Abstract:
There is provided a speaker or a speaker system which has no chance of disabled ventilating air in a space enclosed with a voice coil bobbin to outside of the magnetic circuit through a throughhole C formed in a magnetic circuit to communicate with the space enclosed with a voice coil bobbin, even if mounting a speaker between inner surfaces of a casing, because of enabled ventilating air from a space enclosed with a voice coil bobbin to outside of a magnetic circuit through an air path  3   c  formed in the magnetic circuit to communicate with the throughhole C.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an electrically driven speaker and speaker system used in various audio systems, especially a speaker appropriate to be used for mounting in a casing of a small-size equipment and a speaker system to be constituted with a speaker mounted in a casing. 
     2. Description of the Related Art 
     An electrically driven speaker is used generally in various audio systems, up to now. An electrically driven speaker has two types according to magnetic circuit structures, i.e., an outer magnet type and an inner magnet type defined by a magnet position in a magnetic circuit. However, respective vibrating member of two-type speakers has almost same structural relation for a magnetic circuit. 
     An electrically driven speaker, a half-section shown in FIG. 9, is provided with an outer-magnet-type magnetic circuit comprising an annular top plate  1  having an opening  1   a  in the center, an annular magnet  2  attached to a bottom surface of the top plate  1  and magnetized in a direction of thickness, and a yoke  3  attached to a bottom surface of the magnet  2 . The yoke  3  is provided with a bottom plate  3   a , and a center pole  3   b  projecting from the center of the bottom plate  3   a  and forming a gap G between an inner circular surface of the opening  1   a  in the top plate  1 . 
     In FIG. 9, mark  5  shows a frame attached to a top surface of the top plate  1 , mark  6  shows a voice coil supported in the magnetic gap G and vibrating correspondingly to electrical signals, mark  7  shows a cylindrical voice coil bobbin transmitting driving force generated in the voice coil  6  to a vibrating system, mark  8  shows a vibrating member attached to a top edge of the voice coil bobbin  7 , mark  9  shows a damper joined at an inner circular portion thereof to an intermediate position of the voice coil bobbin  7  and joined at an outer circular portion thereof to the frame  5 , and mark  10  shows a roll-shape edge joined at an inner circular portion to an outer circular portion of the vibrating member  8  and joined at an outer circular portion thereof to the frame  5 . The voice coil  6 , the voice coil bobbin  7 , the vibrating member  8 , the damper  9  and the edge  10  constitute a vibration system  12 . 
     In the speaker by prior art, constituted above, a space A enclosed with the cylindrical voice coil bobbin  7 ; describing in detail, a space A formed by a top surface of the center pole  3   b , an inner circular surface of the voice coil bobbin  7  and a bottom surface of the vibrating member  8 ; is ventilated through a thin gap g 1  formed by an outer circular surface of the center pole  3   b  and an inner circular surface of the voice coil bobbin  7  to a space B formed by an outer circular surface of the center pole  3   b , a top surface of the bottom plate  3   a , an inner circular surface of the magnet  2 , and a bottom surface of the top plate  1 . Further, the space A is ventilated through a thin gap g 2  formed by an inner circular surface of the top plate  1  and an outer circular surface of the voice coil bobbin  6 , and a ventilating opening  5   a  provided in the air-permeable damper  9  and in the frame  5  to an outside of the frame  5 , i.e. an outside space of the speaker. 
     When the above structured speaker is inputted with a large power, a large electric current runs in the voice coil  6  so as to be heated. The heat, generated in the voice coil, is transmitted through air of a space between an outer circular surface of the center pole  3   b  and an inner circular surface of the voice coil bobbin  7  to the center pole  3   b , and transmitted through air of a space between an inner circular surface of the top plate  1  and an outer circular surface of the voice coil  6  to the top plate  1 , and then refrigerated. Furthermore, the heat is also refrigerated by air moving in the thin gap g 2  formed by an inner circular surface of the top plate  1  and an outer circular surface of the voice coil  6 . However, the heat conductivity of air is low and ventilation between the space A and an outside space of the speaker is done through the thin gap g 1  formed by an outer circular surface of the center pole  3   b  and an inner circular surface of the voice coil bobbin  7  so that the ventilation is not enough to refrigerate sufficiently the heat of the voice coil  6 . Therefore, electric resistance of the voice coil  6  increases by heating and electric current goes down then sound pressure corresponding to electric input can not be given. 
     On driving a speaker, expansion and compression of air in the space A is repeated. When driving a speaker by low frequency range with a large input, insufficient ventilation of air causes increasing expansion/compression coefficient of air so that restraining the amplitude of the speaker reduces playback sound pressure and causes sound distortion by non-linearity of air compliance. 
     It is proposed on a speaker to provide a throughhole C, as shown in FIG. 9, through the center of a center pole  3   b , extending from a top surface of the center pole  3   b  to a bottom surface of a bottom plate  3   a , communicating between a space A and an outside of a magnetic circuit, to improve releasing heat generated in a voice coil  6  and transmitted to a center pole  3   b  for reducing temperature rising of the voice coil  6  and increasing allowable input power. According to this proposed speaker structure, ventilation between a space A and an outside of a magnetic circuit is done through the throughhole so that the expansion/compression coefficient of air is decreased and then sound distortion by non-linearity of air compliance is restrained. 
     In an inner-magnet-type magnetic circuit as shown in FIG. 10, a cylindrical magnet  31  is provided on a center of a top surface of a bottom plate  30   a  forming a bottom portion of a bottomed cylindrical yoke  30  and a disk-shaped pole piece  32  forming a magnetic gap G between an inner circular surface of the yoke  30  is joined on the magnet  31 . The inner-magnet-type magnetic circuit is provided with a throughhole C through the pole piece  32 , the magnet  31  and yoke  30 , communicating between a space A and an outside of a magnetic circuit, to improve releasing heat, generated in a voice coil  6  and transmitted to the pole piece  32 , for reducing temperature rising of the voice coil  6  and increasing allowable input power so that the expansion/compression coefficient of air is decreased and then sound distortion by non-linearity of air compliance is restrained. 
     With popularization of a mobile telephone as a small equipment, miniaturization, weight saving, low pricing and higher performance for a mobile phone are required more and technology development regarding the requirements is a mainstream. Study not only on a speaker itself but also a method for mounting a speaker on a casing are required and then a speaker system constituted with a casing applies a structure shown in FIG.  11 . 
     A speaker is shown simply with a vibration system and a magnetic circuit in FIG.  11  and mounted to be held between inner surfaces of a casing  20  by facing a surface of the vibration system  4  and a bottom portion of the magnetic circuit  12  respectively to inner surfaces of the casing  20 . Specifically, a sounding surface of the vibration system  4  is placed to abut on an inner surface of a front wall  21 , having a sounding opening  21   a , of the casing  20  and is pressed by an elastic-material-made pad  23  inserted between an inner surface of a rear wall  22 , parallel to the front wall  21 , of the casing  20  and a bottom surface of the speaker magnetic circuit  12  so that the speaker is mounted and fixed in the casing. In case, pressing the bottom surface of the speaker magnetic circuit  12  directly by the inner surface of the rear wall  22  of the casing  20 , as shown in FIG. 12, the speaker is mounted and fixed in the casing. 
     Objects to be Solved 
     As mentioned above, a casing for mounting a speaker is miniaturized and a structure which a speaker is mounted in a casing to be held between inner surfaces by facing a surface of a vibration system and a bottom portion of a magnetic circuit respectively to the inner surfaces of the casing, as shown in FIG. 10 or  11 , is applied so that a throughhole, formed in a magnetic circuit to communicate with a space enclosed with a voice coil bobbin, is blocked at a bottom portion of a magnetic circuit by the pad  23  or the inner surface of the rear wall  22 . Therefore, air in a space A enclosed with a voice coil bobbin can not be ventilated through a throughhole C from a bottom portion of a magnetic circuit  12 . 
     Thereby, the throughhole C can not perform the function to restrain sound distortion by non-linearity of air compliance by improving releasing heat, generated in a voice coil  6  and transmitted to the pole piece  32 , for reducing temperature rising of the voice coil  6  and increasing allowable input power. 
     This invention has been accomplished to overcome the above drawbacks and an object of this invention is to provide a speaker enabled to ventilate air in a space enclosed with a voice coil bobbin to outside of a magnetic circuit through a throughhole formed in the magnetic circuit to communicate with the space even if the speaker is mounted and fixed between inner surfaces in a casing to face a surface of a vibration system and a bottom portion of the magnetic circuit respectively to inner surfaces of the casing. 
     Another object is to provide a speaker system enabled to ventilate air in a space enclosed with a voice coil bobbin to an outside of a magnetic circuit through a throughhole formed in the magnetic circuit to communicate with the space even if the speaker is mounted and fixed between inner surfaces in a casing to face a surface of a vibration system and a bottom portion of the magnetic circuit respectively to inner surfaces of the casing. 
     SUMMARY OF THE INVENTION 
     How to Attain the Object 
     In order to attain the objects, according to an aspect of this invention, there is provided a speaker which includes a vibration system having a voice coil, a cylindrical voice coil bobbin carrying said voice coil and a vibrating member attached to said voice coil bobbin, and a magnetic circuit generating magnetic force in cooperating with the voice coil to drive said vibrating member, a throughhole formed through said magnetic circuit to communicate with a space enclosed with the voice coil bobbin for ventilating air in said space from a bottom portion of the magnetic circuit; for being used to be fixed between inner surfaces of a casing by facing a surface of the vibration system and a bottom portion of the magnetic circuit respectively to the inner surfaces, and comprises an air path formed in the magnetic circuit to communicate with said throughhole for ventilating air in the space to outside of the magnetic circuit. 
     In the above-mentioned structure, air in the space enclosed with the voice coil bobbin can be ventilated to outside of the magnetic circuit through the air path formed in the magnetic circuit to communicate with the throughhole for ventilating air in the space from a bottom portion of the magnetic circuit so that air in the space can be ventilated to outside of the magnetic circuit even if the throughhole is blocked by fixing between the inner surfaces of the casing to face the surface of the vibration system and the bottom portion of the magnetic circuit respectively to the inner surface. 
     According to another aspect of the invention, there is provided a speaker which comprises a speaker as referred to above, wherein said air path is formed in the bottom portion of said magnetic circuit. 
     In the above-mentioned structure, air ventilation through the air path is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole. 
     According to yet another aspect, there is provided a speaker which comprises a speaker as referred to above, wherein said air path is formed, in the bottom portion of the magnetic circuit, extending to an outer edge of the bottom portion of the magnetic circuit. 
     In the above-mentioned, air ventilation through the air path, formed in the bottom portion of the magnetic circuit extending to an outer edge of the bottom portion of the magnetic circuit, is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole. 
     According to further aspect of the invention, there is provided a speaker which comprises a speaker as referred to above, wherein said air path is formed, in the bottom portion of the magnetic circuit, extending to an area of the bottom portion of the magnetic circuit which can not be blocked by the inner surfaces of the casing. 
     In the above-mentioned structure, air ventilation through the air path, formed in the bottom portion of the magnetic circuit extending to an area of the bottom portion of the magnetic circuit which can not be blocked by the inner surfaces of the casing, is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole. 
     According to further aspect of the invention, there is provided a speaker which comprises a speaker as referred to above, wherein said magnetic circuit is outer-magnet-type and said throughhole is formed extending to the bottom portion of the magnetic circuit through a center pole of said magnetic circuit. 
     In the above-mentioned structure, air ventilation through the air path, formed in the bottom portion of the magnetic circuit, is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole formed extending to the bottom portion of the magnetic circuit through a center pole of the outer-magnet-type magnetic circuit. 
     According to further aspect of the invention, there is provided a speaker which comprises a speaker as referred to claim 2, wherein said magnetic circuit is inner-magnet-type and said throughhole is formed extending to the bottom portion of the magnetic circuit through a pole piece and a magnet of said magnetic circuit. 
     In the above-mentioned structure, air ventilation through the air path, formed in the bottom portion of the magnetic circuit, is kept even if the bottom portion of the magnetic circuit is pressed with any members for fixing between inner surfaces of the casing. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit caused by blocking the throughhole formed extending to the bottom portion of the magnetic circuit through a pole piece and a magnet of the inner-magnet-type magnetic circuit. 
     According to further aspect of this invention, there is provided a speaker system which includes a speaker comprising a vibration system having a voice coil, a cylindrical voice coil bobbin carrying said voice coil and a vibrating member attached to said voice coil bobbin, and a magnetic circuit generating, magnetic force in cooperating with the voice coil to drive said vibrating member, and a casing for receiving said speaker, wherein said speaker is fixed between inner surfaces of said casing by facing a surface of said vibration system and a bottom portion of said magnetic circuit respectively to said inner surfaces, wherein a path is formed in said magnetic circuit to communicate with a space enclosed with the voice coil bobbin for ventilating air in said space from a bottom portion of the magnetic circuit. 
     In the above-mentioned structure, air in the space enclosed with the voice coil bobbin can be ventilated to outside of the magnetic circuit through the path formed in the magnetic circuit even if the speaker, having a vibration system including a voice coil, a cylindrical voice coil bobbin and a vibrating member, and a magnetic circuit, is fixed between the inner surfaces of the casing by facing the surface of the vibration system and a bottom portion of the magnetic circuit respectively to the inner surface. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit. 
     According to further aspect of the invention, there is provided a speaker system which comprises a speaker system as referred to above, and said path provided with a throughhole formed through said magnetic circuit to communicate with a space enclosed with said voice coil bobbin for ventilating air in said space from a bottom portion of said magnetic circuit, and an air path formed, in the bottom portion of the magnetic circuit, to communicate with said throughhole for ventilating air in said space to outside of the magnetic circuit. 
     In the above-mentioned structure, air in the space can be ventilated to outside of the magnetic circuit through the throughhole formed through the magnetic circuit for ventilating air in the space from a bottom portion of the magnetic circuit and the air path formed in the bottom portion of the magnetic circuit, to communicate with the throughhole for ventilating air in the space to outside of the magnetic circuit. So it is no chance that air in the space cannot be ventilated to outside of the magnetic circuit. 
     As mentioned above, there is provided a speaker or a speaker system having no chance of disabled ventilating air in a space enclosed with a voice coil bobbin to outside of the magnetic circuit through a throughhole formed in a magnetic circuit to communicate with the space enclosed with a voice coil bobbin, even if mounting a speaker between inner surfaces of a casing, facing a surface of a vibration system and a bottom portion of a magnetic circuit to inner surfaces of the casing. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various change and modifications can be made with the scope of the present invention. Incidentally, the content of Japanese Patent Application No. 2001-55161 is hereby incorporated by reference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a sectional view of an embodiment of an outer-magnet-type magnetic circuit usable for a speaker according to the invention; 
     FIG. 1B is a bottom view of an embodiment of an outer-magnet-type magnetic circuit usable for a speaker according to the invention; 
     FIG. 2 is a sectional view of an embodiment of a speaker system, according to the invention, which mounts a speaker using the magnetic circuit shown in FIG. 1, in a casing; 
     FIG. 3 is a sectional view of other embodiment of a speaker system, according to the invention, which mounts a speaker using the magnetic circuit shown in FIG. 1, in a casing; 
     FIG. 4 is a bottom view of an example of a partial modified magnetic circuit shown in FIG. 1; 
     FIG. 5 is a bottom view of other example of a partial modified magnetic circuit shown in FIG. 1; 
     FIG. 6A is a sectional view of an embodiment of an inner-magnet-type magnetic circuit usable for a speaker according to the invention; 
     FIG. 6B is a bottom view of an embodiment of an inner-magnet-type magnetic circuit usable for a speaker according to the invention; 
     FIG. 7A is a sectional view of an example of a modified inner-magnet-type magnetic circuit shown in FIG. 6A; 
     FIG. 7B is a bottom view of an example of a modified inner-magnet-type modified magnetic circuit shown in FIG. 6B; 
     FIG. 8 is a sectional view of an embodiment of a speaker system, according to the invention, which mounts a speaker using the magnetic circuit shown in FIGS. 7A,  7 B, in a casing; 
     FIG. 9 is a half-sectional view of an example of a speaker by prior art, using an outer-magnet-type magnetic circuit; 
     FIG. 10 is a sectional view of an example of a speaker by prior art, using an inner-magnet-type magnetic circuit; 
     FIG. 11 is a sectional view of an example of a speaker system, by prior art, which mounts a speaker using the magnetic circuit shown in FIGS. 9,  10 , in a casing; and 
     FIG. 12 is a sectional view of other example of a speaker system, by prior art, which mounts a speaker using the magnetic circuit shown in FIGS. 9,  10 , in a casing; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A speaker and a speaker system, having a speaker in a casing, of embodiments according to this invention will be described with reference to the attached drawings. Parts corresponding to a speaker and a speaker system shown in FIGS. 9-12 are shown with the same marking. 
     FIGS. 1A and 1B show an example of outer-magnet-type magnetic circuits able to be used in a speaker according to this invention. FIG. 1A is a sectional view and FIG. 1B is a bottom view. 
     In FIG. 1, a groove  3   c  is provided by machining or press working, through a center of a bottom plate  3   a , extending an outer circular edge of the bottom plate  3   a , on the bottom surface of the bottom plate  3   a  of a yoke  3  constituting a magnetic circuit. Thereby, the groove  3   c  communicates with a throughhole C through a center of a center pole  3   b , opened from a top surface of the center pole  3   b  to the center of the bottom surface of the bottom plate  3   a.    
     Constituting a speaker system to mount a speaker having above structured magnetic circuit in a casing, a sounding surface of a vibration system  4  of a speaker is abutted on an inner surface of a front wall, having a sounding opening  21   a , of a casing  20  and placed in position and then, a bottom surface of a magnetic circuit  12  of the speaker is pressed by an elastic-material-made pad  23  inserted between an inner surface of a rear wall  22  and the bottom surface of the magnetic circuit  12  as shown in FIG. 2, or pressed directly by an inner surface of the rear wall  22  of the casing  20  as shown in FIG. 3 so that the throughhole C is not blocked. Through an air path formed by the groove  3   c  to communicate with the throughhole C extending to the outer circular edge of the bottom plate  3   a , air ventilation between outside can be done to exhaust air in a space enclosed with not-shown voice coil bobbin to outside of the magnetic circuit and to take air at outside of the magnetic circuit into the space. 
     As mentioned above, air ventilation between outside can be done through an air path formed by a throughhole and a groove to exhaust air in a space enclosed with not-shown voice coil bobbin to outside of the magnetic circuit and to take air at outside of the magnetic circuit into the space so that improving releasing heat and reducing temperature rising of the voice coil and increasing allowable input power, the expansion/compression coefficient of air is decreased and then sound distortion by non-linearity of air compliance can be restrained. 
     According to an above-mentioned embodiment, the air path is given by a groove  3   c  formed on the bottom surface of the bottom plate  3   a  by machining or press working, extending an outer circular edge of the bottom plate  3   a  to communicate with the throughhole C. Preferably, the air path may be given with a concave portion provided between a pair of parallel ribs formed projectionaly on the bottom surface of the bottom plate. According to an embodiment in FIG. 1, a groove  3   c  is formed in a straight line extending an outer circular edge of the bottom plate  3   a  through the center thereof. Preferably, the groove may be formed in cross-shape as shown in FIG. 4 or formed in a radial pattern as shown in FIG. 5 to improve air ventilation within the limits of not affecting magnetic function and strength of the yoke  3 . 
     FIGS. 6A and 6B show an example of inner-magnet-type magnetic circuits able to be used in a speaker according to this invention. FIG. 6A is a sectional view and FIG. 6B is a bottom view. 
     In FIG. 6, a slit opening  30   c  is provided by machining or punching before forming cylindrical shape, through a center of a bottom plate  30   a , extending an outer circular edge of the bottom plate  30   a , on the bottom surface of the bottom plate  30   a  forming a bottom portion of a bottomed cylindrical yoke  30  constituting a magnetic circuit. Thereby, the slit opening  30   c  communicates in a bottom plate  30   a  with a throughhole C opened through a pole piece  32 , a magnet  31  and the yoke  30 . 
     When constituting a speaker system to mount a speaker having above structured magnetic circuit in a casing as mentioned above in FIGS. 2 and 3, the throughhole C is not blocked and air ventilation between outside can be done through an air path formed by the slit opening  30   c  to communicate with the throughhole C and extend to the outer circular edge of the bottom plate  30   a  to exhaust air in a space enclosed with not-shown voice coil bobbin to outside of the magnetic circuit and to take air at outside of the magnetic circuit into the space. Therefore, in the speaker, releasing heat is improved and temperature rising of the voice coil is reduced and allowable input power is increased so that the expansion/compression coefficient of air is decreased and then sound distortion by non-linearity of air compliance can be restrained. 
     According to an embodiment in FIG. 6, the slit opening  30   c  is formed in a straight line, extending an outer circular edge of the bottom plate  30   a  through the center thereof. Preferably, the slit opening may be formed in cross-shape or a radial pattern as mentioned above in FIGS. 4 and 5 to improve air ventilation within the limits of not affecting magnetic function and strength of the yoke  30 . 
     According to the embodiment of this invention, the slit opening  30   c  is formed on the bottom plate  30   a  to provide a air path having a height as same as a thickness of the bottom plate  30   a  so that the slit opening preferably perform also an air path communicating with a space B, formed around an outer circular surface of the magnet, to improve releasing heat. When allowing an air path having a height thinner than the plate thickness, the air path may be formed in a groove as same as the example in FIG.  1 . 
     According to an embodiment in FIG. 6, the slit opening  30   c  is formed in a straight line, extending an outer circular edge of the bottom plate  30   a  through the center thereof. Preferably, a square opening  30   c ′, as shown in FIG. 7, maybe formed to have a larger area than a pad  23  and keep an outer circular edge portion of the bottom plate  30   a  instead of the slit opening  30   c  when the pad  23 , inserted between a inner surface of the rear wall  22  and a bottom surface of the magnetic circuit  12  of the speaker for pressing the bottom surface thereof, is enough smaller than an area of the bottom surface of the magnetic circuit  12 . Such square opening  30   c ′ can be manufactured easier than a slit opening extending to an outer circular edge and also is advantageous to keep strength of a yoke. An air path formed by such square opening  30   c ′ faces to a rear surface direction facing to an inner surface of a casing as shown in FIG. 8, opposing above-mentioned embodiment which an air vent is on a side of the magnetic circuit. 
     In any embodiments mentioned above, an air path is formed in a magnetic circuit to communicate with a throughhole provided in the magnetic circuit to exhaust air in a space enclosed with a voice coil bobbin to outside of the magnetic circuit so that a casing for mounting a speaker can be miniaturized. When mounting a speaker between inner surfaces of a casing by facing a surface of a vibration system and a bottom portion of a magnetic circuit respectively to inner surfaces of the casing, air ventilation between a space enclosed with a voice coil bobbin and outside can be done always. Therefore, in the speaker, releasing heat is improved and temperature rising of the voice coil is reduced and allowable input power is increased so that the expansion/compression coefficient of air is decreased and then sound distortion by non-linearity of air compliance can be restrained.