Electrodynamic Speaker

The present invention relates to an electrodynamic speaker, and more particularly to a miniature, thin and cost-saving electrodynamic speaker with excellent working property of fabrication and a highly efficient magnetic circuit.

FIG. 1 shows the structure of a conventional electrodynamic speaker. The speaker is fabricated in the following order in FIG. 1. A voice coil 5 is secured to a vibrating plate 1. Then a yoke 7, on which a magnet 8 and a pole piece 9 are mounted, is secured to a frame 2. The peripheral portion of the vibrating plate 1 is secured to the frame 2. A lead terminal 6 of the voice coil 5 is fixedly secured to a lead substrate 3 positioned on the lower surface of the frame 2 through a back hole 4 thereof. This structure has the following drawbacks:

(1) Since the voice coil 5 is secured on the thin and easily deformable vibrating plate 1, the voice coil cannot be positioned with accuracy.

(2) Non-uniformity of the clearance between the peripheral portion of the vibrating plate 1 and the frame 2 in the diametrical direction causes a variation in the voice coil position when the vibrating plate 1 is secured to the frame, whereby the voice coil 5 may sometimes be in contact with the pole 9 or the yoke 7.

(3) It takes time to lead the lead terminal 6 of the voice coil 5 through the back hole 4 to the lower surface of the frame 2.

(4) The fragile vibrating plate with the voice coil should be handled with great care since the lead terminal has not been attached.

As illustrated, the accurate positioning of the voice coil and the magnetic circuit is not ensured and the attachment of the voice coil terminal to the lead substrate takes time and is done during the course of securing the frame on which the magnetic circuit is mounted to the vibrating plate on which the voice coil is mounted.

The dimension of a magnetic gap and the position of the voice coil largely affect the efficiency and distortion of the electrodynamic speaker, and thus a speaker with high quality can not be realized without improving these aspects. For cost reduction, on the other hand, the fabrication process, such as securing of the voice coil, attachment of the lead terminal, and regulation of the magnetic gap by use of a jig for inserting the voice coil therein, should be improved.

To miniaturize a speaker, a vibrating member should be thinly made for reproducing a low sound in view of the reproduction frequency zone. Since miniature speakers are mostly used for portable devices, most vibrating plates are formed of a humidity-resistant polyester seat material by thermal pressure molding, as shown in FIG. 1. The accuracy of dimension of the vibrating plate is unstable as the vibrating plate is thin and subjected to the bending work, and the portion serving as a side in mounting the coil is hard to find. Further, the 8.OMEGA. resistance value, equivalent to the conventional type, cannot be obtained by the miniature speaker unless the wire for the voice coil is thinly made. Accordingly, great care should be taken in shifting the process without securing the voice coil terminal and thus it is preferable to treat the voice coil terminal in the same process as mounting the voice coil.

Generally, the effective diameter of a vibrating plate of a speaker largely affects its efficiency, and thus the efficiency of a miniature speaker necessarily deteriorates. Since a miniature portable device, however, operates on a limited power source, it is necessary to have a highly efficient speaker for use in portable devices. In view of the foregoing, the efficiency of the magnetic circuit portion, especially the dimension around the magnetic gap, is a very important point.

FIG. 2 shows another conventional embodiment. The voice coil terminal 6 is led to the peripheral portion of the vibrating plate 1 from where the voice coil is mounted, and connected to the lead substrate 3 provided on the lower surface of the frame 2 through a notched recess 10 at the side surface of the frame 2. In this structure the lead terminal should be carefully secured to the lead substrate lest an abnormal sound should be produced by contact of the lead terminal with the vibrating plate. Therefore this embodiment is not suitable for a miniature and cost-saving speaker because the fabrication or assembly order is identical to that of FIG. 1, and thus the same drawbacks will occur.

The present invention aims to eliminate the above-noted drawbacks, and therefore an object of the invention is to improve the working property of fabrication and the efficiency of the speaker.

Another object of the invention is to provide an electrodynamic speaker comprising a vibrating plate, a voice coil secured to the vibrating plate, a magnetic circuit portion and lead substrates for securing the terminals of the voice coil, wherein the frame supports the vibrating plate at an upper end surface thereof and has a center hole which mates with the magnetic circuit portion and a notch portion in the peripheral direction. The terminals of the coil are secured to the lead substrate provided at the lower surface of the frame through the notch portion, and a step portion or a projection for holding the magnetic circuit portion is provided at both or one of the center hole of the frame and the peripheral portion of the magnetic circuit when the magnetic circuit is assembled from the lower surface of the frame to thereby fixedly secure the magnetic circuit portion to the frame.

FIG. 1 and FIG. 2 show conventional electrodynamic speakers,

FIG. 3 shows a sectional view of an electrodynamic speaker according to the present invention,

FIG. 4 shows a plan view of FIG. 3,

FIG. 5 shows a perspective view of the fabrication order of the speaker in FIG. 3,

FIG. 6 shows another embodiment of the present invention,

FIG. 7 shows a plan view of FIG. 6,

FIG. 8 shows another embodiment of the present invention, and

FIG. 9 shows a plan view of FIG. 8.

FIG. 3 shows a sectional view of a speaker according to the present invention and FIG. 4 is a plan view of the same. Reference numeral 11 denotes a guard frame provided with a step portion 26. 13 denotes a main frame provided with a ring-shaped projection 14 at the upper end surface to mate with the step portion 26 of the guard frame 11. The main frame 13 has a center hole with a notch portion 15 and a recess or step portion 27. The frame 13 has plural back holes 16, and lead substrates 18a and 18b are secured to the lower surface thereof. The frame 13 is molded by plastic injection molding. 12 denotes a vibrating plate molded into a desired shape by heating the polyester seat material. The peripheral portion of the vibrating plate 12 is sandwiched between the projection 14 of the frame 13 and the step portion 26 of the guard frame 11. A voice coil 17 is wound into a hollow cylinder shape, with adjacent wire coils being adhered to each other to keep the hollow cylinder shape, and the ring-shaped upper end of the voice coil 17 is adhered to the vibrating plate 12. The terminals 20a, 20b of the voice coil winding are led in the peripheral direction along the contour of the vibrating plate 12 from where the voice coil is mounted and secured to a securing portion 19 as shown and connected to the lead substrates 18a and 18b through the notch portion 15 of the main frame 13 from the securing portion 19. 21 denotes a dish-shaped yoke made of a soft magnetic material by a choking process and the yoke 21 is provided with a flat projecting portion 23 at the periphery and a step portion 22 at the bottom thereof. Element 25 denotes a disk-shaped pole piece pressed out of a soft magnetic plate. Element 24 denotes a disk-shaped permanent magnet made of samarium cobalt. The pole piece 25 is mounted on an upper surface of the magnet 24, and the lower end surface of the magnet 24 fixedly mates with the step portion 22 at the bottom of the yoke 21. A magnetic circuit assembly portion is formed by the yoke 21, the magnet 24 and the pole piece 25. A magnetic air gap is formed by the side surface of the pole piece 25 and the upstanding sidewell portion of the yoke 21. The peripheral flat projecting portion 23 of the yoke 21 fixedly mates with the recess or step portion 27 of the frame, whereby the frame is connected with the magnetic circuit portion.

FIG. 5 shows the order of fabrication of the speaker. The speaker is fabricated in the order of A.fwdarw.B.fwdarw.C.fwdarw.D.fwdarw.E as shown in FIG. 5. First, the vibration plate 12 is fabricated being guided by the step portion 26 of the guard frame 11, as shown by A. The main frame 13, on which the lead substrate 18 is mounted, is secured to the guard frame 11 to sandwich the vibrating plate 12 therebetween, as shown by B. The voice coil 17 is then adhered to the vibrating plate 12, as shown by C, being guided by a jig (not shown) provided at the step portion 27 of the frame. The yoke 21 with the pole piece 25 and the magnet 24 is secured to the recess or step portion 27 of the frame 13, as shown by D. Thus the speaker as shown by E is assembled or fabricated in the above order.

The structure of the present invention is characterized in that the voice coil is secured after the vibrating plate 12 is secured to the frame 13, and then the magnetic circuit assembly portion is attached. The voice coil 17 is secured after the frame is integral with the vibrating plate as shown by C, and the coil terminals are connected to the lead substrate 18 in the same process as mounting the voice coil. Namely, the process of leading the terminals 20a, 20b to the lead substrates 18a, 18b through the notch portion 15 is easier than the treatment in FIGS. 1 and 2 since the magnetic circuit portion has not as yet been attached. Although the treatment of the voice coil is an extremely troublesome process, the coil terminals can be treated soon after the voice coil is fixedly secured to the firm frame according to the present invention, whereby the voice coil can be roughly treated in conveying it. On the contrary, great care has been required for the thin vibrating plate that has the voice coil whose terminals have not been treated in the conventional type structure.

Further, the efficiency of the speaker is improved in the present invention since the dimension of the magnetic air gap is reduced. Namely, both the voice coil and the magnetic circuit portion are mounted being guided by the step portion 27 of the frame 13, and thus the relative position of the voice coil and the magnetic circuit are decided with accuracy. The relative position of the voice coil and the magnetic circuit in the conventional type structure varies in mass production due to the following factors: variation in the position of the voice coil relative to the outer diameter of the vibrating plate; variation in the outer diameter of the vibrating plate; variation in the clearance between the diameter of the step portion of the vibrating plate and the outer diameter of the vibrating plate; and variation in the position of the magnetic circuit relative to the diameter of the step portion of the vibrating plate. Generally, the larger the dimension of the plastic parts, the more the variation range. Use of the outer diameter of the vibrating plate brings about the above mentioned variation factors, and the amount of variation is large. According to the present invention, however, the voice coil is mounted being guided by the firm frame. Further, the factors of variation comprise only the position on which the voice coil is mounted and the position on which the magnetic circuit is mounted relative to the diameter of the step portion 27 of the frame 13. The diameter of the step portion 27 of the frame 13 is also smaller. Thus the overall variation range can be minimized and the relative position of the voice coil and the magnetic circuit can be decided with accuracy.

The provision of the guard frame 11 and the step portion 26 enables the speaker to be fabricated from one direction as shown in FIG. 5, and thus the set time and conveying time for the next process can be shortened and the automation of fabrication can be easily realized. Further the peripheral portion of the vibrating plate is surely fixed by the guard frame.

FIG. 6 shows another embodiment of the present invention, in which the magnet is provided outside or exteriorly of the coil. FIG. 7 shows a plan view of FIG. 6. Numeral 28 denotes a lower yoke plate made of soft magnetic material provided with a center hole at the center and a projection at the peripheral portion. 30 denotes a ring-shaped magnet and 31 denotes a pole piece comprised of a ring-shaped upper plate made of soft magnetic material. A magnetic circuit portion is made up of the yoke 28, the magnet 30 and the pole piece 31. The magnetic circuit portion is fabricated or assembled from the lower surface of the frame 13, and mates with the upper frame 31 at the step portion 27 of the frame 13, and is connected with the frame at the projection 29 of the lower plate. The remaining structure and order of fabrication of the FIG. 6 embodiment is identical to the embodiment in FIG. 3. Since the magnet 30 is arranged at the outer periphery in the outer magnet type magnetic circuit of this structure, the diameter of the voice coil 17 is smaller in comparison with the embodiment in FIG. 3, and the difference in diameter between the voice coil and the step portion 27 of the frame 13 is larger. Consequently the voice coil can be easily mounted on the vibrating plate. Moreover, since the voice coil 17 is mounted being guided by the inner diameter of the step portion 27 of the frame 13, and since the outer periphery of the upper plate 31 mates with the diameter of the step portion 27, the magnetic gap required to insert the voice coil 17 can be minimized.

FIG. 8 is another embodiment of the present invention having an improved shape of the yoke, and in which the magnet is provided inside or interiorly of the coil. FIG. 9 is a plan view of the same. In this embodiment a yoke 32 having a bowl-shape is provided with a rim portion 35 and an expanded portion 34. The magnet 24 on which the pole piece 25 is mounted is secured to the bottom of the yoke 32, and the outer periphery of the rim portion 35 mates with the inner periphery of the center hole of the frame 13, and a step portion 36 of the frame supports the expanded portion 34 to thereby secure the yoke. The shape of the rim portion 35 is advantageous as the magnetic circuit and the magnetic flux of the magnetic gap is made uniform by the expanded portion 34. In a magnetic circuit with thin magnet, especially, this shape is extremely effective to increase the magnetic flux in the magnetic gap.

As illustrated, according to the present invention, the voice coil can be secured to the vibrating plate after the frame is secured thereto, and the magnetic circuit can be mounted lastly. Accordingly, the lead terminals of the voice coil can be connected to the lead substrates through the notch portion in the same process as mounting the voice coil on the vibrating plate, whereby the working property of the miniature speaker is largely improved. The factor of variation in the magnetic gap dimension which affects the efficiency of the magnetic circuit is also reduced, whereby a highly efficient speaker is realized.