Speaker and electronic device

A speaker includes a diaphragm formed as an elongated box-shaped five face body having one open face; an edge for supporting the diaphragm so as to enable vibration of the diaphragm; a voice coil wound around and fixed to four side faces which are among the five faces of the diaphragm and which are adjacent to the open face; and a magnetic circuit for supplying a drive force to the voice coil. The diaphragm is configured such that a height from the open face to an upper face opposed to the open face is greater than or equal to twice a thickness of the voice coil, and a length of a long side of the upper face is greater than or equal to twice a length of a short side of the upper face, and the upper face and two side faces of the diaphragm define a long side direction of the diaphragm. Additionally, reinforcing ribs are formed as recessed and projecting shapes on the upper face and the two side faces of the diaphragm.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a speaker, and more particularly to a speaker which may be slim and have a reduced thickness.

2. Background Art

In recent years, since high-definition televisions, wide-screen televisions, and the like are widespread, horizontally elongated television screens are becoming common. Further, since living spaces are relatively small in Japan, television sets are required to have reduced widths and thicknesses as a whole.

In general, speaker units (hereinafter, simply referred to as speakers) for use in a television are mounted lateral to both sides of its cathode-ray tube, and this is a cause of increasing the horizontal width of a television set. Therefore, conventionally, speakers having elongated structures such as rectangle-shaped structures and ellipse-shaped structures are used as speakers for televisions. Further, since cathode-ray tubes have become horizontally elongated, it is necessary to increase reduction of the horizontal widths of speakers. Simultaneously, a speaker is required to output an enhanced quality of sound and voice so as to correspond to a screen which enables an enhanced quality of image to be displayed. In addition, since thin-screen televisions for which plasma displays or liquid crystal displays are used become widespread, speakers are required to become slimmer and have further reduced thicknesses.

A conventional elongated (slim-type) speaker will be described.FIG. 37is a diagram illustrating a configuration of a conventional slim-type speaker900.FIG. 37(a) is a plan view of the conventional slim-type speaker900.FIG. 37(b) is a cross-sectional view of the conventional slim-type speaker900in a long side direction (along c-c′).FIG. 37(c) is a cross-sectional view of the conventional slim-type speaker900in a short side direction (along o-o′). As shown inFIG. 37, the conventional slim-type speaker900includes a magnet901, a plate902, a yoke903, a frame904, a voice coil bobbin905, a voice coil906, a damper907, a diaphragm909, a dust cap910, and an edge911.

The voice coil906is a wound lead wire formed of copper, aluminum or the like, and is fixed to the voice coil bobbin905having a cylindrical shape. The voice coil bobbin905supports the voice coil906such that the voice coil906is disposed in a magnetic gap908formed by the magnet901, the plate902, and the yoke903. Further, the voice coil bobbin905is connected to the frame904via the damper907. Furthermore, the voice coil bobbin905is adhered to the diaphragm909having an ellipsoidal shape or an almost ellipsoidal shape, on a side opposite to a side on which the voice coil906is fixed thereto. The dust cap910having an almost semicircular cross section is fixed to the center portion of the diaphragm909. The edge911has an annular shape, and has a semicircular cross section. Further, the inner periphery of the edge911is fixed to the outer periphery of the diaphragm909. The outer periphery of the edge911is fixed to the frame904.

When the conventional slim-type speaker900is driven, a drive current is applied to the voice coil906. In this case, due to the drive current applied to the voice coil906and an effect of a magnetic field generated around the voice coil906, the voice coil bobbin905performs piston movement. Thus, the diaphragm909vibrates in the direction in which the voice coil bobbin905performs the piston movement. As a result, a sound wave is emitted from the diaphragm909. The conventional slim-type speaker900as shown inFIG. 37is disclosed in, for example, Patent Document 1.FIG. 38is a diagram illustrating a relationship between a reproduced-sound pressure level and a frequency characteristic, which is observed when 1 W of electric power is supplied to the conventional slim-type speaker900. InFIG. 38, the vertical axis represents reproduced-sound pressure levels, and the horizontal axis represents drive frequencies. A microphone for measuring the reproduced-sound pressure levels as shown inFIG. 38is disposed, on the central axis of the slim-type speaker900, in front of the slim-type speaker900so as to be distant therefrom by 1 m.Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-32659

SUMMARY OF THE INVENTION

However, the conventional slim-type speaker900described above has the following problems. As shown inFIG. 37, since a driving method, in which the diaphragm909having an elongated structure is driven at the center portion thereof, is used for the conventional slim-type speaker900, resonances are likely to occur in the long side direction of the diaphragm909. As a result, the reproduced-sound pressure level represents a frequency characteristic in which peak dips occur in intermediate to high sound reproduction bandwidths, thereby deteriorating a sound quality. For example, the characteristic shown inFIG. 38is such that distinguished dips occur at about 2 kHz, 3 kHz, and 5 kHz.

Therefore, in order to solve the aforementioned problems, an object of the present invention is to provide a speaker which: has a slim structure (an elongated structure); prevents easy occurrence of resonances; and realizes a flat frequency characteristic over a wide bandwidth, so as to enhance a sound quality.

In order to solve the aforementioned problems, a speaker according to the present invention includes: a diaphragm formed as an elongated box-shaped five face body having one open face; an edge for supporting the diaphragm so as to enable vibration of the diaphragm; a voice coil wound around and fixed to four side faces which are among five faces of the diaphragm and which are adjacent to the open face; and a magnetic circuit for supplying a drive force to the voice coil, and the diaphragm is configured such that a height from the open, face to an upper face opposed to the open face is greater than or equal to twice a thickness of the voice coil, and a length of a long side of the upper face is greater than or equal to twice a length of a short side of the upper face, and the upper face and two side faces of the diaphragm define a long side direction of the diaphragm, and a plurality of reinforcing ribs are formed as recessed and projecting shapes on the upper face and the two side faces of the diaphragm.

Further, it is preferable that a flange is provided around the four side faces adjacent to the open face of the diaphragm, and the voice coil is fixed to the flange as well as the four side faces.

Further, at least one connection wall may be provided inside the diaphragm.

Further, the edge may be formed of a sheet having a cross section of an arc shape, and a thickness of the edge may be gradually increased from a center of the arc shape toward end portions of the arc shape.

Further, the edge may be made of a material different from a material of the diaphragm.

Further, the edge may be formed of a foamed rubber or a high molecular weight elastomer, and the diaphragm may be formed of a polyimide resin or a pulp.

Further, it is preferable that the magnetic circuit includes one inner magnetic pole having a rectangular parallelepiped shape, and two outer magnetic poles each having a rectangular parallelepiped shape, the one inner magnetic pole is disposed adjacent to the open face of the diaphragm, and the two outer magnetic poles are disposed lateral to both sides, respectively, of the diaphragm.

Further, at least one damper, connected to the upper face opposed to the open face of the diaphragm, for supporting the diaphragm so as to enable vibration of the diaphragm may be further provided, and the edge may be connected to end portions of the four side faces adjacent to the open face of the diaphragm to support the diaphragm, and the end portions are adjacent to the open face of the diaphragm.

Further, the at least one damper may be formed of a sector-shaped sheet having an arc-shaped cross section.

Further, the at least one damper may be formed of a rectangular sheet having an arc-shaped cross section.

Further, a plurality of dampers, each connected to the upper face opposed to the open face of the diaphragm, for supporting the diaphragm so as to enable vibration of the diaphragm may be further provided, and the plurality of dampers may support the diaphragm such that at least two of the plurality of dampers each have one end portion connected to the upper face opposed to the open face of the diaphragm at a same one position, and each have the other end portion oriented toward a different direction.

Further, the present invention may be used as an electronic equipment (typically, a television broadcast receiver) including the speaker described above.

According to the present invention, it is possible to provide a speaker which is of a slim type, and which is less likely to cause resonances, and enables a flat frequency characteristic over a wide bandwidth, to enhance a sound quality. Further, according to the present invention, it is possible to provide a speaker having a reduced thickness.

DESCRIPTION OF THE REFERENCE CHARACTERS

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

FIG. 1is a perspective view of an example of a speaker100according to a first embodiment. The speaker100of the first embodiment has distinguished feature that the speaker100has an elongated (slim) shape, and a driven portion of a diaphragm is enlarged, and the diaphragm has an enhanced rigidity.

FIG. 2is a diagram illustrating a vibration system150of the speaker100according to the first embodiment.FIG. 3is a diagram illustrating components of the vibration system150of the speaker100.FIG. 4is a diagram illustrating a cross section of the speaker100shown inFIG. 1along A-A′. As shown inFIG. 1andFIG. 4, the speaker100includes: a diaphragm111; an edge112; upper frames113; lower frames114; a voice coil115; upper magnets116; a lower magnet117; upper yokes118; upper plates119; a lower plate120; a lower yoke121; and side yokes122. Further, as shown inFIG. 1, the speaker100has an elongated shape in which the longitudinal length thereof is unequal to the transverse length thereof.

Firstly, the configuration of the vibration system150of the speaker100will be described. As shown inFIG. 2andFIG. 3, the vibration system150includes the diaphragm111and the edge112. The diaphragm111has an elongated shape, and a ratio of the longitudinal length to the transverse length is preferably 2 or more:1. In other words, when the longitudinal length of the diaphragm111is 1, the transverse length thereof is preferably less than or equal to 0.5. Hereinafter, as shown inFIG. 2, the longitudinal direction of the diaphragm111is referred to as a long side direction while the transverse direction thereof is referred to as a short side direction. The diaphragm111includes a box-shaped five face body101and an inverse-L-shaped flange103. The shape of the box-shaped five face body101is formed by removing, from an elongated rectangular parallelepiped box, one of rectangular faces which extend along the long side direction thereof. The removed face may be referred to as an open face. The inverse-L-shaped flange103has an L-shaped cross section (seeFIG. 4), and has an elongated shape similarly to the box-shaped five face body101. The inverse-L-shaped flange103is fixed to an open portion102of the box-shaped five face body101.FIG. 5is a diagram illustrating the voice coil115of the speaker100. The voice coil115is fixed to a plane portion104(seeFIG. 3) of the inverse-L-shaped flange (seeFIG. 4). An inner periphery portion106of the edge112is connected to a lower edge portion105(seeFIG. 3) of the inverse-L-shaped flange103. The edge112has an elongated annular shape, and is a roll edge (seeFIG. 4) having a cross section of an almost semicircular shape (arc shape). The direction toward which the edge112projects is opposite to the direction toward which the diaphragm111projects. The outer periphery portion107(seeFIG. 3) of the edge112is fixed to and between the upper frames113and the lower frames114(seeFIG. 4). Each of the upper frames113and the lower frames114has an almost rectangular parallelepiped shape.

Material of the diaphragm111and the edge112is a polyimide resin, PEN resin or the like. A polymer film which has a reduced thickness ranging from 50 μm to several hundred μm is preferably selected. The vibration system150shown inFIG. 2is formed as a continuously integrated shape by the polymer film being integrally formed through vacuum forming or the like. Alternatively, the vibration system150may be formed as a continuously integrated shape by the polymer film being integrally molded through injection molding or the like.

Next, the entire configuration of the speaker100will be described by mainly usingFIG. 1andFIG. 4. As shown inFIG. 4, the lower plate120is disposed below the open portion102of the box-shaped five face body101of the diaphragm111so as to form a space therebelow, and the lower magnet117is fixed to and under the lower plate120, and the lower yoke121is in turn fixed to and under the lower magnet117. In this manner, the lower plate120, the lower magnet117, and the lower yoke121are disposed so as to extend toward a direction opposite to a direction toward which the diaphragm111projects. The lower yoke121extends in the short side direction of the diaphragm111, and is fixed to the lower frames114. Each upper plate119is disposed above the edge112so as to form a space therebetween. The upper magnets116are fixed to and on the upper plates119, respectively, and the upper yokes118are fixed to and on the upper magnets116, respectively, and the upper yokes118are fixed to the upper frames113, respectively. The upper yokes118and the lower yoke121are magnetically connected through the side yokes122. A magnetic flux is generated in a magnetic gap G as shown inFIG. 4by a magnetic circuit including the lower plate120and the upper plates119which are configured as described above. The upper magnets116and the lower magnet117each have a rectangular shape as viewed from above, similarly to the diaphragm111. The upper magnets116are disposed such that the direction of the long side of each upper magnet116coincides with the long side direction of the diaphragm111. Similarly, the lower magnet117is disposed such that the direction of the long side of the lower magnet117coincides with the long side direction of the diaphragm111. Further, for the magnetic circuit described above, the lower plate120and the lower magnet117may be referred to as an inner magnetic pole while the upper plates119and the upper magnets116may be referred to as an outer magnetic pole.

The voice coil115shown inFIG. 5is fixed to the diaphragm111as shown inFIG. 4. As shown inFIG. 5, the voice coil115has a rectangular shape as viewed from above. The voice coil115is wound and fixed around a stepped portion on the outer periphery of the diaphragm111such that the central axis of the voice coil115coincides with the central axis of the diaphragm111. More specifically, the voice coil115is fixed to both the lower portion of the side faces of the box-shaped five face body101and the plane portion104of the inverse-L-shaped flange103, by using, for example, an adhesive. The height of the box-shaped five face body101is at least twice greater than the thickness (height) of the voice coil115. Therefore, the voice coil115can be disposed at or around the vertically center position of the vibration system150as shown inFIG. 4. More specifically, the voice coil115can be disposed at or around the center position between the top of the box-shaped five face body101and the projecting top of the edge112. In a typical speaker like the conventional slim-type speaker900as shown inFIG. 37, a voice coil is disposed at or below the lower portion of a diaphragm. Leads110are provided at both ends, respectively, of the voice coil115(seeFIG. 5), and the leads110are connected through a space to input terminals (not shown) provided on, for example, the upper frames113, respectively. A drive current is supplied to the leads110. As shown inFIG. 4, the diaphragm111is disposed in the magnetic gap G by the edge112being supported and held between the upper frames113and the lower frames114. Further, the edge112has an enhanced flexibility. Moreover, as described above, the voice coil115is fixed to the diaphragm111. Thus, the diaphragm111vibrates due to a drive force which is generated for the voice coil115by a current being applied to the voice coil115, so that a sound wave is emitted into a space to reproduce a sound and voice.

A preferable example of dimensions of each of the vibration system150and the voice coil115which enable the speaker100to make an output equivalent to an output from a round speaker having the diameter of 8 cm will be specifically described below. In this case, the diameter of a copper wire used for the voice coil115is typically about Ø0.1 mm to Ø0.2 mm. Therefore, the width of a bundle of the wound copper wire of the voice coil115is about 0.5 mm when the copper wire is wound in two layers. The width of the plane portion104of the inverse-L-shaped flange103is preferably greater than or equal to the width of the wound wire of the voice coil115. Therefore, the plane portion104of the inverse-L-shaped flange103may have the reduced width ranging from about 0.5 mm to 1 mm. In order to cause the speaker100to make an output equivalent to an output from a round speaker having the diameter of 8 cm, the length of the short side of the box-shaped five face body101is preferably 7 mm, and the length of the long side thereof is preferably 120 mm. Further, the length of the short side of the edge112is preferably 20 mm, and the length of the long side thereof is preferably 140 mm. As described above, the width of the plane portion104of the inverse-L-shaped flange103is small, and therefore the length of the long side of the diaphragm111is almost equal to the length of the long side of the box-shaped five face body101. When the dimensions are as described above, the length of the long side of the box-shaped five face body101is 85.7% of the length of the long side of the vibration system150.

In the speaker100having the configuration described above, the diaphragm111is driven entirely along the long side direction, and is driven at the end portion in the short side direction. Further, the configuration described above enables suppression of resonance of the diaphragm111in the speaker100. The resonance suppression effect for the diaphragm111in the speaker100will be described below.

Firstly, the resonance suppression effect for the long side direction of the diaphragm111will be described. If the diaphragm111is driven centrally at only one point in the same manner as that for the conventional slim-type speaker900, multiple resonances are induced, and the sound pressure frequency characteristic that multiple peaks and dips occur (seeFIG. 38) is observed. This is because the diaphragm111is formed of a thin film as an elongated shape, and therefore multiple resonances occur from a low frequency in the long side direction of the diaphragm111.

However, in the speaker100of the present invention, a drive force is applied to the diaphragm111entirely along the long side direction, thereby enabling resonance of the diaphragm111to be suppressed in the long side direction. A relationship between the resonance suppression effect and the length of the driven portion of the diaphragm111in the long side direction, which is obtained for the speaker100, will be described below by using a finite element analysis.

FIG. 6is a plan view of the speaker100to be subjected to the finite element analysis, illustrating the resonance of the diaphragm111in the long side direction. In the finite element analysis, the drive force F which is generated by a drive current being applied to the voice coil115is applied to a predetermined portion (a portion indicated by f_l) of the voice coil115. Outline arrows shown inFIG. 6indicate portions to which the drive force F is applied. The length of the portion indicated by f_l to which the drive force F is applied is gradually increased from “0”, to measure change in the sound pressure frequency characteristic. Specifically, the length of f_l is increased from the length “0” to the length “c_l”, and the length “0” represents a case where the drive force F is applied to only the center line A-A′ of the vibration system150, and the length “c_l” represents a case where the drive force F is applied to the entire length of the voice coil115. In the analysis described above, the vibration system150is formed as a polyimide resin film having the thickness of 0.075 mm, and the entire length d_l of the vibration system150is 90 mm, and the entire length c_l of the voice coil115is 65 mm. In this case, the rate of the voice coil115to the vibration system150in length is about 72%.

FIG. 7is a diagram illustrating a result of an analysis of the sound pressure frequency characteristic of the speaker100, which is obtained when the drive force F is applied to only the center line A-A′ (when f_l=0 is satisfied). As shown inFIG. 7, the earliest great peak dip occurs at about 800 Hz as indicated by X, the immediately following great peak dip occurs at about a frequency indicated by Y, and a great peak dip, which immediately follows the peak dip occurring at about the frequency indicated by Y, occurs at about a frequency indicated by Z. Results of investigating vibration modes at about frequencies indicated by X, Y, and Z indicate that the peak dips occur at about frequencies indicated by X and Y by the resonance mode associated with the long side direction of the vibration system150, and the peak dip occurs at about frequency indicated by Z by the resonance mode associated with the short side direction of the vibration system150. The lowest resonance frequency F0appears at about 140 Hz.

FIG. 8is a diagram illustrating a vibration mode of the voice coil115, which is associated with the long side direction thereof and is observed at a peak occurring at about the frequency indicated by X. Since the vibration mode of the voice coil115at the peak occurring at about the frequency indicated by X represents a shape which is bilaterally symmetric about the center line A-A′ shown inFIG. 6,FIG. 8shows only a right half shape of the mode. InFIG. 8, the left end of the mode shape corresponds to the positions of the center line A-A′ while the right end of the mode shape corresponds to the end of the voice coil115in the long side direction. The resonance mode shown inFIG. 8is a resonance mode in which amplitudes of the center portion and the end portion of the diaphragm111are maximum, and therefore the resonance mode shown inFIG. 8is a first-order resonance mode in the long side direction.

When the length of the portion of f_l to which the drive force F is applied is gradually increased from 0, the resonance of the diaphragm111in the long side direction is suppressed, resulting in the peak dips being attenuated at about the frequencies indicated by X and Y.FIG. 9is a diagram illustrating a result of an analysis of the sound pressure frequency characteristic of the speaker100, which is obtained when the drive force F is applied to the entire voice coil115(when f_l=c_l is satisfied). As shown inFIG. 9, when the drive force F is applied to the entire voice coil115, the peak dips which occur at about the frequencies indicated by X and Y by the resonance mode of the vibration system150in the long side direction are substantially eliminated. Thus, a sound reproduction bandwidth which can be used for enabling the speaker100to output a high quality sound is broadened approximately to the bandwidth of the frequency indicated by Z as shown inFIG. 9. That is, the resonance mode associated with the long side direction is suppressed by increasing the length of the driven portion of the diaphragm111in the long side direction.FIG. 10is a diagram illustrating a relationship between the peak dip (sound pressure deviation) and the rate (f_l/d_l), in length, of the driven portion of the diaphragm to the vibration system150in the long side direction, and the relationship is obtained by using the finite element analysis described above.FIG. 10shows that, when at least 60% of the entire vibration system150is driven in the long side direction, the sound pressure deviation is less than or equal to 3 dB, which is generally regarded as a preferable sound pressure deviation.

The resonance suppression effect for the long side direction of the diaphragm111has been described above. The resonance suppression effect for the short side direction of the diaphragm111will be described below.

As described above, in the speaker100, the diaphragm111is driven entirely along the long side direction while the end portion of the diaphragm111is driven in the short side direction. Therefore, it is difficult to completely suppress the resonance occurring in the diaphragm111in the short side direction. As a result, as shown inFIG. 9, the first-order resonance mode (see Z) occurs in the diaphragm111in the short side direction.

However, in the diaphragm111, the resonance frequency for the short side direction is enhanced due to an effect of the projecting structure of the box-shaped five face body101, as compared to a planar shape. The diaphragm111(the box-shaped five face body101) is formed of a thin film material such as a polyimide resin, and typically has the thickness ranging from 50 μm to several hundred μm as described above. Further, the height (thickness) of the projecting portion of the box-shaped five face body101is preferably at least twice as great as the height (thickness) of the voice coil115. When the speaker100is caused to make an output equivalent to an output from a round speaker having the diameter of 8 cm, the height of the projecting portion of the box-shaped five face body101is about 5 mm. When the thickness of the box-shaped five face body101is 50 μm, and the height of the projecting portion of the box-shaped five face body101is 5 mm, 5 mm is 100 times as great as 50 μm if simply compared. Although the 100 times difference is not directly reflected in the resonance suppression effect for the short side direction, the rigidity of the diaphragm111in the short side direction is substantially enhanced due to the projecting structure described above. As a result, the resonance is suppressed for the diaphragm111in the short side direction, and the resonance frequency of the first-order resonance mode is enhanced.

As described above, in the speaker100according to the first embodiment, the resonance is suppressed in the long side direction by a drive force being applied to a portion of at least 60% of the entire length of the vibration system150along the long side direction thereof whereas the resonance frequency for the short side direction can be enhanced due to the diaphragm111being configured to have an enhanced rigidity. Thus, in the speaker100, the flat sound pressure frequency characteristic can be obtained up to an enhanced frequency, and the diaphragm111can be caused to perform piston movement so as to suppress the influence of the resonance up to an enhanced frequency. As a result, in the speaker100of the first embodiment, the sound quality can be substantially improved as compared to in the conventional slim-type speaker900(seeFIG. 37).

As described above, the dimensions of the diaphragm111are determined such that, when the length of the diaphragm111in the long side direction is 1, the length thereof in the short side direction is preferably less than or equal to 0.5. If the diaphragm111has a planar shape, the first-order resonance frequency in the short side direction is inversely proportional to the square of the first-order resonance frequency in the long side direction, in the diaphragm111. For example, when the diaphragm111has such dimensions that the aspect ratio thereof is 2:1, the first-order resonance frequency of the diaphragm111in the long side direction is fL1[Hz], and the first-order resonance frequency of the diaphragm111in the short side direction is fS1[Hz], the value of fS1is calculated as 4*fL1. When the diaphragm111is formed as a box-shaped five face body, the length in the short side direction is increased due to the projection, thereby lowering the resonance frequency. However, according to the first embodiment, the more elongated shape the diaphragm111has, the greater the resonance suppression effect of the speaker100is.

Realization of the speaker100of the first embodiment having the reduced thickness will be described below. As shown inFIG. 4, in the speaker100of the first embodiment, the voice coil115is disposed at the almost center position between the top of the projecting portion of the box-shaped five face body101and the top of the roll-shaped projection of the edge112. That is, the voice coil115is disposed at almost the vertically center position of the vibration system150. Further, the inner magnetic pole including the lower plate120and the lower magnet117is disposed in the recessed portion of the diaphragm111. Moreover, the two outer magnetic poles each including the upper plate119and the upper magnet116are disposed lateral to both the sides of the diaphragm111so as to extend in the direction of the recessed portion of the roll shape of the edge112. The voice coil115is disposed between the inner magnetic pole and the outer magnetic poles. Such a disposition allows the inner magnetic pole and the outer magnetic poles to be disposed in the recessed portions of the vibration system150having the diaphragm111and the edge112. Further, in such a disposition, a clearance between the inner magnetic pole and the diaphragm111may be considered when a position of the inner magnetic pole is determined whereas a clearance between the outer magnetic poles and the edge112may be considered when positions of the outer magnetic poles are determined. More specifically, only a distance over which the diaphragm111moves downward while vibrating may be considered when a position of the inner magnetic pole is determined. This is because any component which is likely to contact the diaphragm111is not basically provided in the direction in which the diaphragm111moves upward while vibrating, and therefore it is unnecessary to consider a clearance above the diaphragm111. On the other hand, only a distance over which the edge112moves upward while vibrating may be considered when positions of the outer magnetic poles are determined. This is because any component which is likely to contact the edge112is not basically provided in the direction in which the edge112moves downward while vibrating, and therefore it is unnecessary to consider a clearance below the edge112. As described above, in the speaker100of the first embodiment, the inner magnetic pole and the outer magnetic poles are disposed so as to be inserted into the recessed portions of the vibration system150, so that the thickness can be substantially reduced as compared to in a conventional speaker (seeFIG. 37).

As described above, in the speaker100of the first embodiment, a sound quality can be substantially improved as well as the thin shape can be realized as compared to in the conventional slim-type speaker900(seeFIG. 37).

In the above description, an opening is provided near the upper yoke118to emit a sound and voice from near the upper yoke118(seeFIG. 1andFIG. 4). However, as shown inFIG. 11, no opening is provided near the upper yoke118and an opening125may be provided near the lower yoke121to emit a sound and voice from near the lower yoke121. Thus, a sound and voice generated in the reverse side of the vibration system150may be emitted.

Moreover, as shown inFIG. 12, no opening is provided near the upper yoke118, and an opening127may be provided near the side yoke122to emit a sound and voice from near the side yoke122. In this case, the opening near the upper yoke118is enclosed by, for example, a top frame130. Thus, a sound and voice can be emitted from the side face of the speaker100, thereby enabling the speaker100to be mounted in a reduced space.

Second Embodiment

A speaker200according to a second embodiment has a distinguished feature, in addition to the features of the speaker100according to the first embodiment, that a reinforcing rib for enhancing rigidity of a diaphragm in the short side direction is provided on a diaphragm. For the speaker200of the second embodiment, the same components as described for the speaker100of the first embodiment are denoted by the same corresponding reference numerals, and the description thereof is not basically given.

FIG. 13is a perspective view of an example of the speaker200according to the second embodiment.FIG. 14andFIG. 15are diagrams illustrating a vibration system250of the speaker200according to the second embodiment.FIG. 16is a perspective view of a box-shaped five face body201of the vibration system250.

As shown inFIG. 13toFIG. 15, the speaker200of the second embodiment has the same configuration as the speaker100(seeFIG. 1andFIG. 2) of the first embodiment except that the vibration system250is used for the speaker200instead of the vibration system150. The vibration system250has the same configuration as the vibration system150except that a diaphragm211is used for the vibration system250instead of the diaphragm111. The diaphragm211has the same configuration as the diaphragm111except that a box-shaped five face body201is used for the diaphragm211instead of the box-shaped five face body101.

As shown inFIG. 16, the box-shaped five face body201is configured to include a plurality of reinforcing ribs235, and the plurality of reinforcing ribs235are formed by projections and recesses being disposed on three faces of the box-shaped five face body101(seeFIG. 3) which are parallel to the long side direction thereof, to enhance rigidity in the short side direction. The reinforcing ribs235are preferably provided on the three faces parallel to the long side direction in the box-shaped five face body201so as to form a continuous recessed and projecting shape, as shown inFIG. 16. Further, the reinforcing ribs235are preferably integrated simultaneously when the vibration system250is integrally formed.

An effect exerted by the speaker200of the second embodiment will be described below. The speaker200of the second embodiment exerts not only the effect exerted by the speaker100of the first embodiment, but also the effect that enhancement of the resonance frequency is increased by the reinforcing ribs235allowing increased enhancement of the rigidity of the diaphragm211in the short side direction. The effect exerted by the reinforcing ribs235will be specifically described below by using the finite element analysis.

FIG. 17is a diagram illustrating a model250-1representing a cross-sectional shape of the vibration system250in the short side direction, and also showing that the reinforcing ribs235are formed only on the upper face of the box-shaped five face body201. InFIG. 17, the model250-1is a model representing a left half portion of the cross-sectional shape of the vibration system250which is bilaterally symmetric with respect to the center line o-o′. As shown inFIG. 17, the reinforcing ribs235are formed only on the upper face of the box-shaped five face body201. The voice coil115is fixed to the box-shaped five face body201and the inverse-L-shaped flange103near a joining point therebetween. The inner periphery portion of the edge112is joined to the end portion of the inverse-L-shaped flange103, and the outer periphery portion of the edge112is fixed by the upper frames113or the like (not shown). In the model250-1, the thickness is 50 μm, the width (the width from the center line o-o′ to the outer periphery of the edge112) of the left half portion of the vibration system250is 10 mm, the width of the left half portion of the box-shaped five face body201is 3.5 mm, and the material is a polyimide resin. In accordance with the finite element analysis, a drive force is applied to the voice coil115of the model250-1, the deformation of the model250-1is analyzed, and the sound pressure frequency characteristic is calculated at an observation point which is on the center line o-o′ and is distant from the upper face of the box-shaped five face body201by 1 m.

FIG. 18is a diagram illustrating the result of the finite element analysis of the model250-1described above. InFIG. 18, the horizontal axis represents reproduction frequencies for a sound and voice, and the vertical axis represents reproduced-sound pressure levels of the sound and voice. As shown inFIG. 18, peaks of reproduced-sound pressure which are caused by the resonance occur at frequency 5.5 kHz and frequency 10.05 kHz, and the characteristic is unstable. F0represents a lowest resonance frequency. In general, a speaker is required to have a characteristic that the reproduced-sound pressure is constant even when the reproduction frequency varies. Therefore, in the model250-1, a usable bandwidth in which a sound and voice can be reproduced with enhanced quality is up to 5.5 kHz. Therefore, peaks of reproduced-sound pressure which occur at 5.5 kHz and 10.05 kHz need to occur at a higher frequency in order to enlarge the usable bandwidth in which a sound and voice can be reproduced with enhanced quality.

As described in the first embodiment, in the speaker200, the diaphragm211is driven entirely along the long side direction of the vibration system250, and therefore the resonance is suppressed in the long side direction. Therefore, the limit of the usable bandwidth (hereinafter, simply referred to as a usable bandwidth) in which a sound and voice can be reproduced with enhanced quality is defined based on the resonance frequency for the short side direction of the vibration system250. Therefore, two models250-2and250-3, each of which has the vibration system250having the same width as that of the model250-1in the short side direction as a whole, and has the box-shaped five face body201having the width different from that of the model250-1, are prepared. The usable bandwidth is compared among the three models including the model250-1.

FIG. 19is a diaphragm illustrating the models250-2,250-1, and250-3. As shown inFIG. 19, half the width of the box-shaped five face body201of the model250-2is 4.5 mm, half the width of the box-shaped five face body201of the model250-1is 3.5 mm, and half the width of the box-shaped five face body201of the model250-3is 2.5 mm. InFIG. 19, as inFIG. 17, models each representing the left half portion of the vibration system250are shown. Further, the model250-1shown inFIG. 19is the same as the model250-1shown inFIG. 17.

FIG. 20is a diagram illustrating results of the finite element analyses of the models250-2,250-1, and250-3shown inFIG. 19. The analysis result for the model250-1shown inFIG. 20is the same as the analysis result for the model250-1shown inFIG. 18. Further, F0represents a lowest resonance frequency. As shown inFIG. 20, the comparison in the sound pressure frequency characteristic among the three models indicates that a frequency at which the second peak β of the reproduced-sound pressure occurs is 9.9 kHz in the model250-2, is 10.5 kHz in the model250-1, and is 10.9 kHz in the model250-3. Thus, it can be understood that the smaller the width of the box-shaped five face body201, the higher the frequency at which the peak β occurs. On the other hand, as shown inFIG. 20, a frequency at which the first peak α of the reproduced-sound pressure occurs is about 5.5 KHz in each of the three models. Thus, it can be understood that the usable bandwidth is not enlarged by the width of the box-shaped five face body201being simply changed as in the models shown inFIG. 19.

FIG. 21is a diagram showing that, in the model250-1shown inFIG. 17, a shape (deformed shape) of the resonance mode at 5.5 kHz is put on an undeformed shape. As shown inFIG. 21, it is understood that the resonance occurring at 5.5 kHz is caused by deformation occurring at the side face portion (a portion represented by X inFIG. 21) of the box-shaped five face body201, to which the voice coil115is fixed.

In order to enlarge the usable bandwidth, the Young's modulus of the side face portion of the box-shaped five face body201is increased tenfold, and the analysis is performed again.FIG. 22is a diagram illustrating a result of the analysis performed in the case of the Young's modulus of the side face portion of the box-shaped five face body201being increased tenfold in the model250-1shown inFIG. 17.FIG. 22(a) is a diagram illustrating the model250-1in which the Young's modulus of the side face portion of the box-shaped five face body201is increased tenfold. InFIG. 22(a), the side face portion of the box-shaped five face body201as indicated by RF has the Young' modulus which is increased tenfold. The other conditions are the same as described for the model250-1shown inFIG. 17.FIG. 22(b) is a diagram illustrating a result of the finite element analysis for the model250-1shown inFIG. 22(a). As shown inFIG. 22(b), the peak α of the reproduced-sound pressure occurring at 5.5 kHz is eliminated, and the usable bandwidth is enlarged up to 10.05 kHz. The result of the analysis indicates that, when the rigidity of the side face portion of the box-shaped five face body201is enhanced in the short side direction, the usable bandwidth can be enlarged.

In order to enhance the rigidity of the side face portion of the box-shaped five face body201in the short side direction, reinforcing ribs forming a plurality of projections and recesses are disposed on the side face portion of the box-shaped five face body201in addition to the upper face portion of the box-shaped five face body201. As described below, the effect of the reinforcing ribs is verified by using the finite element analysis.FIG. 23shows that the model250-1shown inFIG. 17, which is represented as a three-dimensional model, has the reinforcing ribs235formed, as a continuous projecting and recessed shape, on the side face and the upper face of the box-shaped five face body201. For the convenience of the calculation, in the model shown inFIG. 23, the width of the vibration system250in the long side direction (B-B′ direction) corresponds to the width of a single reinforcing rib among the reinforcing ribs235.FIG. 24is a diagram illustrating the result of the finite element analysis of the model having the reinforcing rib235shown inFIG. 23. As shown inFIG. 24, the peak α of the reproduced-sound pressure occurring at 5.5 kHz is eliminated, and the usable bandwidth is enlarged up to 10.05 kHz. In the above description, the reinforcing ribs235are formed only on the box-shaped five face body201. However, the reinforcing ribs235may be integrally formed so as to extend from the box-shaped five face body201up to the edge of the inverse-L-shaped flange103.

According to the result of the finite element analysis as described above, in the speaker200according to the second embodiment, when the box-shaped five face body201forming the vibration system250has a plurality of the reinforcing ribs235, improvement of the sound quality can be increased in addition to the effect of the speaker100(seeFIG. 1) of the first embodiment being exerted.

Third Embodiment

In each of the speaker100of the first embodiment and the speaker200of the second embodiment, the diaphragm and the edge which form the vibration system are made of the same material and integrated into one component. A speaker300(not shown) according to the third embodiment has a distinguished feature that a diaphragm and an edge which form the vibration system are formed as different components, respectively, and the different components are coupled to each other. Difference from the speaker200according to the second embodiment will be mainly described below as an example. The components which are the same between the speaker200of the second embodiment and the speaker300of the third embodiment are denoted by the same corresponding reference numerals, and the description thereof is not basically given.

FIG. 25is a diagram illustrating a vibration system350of the speaker300according to the third embodiment. As shown inFIG. 25, an edge312is fixed to the lower end portion of the inverse-L-shaped flange103. The diaphragm211may be formed through vacuum forming or the like, for example, by using, as material, a polymer film formed of a polyimide resin or the like. Alternatively, the diaphragm211may be formed by using pulp or the like as material. The edge312is made of a material different from that of the diaphragm211. In order to form the edge312, for example, a rubber may be foamed and formed in a die as a foamed rubber which is a viscoelastic component. Alternatively, for example, the edge312may be formed through injection molding by using a high-molecular weight elastomer material which is a polymer of a rubber and a high molecular weight component.

Further, the edge312is a roll edge having an almost semicircular (arc-shaped) cross section as shown inFIG. 25, and, in a roll shape thereof, the thickness of a deepest portion357is less than the thickness of a base portion358. In the roll shape thereof, the thickness of the base portion358is preferably at least 1.5 times as great as the thickness of the deepest portion357.

Further, as shown in an enlarged view (b) ofFIG. 25, the inner periphery portion of the edge312is joined to and along the outer periphery portion of the inverse-L-shaped flange103. The edge312and the inverse-L-shaped flange103may be joined to each other by using an adhesive, or may be fused with each other through insert molding. In addition, a projection356is preferably formed when the edge312and the inverse-L-shaped flange103are joined to each other.

An operation and effect of the speaker300according to the third embodiment will be described below. In the speaker300, the diaphragm211and the edge312which form the vibration system350are made of different materials, respectively. Therefore, materials of the diaphragm211and the edge312may be selected in accordance with a required characteristic for the speaker300. As a result, improvement of the performance of the speaker300can be increased. This will be specifically described below.

As described above, for example, the diaphragm211is formed of a polymer film made of a polyimide resin or the like, or formed of pulp, and the polymer film and the pulp each have light weight and high rigidity. Thus, the diaphragm211can vibrate up to an enhanced frequency and with reduced deformation, thereby elevating the upper limit of the usable bandwidth. On the other hand, the edge312is formed of foamed rubber, a high molecular weight elastomer, or the like, which have enhanced flexibility. Thus, the lowest resonant frequency F0is lowered in the vibration system350, thereby lowering the lower limit of the usable bandwidth. As a result, the usable bandwidth is substantially enlarged.

In addition, as described above, in the edge312, the thickness of the deepest portion357is less than the thickness of the base portion358in the roll shape. Thus, the edge312may have a force displacement characteristic that the deepest portion357of the roll shape is mainly deformed in a range in which the vibration amplitude of the diaphragm211is small, and the base portion358of the roll shape is gradually deformed in accordance with the vibration amplitude being increased. As a result, the edge312can have the force displacement characteristic representing improved linearity while the reduced rigidity is realized. Furthermore, the base portion358(thicker portion) of the roll shape is gradually deformed in accordance with the vibration amplitude being increased, and this means that the edge312has an enhanced flexibility resistance.

Moreover, when the projection356is formed as shown in the enlarged view (b) ofFIG. 25, the projection356easily dams up and keeps an adhesive which is used to adhere the voice coil115(not shown) to the diaphragm211. Thus, it is possible to prevent change of the lowest resonance frequency F0and generation of an abnormal sound which are caused by the adhesive flowing into the rolled section of the edge312.

As described above, in the speaker300according to the third embodiment, enlargement of the usable bandwidth can be increased, and a speaker can have an enhanced reliability, in addition to the effect of the speaker200of the second embodiment being exerted.

In the above description, the speaker300includes the diaphragm211having the reinforcing ribs. However, the speaker300may include the diaphragm111having no reinforcing rib.

Further, in the speaker300, a connection wall362may be provided inside a recessed portion of the box-shaped five face body201.FIG. 26is a diagram showing that the connection wall362is provided inside the recessed portion of the box-shaped five face body201in the vibration system350of the speaker300.FIG. 27is a cross-sectional view of the vibration system350shown inFIG. 26. For example, the connection wall362is shaped so as to connect three faces parallel to the long side direction, to each other, at the center of the box-shaped five face body201. Further, the connection wall362is preferably formed so as to have the height which is equivalent to the depth of the recessed portion of the box-shaped five face body201. The provision of the connection wall362enables increased enhancement of the rigidity of the diaphragm211. The speakers according to the other embodiments may similarly include the connection wall. However, the speaker300according to the third embodiment is formed such that the diaphragm211and the edge312are separately formed, and therefore the connection wall can be provided, in the production of the speaker300, with enhanced ease, as compared to in the speakers of the other embodiments. When the connection wall362is provided, the magnetic circuit needs to have a divided structure so as to prevent contact between the connection wall362and the magnetic circuit. An exemplary case in which the connection wall362described above is used for a speaker which is configured to emit a sound and voice from the reverse side as shown inFIG. 11will be described.FIG. 28is a perspective view of the lower portion of the magnetic circuit used in this exemplary case.FIG. 29is a cross-sectional view of the lower portion of the magnetic circuit shown inFIG. 28. As shown inFIG. 28andFIG. 29, a gap366is formed in the lower magnet117and the lower plate120so as to prevent contact with the connection wall362.

Fourth Embodiment

A speaker400according to a fourth embodiment has a distinguished feature that a damper for suppressing rolling of a diaphragm is provided, in addition to the features of the speakers100to300according to the first to the third embodiments, respectively. Difference from the speaker200according to the second embodiment will be mainly described below as an example. The components which are the same between the speaker200of the second embodiment and the speaker400of the fourth embodiment are denoted by the same corresponding reference numerals, and the description thereof is not basically given.

FIG. 30is a perspective view of the speaker400according to the fourth embodiment.FIG. 31is a plan view of a vibration system450of the speaker400shown inFIG. 30.FIG. 32is a diagram illustrating a cross section of the vibration system450shown inFIG. 31along B-B′. As shown inFIG. 30toFIG. 32, the speaker400includes dampers471, and one end of each damper471is attached to a corresponding one of both end portions of the upper face of the box-shaped five face body201of the diaphragm211in the long side direction. Each damper471is roll-shaped, and has an almost semicircular (arc-shaped) cross section, as shown inFIG. 32. The other end of each damper471is attached to a corresponding one of damper bases473provided on the upper frames113, as shown inFIG. 30. Each damper base473may be formed as an extended portion of a corresponding one of the upper frames113. As a material of the dampers471, a component formed by a fabric being impregnated with a phenolic resin and hardened, a polymer film, a thin sheet formed of, for example, a foamed rubber or a viscoelastic component, or the like is used.

As shown inFIG. 32, the diaphragm211is supported by the edge112and the dampers471so as to be able to vibrate in the Z direction. More specifically, the diaphragm211is supported by the dampers471on the both end portions of the upper face of the box-shaped five face body201in the long side direction, and is supported by the edge112on the outer periphery lower portion of the inverse-L-shaped flange103. Thus, the diaphragm211is spatially supported, so that the rolling of the diaphragm211can be effectively suppressed. As a result, in the speaker400according to the fourth embodiment, the diaphragm211vibrates only in the Z direction shown inFIG. 32, thereby realizing reproduction of a sound and voice with enhanced quality.

The shape of the dampers471is not limited to a rolled rectangular shape as shown inFIG. 30toFIG. 32. Each damper471may have, for example, a rolled sector shape as shown inFIG. 33. Further, for example, as shown inFIG. 34, the diaphragm211may be supported, by a plurality of the dampers471which are radially connected to each other, on each of both the end portions of the upper face of the box-shaped five face body201in the long side direction. The damper having a structure shown inFIG. 33orFIG. 34enables the rolling of the diaphragm211to be suppressed with enhanced effectiveness. Further, the rolling directions of the dampers471may be reversed as shown inFIG. 35which is a cross-sectional view of the vibration system450, and in this case, the same effect can be obtained (seeFIG. 32).

The speaker according to each embodiment described above is not only capable of outputting a high quality sound, but also is easily formed so as to become slim and to have its thickness reduced. Therefore, as shown inFIG. 36, the speaker can be effectively mounted to a thin-screen television (thin-screen television broadcast receiver). Similarly, the speaker can be effectively mounted to an electronic equipment such as a mobile telephone or a PDA.

The present invention is useful as a speaker or the like, and is particularly useful when a sound and voice needs to be reproduced with high quality by a slim-type speaker.