Patent Publication Number: US-6665414-B1

Title: Speaker system and cooling device therefor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a speaker system and a cooling device therefor. 
     2. Description of the Related Art 
     Conventionally, a sound system for automobile use and the like has been actively high-powered, and accordingly, heat dissipation of the speaker system has been increasingly important. FIGS. 1A and 1B are diagrams each showing the construction of a conventional speaker. The construction of the speaker  10  will be briefly described with reference to these figures. FIG. 1A is a cross-sectional view showing essential parts of the speaker  10 . FIG. 1B is a cross-sectional view showing essential parts of the speaker  10  to which a cooling device  11  is attached. 
     Speaker  10  has a magnetic circuit including a disk-shaped bottom yoke  1  formed of a magnetic metal member and having a hollow cylindrical pole portion la, an annular magnet  2  placed on the bottom yoke  1 , and an annular top yoke  3  formed of a magnetic metal member and placed on the magnet  2 . Further, a diaphragm  7  with a dust cap  7   a  arranged at a center thereof is suspended on a frame  4  via an edge  5  and a damper  6 , and joined to a coil bobbin  9  having a voice coil  8  wound therearound. The coil bobbin  9  is arranged in a magnetic gap formed by the magnetic circuit. 
     The magnetic circuit has a magnetic path (indicated by arrows in the figures, for instance) formed by the bottom yoke  1 , the top yoke  3 , and the magnet  2 . A gap between an end of the pole portion la and the top yoke  3  forms the magnetic gap for collecting the magnetic flux of the magnet  2  and thereby generates a high-density uniform magnetic field. When a drive current is supplied to the voice coil  8  through a power amplifier circuit, not shown, the coil bobbin  9  arranged in the magnetic gap with predetermined spaces from the pole portion la and the top yoke  3  is actuated to perform a reciprocating motion by an electromagnetic force generated in the magnetic gap. The reciprocating motion is transmitted to the diaphragm  7  whereby sounds are emitted. In short, an electrical signal is converted to acoustic vibrations. In the case of speaker  10 , especially when a large drive current is continuously supplied, the voice coil  8  generates Joule heat to thereby increase the temperature of the whole magnetic circuit formed by the bottom yoke  1  and its associated components. 
     To eliminate the above inconvenience, it is possible to employ a method of fitting a cooling device  11 , which is formed by a disk-shaped member highly efficient in thermal conductivity, with a concentric groove formed therein, in the pole portion la of the bottom yoke  1 . That is, if the cooling device  11  formed with the groove in which the disk-shaped bottom yoke  1  can be fitted is used, heat from the magnetic circuit can be emitted simply by mounting the device  11  on the bottom yoke  1  of the speaker  10 , as shown in FIG.  1 B. 
     However, heat generated by the voice coil  8  is gradually transferred to the bottom yoke  1  and the top yoke  3 . Therefore, it takes time before the heat generated by the voice coil  8  is accumulated in the bottom yoke  1  and the top yoke  3 , which prevents effective transfer of heat from the voice coil  8  to the cooling device  11 . 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The invention has been made in view of the above problems, and it is an object of the invention to provide a speaker system and a cooling device therefor which are capable of effectively dissipating heat generated by a voice coil. 
     To attain the above object, according to a first aspect of the invention, there is provided a speaker system including a magnetic circuit having a magnetic gap, a voice coil arranged in the magnetic gap, and a diaphragm attached to the voice coil, the voice coil and diaphragm being driven by supplying a drive current to the voice coil, comprising a first member arranged adjacent to the voice coil and inside a magnetic flux loop generated by the magnetic circuit, a second member arranged outside the magnetic flux loop generated by the magnetic circuit, and a third member connecting the first member and the second member to each other, wherein the first to third members are formed of a material excellent in thermal conductivity. 
     Preferably, the magnetic circuit is of an outer magnet type. 
     Preferably, the magnetic circuit is of an inner magnet type. 
     To attain the above object, according to a second aspect of the invention, there is provided a cooling device for a speaker system, comprising a first member arranged adjacent to a voice coil and inside a magnetic flux loop generated by a magnetic circuit, a second member arranged outside the magnetic flux loop generated by the magnetic circuit; and a third member connecting the first member and the second member to each other, wherein the first to third members are formed of a material excellent in thermal conductivity. 
     Preferably, heat generated in the voice coil is transferred to the second member via the first member and the third member to thereby allow the heat to be dissipated from the second member. 
     Preferably, the first to third members are integrally formed as a unitary member. 
     According to the speaker system and the cooling device therefor, the first member is arranged adjacent to the voice coil and at the same time inside the magnetic flux loop generated by the magnetic circuit, and the second member is arranged outside the magnetic flux loop, with the third member connecting the first member and the second member. Further, the first to third members are formed of a material excellent in thermal conductivity. Therefore, heat generated by the voice coil is transferred in the order of the first member, the third member, and the second member, thereby being dissipated from the second member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a cross-sectional view showing essential parts of a prior art speaker; 
     FIG. 1B is a cross-sectional view showing essential parts of the FIG. 1A prior art speaker having a cooling device mounted thereon; 
     FIGS. 2A and 2B are outline views of a cooling device for a speaker system according to an embodiment of the invention; 
     FIGS. 3A and 3B are outline views of a bottom yoke for having the cooling device mounted thereon according to the embodiment of the invention; 
     FIGS. 4A and 4B are outline views of the bottom yoke with the cooling device mounted thereon according to the embodiment of the invention; 
     FIG. 5 is a cross-sectional view of the speaker system having the cooling device mounted thereon, according to the embodiment of the invention; 
     FIGS. 6A and 6B are outline views of a cooling device for a speaker system according to another embodiment of the invention; and 
     FIG. 7 is a cross-sectional view of an inner magnet type speaker system, to which the cooling device according to the embodiment of the invention is applied. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 2A and 2B are outline views of a cooling device  20  for a speaker system, according to an embodiment of the invention. The cooling device  20  according to the embodiment of the invention is mounted on the inside of a bottom yoke  21  shown in FIGS. 3A,  3 B, and FIGS. 4A,  4 B. Therefore, not only the construction of the cooling device  20  but also that of the bottom yoke  21  will be described with reference to FIGS. 2A to  4 B. It should be noted that FIGS. 2A and 2B are outline views of the cooling device  20 , FIGS. 3A and 3B are outline views of the bottom yoke  21  of the speaker system, and FIGS. 4A and 4B are outline views of the bottom yoke  21  with the cooling device  20  attached thereto. 
     As shown in FIGS. 2A and 2B, the cooling device  20  is comprised of a first member  20   a  having a hollow cylindrical shape, a second member  20   b  having a hollow cylindrical shape, which is concentric with and has a larger diameter than the first member  20   a , and a plurality of third members  20   c  each in the form of a plate, which are radially arranged between first member  20   a  and second member  20   b  for connecting first member  20   a  and second member  20   b  to each other. Further, the first member  20   a  and the third members  20   c  are welded to or integrally formed with each other, and the second member  20   b  and the third members  20   c  are also welded to or integrally formed with each other. All these members are formed of a material that is highly efficient in thermal conductivity, such as copper or the like. FIGS. 2A and 2B show an example of the cooling device  20  formed by the above-mentioned members integrally formed with each other. 
     As shown in FIGS. 3A and 3B, the bottom yoke  21  is comprised of a pole portion  21   a  having a hollow cylindrical shape, and a bottom board portion  21   b  having a disk shape. On an upper surface  21   d  of the bottom board portion  21   b , a plurality of insertion grooves  21   c  for mounting the third members  20   c  of the cooling device  20  are radially arranged at positions corresponding to the respective third members  20   c.    
     The insertion grooves  21   c  of the bottom yoke  21  each have a depth approximately equal to the thickness of each of the third members  20   c . Accordingly, when the cooling device  20  is mounted on the bottom yoke  21 , as shown in FIGS. 4A and 4B, the upper surface  21   d  of the bottom board portion  21   b  is at substantially the same level as an upper surface  20   d  of each of the third members  20   c , so that when the annular magnet  2  as a component of the magnetic circuit is placed on the bottom yoke  21 , a bottom surface of the magnet  2  is brought into intimate contact with the upper surface  21   d  of the bottom board portion  21   b  and the upper surface  20   d  of each of the third members  20   c.    
     Next, the construction of a speaker system  30  incorporating the cooling device  20  according to the embodiment of the invention will be described with reference to FIG.  5 . It should be noted that reference numbers of the components which correspond to the prior art components are numbered in the same manner. FIG. 5 shows the speaker system  30  including a magnetic circuit of an outer magnet type. 
     Referring to FIG. 5, the speaker system  30  includes a disk-shaped bottom yoke  21  with the pole portion  21   a , which is formed of a magnetic metal member, and the cooling device  20  arranged at a predetermined position of the bottom yoke  21 . The first member  20   a  as a component of the cooling device  20  is arranged adjacent to a voice coil  8  of the speaker system and at the same time inside a magnetic flux loop of a magnetic circuit of the speaker system. Hence, the first member  20   a  is formed to have an inner diameter larger than an outer diameter of the voice coil  8  such that a predetermined magnetic gap can be obtained. Further, the second member  20   b  forming the cooling device  20  is arranged outside the magnetic flux loop of the magnetic circuit, so that the second member  20   b  is formed to have an inner diameter larger than an outer diameter of an annular magnet  2 . The annular magnet  2  and an annular top yoke  3  formed of a magnetic metal member are placed on the cooling device  20  to thereby form the magnetic circuit. Further, a diaphragm  7  with a dust cap  7   a  arranged at a center thereof is suspended on a frame  4  via an edge  5  and a damper  6 , and joined to a coil bobbin  9 . The coil bobbin  9  having a voice coil  8  wound therearound is arranged in a magnetic gap formed between the outer periphery of the pole portion  21   a  and the inner periphery of the top yoke  3 . 
     As described above, when the cooling device  20  is mounted on the bottom yoke  21 , the third members  20   c  are inserted into the insertion grooves  21   c , and the upper surface  20   d  of the speaker system  20  is at substantially the same level as the upper surface  21   d  of the bottom yoke  21 . Further, when the annular magnet  2  is placed at a predetermined position of the cooling device  20 , most of the bottom surface of the magnet  2  is brought into intimate contact with the upper surface  21   d  of the bottom yoke  21 . That is, the third members  20   c  of the cooling device  20  are interposed between the magnet  2  and the bottom yoke  21 . By forming each of these third members  20   c  in the form of a plate and at the same time radially arranging the same, the magnetic flux density of the magnet  2  is prevented from being reduced. Therefore, the magnetic circuit constructed by fixedly attaching the top yoke  3  to the magnet  2  forms a magnetic path (indicated by arrows in the figure, for instance) extending from the magnet  2 , through the bottom board portion  21   b  and pole portion  21   a  of the bottom yoke  2 , to the top yoke  3  and a high-density uniform magnetic field is generated in the magnetic gap formed between the pole portion  21   a  and the top yoke  3 . 
     When a drive current is supplied to the voice coil  8 , the coil bobbin  9  arranged in the magnetic gap with predetermined spaces from the pole portion  21   a  and the top yoke  3  is actuated to perform a reciprocating motion by an electromagnetic force in the magnetic gap. When a large drive current is continuously supplied, the voice coil  8  generates Joule heat. 
     Since the speaker system  30  and the cooling device  20  therefor according to the invention are constructed such that the first member  20   a  is arranged adjacent to the voice coil  8 , heat generated by the voice coil  8  is quickly transferred to the first member  20   a . The heat transferred to the first member  20   a  is then transferred to the second member  20   b  via the third members  20   c . The second member  20   b  is cooled off by the outside air temperature since the second member  20   b  is arranged outside the magnetic flux loop of the magnetic circuit. 
     The second member  20   b  of the cooling device  20  is always cooled off by the outside air temperature to thereby cool off the third members  20   c  joined to the second member  20   b . The third members  20   c  then cool off the first member  20   a  joined thereto. The voice coil  8  has a periphery thereof covered by the first member  20   a  arranged adjacent to the same and cooled off as described above, which makes it possible to hold down an increase in the temperature of the voice coil  8 . 
     FIGS. 6A and 6B are outline views of a cooling device  22  for a speaker system according to another embodiment of the invention. A second member  22   b  of the cooling device  22  is arranged outside a magnetic flux loop of a magnetic circuit of the speaker system, so that if the cooling device  22  is used which is formed to have e.g. concave and convex portions  22   e  arranged on an outer peripheral surface of the second member  22   b , as shown in FIG. 6A, or e.g. a fin  22   f  arranged on an outer periphery of the second member  22   b , as shown in FIG. 6B, the speaker system  30  can be provided with increased heat dissipation. 
     FIG. 7 shows a speaker system  40  according to still another embodiment of the invention, which includes a magnetic circuit of an inner magnet type. 
     In the speaker system  40  of the inner magnet type, the cooling device  22  is mounted on a disk-shaped bottom yoke  23 . On the cooling device  22  is fixedly attached a top yoke  24 , while a magnet  26  is placed on a portion of the bottom yoke  23  inside the coil bobbin  9 , and further a center yoke  25  is fixedly attached to the magnet  26 , whereby a magnetic circuit is formed. 
     In the case of the speaker system  40  of the inner magnet type, similar to the speaker system of the outer magnet type, the first member  22   a  of the cooling device  22  is arranged adjacent to the voice coil  8 . Therefore, heat generated by the voice coil  8  is quickly transferred to the first member  22   a , and then to the second member  20   b  via the third members  20   c , thereby being cooled of f by the outside air temperature. 
     According to the speaker system and the cooling device of the invention, the first member is arranged adjacent to the voice coil  8 , and inside the magnetic flux loop of the magnetic circuit, while the second member is arranged outside the magnetic flux loop. Further, the first member and the second member are connected to each other by the third members, and the first to third members are formed of a material that is highly efficient in thermal conductivity. Therefore, heat generated by the voice coil can be efficiently dissipated from the second member. 
     While there have been described preferred embodiments of the present invention, it is to be understood that various modifications and variations will occur to those skilled in the art without departing from the spirit and scope of the invention as hereinafter claimed.