Loudspeaker and electronic apparatus using the same

In a loudspeaker, three magnets are disposed to provide magnetic gaps therebetween and a voice coil is fit therein. The magnets disposed at both sides are magnetized so that their opposing poles exhibit the same magnetic polarity. The magnet in the middle has its magnetic poles in the direction perpendicular to the line connecting the poles of the side magnets. The side magnets are fixed to a plate made of non-magnetic material. Those magnetic poles of the side magnets and the middle magnet not facing the magnetic gaps are magnetically coupled by a magnetic member.

TECHNICAL FIELD

The present invention relates to a slim-profile loudspeaker and an electronic apparatus which incorporates the loudspeaker.

BACKGROUND ART

Many of the portable electronic apparatuses are requested to have slim designs. So, loudspeakers built in such apparatuses are also required to have slim designs as well.

A generally practiced way of making conventional loudspeakers thinner is reducing the size of magnet which forms magnetic circuit; such as the one described in the Patent Document 1 below. The smaller-sized magnet can provide the smaller magnetic force; as the results, the sound output shrinks. Therefore, the magnet size can not be reduced very much, so that the efforts for thickness reduction with conventional loudspeakers have not yielded significant achievements.

There is another approach for improving the disadvantage due to size reduction of magnet; that is splitting a magnet into pieces and placing the split pieces of the magnet at appropriate locations. However, placing those magnetized pieces precisely at specific locations is a difficult job because each one exhibits magnetic attracting force or repelling force.

SUMMARY OF THE INVENTION

A loudspeaker of slim profile which generates high sound outputs, and provides superior capabilities of withstanding vibrations and mechanical shocks. The loudspeaker in the present invention includes a first magnet, a second magnet, a third magnet, a voice coil, a diaphragm, a plate made of non-magnetic material, and magnetic member. The first magnet has a first pole and a second pole whose polarity is opposite 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. These magnets are disposed so that the first pole and the third pole oppose face to face each other. The third magnet, which 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, is disposed so that the direction containing the fifth pole and the sixth pole is perpendicular to the line connecting the first pole of the first magnet and the third pole of the second magnet, and that the sixth pole is positioned at the side which is closer to the first and the third poles. The third magnet provides magnetic gap in a space formed with respect to the first magnet and a space with respect to the second magnet, respectively. The voice coil is placed to be fitting in the magnetic gaps. The diaphragm supports the voice coil thereon. The plate supports the first magnet at a portion other than the first and second poles, and the second magnet at a portion other than the third and fourth poles. The magnetic member magnetically couples the second pole with the fifth pole, and the fourth pole with the fifth pole, respectively.

In the structure as described above, a loudspeaker in the present invention implements a slim overall profile, and the magnetic flux therein crosses the voice coil in the magnetic gap at a substantially perpendicular angle. In addition, since the loudspeaker is provided with three magnets, the magnetic force is strengthened for generating higher sound outputs. Furthermore, since the first and the second magnets are fixed on the plate, the properties of withstanding vibrations and mechanical shocks are enhanced.

REFERENCE MARKS IN THE DRAWINGS

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Now in the following, an exemplary embodiment of the present invention is described referring to the drawings, using a mobile phone unit to represent an electronic apparatus.FIG. 1is a perspective view of a mobile phone unit which contains a loudspeaker in accordance with an exemplary embodiment of the present invention.FIG. 2Ais a perspective view of the mobile phone unit shown inFIG. 1, with its cover detached.FIG. 2Bis block diagram of the mobile phone unit shown inFIG. 1.FIG. 3is an exploded perspective view of the loudspeaker shown inFIG. 2A.FIG. 4is a cross sectional view of the loudspeaker shown inFIG. 2A, sectioned along the longitudinal direction.FIG. 5is a cross sectional view, sectioned along the direction of shorter side.FIG. 6is a magnified cross sectional view showing the portion A ofFIG. 5.

An electronic apparatus, viz. mobile phone unit, is provided at the outer surface of body1with two pieces of cover3as shown inFIG. 1. Loudspeaker4is mounted into body1at the back of cover3, as shown inFIG. 2.

Lid2is attached to body1, coupled so that the lid can be opened/dosed freely. Like other mobile phone units, body1has input section42formed of operation buttons and microphone43, as described inFIG. 2B, at the reverse surface of illustration inFIG. 1. Lid2has display section44of LCD and loudspeaker45for receiving conversation. Circuit section41housed within body1receives input signal delivered from input section42, and displays the input on display section44together with other incoming information, etc. During telephone conversation, circuit section41receives voice input signal from microphone43, and reproduces the voices from counterpart through loudspeaker45. Furthermore, circuit section41drives loudspeaker4for generating ringtone.

As shown inFIG. 3, loudspeaker4includes plates5and6, first magnet12A, second magnet12B and third magnet7, each of which has a platy shape, ring11, diaphragm9and voice coil10. Plate5which is exposed to the outside of body1is made of a non-magnetic material, for example, a stainless steel (e.g. SUS301), while plate6is made of cold rolled steel sheet, a magnetic material. The outer surface in part of plate5and respective outer circumferences of the constituent components are covered with resin-made frame13, as shown inFIG. 4andFIG. 5. Namely, plates5,6and frame13constitute case4A. Plate5has sound hole5A.

Platy first magnet12A, second magnet12B and third magnet7, each having longitudinal direction, are made of neodymium, for example. The neodymium magnet exhibits strong magnetic polarity, so it is preferable for use in the small and slim loudspeakers, like loudspeaker4in the present embodiment. The magnet, however, is not necessarily be a neodymium-made. What is needed for the magnet is to have strong magnetic force; it is not limited to a neodymium magnet. Each of first magnet12A, second magnet12B and third magnet7has its own N-pole and S-pole. In the following descriptions, N-pole of first magnet12A is called as first pole while S-pole is called as second pole whose magnetic polarity is opposite to the first pole. In the same token, N-pole of second magnet12B is third pole while S-pole is fourth pole whose magnetic polarity is opposite to the third pole. N-pole of third magnet7is fifth pole while S-pole is sixth pole whose magnetic polarity is opposite to the fifth pole. The polarity setting for these magnets is not limited to the above-described arrangements, but the N- and S-arrangements may be reversed with respect to the whole magnets.

Diaphragm9is provided using, for example, a polyether-imide film. Voice coil10is made of copper wire, or the like item. Projected view of voice coil10is an oblong shape having a couple of long sides; these long sides are arranged in the magnetic gaps provided in the longitudinal direction at both sides of third magnet7. Ring11is formed of a cold rolled steel sheet, which is a magnetic material.

Third magnet7, diaphragm9, voice coil10, ring11, first magnet12A and second magnet12B are disposed in this order from plate6to plate5in case4A.

As shown inFIG. 3andFIG. 5, plate6has an oblong shape. It has fixing section6A of a rectangular shape disposed in the longitudinal direction along the center axis portion (central portion). As shown inFIG. 6, third magnet7is fixed on the upper surface of fixing section6A with adhesive agent7A applied at the bottom of the magnet. Open area6B having rectangular shape is provided a both sides of fixing section6A t. Open areas6B functions as a sound hole at the back, which enables loudspeaker4to discharge sounds also from the back.

On the outer circumference of plate6, outer circumference of diaphragm9is placed allowing the magnetic flux to go through, as indicated inFIG. 3with an arrow mark. Ring11is disposed on the outer circumference of diaphragm9. In order to avoid too much complexity of the illustration,FIG. 3shows the magnetic flux generated from first magnet12A alone, among other magnetic fluxes.

First magnet12A and second magnet12B are disposed above diaphragm9and fixed there to be facing towards open areas6B of plate6, respectively. Part of adhesive agent5B intrudes into spaces formed by respective outer circumferential surfaces of first magnet12A, second magnet12B and inner circumferential surfaces of ring11and frame13. In this way, the respective outer circumferential surfaces of first magnet12A and second magnet12B are fixed also to ring11and frame13at their inner circumferential surfaces.

As shown inFIG. 3andFIG. 5, diaphragm9has top portion9A, side portions9B,9C and barrel portion9D. Top portion9A is disposed to oppose to S-pole of third magnet7, side portion9B to oppose to a surface of first magnet12A other than its N-pole and S-pole, while side portion9C to oppose to a surface of second magnet12B other than its N-pole and S-pole. Voice coil10of an oblong is disposed on the upper surface of diaphragm9and fixed to barrel portion9D which corresponds to the outer circumference of third magnet7. Barrel potion9D is disposed in the magnetic gaps formed between first magnet12A and third magnet7, and between second magnet12B and third magnet7. Consequently, voice coil10is also disposed in the magnetic gap. Thus, diaphragm9is disposed so as to separate third magnet7from first and second magnets12A,12B.

First magnet12A and second magnet12B are fixed to the bottom surface of plate5with adhesive agent5B. In other words, plate5holds first magnet12A and second magnet12B at their portions other than their magnetic poles. Describing more specifically, plate5is fixed to first magnet12A at a portion (side surface) which is parallel to direction connecting its magnetic poles. The same applies to second magnet12B.

As shown inFIG. 6, first magnet12A and second magnet12B are magnetized so that their longitudinal side-surfaces opposing to each other make the N-poles, while the opposite side-surfaces make the S-poles. Namely, second magnet12B is disposed so that its N-pole faces N-pole of first magnet12A.

Third magnet7has been magnetized with its upper surface in the thickness direction making the S-pole while the lower surface making the N-pole. First magnet12A, second magnet12B and third magnet7are disposed substantially in a horizontal state. The substantially horizontal state includes the state as illustrated inFIG. 5, where first and second magnets12A,12B are partially overlapping with third magnet7in the direction of thickness, as well as a state where they are not actually overlapping in the thickness direction but are in the proximity. In this way, third magnet7is disposed so that the direction connecting its N-pole and S-pole is perpendicular to the direction connecting N-pole of first magnet12A and N-pole of second magnet12B, and S-pole of third magnet7is at the side closer to N-pole of first magnet12A and N-pole of second magnet12B. First magnet12A, second magnet12B and third magnet7are orientated so that their longitudinal directions are parallel among each other.

In the above-described arrangements, magnetic flux coming from the N-pole, which is at the inner side-surface of respective first and second magnets12A and12B, proceeds inwards along an approximate horizontal direction and crosses voice coil10substantially perpendicularly, as shown inFIG. 3andFIG. 6. And then, it goes into the S-pole at the upper surface of third magnet7. Namely, when first magnet12A, second magnet12B and third magnet7are disposed in the horizontal state, the magnetic flux proceeds to cross voice coil10substantially perpendicularly. In this respect, the horizontal state may be given with some margin of tolerance. Then the magnetic flux, after going through the lower surface, or the N-pole, of third magnet7, proceeds along fixing section6A of plate6to enter into ring11via the outer circumference of diaphragm9. And then the magnetic flux enters into the S-pole locating at the outer side-surface of first magnet12A, second magnet12B fixed to the inner circumference of ring11, after traveling through ring11for e.g. a quarter of a round.

The above-described flow route of magnetic flux represents a magnetic circuit. In the magnetic circuit, a space formed between the N-pole, which is at the inner side-surfaces of first magnet12A and second magnet12B, and the S-pole, which is at the upper surface of third magnet7makes magnetic gap. The magnetic gap provides voice coil10with electromagnetic field force, and diaphragm9which has been fixed to voice coil10is vibrated for generating sound outputs.

Now In the following, traveling path of magnetic flux at the magnetic gap is described once again. As shown inFIG. 3andFIG. 6, magnetic flux coming out of the N-pole at the inner side-surface of first magnet12A and second magnet12B, respectively, goes through the magnetic gap towards inside along approximately horizontal direction and crosses voice coil10substantially perpendicularly. This is a point of significant importance from the view of increasing the driving force of electromagnetic field, and constitutes a major feature point of the present embodiment.

Now, the reason why the magnetic flux proceeds along the substantially horizontal direction in the magnetic gap and crosses voice coil10substantially perpendicularly is deliberated on.

The magnetic flux coming from the N-pole of first magnet12A and second magnet12B is generally considered to go obliquely towards the S-pole at the upper surface of third magnet7. In this case, the magnetic flux slightly crosses voice coil10obliquely. Actually, however, the magnetic flux is uplifted by repelling force due to the N-pole which locates at the lower surface of third magnet7, and goes through the magnetic gap towards inside along the substantially horizontal direction, as illustrated inFIG. 6. Therefore, the magnetic flux is considered to cross voice coil10in a substantially perpendicular state.

As described in the above, magnetic gaps in the present embodiment are provided at their both sides with first magnet12A and third magnet7, and second magnet12B and third magnet7, respectively. As the results, so-called magnetic force is enhanced, and diaphragm9generates greater sound outputs. Furthermore, since each of these first magnet12A, second magnet12B and third magnet7is platy shaped and thin in the thickness, the overall thickness of loudspeaker4can be reduced significantly.

Furthermore, first magnet12A and second magnet12B are fixed firm at their upper surface of large surface area with the lower surface of plate5using adhesive agent5B. So, the strength against vibration and shock given to case4A are enhanced. Third magnet7is fixed at the lower surface, which also has a large surface area, onto the upper surface of plate6using adhesive agent7A. This also contributes to the enhancement of strength against vibrations and shocks exerted on case4A.

Since plate5is made of a non-magnetic material, it does not cause a magnetic short-circuit phenomenon although it entirely covers the upper surfaces of first magnet12A and second magnet12B whose side-surfaces make the N-pole and the S-pole. Meanwhile, since plate6is made of a magnetic material, it does not disturb the formation of magnetic circuit shown inFIG. 3although it covers the entire bottom surface of third magnet7whose upper surface and bottom surface make the S-pole and the N-pole, respectively. Rather, plate6functions together with ring11to magnetically couple the S-pole of first magnet12A with the N-pole of third magnet7, and the S-pole of second magnet12B with the N-pole of third magnet7. Thus, no unwanted magnetic gap would be formed in the magnetic circuit.

Plate6has open areas6B. Because of these areas, barrel portion9D, or the edge portion of diaphragm9, does not hit plate6when diaphragm9vibrates. Open areas6B secure a vibration space for barrel portion9D. This helps making loudspeaker4thinner. Furthermore, since the structure helps making the distance between magnet7and magnet12shorter, the magnetic flux density is increased. This would make up for the deterioration of flux density caused as a result of the thickness reduction.

Although plate5in the present embodiment holds both of first magnet12A and second magnet12B, plate5may be split into two sections so that first magnet12A and second magnet12B are held respectively by the split sections. In this configuration, a gap between the sections functions as sound hole. However, the structure where plate5is provided covering the entire diaphragm9and both of first magnet12A and second magnet12B are held by plate5is easier to manufacture.

Loudspeaker4may be assembled and built direct in an electronic apparatus without employing frame13. However, the procedure of forming case4A using frame13is easier for the assembling.

Now in the following, description will be made on a method of building the component which is structured of first magnet12A, second magnet12B and third magnet7in accordance with the present embodiment. First, fix first magnet12A and second magnet12B on plate5with a specific space between the two. The specific space means a space that can still afford magnetic gap after third magnet7is inserted, which magnet7being covered by diaphragm9integrated with voice coil10. However, it is not easy to dispose first magnet12A and second magnet12B precisely at specific location, because of influence of magnetic attracting force or repelling force. So, it is preferred to dispose first magnet12A and second magnet12B through the following procedure.FIG. 7is a cross sectional view showing the vicinity of plate5during manufacturing of loudspeaker4.FIG. 8is a cross sectional view of magnetizing device and holding jig used to manufacture loudspeaker4, andFIG. 9shows their plan view.

Turn plate5fixed with frame13upside down, as shown inFIG. 7. Dispose ring11in the inside of frame13. Place un-magnetized first magnetic substance32A and second magnetic substance32B on plate5inside ring11, so that they oppose to each other with a certain specified clearance between the two, and fix them thereon using adhesive agent5B.

Make part of adhesive agent5B intrude into respective gaps between the outer circumference of first magnetic substance32A, second magnetic substance32B and the inner circumference of ring11, frame13. By so doing, the respective outer circumferential surfaces of first magnetic substance32A and second magnetic substance32B are fixed also to ring11and frame13.

Next, set an assembled component of plate5, ring11, first magnetic substance32A, second magnetic substance32B and frame13shown inFIG. 7on magnetizing device14, as illustrated inFIG. 8andFIG. 9. Using magnetizing device14, magnetize the inner side-surfaces of first magnetic substance32A and second magnetic substance32B into the N-pole, while the outer side-surfaces into the S-pole. Namely, make the surface of first magnetic substance32A opposing to second magnetic substance32B into the N-pole, while the opposite surface into the S-pole; make the surface of second magnetic substance32B opposing to first magnetic substance32A into the N-pole, while the opposite surface into the S-pole. Thus first magnet12A and second magnet12B are provided.

Magnetizing device14includes case15, and first magnetizing yoke16, second magnetizing yoke17and third magnetizing yoke18(hereinafter, these will be referred to as yoke) provided upright in case15with specific intervals. Dispose yoke16between first magnetic substance32A and second magnetic substance32B. Dispose yoke17at the side of first magnetic substance32A that is opposite to yoke16; dispose yoke18at the side of second magnetic substance32B that is opposite to yoke16. Yokes16,17,18are wound around respectively with coils16A,17A,18A. Coil16A is wound in the direction that is opposite to that of coils17A and18A. Consequently, when coils16A,17A,18A are supplied with electricity, upper part of yoke16is magnetized into the N-pole, while the upper parts of yokes17,18are magnetized into the S-pole. During the magnetizing operation, yoke16represents a polarity that is opposite to that of yokes17,18.

Yokes16,17,18and coils16A,17A,18A are covered with resin19in the inside of case15, protruding only the upper part of yokes16,17,18above resin19.

Place holding jig20on case15at the upper surface. AsFIG. 9shows, holding jig20has a square-shaped projected view, and has open area21for allowing the upper part of yokes16,17,18to come in. Platform22is provided in the direction perpendicular to open area21. Set both ends in the longitudinal direction of the assembled component of plate5, ring11, first magnetic substance32A, second magnetic substance32B and frame13(ref.FIG. 7) on platform22, as illustrated inFIG. 10.

In this state, the upper end of yoke16comes in through sound hole5A of plate5to be getting close to, or making contact with, the inner side-surfaces of first magnetic substance32A and second magnetic substance32B. At the outside of frame13, yokes17,18are in the proximity to the outer side-faces of first magnetic substance32A, second magnetic substance32B.

When coils16A,17A,18A in this arrangement are activated with magnetizing current, the upper part of yoke16is made into the N-pole, while the upper part of yokes17,18are made into the S-pole, as already described. Thereby, the inner side-surfaces of first magnetic substance32A and second magnetic substance32B are made into the N-pole, while the outer side-surfaces into the S-pole.

As described in the above, first magnetic substance32A and second magnetic substance32B are disposed on plate5with a specific clearance, and then these are magnetized to have the magnetic pole formed at the inner side-surfaces. In other words, first magnetic substance32A and second magnetic substance32B have not been magnetized yet when they are disposed on plate5. There is neither magnetic attracting force nor magnetic repelling force at the time when they are placed on plate5. Therefore, first magnetic substance32A and second magnetic substance32B can be disposed and fixed precisely at their specific locations on plate5with ease. First magnetic substance32A and second magnetic substance32B can be fixed firm on plate5using adhesive agent5B.

Furthermore, since first magnetic substance32A and second magnetic substance32B are not magnetized, they do not attract foreign magnetic items inadvertently, and can be managed or stored with ease. Still further, these un-magnetized first magnetic substance32A and second magnetic substance32B may be disposed on plate5without paying attention to the magnetic polarity.

First magnetic substance32A and second magnetic substance32B are magnetized only after they are disposed and fixed firm on plate5. Therefore, even though the opposing inner side-surfaces of first magnet12A and second magnet12B are of the same magnetic polarity, the first and the second magnets would not be peeled off from plate5or displaced by repelling force. This significantly improves the efficiency of manufacturing process.

Next descriptions will be on the assembling of the assembled component of plate5, ring11, first magnet12A, second magnet12B and frame13, and diaphragm9and plate6. In the present example, dispose third magnet7so that its N-pole to S-pole direction is perpendicular to the direction connecting the N-pole of first magnet12A and the N-pole of second magnet12B. Third magnet7is positioned so that its S-pole is at the side closer to the N-poles of first magnet12A and second magnet12B. Provide the magnetic gap at respective spaces between first magnet12A and third magnet7, and between second magnet12B and third magnet7. Place diaphragm9integrated with voice coil10on plate5so that voice coil10fits in the magnetic gap. Magnetically couple the S-pole of first magnet12A with the N-pole of third magnet7, and the S-pole of second magnet12B with the N-pole of third magnet7.

When disposing third magnet7into a space formed between first magnet12A and second magnet12B, however, third magnet7is exposed to magnetic attracting force, or repelling force, due to first magnet12A and second magnet12B. Thus, it is not an easy job to dispose third magnet7at a certain specified position in a space between first magnet12A and second magnet12B.

So, the following procedures are preferred.FIG. 11andFIG. 12are cross sectional views used to describe the steps of manufacturing loudspeaker4. First, fix voice coil10to diaphragm9for unitization. And, fix third magnet7on fixing section6A of plate6with adhesive agent7A for unitization. At this stage, set the assembled component of plate5, ring11, first magnet12A, second magnet12B and frame13on base23with plate5down, as shown inFIG. 11. Base23is made of iron or other magnetic material, and provided integrally on the upper surface with protrusion23A which fits to sound hole5A.

Set diaphragm9on ring11. And then, place the bottom end of assembly jig24on frame13, as illustrated inFIG. 11. Assembly jig24has built-in movable member25which is made of iron or other magnetic material and can move freely ups and downs. Movable member25is provided on the bottom surface at the place corresponding to third magnet7with hollow25A whose projected area on plate6being smaller than that of third magnet7.

Meanwhile, set plate6at the bottom end of movable member25with third magnet7down. Third magnet7had been magnetized so that the surface at plate6side to be the N-pole while the opposite surface to be the S-pole, before it is fixed onto the lower surface of plate6using adhesive agent7A. Therefore, plate6is attached magnetically to the bottom surface of movable member25by the magnetic force of third magnet7.

When movable member25is lowered, plate6leaves off the bottom end of movable member25just before the lower surface of plate6makes contact with the upper surface of diaphragm9. This is caused by the magnetic pulling force due to third magnet7, which became stronger at protrusion23A side of the base23than at the movable member25side. In this way, plate6moves onto the upper surface side of diaphragm9, as shown inFIG. 12.

In order to cause the transfer of plate6by taking advantage of a difference in the magnetic pulling force, base23is provided with protrusion23A while movable member25is provided with hollow25A. For example, by making the volume of hollow25A to be greater than the volume of protrusion23A, the magnetic attracting force due to third magnet7becomes to be greater with respect to protrusion23A side of the base23rather than with the movable member25side.

During lowering of plate6, third magnet7is exposed to certain forces caused by magnetic attraction due to first magnet12A and second magnet12B. These forces tend to displace third magnet7towards the direction of first magnet12A or second magnet12B. This happens because third magnet7has been magnetized into the N-pole at the plate6side and the opposite side into the S-pole, whereas the inner side-surfaces of first magnet12A and second magnet12B have the N polarity. However, such a displacement hardly occurs, because assembly jig24is provided at the inner surface with a means to restrict such a horizontal displacement. So, it is placed at an appropriate location, as illustrated inFIG. 12. Namely, assembly jig24has at its inner surface a restriction wall (not shown) for restricting displacement of plate6in horizontal direction.

After plate6left the bottom end of movable member25, and moved onto the upper-surface side of diaphragm9as shown inFIG. 12, assembly jig24and movable member25are lifted upward. Thus, third magnet7is placed so that the N-pole and the S-pole direction is perpendicular to a direction connecting the N-pole of first magnet12A and the N-pole of second magnet12B. At the same time, third magnet7is positioned with its S-pole at the side closer to the N-pole of first magnet12A and second magnet12B.

In this way, a structure of magnets orientation is completed so that first magnet12A, second magnet12B and third magnet7are disposed with their respective longitudinal sides facing each other as viewed from the magnetizing direction of third magnet7. Also, magnetic gaps are formed between first magnet12A and third magnet7, and between second magnet12B and third magnet7, and diaphragm9can be placed on plate5fitting voice coil10in the magnetic gap. Namely, the longitudinal sides of voice coil10, which has an oblong shape as viewed from the magnetizing direction of third magnet7, are disposed in the magnetic gap.

Finally, fix plate6to frame13using an adhesive agent. This magnetically couples the S-pole of first magnet12A with the N-pole of third magnet7, and the S-pole of second magnet12B with the N-pole of third magnet7. The assembling operation thus completes.

In the present exemplary embodiment, third magnet7is fixed on plate6at the central fixing section6A with its N-pole making contact with the plate. On the other hand, diaphragm9fixing voice coil10is placed on plate5, which has been mounted with first magnet12A and second magnet12B at specific intervals, at the first and second magnets side. And then, plate6is disposed so that it opposes plate5from above diaphragm9, and they are made to get closer. Third magnet7is placed between first magnet12A and second magnet12B, providing magnetic gaps between first magnet12A and third magnet7, and second magnet12B and third magnet7, respectively. At the same time, voice coil10is disposed in the magnetic gap. In the present assembling procedure, third magnet7has been fixed to plate6. So, third magnet7can be placed with ease at a certain specified location, despite the magnetic attracting force, or repelling force of first magnet12A and second magnet12B. As a result, this improves manufacturing productivity.

Plate5is provided with sound hole5A of an rectangular shape to have diaphragm9exposed to the outside. The sound hole shape is not limited to the above-described. Instead, the hole may be formed of a plurality of small round perforations. In this case, however, the shape of sound hole5A needs to be substantially matching with the plan views of yoke16and protrusion23A in order to engage yoke16and protrusion23A of base23to sound hole5A. So, the rectangular shape, for example, as described in the present embodiment is preferred.

INDUSTRIAL APPLICABILITY

A loudspeaker in the present invention has three magnets which are disposed on the same horizontal plane or in a substantially horizontal direction. The magnets provide magnetic gaps in between the magnets for fitting a voice coil M. Under such arrangements, magnetic flux crosses the voice coil at a substantially perpendicular angle even in a case where the used magnets have thin plate shapes. As the results, a loudspeaker can be designed in a slim profile, yet it can generate increased sound outputs because of the increased magnetic force. In addition, since first and second magnets are fixed on a plate made of non-magnetic material, the loudspeaker exhibits the property of high withstanding capability against vibrations and mechanical shocks. The loudspeakers having such performance specifications would demonstrate some advantages when use in portable telephone units and the like electronic apparatus, among other application fields.