Patent Publication Number: US-6219431-B1

Title: Loudspeaker with improved cooling structure

Description:
FIELD OF THE INVENTION 
     This invention relates to loudspeakers, and, more particularly, to structure associated with the frame and top plate of a loudspeaker which is effective to direct a flow of cooling air along the surface of the top plate and at least a portion of the voice coil of the loudspeaker. 
     BACKGROUND OF THE INVENTION 
     Loudspeakers generally comprise a frame, motor structure, a diaphragm, a lower suspension or spider and a surround. In one common type of speaker, the motor structure includes a top plate spaced from a back plate with a permanent magnet mounted therebetween. The magnet and top plate define an air gap within which a hollow, cylindrical-shaped voice coil is axially movable with respect to a fixed pole piece which is centrally mounted atop the back plate. 
     The voice coil generally comprises a cylindrical former which receives a winding of wire. The diaphragm extends between the voice coil and the surround, which, in turn, is mounted to the upper end of the frame. The spider is connected at one end to the voice coil, and at its opposite end to a point between the upper and lower ends of the frame. In this construction, one cavity or space is formed in the area between the diaphragm and spider, and a second cavity is formed in the area between the spider and the top plate of the motor structure. Many speaker designs include a dust cap mounted to the diaphragm in position to overlie and cover the voice coil and pole piece. 
     In the course of operation of a speaker of the type described above, electrical energy is supplied to the voice coil causing it to axially move relative to the pole piece and within the air gap formed by the top plate and magnet. The diaphragm, spider and the surround, move with the excursion of the voice coil. A pervasive problem associated with speaker operation involves the build up of heat produced by the voice coil and radiated to surrounding surfaces. Both the voice coil and top plate become quite hot during speaker operation which can reduce the power handling of the speaker, and increase power compression, i.e. a reduction in acoustic output due to temperature-related voice coil resistance. 
     A variety of designs have been employed in the prior art to address the problems associated with heat build up in speakers. Much of the design effort has been devoted to creating a flow of cooling air over the voice coil itself, such as disclosed, for example, in U.S. Pat. Nos. 5,042,072 to Button; 5,081,684 to House; and 5,357,586 to Nordschow et al. A typical construction in speaker designs of this type involves the formation of passages in or along the voice coil which form a flow path for the transfer of cooling air from the cavity between the voice coil and the dust cap and/or diaphragm, and vent openings usually formed in the back plate of the motor structure. An air flow through these passages is created in response to movement of the diaphragm with the excursion of the voice coil. When the diaphragm moves in one direction, air is drawn from outside of the speaker, through the vent opening in the back plate, along the passages in or along the voice coil and then into the cavity. Movement of the diaphragm in the opposite direction creates a flow out of the cavity along the reverse flow path. 
     One problem with the approach described above is that the design and construction of the flow passages often do little more than provide venting of the area or cavity between the diaphragm and voice coil. The actual air flow generated by movement of the diaphragm is typically relatively low volume. As a result, very little cooler ambient air from outside of the speaker actually flows along the voice coil to provide effective cooling. Additionally, little or no air flow is directed along the top plate, which remains hot. 
     Alternative designs depend upon thermal conduction and convection to cool the voice coil and/or top plate. Typically, structure associated with the frame is positioned in engagement with or proximate the top plate of the motor to provide a heat sink or thermally conductive path along which heat can move from the relatively hot top plate to the relatively cool frame. See, for example, U.S. Pat No. 4,933,975 to Button and French Application FR 2667212-A. 
     Constructions of the type described above provide some benefit, but reliance on conduction and convection alone to remove heat from the top plate and voice coil is of limited effectiveness with today&#39;s high performance, high excursion speakers. This is particularly true in applications such as vehicle speakers where space is at a premium and the speaker frame must be as compact as possible. In such designs, it is often not feasible to incorporate additional frame structure whose purpose is primarily or exclusively intended for the conduction of heat away from the voice coil and top plate. 
     SUMMARY OF THE INVENTION 
     It is therefore among the objectives of this invention to provide a loudspeaker construction which provides a comparatively high velocity, high volume flow of cooling air over the top plate and at least a portion of voice coil of the motor structure, which increases power handling of the speaker, which reduces power compression and which is efficient and economical to manufacture. 
     These objectives are accomplished in a loudspeaker including a frame mounted to a motor structure, a diaphragm connected between the voice coil of the motor structure and a surround carried by the frame, and, a spider extending from the voice coil to the frame in position to form a cavity between the top plate of the motor and the spider. An air flow path is formed at the juncture of the frame and top plate of the motor through which a comparatively high volume of cooling air is circulated at relatively high velocity in and out of the cavity between the spider and top plate in response to excursion of the voice coil during operation of the speaker. The air flow path is positioned to direct such cooling air over the top plate and at least along a portion of the voice coil to aid in cooling of these elements. 
     This invention is predicated upon the concept of using the “pumping” action of the diaphragm and spider created by excursion of the voice coil to obtain a high volume, high velocity flow of cooling air in and out of the cavity formed between the spider and top plate, along a flow path which is thermally adjacent to the top plate and voice coil. A stand-off is located between the bottom of the frame and the top plate of the motor to form the flow path for the cooling air moving in and out of the cavity. In some embodiments, the cooling air is made to flow directly into contact with the voice coil in the course of movement in and out of the cavity. Alternatively, the frame is formed with an inner ring which encircles the voice coil and directs the air flow in and out of the cavity through bores formed in the bottom of the frame. 
     In one group of presently preferred embodiments, the frame is fabricated from comparatively thin sheet metal in a stamping operation which forms a bottom surface. In one particular embodiment, a series of circumferentially spaced inserts or spacers are located between the bottom surface of the frame and the top plate of the motor to create a flow path for the cooling air entering and leaving the cavity. Alternatively, the stand-offs comprise extrusions or detents formed either in the top plate or the bottom surface of the frame, which are circumferentially spaced from one another to create the spacing between the frame and top plate. In all of these embodiments, the space formed between the bottom of the frame and the top plate defines the flow path for cooling air moving in and out of the speaker. When the voice coil axially moves in one direction, a flow of comparatively cool, ambient air from outside of the speaker is drawn into the speaker, over the top plate and against at least a portion of the voice coil into the cavity between the lower suspension and the top plate. Upon movement of the voice coil in the opposite direction, the air within such cavity is forced out of the cavity in the reverse direction along the same flow path. 
     In an alternative group of embodiments, the frame has a cast construction with a bottom surface formed with a number of circumferentially spaced extensions which rest against the top plate to form a flow path for transmitting cooling air toward the voice coil. The flow path in some cast frame designs directs cooling air against the voice coil as it enters and leaves the cavity between the spider and top plate. In one alternative embodiment, the bottom of the cast frame is formed with a ring which encircles the voice coil so that the air flow into and out of the cavity is prevented from directly impinging against the voice coil, but instead flows through bores formed in the bottom of the frame which communicate with the cavity. This flow of air is intended to transfer heat from the ring, which, in turn, conducts heat away from the voice coil. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The structure, operation and advantages of the presently referred embodiment of this invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective, cross sectional view of one embodiment of the speaker of this invention employing spacers to create a space between the frame and top plate; 
     FIG. 2 is view similar to FIG. 1 except of an alternative stand-off construction; 
     FIG. 3 is a perspective, cross sectional view depicting a still further stand-off embodiment; 
     FIG. 4 is a view similar to FIG. 3 except with the bottom surface of the frame formed with a vertically upwardly extending lip; 
     FIG. 5 is a perspective, cross-sectional view of a speaker construction according to this invention employing a cast frame having a bottom surface formed with extensions resting atop the top plate; 
     FIG. 6 is a perspective, cross-sectional view of an alternative embodiment of a speaker having a cast frame formed with spaced extensions, a collar encircling the voice coil and bores formed in the bottom of the frame; 
     FIG. 7 is view similar to FIG. 6, except with an inner ring which is spaced from the top plate of the motor; and 
     FIG. 8 is a view similar to FIG. 5, except with a portion of the bottom of the frame angled upwardly with respect to the top plate of the motor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, one group of embodiments of a loudspeaker  10  is illustrated in FIGS. 1-4, a second group of embodiments depicting a loudspeaker  100  are shown in FIGS. 5-7, and a third loudspeaker  120  is shown in FIG.  8 . The speakers  10 ,  100  and  120  each generally comprise a motor structure  12 , a diaphragm  16 , a lower suspension or spider  18  and a surround  20 . The speakers  10  illustrated in FIGS. 1-4 include a frame  14  which is preferably fabricated from a relatively thin sheet metal which can be formed in a stamping operation or the like. A cast frame  102  is employed in the speakers  100  and  120  of FIGS. 5-8. Except for specific differences in a portion of the construction of frames  14  and  102  and/or the manner of mounting the frames  14 ,  102 , to the motor structure  12 , as described below, the speakers  10 ,  100  and  120  have the same construction. Consequently, the same reference numbers are used in each of the FIGS. 1-8 to denote the same structure, and the overall speaker design is discussed with reference to speaker  10 , it being understood that the same description applies to speakers  100  and  120 . 
     Conventionally, the motor structure  12  includes a top plate  22  and a back plate  24  which are spaced from one another and mount a permanent magnet  26  therebetween. The central bore  28  of the magnet  26  and the top plate  22  form an air gap within which a pole piece  30  is mounted atop the back plate  24 . A voice coil  32  is concentrically disposed about the pole piece  30 , and axially movable relative thereto during operation of the speaker  10 . Preferably, the voice coil  32  includes a hollow, cylindrical-shaped former  34 , whose exterior surface receives a wire winding  36 . 
     The voice coil  32  is held in place with respect to the pole piece  30  by the diaphragm  16 , the spider  18  and the surround  20 . One end of the diaphragm  16  is affixed to the former  34  by adhesive or the like, and its opposite end connects to the surround  20 . The surround  20 , in turn, is mounted by adhesive to a seat  38  formed at the upper end of frame  14  and partially covered by a speaker gasket  39  as shown in FIG.  1 . The diaphragm  16  and surround  20  collectively form an upper suspension to support the voice coil  32 . Similarly, the lower suspension or spider  18  mounts to the former  34  in the same location as the diaphragm  16 , and the opposite end of spider  18  is mounted to a shoulder  40  formed in the lower end  42  of frame  14 . A dust cap  44  is mounted near the lower end of the diaphragm  16  immediately above the former  34  which, when connected to the diaphragm  16  and spider  18  as shown, is concentrically disposed about the pole piece  30 . For purposes of the present discussion, the terms “upper” or “upwardly” refer to the vertically upward direction in the orientation of the speaker  10  depicted in FIG.  1 . The terms “lower” or “downwardly” refer to the opposite direction. 
     In the embodiments of speaker  10  illustrated in FIGS. 1-4, the upper portion of the frame  14  is formed with a number of spaced openings or windows  41 . The lower end  42  of frame  14  is formed with an downwardly extending wall  48  beneath the shoulder  40  which, in turn, is integrally connected to an annular or ring-shaped bottom portion  50  which forms the base of the frame  14 . This bottom portion  50  of the frame  14  rests atop a number of stand-offs or spacers  52 , preferably formed of a thermally conductive material, which, in turn, mount to the top plate  22 . The spacers  52  are circumferentially spaced along the top plate  22 , and collectively provide a flow path  54  between the bottom portion  50  of frame  14  and the top plate  22  of motor  12 . 
     In the embodiment of FIG. 1, an extrusion  56  extends upwardly from the top plate  22  where each spacer  52  is located. Each extrusion  56  protrudes through a central bore in a corresponding spacer  52 , and through a bore formed in the bottom portion  50  of frame  14 . The top edge of each extrusion  56  is bent over or staked against the bottom portion  50  of fame  14 , as shown in FIG. 1, to securely interconnect the frame  14 , spacers  52 , and top plate  22 . Alternatively, the spacers  52  can be mounted between the top plate  22  and frame  14  with screws, rivets, pins or other mounting devices. 
     In the course of normal operation of the speaker  10 , the voice coil  32  is moved vertically upwardly and downwardly with respect to the pole piece  30 . Because the diaphragm  16  and spider  18  are mounted to the voice coil  32 , these elements also move vertically during speaker operation. The purpose of the flow path  54  formed by the spacers  52  between the bottom  50  of frame  14  and top the plate  22  is to take advantage of the natural “pumping” action of the diaphragm  16 , and to a lesser extent the lower suspension or spider  18 . When the diaphragm  16  and spider  18  are moved vertically upwardly in response to excursion of the voice coil  32 , ambient air from outside the speaker  10  is drawn through the flow path  54  into a cavity  60  which is formed between the spider  18 , and the top plate  22  and lower end  42  of frame  14 . Conversely, in the course of movement of the diaphragm  16  and spider  18  vertically downwardly with the voice coil  32 , air within the cavity  60  is forced outwardly through the flow path  54  to a location externally of the speaker  10 . The flow path  54  between the frame  14  and top plate  22  is positioned to transmit air entering and leaving the cavity  60  directly over the top plate  22  and against the voice coil  32 . These elements comprise two of the hottest areas of the speaker  10  during its operation and need to be cooled, to the extent possible, to maximize the power handling of the speaker and reduce power compression. The comparatively cool, ambient air drawn into the speaker  10  via the flow path  54  as described above provides significant cooling and heat transfer away from the top plate  22  and voice coil  32 . 
     Referring now to FIG. 2, an alternative embodiment of the speaker  10  is illustrated in which the bottom portion  50  of the lower end  42  of frame  14  is formed with a number of circumferentially spaced, basket-shaped detents  62  each having a throughbore. The stand-off or detents  62  extend vertically downwardly from the remainder of the bottom portion  50  and rest atop the top plate  22  to form a flow path  54  therebetween. The frame  14  is secured to the motor structure  12  by extrusions  56  formed in the top plate  22 , each of which protrudes through a detent  62  where they are bent over or staked in place against the interior thereof. The flow path  54  provided by the extrusions is substantially the same as that described above in connection with the embodiment of FIG. 1, and, consequently, essentially the same flow of cooling air into and out of the cavity  60  is achieved in this embodiment of speaker  10 . 
     A still further embodiment of a stand-off construction for spacing the lower end  42  of frame  14  vertically above the top plate  22  of motor structure  12  is shown in FIGS. 3 and 4. In these embodiments, the top plate  22  is formed with a series of circumferentially spaced extrusions  68 . Each extrusion  68 , in turn, has a base section  70  and an extension  72 . The lower end  42  of frame  14  rests atop the base section  70  of each extrusion  68 , and the extension  72  of each extrusion  68  protrudes through one of a number of circumferentially spaced bores formed in the bottom portion  50  of frame  14 . The extensions  72  are bent over or staked as depicted in FIGS. 3 and 4 to secure the frame  14  in place atop the top plate  22 . The space between the frame  14  and top plate  22  which is created by the extrusions  68  forms essentially the same flow path  54  as described above in the previous embodiments of this invention. 
     The distinction between the speakers  10  illustrated in FIGS. 3 and 4 is that a vertically upwardly extending ring  74  is formed on the inside edge of the bottom portion  50  of the frame  14  in FIG.  4 . The ring  74  is concentrically disposed about the voice coil  32  and in relatively close proximity thereto. Although the flow path  54  of the speakers  10  depicted in both FIGS. 3 and 4 transmits cooling directly against the voice coil  32 , the ring  74  functions to direct the air flow from the flow path  54  in a generally vertically upward direction in and out of the cavity  60 . Because the ring  74  is located immediately adjacent to and encircles the voice coil  32 , the ring  74  tends to maintain the flow of cooling air proximate to the voice coil  32  for a longer period of time than can be achieved with the frame construction shown in FIG.  3 . Additionally, the ring  74  conducts at least some of the heat produced by the voice coil  32  to the remainder of the frame  14 . Consequently, improved heat transfer is obtained by the combination of conduction along the frame  14 , and the passage of cooling air along the voice coil  32 , with the construction of speaker  10  illustrated in FIG.  4 . 
     Referring now to FIGS. 5-7, speakers  100  are illustrated which employ a cast frame  102  instead of the sheet metal, stamped frames  14  of the speakers  10  of FIGS. 1-4. The same concept of creating a space between the frame  102  and top plate  22  of motor  12  is present in the speakers  100 , as described above with reference to speakers  10 , with some variation in the particular structure of speakers  100  as described below. 
     The speakers  100  in FIGS. 5-7 are similar to one another in that they include a frame  102  having a bottom portion  106  formed with circumferentially spaced, cast extensions  108 . The stand-offs or extensions  108  rest atop the top plate  22  to form essentially the same flow path  54  as described above in connection with the previous embodiments. Each extension  108  is secured to the top plate  22  by a screw  110  which extends through a bore  112  in the extension  108  and into a bore  114  formed in the top plate  22 . The top plate bores  114  can be tapped, or, alternatively, self-tapping screws  110  are used. 
     The bottom portion  106  of frame  102  in the speaker  100  of FIG. 5 is spaced from the voice coil  32  approximately the same distance as are the frame bottoms  50  in the speakers  10  depicted in FIGS. 1-4. A similar air flow in and out of cavity  60  is therefore produced, wherein ambient air from outside of the speaker  100  is transmitted via the low path  54  along the top plate  22 , against the voice coil  32  and into the cavity  60  when the voice coil moves in one direction. The air exits the cavity  60  along the reverse flow path when the voice coil  32  moves in the opposite direction. 
     In the embodiment of speaker  100  shown in FIG. 6, a collar  116  is provided which extends vertically downwardly from the inner diameter of the bottom portion  106  of frame  102  and rests atop the top plate  22 . The collar  116  is located relatively close to the voice coil  22 , compared to the position of the inner diameter of the frame  14  or frame  102  in previous embodiments, and a number of circumferentially spaced holes  118  are formed in the bottom portion  106  of the frame  102  in FIG. 6 at a location radially outwardly from the collar  116 . 
     The construction of the speaker  100  depicted in FIG. 6 provides for a somewhat different manner of heat transfer from the top plate  22  and voice coil  32  than that described in FIGS. 1-5. In FIG. 6, the close proximity of the collar  116  to the voice coil  32  results in the conduction of heat from the voice coil  32  into the collar  116 , and, in turn, to the bottom portion  106  of frame  102 . Cooling air entering the speaker  100  via the flow path  54  created between the frame  102  and top plate  22  is directed against the collar  116  and flows through the holes  118  in and out of the cavity  60 . In the course of movement along this path, heat transfer occurs between the cooling air and the top plate  22 , and between the cooling air and the collar  116  as well as a portion of the frame  102 . Unlike the embodiments described in connection with a discussion of FIGS. 1-5, there is little or no direct contact of the cooling air with the voice coil  22  in the speaker  100  of FIG.  6 . 
     The speaker  100  illustrated in FIG. 7 is modified to some extent from that depicted in FIG. 6 with respect to the structure in the area of voice coil  32 . In this embodiment, a collar  117  is mounted along the inner diameter of the bottom portion  106  of frame  102 , but unlike the collar  116  of FIG. 6, the collar  117  extends only part way toward the top plate  22  and has a bottom edge  119  which is spaced therefrom. The same circumferentially spaced holes  118  employed in the embodiment of FIG. 6 are present in the speaker  100  of FIG.  7 . 
     The purpose of the space between collar  117  and top plate  22  is to provide an additional flow path for the cooling air entering and leaving cavity  61 . At least some of the cooling air transmitted through the flow path  54  is directed against the collar  117  and into holes  118  as in FIG. 6, but the space between the collar  117  and top plate  22  also permits the flow of cooling air directly against the voice coil  32  as in the embodiments of FIGS. 1-5. As such, the speaker  100  depicted in FIG. 7 employs a combination of the heat transfer characteristics found in all of the previously described embodiments. 
     A still further embodiment of this invention is illustrated in the speaker  120  of FIG.  8 . The speaker  120  is similar to speaker  100  shown in FIG. 5, except for the configuration of the bottom portion  122  of the frame  102 . Preferably, the bottom portion  122  of speaker  120  is substantially parallel to the top plate  22  from its inner edge  124  to the area where the extensions  108  are formed, but then a tapered portion  126  extends from the extensions  108  to the outer edge  125  thereof, i.e., in the area of the seat  40  where the spider  18  is mounted. The tapered portion  126  is angled upwardly from the top plate  22  so that the space or cross sectional area therebetween increases in a direction from the extensions  108  to the seat  40 . 
     As described above, the flow of cooling air in and out of the cavity  60  is obtained by the pumping action of the diaphragm  18  and spider  18 . The cooling air is drawn from outside of the speakers  10  and  100  into the cavity  60  in response to movement of the diaphragm  16  and spider  18  in a vertically upward direction, and then the air exits the cavity  60  upon movement of the diaphragm  16  and spider  18  in the opposite direction. In the embodiments of FIGS. 1-7, the flow path  54  between the bottom of the frame  14  or  102 , and the top plate  22 , has substantially the same height dimension from the outside of the frame  14  or  102  to the voice coil  32 . It is contemplated that while there is movement of air in and out of cavity  60  with this construction, there may be a limited exchange of “new” or fresh air within the cavity  60  during operation of the speakers  10  and  100 . 
     The speaker  120  is designed to obtain a more complete exchange of the air within cavity  60  than is achieved with the embodiments of FIGS. 1-7. As noted above, the bottom portion  122  of speaker  120  is spaced increasingly further away from the top plate  22  from its inner edge  124  to the seat of frame  40 , particularly along the tapered portion  126 . In response to movement of the diaphragm  16  and spider  18  in the vertically upward direction, a comparatively large volume of air enters the cavity  60  because the velocity of the air flow is increased in moving from the larger cross sectional area leading into the tapered portion  126  of the frame  102  to the relatively small cross sectional area at the inner edge  124  of the frame  102  near the voice coil  32 . More air, in turn, enters the cavity  60  than can be obtained with the embodiments of FIGS. 1-7. When the diaphragm  16  and spider  18  move in the opposite direction, air is emitted from the cavity  60  but at a comparatively lower velocity and lower volume because the flow of air is transmitted from the smaller cross sectional area near the voice coil  32  to the larger cross sectional area at the tapered portion  126  of the frame  102 . The additional volume of air entering the cavity  60 , compared to the volume exhausted as the voice coil  32  moves downwardly, is simply vented through the relatively porous spider  18 . 
     The overall intent of the speaker design in FIG. 8 is to obtain a higher volume flow of cooling air from outside of the speaker  120  into the cavity  60  so that the air within the cavity  60  is circulated and exchanged, rather than the same air simply being “recycled” or alternately moved in and out of the cavity  60  in the course of operation of the speaker  120 . Although the embodiments of speaker  10  depicted in FIGS. 1-7 do provide an increasingly larger area in moving from the inside diameter of the bottom plate  50  to its outside diameter, i.e., the overall cross sectional area of the flow path  54  at the inside diameter of bottom plate  50  is less than that at the outside diameter, the tapered design of the bottom portion  122  of the speaker  10  in FIG. 8 nevertheless promotes an even greater inflow of air to the cavity  60  via flow path  54  and therefore improved exchange of cooling air within the speaker  10 . It is contemplated that the design of the bottom portion  122  of speaker  120  could be incorporated into the speakers  10  and  100  depicted in FIGS. 1-6, to obtain the same benefit described above. 
     While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made in equivalents and may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the intended claims.