Patent Publication Number: US-7899204-B2

Title: Speaker

Description:
This application is a U.S. National Phase Application of PCT International Application PCT/JP2005/009225. 
     TECHNICAL FIELD 
     The present invention relates to a speaker to be used for various electronic devices. 
     BACKGROUND OF THE INVENTION 
     An example of a conventional speaker is described in Japanese Patent Unexamined Publication No. H07-162992.  FIG. 11  is a cross-sectional view of a conventional speaker showing a construction of the speaker. 
     In  FIG. 11 , the conventional speaker includes lower plate  20 , magnet  21 , upper plate  22 , frame  24 , diaphragm  25 , edge  26 , voice coil  27 , dumper  28 , and dust cap  29 . Lower plate  20  is made of magnetic material, and pole  20   a  is formed at a center of lower plate  20 . Magnet  21  is formed in a ring shape. A magnet for a speaker application is generally made of a material of neodymium group or of ferrite group, as magnet  21 . Upper plate  22  is also formed in a ring shape and is made of magnetic material. Upper plate  22 , magnet  21  and lower plate  20  constitute magnetic circuit  23 . Magnetic gap  23   a  is formed in a ring shape between a peripheral wall of pole  20   a  of lower plate  20  and an inner peripheral wall of upper plate  22 . 
     Frame  24  is bonded with upper plate  22  at a center of frame  24 . Diaphragm  25  is bonded through edge  26  to a peripheral edge of frame  24  at a outer peripheral part of diaphragm  25 , and an inner peripheral part of the diaphragm  25  is bonded with voice coil  27  placed in magnetic gap  23   a  in a freely movable manner. 
     Damper  28  is bonded with voice coil  27  at an inner peripheral part of damper  28 , and an outer peripheral part of damper  28  is bonded with frame  24 , thus supporting voice coil  27 . Dust cap  29  is a dust-roofing cover attached to an upper center part of diaphragm  25 . 
     Thus constituted conventional speaker generates an up and down amplitude movements of voice coil  27  with a sound signal inputted from an outside source (not illustrated) converted to a mechanical signal by the Fleming&#39;s left-hand rule, vibrating diaphragm  25  bonded with voice coil  27  and reproducing a sound. 
     In recent years, various electronic devices require that speakers using for the electronic devices reproduce a higher-quality sound. In-car speakers are especially required a light in weight with the high-quality sound. For this reason, many proposals are made for improving magnetic circuit  23  and diaphragm  25 . 
     For example, diaphragm  25  is made lighter in weight by reducing a thickness of material or by using a material in a low density. However, diaphragm  25  which is made lighter in this way has lower modulus of elasticity, causing a split resonance of diaphragm  25 , or causing a resonance of edge  26  bonded with the outer peripheral part of diaphragm  25 .  FIG. 12  exemplarily shows graphical data indicating a frequency characteristic of a conventional speaker. A unit of a vertical axis, which indicates a sound pressure characteristic  111 , second-harmonic distortion characteristic  112  and third-harmonic distortion characteristic  113 , is in dB SPL (Sound Pressure Level). A unit of a vertical axis, which indicates impedance characteristic  114 , is in ohm. The characteristic of a sound pressure level versus frequency is sometimes called a SPL characteristic, hereinafter. 
     In order to control the split resonance, the inventors of this invention proposed a technique in Japanese Patent Application No. 2003-354832. The technical can control the split resonance of diaphragm  25 , however, it is difficult to control the resonance of edge  26 , so is hard to realize both of the requirement, light in weight and the high sound quality. 
     SUMMARY OF THE INVENTION 
     The present invention provides a speaker realizing both light in weight and high sound quality at one time. 
     The speaker of the present invention includes a magnetic circuit, a frame and a diaphragm. The magnetic circuit has a magnetic gap in a ring shape. The frame is bonded with the magnetic circuit at a central part of the frame. The diaphragm is bonded with a voice coil placed in the magnetic gap in a freely movable manner at a central part of the diaphragm, and the outer peripheral part of the diaphragm is bonded with a peripheral edge of the frame through an edge. An external shape of the edge bonded with the outer peripheral part of the diaphragm is formed in a perfect circle, and at least one of the outer peripheral part of the diaphragm and an inner peripheral part of the edge, which becomes a mutual bonding portion, is formed in a different shape than the perfect circle. 
     This constitution controls split resonance, thereby providing a speaker which realizes both the light in weight and high sound quality. 
     One other speaker according to the present invention includes a magnetic circuit, a frame and a diaphragm. The magnetic circuit has a magnetic gap in a ring shape. The frame is bonded with the magnetic circuit at a central part of the frame. The diaphragm is bonded with a voice coil placed in the magnetic gap in a freely movable manner at a central part of the diaphragm, and the outer peripheral part of the diaphragm is bonded with a peripheral edge of the frame through an edge. An internal shape and an external shape of the edge, and an external shape of the diaphragm are formed in a perfect circle respectively. The diaphragm and the edge can be overlaid with respective center shifted each other and are bonded together. 
     With this constitution, the split resonance is further controlled, thereby providing a speaker achieving both a light in weight and high sound quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a half sectional view for showing a structure of a speaker in accordance with a first exemplary embodiment of the present invention. 
         FIG. 2  is a plan view of a diaphragm to be used for the speaker, viewed from a rear side. 
         FIG. 3  is a characteristic diagram showing a frequency characteristic of the speaker. 
         FIG. 4  is a plan view of a diaphragm to be used for the speaker, viewed from a rear side. 
         FIG. 5  is a plan view of a diaphragm to be used for a speaker in accordance with a second exemplary embodiment of the present invention, viewed form a rear side. 
         FIG. 6  is a characteristic diagram showing a frequency characteristic of the speaker. 
         FIG. 7  is a characteristic diagram showing a frequency characteristic of the speaker. 
         FIG. 8  is a characteristic diagram showing a frequency characteristic of the speaker. 
         FIG. 9  is a characteristic diagram showing a frequency characteristic of the speaker. 
         FIG. 10  is a plan view of a diaphragm to be used for a speaker in accordance with a third exemplary embodiment of the present invention, viewed from a rear side. 
         FIG. 11  is a cross-sectional view showing a structure of a conventional speaker. 
         FIG. 12  is a characteristic diagram showing a frequency characteristic of the speaker. 
     
    
    
     REFERENCE MARKS IN THE DRAWING 
     
         
           1  yoke 
           2  magnet 
           3  top plate 
           4  magnetic circuit 
           4   a  magnetic gap 
           5  frame 
           6  voice coil 
           6   a  coil portion 
           7 ,  10 ,  11  diaphragm 
           7   a ,  10   a ,  11   a  diaphragm main body 
           7   b ,  10   b ,  11   b  edge 
           7   c ,  10   c ,  11   c  bonding portion 
           8  damper 
           9  dust cap 
           10   d  thick portion 
           10   e  quasi-thick portion 
           10   f  thin portion 
           31 ,  51 ,  61 ,  71 ,  81  sound pressure characteristic 
           32 ,  52 ,  62 ,  72 ,  82  second-harmonic distortion characteristic 
           33 ,  53 ,  63 ,  73 ,  83  third-harmonic characteristic 
           34 ,  54 ,  64 ,  74 ,  84  impedance characteristic 
       
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are explained hereinafter using the drawings. 
     First Exemplary Embodiment 
       FIG. 1  is a half sectional view for showing a structure of a speaker in accordance with the first exemplary embodiment of the present invention. The speaker as shown in  FIG. 1  includes yoke  1 , magnet  2 , top plate  3 , frame  5 , voice coil  6 , diaphragm  7 , damper  8  and dust cap  9 . Yoke  1  is made of magnetic material, with its bottom central portion protruded upward. Yoke  1  has an external wall in a cylindrical shape. Magnet  2  is in a disk shape and is generally made of a material of ferrite group or of neodymium group. Top plate  3  is made of magnetic material and formed in a disk shape. Yoke  1 , magnet  2  and top plate  3  are overlaid and bonded together, constituting magnetic circuit  4 . Magnetic gap  4   a  is formed in a ring shape between yoke  1  and top plate  3 , between an inner peripheral side of the cylindrical wall of the yoke  1  and an outer peripheral side of the top plate  3 . 
     Frame  5  is made of resin. Magnetic circuit  4  is attached to a center of frame  5 . More concretely, frame  5  is bonded with yoke  1  with an adhesive, otherwise yoke  1  can be press-fit to frame  5 . Yoke  1  can also be fit into frame  5  by an already known method such as outsert-molding. Voice coil  6  is placed in magnetic gap  4   a  in a freely movable manner where magnetic circuit  4  is formed with coil portion  6   a.    
     Diaphragm  7  is composed of diaphragm main body  7   a  in a cone shape and edge  7   b  in a ring shape, details of which are described later. Edge  7  is attached to an outer peripheral part of diaphragm main body  7   a . Damper  8  is attached to voice coil  6  at an inner peripheral part of damper  8 . Damper  8  is attached to frame  5  at an outer peripheral part of damper  8 . So damper  8  sustains voice coil  6 . Dust cap  9  is a dust-proofing cap attached to an upper center part of diaphragm  7 . 
       FIG. 2  is a plan view of diaphragm  7  of the speaker in accordance with the present exemplary embodiment, viewed from a rear side. In  FIG. 2 , edge  7   b  is attached to the outer peripheral part of diaphragm main body  7   a , with forming a ring shape. Edge  7   b  is formed in a substantially perfect circle both in the inner peripheral part and the outer peripheral part. The word of the perfect circle includes a substantially perfect circle, hereinafter. The other hand, the outer peripheral part of diaphragm main body  7   a  is formed in an oval shape. The outer peripheral part of diaphragm  7   a  formed in the oval shape and the inner peripheral part of edge  7   b  formed in the perfect circle are overlaid and bonded together at bonding portion  7   c , a hatched portion of the drawing. 
     By constituting diaphragm  7  as above, the shape of diaphragm  7  including edge  7   b  is formed partially asymmetric, making a specific frequency derived from a natural resonance of edge  7   b  to be different. Thus, by controlling the natural resonance of edge  7   b , a good characteristic of sound pressure level versus frequency can be obtained.  FIG. 3  is a characteristic diagram of the sound pressure vs. frequency of a 16 cm bore diameter speaker manufactured in accordance with the exemplary embodiment of the present invention. 
     In  FIG. 3 , a unit of the vertical axis, which indicates sound pressure characteristic  31 , second-harmonic distortion characteristic  32  and third-harmonic distortion characteristic  33 , is in dB SPL, and a unit of the vertical axis, which indicates impedance characteristic  34 , is in ohm. 
     According to  FIG. 3 , the speaker in accordance with the exemplary embodiment of the present invention, second-harmonic distortion derived from the natural resonance is reduced by about 7 dB than a conventional speaker, because the natural resonance of edge  7   b  is controlled. 
     In this exemplary embodiment, a case is explained that edge  7   b  is formed in a perfect circle both in the outer peripheral part and the inner peripheral part, that the outer peripheral part of diaphragm main body  7   a  is formed in an oval shape, and that the outer peripheral part of diaphragm  7   a  formed in the oval shape and the inner peripheral part of edge  7   b  formed in the perfect circle are overlaid and bonded together. However, the present invention is not limited to this case. As long as the outer peripheral part of edge  7   b  is formed in a perfect circle, one of the outer peripheral part of diaphragm main body  7   a  and the inner peripheral part of edge  7   b , which becomes the bonding part of the other, can be formed in a different shape than the perfect circle. 
     Further, as long as the shape is different from the perfect circle, the shape can be an even number polygonal shape or an odd number polygonal shape, as well as it can be an oval shape.  FIG. 4  is a plan view of diaphragm  7  of a speaker in accordance with the exemplary embodiment of the present invention, viewed from a rear side. An outer peripheral part of diaphragm main body  7   a  is formed in a perfect circle, then the outer peripheral part of diaphragm main body  7   a  formed in the perfect circle and an inner peripheral part of edge  7   b  formed in a pentagon shape are overlaid and bonded together. Because the natural resonance of edge  7   b  is caused at distorted frequencies of even number, much preferable shape of edge  7   b  is either an oval or an odd number polygon. 
     Second Exemplary Embodiment 
     A speaker in accordance with the second exemplary embodiment in the present invention is different from the first exemplary embodiment in a structure of the diaphragm. Structure other than the diaphragm is the same as that of the first exemplary embodiment, so the same numerical reference is given to an identical part and its detailed explanation is omitted. Below, only different parts are explained using the drawings. 
       FIG. 5  is a plan view of a diaphragm to be used for the exemplary embodiment of the present invention. In  FIG. 5 , diaphragm  10  is composed of diaphragm main body  10   a  in a cone shape and edge  10   b  in a ring shape. Edge  10   b  is bonded with an outer peripheral part of diaphragm main body  10   a . Edge  10   b  is formed in a perfect circle both in an outer peripheral part and an inner peripheral part thereof. The outer peripheral part of diaphragm main body  10   a  is formed in an oval shape. The outer peripheral part of diaphragm main body  10   a  formed in the oval shape and an inner peripheral part of edge  10   b  formed in the perfect circle are overlaid and bonded together at bonding portion  10   c . This structure is the same as the one in the first exemplary embodiment. 
     Diaphragm main body  10   a  includes thick portion  10   d , quasi-thick portion  10   e  and thin portion  10   f . Seven thick portions  10   d  are extended radially from a central part of diaphragm main body  10   a  with a substantially same angle between each other. Quasi-thick portion  10   e  is formed between radially extended thick portions  10   d  and its thickness is becoming thinner as it goes from outer peripheral part toward the center of diaphragm main body  10   a . Thin portion  10   f  is formed in substantially web-like shape toward an inner side of quasi-thick portion  10   e . Above described, diaphragm main body  10   a  is similar to the diaphragm which the inventors of this invention claimed for a patent in Japanese Patent Application No. 2003-354832. 
     For example, diaphragm main body  10   a  is made of polypropylene and is injection-molded into a bore diameter of 16 cm, average thickness of thick portion  10   d : t=0.25 mm, and average thickness of thin portion  10   f : t=0.15 mm. 
     With the speaker in accordance with the exemplary embodiment, diaphragm  10  is so constituted that new effects are added to the first exemplary embodiment. Namely, thick portion  10   d  disposed in odd number prevents a line-symmetric portion to be formed in diaphragm main body  10   a . Still more, quasi-thick portion  10   e  enforces bending rigidity of diaphragm main body  10   a  from the central part toward an outer direction, preventing a split resonance to be caused at a natural resonance mode. Split resonance which is caused along the peripheral part by the natural resonance mode is also prevented by quasi-thick portion  10   e . With these arrangements, the split resonance of diaphragm main body  10   a  and the natural resonance of edge  10   b  are controlled, providing the speaker with a good sound pressure vs. frequency characteristic. 
       FIG. 6  is a characteristic diagram showing a frequency characteristic of a 16 cm bore diameter speaker manufactured in accordance with the exemplary embodiment. In  FIG. 6 , a unit of the vertical axis, which indicates sound pressure characteristic  51 , second-harmonic distortion characteristic  52  and third-harmonic distortion characteristic  53 , is in dB SPL, and a unit of the vertical axis, which indicates impedance characteristic  54 , is in ohm. 
     According to data in  FIG. 6 , because of the effects of thick portion  10   d  and quasi-thick portion  10   e , deviation in SPL characteristic of the speaker is improved by 4 dB at a frequency band between 2 kHz and 10 kHz, from 10 dB of the conventional speaker to 6 dB of the speaker in accordance with the exemplary embodiment. By the similar effect of the first exemplary embodiment, natural resonance in edge  10   b  is controlled so a causing second-harmonic distortion is reduced by about 9 dB. 
     The natural resonance of edge  10   b  is controlled differently depending on how oval diaphragm main body  10   a  is formed. Actually, the difference in the control depends on how thick portion  10   d , quasi-thick portion  10   e  and thin portion  10   f  are disposed, when the outer peripheral part of diaphragm main body  10   a  formed in the oval shape and the inner peripheral part of edge  10   b  formed in a perfect circle are overlaid and bonded together. By utilizing the difference, sound characteristic can be arbitrarily controlled. Such difference is explained in  FIG. 7  to  FIG. 9 . 
       FIGS. 7 to 9  are characteristic diagrams showing a frequency characteristic of a speaker in accordance with the second exemplary embodiment of the present invention. They indicate SPL characteristics of a case in which the inner peripheral part of edge  10   b  formed into a perfect circle and the outer peripheral part of diaphragm main body  10   a  formed into an oval shape are bonded together.  FIG. 7  indicates a SPL characteristic of a speaker in which thick potion  10   d  is disposed along a longer diameter of the oval shape.  FIG. 8  indicates a SPL characteristic of a speaker in which a middle part of thick portion  10   d  and quasi-thick portion  10   e  is disposed along the longer diameter of the oval.  FIG. 9  indicates a SPL characteristic of a speaker in-between one of  FIG. 7  and one of  FIG. 8 . 
     Comparing the SPL characteristics in  FIG. 7  to  FIG. 9 , following facts can be identified. The speaker having the characteristic shown in  FIG. 7  in which thick portion  10   d  is disposed along the longer diameter in the oval shape can reduce most effectively the second-harmonic distortion derived from the natural resonance of edge  10   b , reproducing a sound clearly. 
     The speaker having the characteristic shown in  FIG. 8  in which the middle part of thick portion  10   d  and quasi-thick portion  10   e  is disposed along the longer diameter of the oval causes little larger second-harmonic distortion derived from the natural resonance of edge  10   b  as compared with  FIG. 7 . However, with the speaker, a frequency band where a sound pressure level falls down due to natural resonance of edge  10   b , so-called “a midrange valley”, can be narrowed. Consequently, bits fall of musical information can be most effectively minimized, enabling the speaker to reproduce the original sound in high fidelity. 
     In this exemplary embodiment, a case having seven thick portions  10   d  is explained. However, the invention is not limited to this case. As long as three or more odd-number thick portions  10   d  are disposed in substantially a same angle and a space, a similar effect can be obtained. 
     In the explanation of the exemplary embodiment of the invention, thick portion  10   d  and quasi-thick portion  10   e  are disposed at the rear side of diaphragm  10 . As in this arrangement, by not having an uneven front surface on diaphragm  10  of thick portion  10   d  and quasi-thick portion  10   e , phase disturbance of an acoustic wave caused by vibration of diaphragm  10  can be prevented. 
     Third Exemplary Embodiment 
     The speaker in accordance with the third exemplary embodiment is different from the speaker in the first exemplary embodiment in a structure of a diaphragm. Other structure is identical to that of the first exemplary embodiment, so that a same numerical reference is used for the identical part and detailed explanation of it is omitted. Below, only different parts are explained using the drawing. 
       FIG. 10  is a plan view of a diaphragm used for a speaker in accordance with the third exemplary embodiment, viewed from a rear side. In  FIG. 10 , diaphragm  11  is composed of diaphragm main body  11   a  in a cone shape and edge  11   b  formed in a ring shape. Edge  11   b  is attached to an outer peripheral part of diaphragm main body  11   a . Edge  11   b  is formed in a perfect circle both in an inner peripheral part and an outer peripheral part, which is the same as that of the first exemplary embodiment. 
     Diaphragm main body  11   a  is also shaped in a perfect circle shape in its outer peripheral part. The outer peripheral part of diaphragm main body  11   a  formed in the perfect circle and the inner peripheral part of edge  11   b  formed in the perfect circle are overlaid except for each center shifted from the other, and both are bonded together at bonding portion  11   c.    
     With the above structured speaker in accordance with the exemplary embodiment, the shape of the diaphragm including the edge becomes partially asymmetric, similar to the cases where the outer peripheral part of the diaphragm main body is formed into a shape other than the perfect circle in the first and the second exemplary embodiments. Thus, with the speaker in accordance with the exemplary embodiment, specific frequency derived from the natural resonance of the edge is made different. By controlling the natural resonance of the edge in this manner, a good sound pressure vs. frequency characteristic is obtained. With the speaker, the split resonance of the diaphragm can also be controlled similarly with the second exemplary embodiment, if thick portions and quasi-thick portions in odd-number are disposed onto the diaphragm, and if the thin-portions in the web-like shape are further added to the rear side of diaphragm main body  11   a.    
     INDUSTRIAL APPLICABILITY 
     The speaker according to the present invention can control a split resonance of a diaphragm main body and a natural resonance of an edge, therewith providing a good sound pressure versus frequency characteristic, namely a high sound quality. The speaker is useful for a variety of electronic devices including an audio instrument and an in-car acoustic device.