Patent Publication Number: US-2010111334-A1

Title: Speaker and electronic apparatus using the same

Description:
TECHNICAL FIELD 
     The present invention relates to a low-profile loudspeaker and an electronic apparatus using the same. 
     BACKGROUND ART 
     With the demand for sliming down of electronic apparatuses such as portable devices, there are also growing demands for reducing thickness of loudspeakers built into their housing cases. 
     It is the common practice to reduce dimensions of a magnet that forms a magnetic circuit in order to reduce the thickness of a conventional loudspeaker such as the one described in the Patent Literature 1 below. When the magnet is reduced in size, a magnetic force of it weakens, which in turn decreases a sound output. It is thus impractical to reduce substantially the size of the magnet, and therefore not feasible to achieve a significant reduction in the thickness of the conventional loudspeaker. 
     Patent literature 1: Japanese Patent Unexamined Publication, No. 2005-51283. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a low-profile loudspeaker having a high sound output and robustness capable of withstanding vibrations and physical shocks. The loudspeaker of the present invention has a first magnet, a second magnet, a third magnet, a voice coil, a diaphragm and a magnetic fluid. The first magnet has a first pole and a second pole of an opposite polarity to that of the first pole. The second magnet has a third pole of the same polarity as the first pole of the first magnet and a fourth pole of the same polarity as the second pole, and is so disposed that the third pole confronts the first pole of the first magnet. The third magnet has a fifth pole of the same polarity as the first pole of the first magnet and a sixth pole of the same polarity as the second pole, and is disposed in such an orientation that an axial direction connecting the fifth pole and the sixth pole is perpendicular to a line connecting the first pole of the first magnet and the third pole of the second magnet, and that the sixth pole is positioned closer to the first and the third poles. There are magnetic gaps, one formed between the third magnet and the first magnet, and another formed between the third magnet and the second magnet. The voice coil is placed in these magnetic gaps. The diaphragm supports the voice coil. The diaphragm is provided with an aperture formed in a position confronting the third magnet. The magnetic fluid is kept suspended between the sides of the third magnet facing the magnetic gaps and the voice coil. 
     By virtue of the above structure, the loudspeaker of the present invention is provided with magnetic flux of a direction substantially perpendicular to the voice coil within the magnetic gaps while achieving a reduction in the thickness. In addition, the above arrangement of the three magnets enhances the magnetic force to increase the sound output. Moreover, the magnetic fluid helps prevent a rolling phenomenon and reduces gap failures. Furthermore, the magnetic fluid also improves the effect of heat dissipation from the voice coil and increases a resistance of the loudspeaker against high input. In this structure, vibration of the diaphragm is not impeded since the diaphragm is provided with the aperture in the position confronting the third magnet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a mobile phone unit equipped with a loudspeaker according to an exemplary embodiment of the present invention. 
         FIG. 2  is a perspective view of the mobile phone unit shown in  FIG. 1  with a cover thereof removed. 
         FIG. 3  is a block diagram of the mobile phone unit shown in  FIG. 1 . 
         FIG. 4  is an exploded perspective view of the loudspeaker shown in  FIG. 2 . 
         FIG. 5  is another exploded perspective view of the loudspeaker as in  FIG. 4 , showing a flow of magnetic flux. 
         FIG. 6  is a longitudinal sectional view of the loudspeaker shown in  FIG. 2 . 
         FIG. 7 . is a cross sectional view of the loudspeaker shown in  FIG. 2 . 
         FIG. 8  is a enlarged cross sectional view of a portion marked A in  FIG. 7 . 
     
    
    
     REFERENCE MARKS IN THE DRAWINGS 
     
         
           1  Body 
           2  Lid 
           3  Cover 
           4  Loudspeaker 
           4 A Case 
           5 ,  6  Plate 
           5 A Sound hole 
           5 B,  7 A Adhesive agent 
           6 A Fixing section 
           6 B Opening 
           7  Third magnet 
           8 ,  11  Ring 
           9  Diaphragm 
           9 A Top portion 
           9 B,  9 C Side portion 
           9 D Barrel portion 
           10  Voice coil 
           12 A First magnet 
           12 B Second magnet 
           13  Frame 
           14  Magnetic fluid 
           15  Aperture 
           41  Circuit section 
           42  Input section 
           43  Microphone 
           44  Display section 
           45  Loudspeaker 
       
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to the accompanying drawings, description is provided hereinafter of an exemplary embodiment of the present invention by using a mobile phone unit as an example of electronic apparatus.  FIG. 1  is a perspective view of a mobile phone unit equipped with a loudspeaker according to this exemplary embodiment of the invention.  FIG. 2  is a perspective view of the mobile phone unit shown in  FIG. 1  with a cover removed, and  FIG. 3  is a block diagram of the mobile phone unit shown in  FIG. 1 .  FIG. 4  and  FIG. 5  are exploded perspective views of the loudspeaker shown in  FIG. 2 , wherein  FIG. 5  shows a flow of magnetic flux.  FIG. 6  is a longitudinal sectional view and  FIG. 7  is a cross sectional view of the loudspeaker shown in  FIG. 2 .  FIG. 8  is an enlarged cross sectional view of a portion marked A in  FIG. 7 . 
     The mobile phone unit as an electronic apparatus is provided with two pieces of cover  3  on an outer surface of body  1  as shown in  FIG. 1 , and loudspeakers  4  are mounted inside body  1  behind each of covers  3  as shown in  FIG. 2 . 
     Lid  2  is attached to body  1  in a freely openable manner. Like any ordinary mobile phone, this mobile phone unit is also provided with input section  42  formed of operation buttons and microphone  43  shown in  FIG. 3  on the side of body  1  opposite the side illustrated in  FIG. 1 . Lid  2  has display section  44  of an LCD and loudspeaker  45  for receiving conversation. Circuit section  41  housed inside body  1  receives an input from input section  42 , and displays the input, incoming information and the like on display section  44 . During a telephone conversation, circuit section  41  receives a voice input from microphone  43 , and reproduces an incoming voice of another party via loudspeaker  45 . In addition, circuit section  41  drives loudspeakers  4  to generate a ring tone. 
     As shown in  FIG. 4 , loudspeaker  4  has plates  5  and  6 , first magnet  12 A, second magnet  12 B and third magnet  7 , each of which has a plate-like shape, rings  8  and  11 , diaphragm  9  and voice coil  10 . Plate  5  positioned on the exterior side of body  1  is made of a stainless steel having a non-magnetic property (e.g., SUS301). On the other hand, plate  6  is made of a cold rolled steel sheet having a magnetic property. Frame  13  made of a resin covers a part of front surface of plate  5  as well as the periphery of all components, as shown in  FIG. 6  and  FIG. 7 . In other words, plates  5 ,  6  and frame  13  constitute case  4 A. Plate  5  is provided with sound hole  5 A. 
     First magnet  12 A, second magnet  12 B and third magnet  7 , each of the plate-like shape having a longitudinal direction are made of such material as neodymium. Neodymium magnets are suitable for use in small and low-profile loudspeaker  4  of this exemplary embodiment since they exhibit strong magnetic polarities. The material needs not be limited only to neodymium, however, that it can be of any other materials so long as they have strong magnetism. Each of first magnet  12 A, second magnet  12 B and third magnet  7  has the N-pole and the S-pole. In the embodiment described below, the N-pole of first magnet  12 A may be referred to as a first pole while the S-pole may be referred to as a second pole of opposite polarity to that of the first pole. Likewise, the N-pole and the S-pole of second magnet  12 B may be referred to as a third pole and a fourth pole of opposite polarity to that of the third pole, and the N-pole and the S-pole of third magnet  7  may also be referred to as a fifth pole and a sixth pole of opposite polarity to that of the fifth pole. It is to be noted, however, that the arrangement of the N-poles and the S-poles of these magnets may entirely be reversed. 
     Diaphragm  9  is formed of such a material as polyether-imide film. Voice coil  10  is made of a copper wire or the like. Voice coil  10  is oblong in shape having a pair of long sides in plan view, and these long sides are disposed in the magnetic gaps provided at both sides of third magnet  7  along the longitudinal direction. Both rings  8  and  11  are formed of a cold rolled steel sheet having a magnetic property. 
     Third magnet  7 , ring  8 , diaphragm  9 , voice coil  10 , ring  11 , first magnet  12 A and second magnet  12 B are disposed inside case  4 A in the above order from plate  6  toward plate  5 . Third magnet  7  and ring  8  are disposed on plate  6 . Ring  8  is fixed to the peripheral portion of plate  6  in a manner to allow the magnetic flux to pass through as shown by the arrow in  FIG. 5 . 
     Plate  6  has an oblong shape as shown in  FIG. 4  and  FIG. 5 , and has fixing section  6 A of a rectangular shape in an area of the center axis (i.e., central portion) along its longitudinal direction. Third magnet  7  is fixed to the upper surface of fixing section  6 A with adhesive agent  7 A applied to the bottom of third magnet  7  as shown in  FIG. 8 . Plate  6  is also provided with openings  6 B of a rectangular shape at both sides of fixing section  6 A. Openings  6 B serve as back sound holes enabling loudspeaker  4  to radiate sound also from the backside. 
     Diaphragm  9  is placed with its periphery on ring  8 , and ring  11  is placed on the periphery of diaphragm  9 .  FIG. 5  shows only the magnetic flux originated from first magnet  12 A in order to avoid complexity of the drawing. 
     First magnet  12 A and second magnet  12 B are fixed in positions above diaphragm  9  in a manner to confront respective openings  6 B of plate  6 . Parts of adhesive agent  5 B are spread to enter into spaces between the peripheral surfaces of first magnet  12 A and second magnet  12 B and inner surfaces of ring  11  and frame  13 . In this way, first magnet  12 A and second magnet  12 B are also secured to ring  11  and frame  13  with adhesive agent  5 B on their peripheral surfaces. 
     Diaphragm  9  has top portion  9 A, side portions  9 B and  9 C and barrel portion  9 D, as shown in  FIG. 4  and  FIG. 7 . Top portion  9 A confronts the S-pole of third magnet  7 , and side portion  9 B confronts one of the surfaces of first magnet  12 A other than the N-pole and the S-pole, whereas side portion  9 C confronts one of the surfaces of second magnet  12 B other than the N-pole and the S-pole. Voice coil  10  of elongated-shape is fixed to the upper surface of diaphragm  9  around its barrel portion  9 D corresponding to the outer periphery of third magnet  7 . Barrel potion  9 D is disposed in the magnetic gaps formed between first magnet  12 A and third magnet  7  and between second magnet  12 B and third magnet  7 . Voice coil  10  is thus located inside the magnetic gaps. Accordingly, diaphragm  9  is so disposed as to separate first magnet  12 A and second magnet  12 B from third magnet  7 . 
     Magnetic fluid  14  is kept mediating between the sides of third magnet  7  facing the magnetic gaps and voice coil  10 . Since voice coil  10  is fixed to the upper surface of diaphragm  9  at a portion corresponding to the outer periphery of third magnet  7 , magnetic fluid  14  stays between third magnet  7  and the portion of diaphragm  9  where voice coil  10  is fixed, to be more precise. Diaphragm  9  is provided with aperture  15  in a position confronting third magnet  7 . Magnetic fluid  14  is prepared by having ultra-fine magnetic particles of about  10  nm in particle diameter adsorb a surface-active agent, and dispersing the particles in a dispersion medium such as an organic liquid. 
     First magnet  12 A and second magnet  12 B are fixed to the bottom surface of plate  5  with adhesive agent  5 B. In other words, plate  5  supports first magnet  12 A and second magnet  12 B by securing their surfaces other than the magnetic pole portions. To be more specific, first magnet  12 A is fixed to plate  5  at the portion (i.e., side surface) which is parallel to the axial direction through its magnetic poles. The same also applies to second magnet  12 B. 
     As shown in  FIG. 8 , first magnet  12 A and second magnet  12 B are so magnetized as to have the N-poles on their longitudinal side surfaces that confront each other and the S-poles on the opposite side surfaces. In other words, second magnet  12 B is placed in such an orientation that its N-pole confronts the N-pole of first magnet  12 A. 
     Third magnet  7  is magnetized to have the S-pole on the upper surface and the N-pole on the lower surface in a direction of the thickness. First magnet  12 A, second magnet  12 B and third magnet  7  are disposed horizontally or substantially horizontally. This expression of “substantially horizontally” includes such arrangements of first magnet  12 A, second magnet  12 B and third magnet  7  that they overlap partially in the direction of their thickness as shown in  FIG. 7 , or that they are close to each other without overlapping in the direction of their thickness. As described, third magnet  7  is disposed in such an orientation that the axial direction connecting the N-pole and the S-pole is perpendicular to the direction connecting the N-pole of first magnet  12 A and the N-pole of second magnet  12 B, and that the S-pole of third magnet  7  is at the side closer to the N-pole of first magnet  12 A and the N-pole of second magnet  12 B. First magnet  12 A, second magnet  12 B and third magnet  7  are hence disposed so that their longitudinal sides become parallel to one another. 
     In the above arrangement, magnetic fluxes originated from the N-poles at the inner sides of respective first magnet  12 A and second magnet  12 B travel inward in a direction generally horizontally and traverse voice coil  10  substantially orthogonally, as shown in  FIG. 5  and  FIG. 8 . The magnetic fluxes then reach the S-pole on the upper surface of third magnet  7  through magnetic fluid  14 . In other words, the magnetic fluxes can traverse voice coil  10  substantially orthogonally because of the horizontal arrangement of first magnet  12 A, second magnet  12 B and third magnet  7 . In this respect, a certain degree of tolerance is allowable in the arrangement of horizontality. 
     The magnetic fluxes exiting from the N-pole on the lower surface of third magnet  7  then travel through fixing section  6 A of plate  6  and enter into ring  11  after passing through ring  8  and the outer periphery diaphragm  9 . The magnetic fluxes then travel through ring  11  for about a quarter turn, for instance, and reach the S-poles on the outer sides of first magnet  12 A and second magnet  12 B fixed to the inner periphery of ring  11 . As described, rings  8 ,  11  and plate  6  constitute a magnetic circuit structuring unit for magnetically coupling the S -poles of first magnet  12 A and second magnet  12 B and the N-pole of third magnet  7 . 
     The above flow path of the magnetic fluxes represents the magnetic circuit. In this magnetic circuit, spaces between the N-poles on the inner sides of first magnet  12 A and second magnet  12 B and the S-pole on the upper surface of third magnet  7  serve as the magnetic gaps. The magnetic fluxes in these magnetic gaps impart an electromagnetic motive force to voice coil  10 , which is transmitted to diaphragm  9  fixed to voice coil  10  in a form of vibration to generate a sound output. 
     Here, description is again provided of how the magnetic fluxes travel in the magnetic gaps. As shown in  FIG. 5  and  FIG. 8 , the magnetic fluxes originated from the N-poles at the inner sides of respective first and second magnets  12 A and  12 B travel inward in the direction substantially horizontally in the magnetic gaps and traverse voice coil  10  substantially orthogonally. This is of significant importance in view of increasing the electromagnetic motive force, and constitutes a major feature in this exemplary embodiment. 
     Consideration is given now to the reason why the magnetic fluxes travel inward in the direction generally horizontally in the magnetic gaps and traverse voice coil  10  substantially orthogonally. 
     It is generally considered that the magnetic fluxes originated from the N-poles of first magnet  12 A and second magnet  12 B travel in a slanting direction toward the S-pole on the upper surface of third magnet  7 . If this is the case, the magnetic fluxes traverse voice coil  10  slightly slantly. In reality, however, the N-pole on the lower surface of third magnet  7  exerts a repelling force upon the magnetic fluxes to lift and make them travel inward across the magnetic gaps in generally the horizontal direction as shown in  FIG. 8 . It is hence considered for this reason that the magnetic fluxes traverse voice coil  10  substantially orthogonally. 
     According to the present exemplary embodiment as described above, first magnet  12 A and third magnet  7  are disposed to form the two sides of the magnetic gap, and second magnet  12 B and third magnet  7  are disposed to form the two sides of another magnetic gap. This increases the so-called magnetic force, thereby resulting in an enhancement of the sound output generated by diaphragm  9 . In addition, an overall thickness of loudspeaker  4  is significantly reduced as a result since all of first magnet  12 A, second magnet  12 B and third magnet  7  have the plate-like shape of low profile. 
     Furthermore, magnetic fluid  14  is kept to mediate between the sides of third magnet  7  and voice coil  10 . Magnetic fluid  14  can suppress a rolling phenomenon. It also improves the effect of heat dissipation from voice coil  10  thereby increasing a resistance of voice coil  10  against high input. In addition, magnetic fluid  14  contributes to the ease of positioning voice coil  10  in a process of disposing voice coil  10  over third magnet  7 , which reduces a gap failure. 
     Diaphragm  9  is provided with aperture  15  in a position confronting third magnet  7 . Aperture  15  allows free circulation of the air in a space enclosed by third magnet  7 , diaphragm  9  and magnetic fluid  14  without obstruction, so as not to impede vibration of diaphragm  9 . 
     Furthermore, first magnet  12 A and second magnet  12 B are fixed to the lower surface of plate  5  with adhesive agent  5 B on their upper surfaces having large surface areas. This can provide a high strength against vibrations and shocks exerted on case  4 A. Likewise, third magnet  7  is fixed to the upper surface of plate  6  with adhesive agent  7 A on the lower surface having a large surface area. This also helps improve the strength against the vibrations and shocks exerted on case  4 A. 
     Moreover, plate  5  is free from causing a magnetic short-circuit even though it covers the entire upper surfaces of first magnet  12 A and second magnet  12 B having the N-poles and the S-poles on both sides thereof since plate  5  is made of a non-magnetic material. On the other hand, plate  6  does not adversely influence to formation of the magnetic circuit shown in  FIG. 4  even though it covers the entire lower surfaces of third magnet  7  having the S-pole and the N-pole on both upper and lower surfaces since plate  6  is made of a magnetic material. Plate  6  rather helps, in combination with ring  11 , to magnetically couple between the S-pole of first magnet  12 A and the N-pole of third magnet  7  as well as the S-pole of second magnet  12 B and the N-pole of third magnet  7 . This structure thus obviates formation of an undesired magnetic gap within the magnetic circuit. 
     Plate  6  is provided with openings  6 B. Openings  6 B prevent barrel portion  9 D, which is the edge portion of diaphragm  9 , from hitting on plate  6  while diaphragm  9  is in vibration. In other words, openings  6 B can provide an adequate space for the vibration of barrel portion  9 D, which helps reduce the thickness of loudspeaker  4 . In addition, the structure constructed as above can increase the magnetic flux density since it reduces a distance from third magnet  7  to first magnet  12 A and second magnet  12 B. As a result, this structure can compensate for a deficiency of the magnetic flux density due to the reduction in the thickness. 
     Although plate  5  illustrated in this exemplary embodiment is designed to secure both first magnet  12 A and second magnet  12 B, plate  5  may be split into two parts to secure first magnet  12 A and second magnet  12 B individually with the split parts. In such a configuration, a space between these parts serves as the sound hole. It is easier to manufacture, however, when plate  5  is formed to cover the entire diaphragm  9  and both first magnet  12 A and second magnet  12 B are fixed to it. 
     Loudspeaker  4  may be constructed without using frame  13 , and built directly into an electronic apparatus. It is also easier to manufacture, however, when case  4 A is formed with frame  13 . 
     Aperture  5 A provided in plate  5  is illustrated as having a rectangular shape in a manner to expose diaphragm  9 . However, this is not restrictive, and that it may instead be composed of, for instance, a plurality of small circular holes. 
     INDUSTRIAL APPLICABILITY 
     As described above, the loudspeaker of the present invention has three magnets, all positioned horizontally or generally horizontally over the magnetic gaps for disposing the voice coil. This structure helps make magnetic fluxes traverse the voice coil generally orthogonally even though the magnets have thin plate-like shapes. As a result, the invented structure can increase the magnetic force and hence the sound output while also achieving a reduction in the thickness of the loudspeaker. The loudspeaker is also provided with the magnetic fluid kept mediating between the sides of the third magnet disposed at the center and the voice coil, and the diaphragm having the aperture formed in the position confronting the third magnet. This structure helps suppress the rolling phenomenon and reduces gap failures. It also improves the effect of heat dissipation from the voice coil and increases the resistance of the loudspeaker against high input. The loudspeaker constructed as above is very useful for any electronic apparatus including portable equipment such as a mobile phone.