Patent Publication Number: US-6661898-B2

Title: Speaker for an electronic instrument

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a speaker for an electronic instrument such as a portable telephone. 
     In recent years, there is used a thin electrodynamic speaker having an excellent quality for the portable telephone. Dimensions of parts in the speaker, in particular, position accuracy of the voice coil disposed in the magnetic circuit have an influence on sound quality. Therefore, it is necessary to severely check the position accuracy. 
     A conventional speaker will be described hereinafter with reference to FIGS. 4 and 5. 
     The speaker comprises a lower frame assembly  51  and an upper frame assembly  52 . 
     The lower frame assembly  51  comprises an annular lower frame  61  made of plastic, a tray shape yoke  62  made of magnetic material and embedded in the lower frame, a permanent magnet  63  secured to the yoke and a top plate  64  made of magnetic material and secured to the permanent magnet  63 . A magnetic circuit is formed by the top plate  64 , permanent magnet  63  and the yoke  62  to form a magnetic gap  66  between the peripheral wall of the top plate  64  and the inside wall of an upper portion of the yoke  62 . 
     On the upper surface of the lower frame  61 , an annular projection  61   a  is formed at a peripheral portion thereof and an annular step  61   b  is formed outside the projection  61   a.    
     The upper frame assembly  52  comprises an annular upper frame  71  made of plastic, a diaphragm  73 , a voice coil  74  secured to the underside of the diaphragm  73 , and a protector  75  having a plurality of sound discharge openings. A pair of leads  72  are embedded in the upper frame  71  and projected from the upper frame and downwardly bent. 
     The upper frame  71  has an annular upper step  71   a  on the upper surface thereof, and an annular lower step  71   b . The diaphragm  73  is adhered to the lower step  71   b  and the protector  75  is adhered to the upper step  71   a.    
     Both ends  74   a  of the voice coil  74  are projected from the upper frame  71  passing through holes formed in the frame and connected to the leads  72 , respectively. 
     FIG. 5 shows both the lower and upper frame assemblies  51  and  52 . 
     The upper frame  71  is secured to the step  61   b  of the lower frame  61  by the ultrasonic welding, so that the voice coil  74  is disposed in the magnetic gap  66 . 
     In order to allow the vibration of one of the frame assemblies in the ultrasonic welding operation, there is provided a clearance B between the inside wall of the upper frame  71  and the outside wall of the projection  61   a  of the lower frame  61 . However, the clearance (0.05-0.1 mm) causes central positions of the lower and upper frames  61  and  71  to deviate from each other when both frame assemblies are coupled with each other. As a result, the position of the voice coil  74  is not accurately positioned in the magnetic gap  66 , so that the sound quality of the speaker deteriorates. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a speaker in which the voice coil can be accurately positioned in the magnetic gap. 
     According to the present invention, there is provided a speaker for an electronic instrument comprising a lower frame assembly comprising a lower frame provided with a yoke, a permanent magnet secured to the yoke, and a top plate secured to the permanent magnet, an upper frame assembly comprising an upper frame provided with a diaphragm secured to the upper frame, and a voice coil secured to the diaphragm and disposed in a magnetic gap between the yoke and the top plate, wherein a plurality of grooves are formed in a peripheral wall of the lower frame, a plurality of engaging portions are formed on the upper frame, corresponding to the grooves of the lower frame, each of the engaging portions comprises an engaging plate and a hook formed at an end of the engaging plate. 
     Each of the engaging portions comprises an elastic engaging plate axially projected from an underside of the upper frame, and a hook formed at an end of the elastic engaging plate so as to be engaged with an underside of the lower frame. 
     These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a speaker of the present invention; 
     FIG. 2 is a sectional view taken along a line II—II of FIG. 1; 
     FIG. 3 is an exploded perspective view of the speaker; 
     FIG. 4 is a sectional view of a conventional speaker; and 
     FIG. 5 is an exploded sectional view of the speaker. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 through 3, the speaker of the present invention comprises a lower frame assembly  1  and an upper frame assembly  2 . 
     The lower frame assembly  1  comprises an annular lower frame  11  made of plastic, a tray shape yoke  12  made of magnetic material and embedded in the lower frame  11 , a permanent magnet  13  secured to the yoke  12  and a top plate  14  made of magnetic material and secured to the permanent magnet  13 . A magnetic circuit is formed by the top plate  14 , permanent magnet  13  and the yoke  12  to form a magnetic gap  16  between the peripheral wall of the top plate  14  and the inside wall of an upper portion of the yoke  12 . 
     On the upper surface of the lower frame  11 , an annular projection  11   a  is formed at a peripheral portion thereof and an annular step  11   b  is formed outside the projection  11   a.    
     In the present invention, a plurality of axial grooves  11   c  are formed in the lower frame  11  at the peripheral wall thereof so that the bottom of the groove becomes coplanar with the outer surface of the projection  11   a.    
     The upper frame assembly  2  comprises an annular upper frame  21  made of plastic, a diaphragm  23 , a voice coil  24  secured to the underside of the diaphragm  23 , and a protector  25  having a plurality of sound discharge openings  26 . A pair of leads  22  are embedded in the upper frame  21  and projected from the upper frame and downwardly bent. 
     The upper frame  21  has an annular upper step  21   a  on the upper surface thereof, and an annular lower step  21   b.    
     The diaphragm  23  is adhered to the lower step  21   b  and the protector  25  is adhered to the upper step  21   a.    
     Both ends  24   a  of the voice coil  24  are projected from the upper frame  21  passing through holes formed in the frame and connected to the leads  22 , respectively. 
     A plurality of engaging portions  21   c  are axially and downwardly projected from the underside of the upper frame  21  corresponding to the grooves  11   c.    
     Each of the engaging portions  21   c  comprises an elastic engaging plate  21   d  and a hook  21   e  formed at the lower end of the engaging plate  21   d  so as to be engaged with the underside of the lower frame  11 . The elastic engaging plate  21   d  and the hook  21   e  are provided to be engaged with the bottom of the groove  11   c  without a gap there-between or with a very small gap of 0.01-0.05 mm. 
     In coupling of both frame assemblies  1  and  2 , the hooks  21   e  are engaged with the grooves  11   c  and downwardly pushed, so that the hook end of each hook  21   e  snugly engages with the underside of the lower frame  11 , and each of the elastic engaging plates  21   d  is pressed against the bottom of the groove  11   c . Thus, both frame assemblies are engaged with each other without welding. 
     In accordance with the present invention, the lower frame assembly and the upper frame assembly are snugly engaged with each other by the engaging portions  21   c  without gaps there-between. Therefore, the voice coil  24  can be positioned in the magnetic gap  16  at a desired position. Consequently, excellent sound quality can be obtained. 
     While the invention has been described in conjunction with preferred specific embodiment thereof, it will be understood that this description is intended to illustrate and not limit the scope of the invention, which is defined by the following claims.