Patent Publication Number: US-9426549-B2

Title: Flat panel loudspeaker system and method of making

Description:
TECHNICAL FIELD 
     The disclosure relates to a loudspeaker system, and more particularly, to loudspeaker systems mounted in wall panels. 
     BACKGROUND 
     Vehicles, such as aircraft, include passenger cabins and other compartments enclosed at least partially by lightweight panels. It is necessary for the pilot of such vehicles to communicate with the passengers in the passenger cabin of such vehicles, and therefore such cabins require speaker systems to transmit the pilot&#39;s voice, as well as other informational messages, music, motion picture soundtracks and the like. 
     Traditionally, cone speakers are used as part of a loudspeaker system. Such cone speakers include a driver having a cone driven by a voice coil. Such cone speakers typically are mounted above a ceiling panel over passenger seats in a vehicle. A disadvantage with such cone speakers is that the cone component takes up valuable space above the ceiling panel. Another disadvantage is that it is necessary to cut a hole through the ceiling panel to allow the sound energy generated by the cone to pass through the ceiling panel. In addition, cone speakers project sound at a relatively narrow dispersion angle (±30 degrees). Therefore, for short distance sound projection, such as in an aircraft or other vehicle cabin environment, many cone speakers must be used, and spaced to cover the entire passenger cabin area. 
     The disadvantages of cone speakers with respect to space, narrow sound projection, and the necessity of cutting a hole through the panel may be overcome by using a flat panel speaker. Currently, there are two types of flat panel speakers: electrostatic speakers and electromagnetic induction (EMI) speakers. However, a disadvantage with electrostatic speakers is that they are dipole, and therefore require openings in both the front and back, and require a thin, soft film diaphragm that is too fragile for use in, for example, an aircraft cabin due to pressure changes during a flight. Electrostatic speakers are coherence speakers and are very directional—making them a poor choice for short distance sound coverage. Further, electrostatic speakers require high voltage—on the order of 2,000 volts—and require heavy metal core transformers. All of this is undesirable for use in applications such as an aircraft cabin. A disadvantage with EMI speakers is that they require a relatively heavy magnetic bar and a printed or wired coil diaphragm. The magnetic bar adds weight to the aircraft. Magnetic field radiation is prohibited for plane use, and the diaphragm, which also must work on dipole principle, is too fragile for use in environments such as an aircraft cabin, and is a coherence speaker, having a projection angle narrower than that of a cone speaker. 
     Accordingly, there is a need for a loudspeaker system that may take up less space than a conventional cone speaker, not require cutting a hole through a passenger compartment panel, and that is able to project sound over a wider area than current loudspeaker systems. 
     SUMMARY 
     The present disclosure describes a flat panel loudspeaker system that, in aspects, is relatively compact, does not require cutting a hole through a passenger compartment panel, and projects sound over a wider area than current loudspeaker systems. In one aspect, an exciter assembly is for use with a flat panel loudspeaker system including a panel having a core, an inner sheet coupled to an inner surface of the core and an outer sheet coupled to an outer surface of the core. The exciter assembly may include an exciter having an exciter housing, a voice coil assembly attachable to the outer sheet of the panel, the voice coil assembly having a lock pad, and a lock base releasably engaging the lock pad and attachable to the outer sheet of the panel, to vibrate the panel to generate sound energy; and an exciter support bracket connected to the exciter housing and attachable to the outer sheet of the panel. 
     In another aspect, a flat panel loudspeaker system for a vehicle may include a panel forming a cabin wall in a vehicle, the panel having a core, an inner sheet coupled to an inner surface of the core and an outer sheet coupled to an outer surface of the core; an exciter having an exciter housing, a voice coil assembly attached to the outer sheet of the panel, the voice coil assembly having a lock pad and a lock base releasably engaging the lock pad and mounted on and contacting the outer sheet of the panel, to vibrate the panel to generate sound energy within the vehicle; and an exciter support bracket connected to the exciter housing and attached to the outer sheet. 
     In yet another aspect, a method of constructing a flat panel loudspeaker system for transmitting sound energy within a vehicle cabin including a panel, the panel having a core, an inner sheet coupled to an inner surface of the core, and an outer sheet coupled to an outer surface of the core, may include attaching an exciter having an exciter housing, a voice coil assembly to the outer sheet of the panel, the voice coil assembly having a lock pad and a lock base, by attaching the lock pad to the outer sheet of the panel, and releasably attaching the lock pad the lock base, such that vibration of the exciter vibrates the panel to generate sound energy within the vehicle cabin; attaching an exciter support bracket to the outer sheet; and connecting the exciter support bracket to the exciter housing. 
     Other objects and advantages of the disclosed flat panel loudspeaker system and method of making will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the disclosed flat panel loudspeaker system; 
         FIG. 2  is a plan view of the panel of the system of  FIG. 1 , showing the weakened area defined by at least one slot formed through the outer sheet of the panel; 
         FIG. 3  is a plan view of the panel of  FIG. 2 , shown with damping elements in the form of segments of tape covering portions of the slots; 
         FIG. 4  is a perspective view of the flat panel loudspeaker system of  FIG. 1 , in which the panel and exciter are in section; 
         FIG. 5  is a perspective view of the coil, coil former and lock pad of the flat panel loudspeaker system of  FIG. 1 ; 
         FIGS. 6A and 6B  are plan views of the lock pad, lock base and support bracket, in which the lock pad is shown in an unlocked and a locked position, respectively; 
         FIG. 6C  is a detail in perspective showing an alternate engagement between the lock pad and lock base; and 
         FIG. 7  is a perspective view of an alternate design of the exciter housing. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , a flat panel loudspeaker system, generally designated  10 , may incorporate a panel  12  having a core  14 , an inner sheet  16  coupled to an inner surface of the core  14 , and an outer sheet  18  coupled to an outer surface of the core  14 . As shown in  FIGS. 2 and 3 , the panel  12  may have a weakened area, generally designated  20 , defined by at least one slot  22  formed through the outer sheet  18 , thereby exposing the core  14 . In other embodiments, the at least one slot  22  may be formed only partially through the outer sheet  18 . As shown in  FIG. 1 , the loudspeaker system  10  may include an exciter, generally designated  24 , attached to the panel  12  at the weakened area  20  and configured to vibrate the panel to generate sound energy. In an embodiment, the inner sheet  16  may be imperforate over the weakened area  20 ; that is, there may be no holes, slots or cuts formed in the inner sheet opposite the weakened area  20 . 
     In an embodiment, the panel  12  may be a portion of a vehicle  26 , such as an aircraft, a spacecraft, a land vehicle, a marine vehicle, and a submarine vehicle. In still other embodiments, the panel  12  may be used as part of a wall or ceiling of a building or other static structure. In an embodiment, the panel  12  may be a ceiling panel, or interior wall enclosing a passenger compartment of an aircraft. In an embodiment, the inner sheet  16  and outer sheet  18  may be made of fiberglass, and in other embodiments may be made of aluminum, KEVLAR (a trademark of E. I. du Pont de Nemours and Company of Wilmington, Del.), carbon fiber, composite or graphite. In an embodiment, the core  14  may be a honeycomb core or foam core, and may be made of fiberglass, aluminum or NOMEX (a trademark of E. I. du Pont de Nemours and Company of Wilmington, Del.). The panel  12  may be on the order of ⅜ inches to ¾ inches thick, or thicker if the size of the panel is expanded. In other embodiments, the panel  12  may be a sandwich panel having balsa wood/fiberglass resin skins coupled to a foam core  14 . For domestic applications, the sandwich panel may be made of cardboard paper skins with a paper honeycomb core, thin metal, plastic or thin wood skins with a paper honeycomb or foam core, and the like. Core material may include balsa wood configured as many thin beams that cross to form a support structure or matrix, or large, open-cell plastic structure. 
     As shown in  FIGS. 2 and 3 , the at least one slot  22  may take the form of a plurality of slots extending generally radially from a center  28  of the weakened area  20 . In an embodiment, the plurality of slots  22  may be evenly spaced about the center  28 . In an embodiment, the slots  22  may include at least two pairs of slots  30 ,  32  arranged to intersect at a pre-set angle. In an embodiment, the pre-set angle may be a right angle. In an embodiment, the slots  22  may include a plurality of slots  34  positioned in between the intersecting slots  30 ,  32 . However, any suitable configuration of slots (more or less, longer or shorter) to achieve the required audio performance may be employed. In embodiments, the slots  22  may be rectilinear, curvilinear, or combinations of both. 
     As shown in  FIG. 3 , in an embodiment, the loudspeaker system  10  may include a damping element, generally designated  36 . The damping element  36  may be attached to the outer sheet  18  at the weakened area  20 . In an embodiment, the damping element  36  may include tape  38  covering less than the entirety of at least one slot  34 . In an embodiment, the tape  38  may be formed in segments, and the segments may be spaced evenly about the weakened area  20 . In embodiments, the tape segments  38  may be made of vinyl, such as electrical tape, and in other embodiments, may be made of paper, such as masking tape. In yet another embodiment, the tape segments  38  may be an aluminum tape. In still other embodiments, other materials may be used. The tape segments  38  may be attached to the outer sheet  18  by a suitable adhesive. 
     As shown in  FIGS. 1 and 4 , the exciter  24  may include a voice coil assembly, generally designated  40 , attached to the outer sheet  18  at the weakened area  20 . In an embodiment, the voice coil assembly  40  may include a coil  42  configured to be energized by an electric current, and a lock pad  44 . The lock pad  44  may include a coil former  46 , as shown in  FIG. 5 . In embodiments, the coil  42  may be made of thin gauge copper wire, or other conductive wire such as aluminum. The lock pad  44  may be made of plastic, nylon or other suitable solid, lightweight material, and the coil former  46  that may include the voice coil assembly  40 , may be mounted above the lock pad  44 , and may be made of KAPTON (a trademark of E. I. du Pont de Nemours and Company of Wilmington, Del.), plastic, nylon, stiff paper, or any suitable dielectric. The lock pad  44  may include a base  48  having radially projecting tabs  50 . In an embodiment, the tabs  50  may be spaced evenly about the base  48 . The coil former  46  may be cylindrical in shape and sized to slip over the outer surface of a cylindrical projection  52  of the lock pad  44  and secured to the cylindrical projection by a suitable adhesive. The cylindrical projection  52  and coil former  46  may be shaped to define an opening  54  centrally through the lock pad  44 . 
     As shown in  FIGS. 1, 4, and 6A and 6B , the exciter  24  may include a lock base  56  mounted on and contacting the outer sheet  18  of the panel  12 , and configured to releasably engage the lock pad  44 . The lock base  56  may include an annular base  58  that contacts the outer sheet  18  and that defines an opening  60  that may be coaxial with the opening  54  formed by the lock pad  44 . The base  48  of the lock pad  44  may be shaped to align with the annular base  58  of the lock base  56  in an axial direction with respect to the openings  54 ,  60 . The lock base  56  may include an outer flange  62  having slots  64  shaped to receive the tabs  50  of the lock pad  44 . The slots  64  may include pockets  66  for securing the tabs  50  in a releasable friction fit, bayonet connection. 
     As shown best in  FIGS. 6A and 6B , the lock pad  44  may be placed on the lock base  56  so that the tabs  50  may be centered in the slots  64 . The lock pad  44  may then be rotated clockwise relative to the lock base  56 , as shown in  FIG. 6B , so that the tabs  50  engage the pockets  66  of the slots  64 , thus securing the lock pad to the lock base. Thereafter, the lock pad  44  may be rotated in a counter-clockwise direction from the orientation in  FIG. 6B  to the orientation in  FIG. 6A  to release the engagement between the lock pad and the lock base  56 . 
     As shown in  FIG. 6C , in an embodiment, the lock pad  44 ′ may include one or more tabs  50 ′ (only one of which is shown) that may have a raised locking detent  51  that is shaped and positioned on an upper surface of the tab to engage a correspondingly shaped catch, which in the embodiment shown is a hole  57  formed in the slot  64 ′ of the lock base  56 ′. Other shapes of locking detent  51 ′ may be employed without departing from the scope of the disclosed system  10 . The use of a locking detent  51  and hole  57  may prevent inadvertent disengagement of the lock pad  44 ′ from the lock base  56 ′. 
     As shown in  FIGS. 1 and 4 , the exciter  24  may include an exciter housing  68  shaped to receive a magnet  70 , which in an embodiment may be a permanent magnet. The magnet  70  may be cylindrical in shape and concentric with the coil  42 . The magnet  70  may extend from the exciter housing inside the coil former  46  to form a magnetic gap with the coil  42 . The exciter housing  68  may be made of metal, such as steel, which may be part of the magnetic circuitry to redirect the magnetic field of the magnet  70  to the gap between the magnet and coil  42  to reduce flux leakage. 
     The exciter  24  also may include a suspension spring  72  that may be attached at an inner periphery to the coil former  46 , and at an outer periphery to an annular flange  86  of the exciter housing  68 . In embodiments, the attachment may be by a suitable adhesive. The suspension spring  72  may be made of a fabric, such as KEVLAR (a trademark of E. I. Du Pont de Nemours and Company). Thus, the suspension spring  72  may support the coil  42  and lock pad  44  and keep them centered relative to the exciter housing  68  and magnet  70 . 
     An exciter support bracket  76  may be connected to the exciter housing  68 , and include an annular base  80  that may be mounted on the outer sheet  18  of the panel  12 . The base  80  may be attached to the outer sheet  18  by a suitable adhesive, or by mechanical means, such as screws, rivets or fasteners. The support bracket  76  may include resilient arms  82  projecting upwardly from the base  80  and spaced evenly about the periphery of the base. The arms  82  may be shaped to form arcuate slots  84  that may be biased radially inwardly to releasably receive the outer annular flange  86  of the exciter housing  68 . As shown in  FIG. 1 , the flange  86  of the housing  68  may include tabs  88  to which a terminal  90  may be attached. Terminal  90  may serve as leads for the wires  92  (only one of which is shown) of the coil  42 . The tabs  88 , in conjunction with terminal  90 , may be attached to audio equipment (not shown), such as an amplifier, to receive audio signals to drive the exciter  24 . 
     In an embodiment shown in  FIG. 7 , the exciter support bracket  76 ′ may include a base  80 ′ having cutouts  81  that may be shaped and positioned to avoid contact with the plurality of slots  22  formed in the outer sheet  18  of the panel  12 . The cutouts  81  may reduce or prevent the exciter bracket  76 ′ from interfering from the vibration of the panel  12 . The arms  82 ′ may include openings  83  that may reduce the spring value of the arms. In embodiments, the arms  82 ′ may taper in thickness, increasing in thickness from the slots  84 ′ to the base  80 ′. This tapering also may reduce the spring value of the arms  80 ′ of the exciter housing  76 ′. 
     In operation, a method of constructing a flat panel loudspeaker system for transmitting sound energy within a vehicle cabin defined by the panel  12  may include forming the weakened area  20  ( FIGS. 2 and 3 ) in the outer sheet  18  of the panel  12 , in which the weakened area is defined by at least one slot  22  formed in the outer sheet. The slots  22  may be linear or curved in shape and formed by cutting, as by laser or router cutting, or abrading the material of the outer sheet  18 . In other embodiments, the outer sheet  18  may be formed or cast with the slots  22  already present. The inner sheet  16  of the panel  12  ( FIG. 1 ) may be formed to be imperforate over the weakened area  20 . 
     The exciter  24  ( FIGS. 1 and 4 ), may be attached to the panel  12  at the weakened area  20 . In an embodiment, the annular base  58  of the lock base  56  may be attached to the panel  12  by an adhesive or other means, and in an embodiment, may be positioned so that it may be concentric with the center  28  ( FIGS. 2 and 3 ) of the weakened area  20 . The exciter support bracket  76  may be attached to the outer sheet  18  either before or after attaching the lock base  56  to the panel  12 . In an embodiment, the exciter bracket  76  may be attached to the outer sheet  18  so that it may be centered relative to the center  28  of the weakened area  20 , then the exciter housing  68 , lock pad  44  and lock base  56  pressed downwardly (in  FIG. 4 ) toward the sheet until the base  58  contacts the outer sheet and the flange  86  of the exciter housing engages and is retained in the slots  84  of the arms  82 . 
     In embodiments, the lock base  56  may be attached to the panel  12  by itself, or as a unit along with the lock pad  44  and exciter housing  68 . If the former, the lock pad  44  may thereafter be attached to the lock base  56  as shown in  FIGS. 6A and 6B . The leads  88 ,  90  ( FIG. 1 ) may be connected to a sound amplifier (not shown) and the sound amplifier provides a signal to the coil  42  of the exciter  24 . The signal energizes the coil  42 , and movement of the voice coil  40  causes the weakened area  20  to deflect. Thus, the exciter  24  vibrates the panel  12  at the weakened area  20  to generate sound energy within the vehicle cabin  26 . 
     In an embodiment, the signal (which may be a sine wave) may be in the form of an electric current and voltage that energizes the coil  42 , causing the coil to move in a direction perpendicular to the panel  12 . This movement may be transmitted by the lock pad  44  to the lock base  56 , and from the lock base directly to the outer sheet  18  of the panel  12 , causing the panel  12  to flex and thus vibrate at the weakened area  20 . In an embodiment, the signals may be representative of a human voice, so that the vibration of the panel  12  transmits sound energy to reproduce a human voice through the panel  12  and to the interior of the vehicle  26 . Referring to  FIG. 3 , the quality of the sound produced by the system  10  may be altered and/or enhanced as needed by the addition of the damping element  36 . 
     An advantage of the flat panel loudspeaker system  10  is that it may incorporate a panel  12  that is a current production base panel without need to make a specific custom layup formulation to act as the diaphragm of a speaker to transmit sound energy, including sound replicating a human voice, to the interior of a cabin defined by the panel. In embodiments, the pattern of slots  22  may be any suitable cut pattern that enables the panel  12  to vibrate a few nano-inches to produce audible sound waves. In an exemplary embodiment, the cut pattern may be a starburst pattern with intersecting cuts at the center  28  of the starburst. In embodiments, the cuts may be about 0.025 inches wide and may be formed by computer routing. 
     While the form of apparatus herein described constitutes a preferred embodiment of the disclosed flat panel loudspeaker system, it is to be understood that the flat panel loudspeaker system is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the claims.