice coil former  64   a , the voice coil may be larger in diameter, enabling it to handle more power. The sound transducer  10   a  also includes a solid shaft  24   a  that is directly threaded into or otherwise coupled with the actuator foot  70   a  so that a separate actuator stud or pin is not needed. Operation of the sound transducer  10   a  shown in  FIG. 3  is otherwise the same as the operation of the sound transducer shown in  FIG. 2 .  
         [0042]     The embodiment of  FIG. 3  also presents more open space inside the voice coil in which weights, in addition to the ballast  63   a , may be placed to further increase the overall weight of the housing and enclosed components. For example, weights may be glued or otherwise attached to the top plates of the magnet assemblies.  
         [0043]     Although the invention has been described with reference to the preferred embodiment illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.