Patent Publication Number: US-8532327-B2

Title: Diaphragm and speaker device provided with the same

Description:
BACKGROUND 
     1. Field 
     The disclosure of the present application relates to a diaphragm and a speaker device provided with the same. 
     2. Description of Related Art 
     The conventional speaker device includes a drive system equipped mainly with a magnetic circuit and a voice coil, a diaphragm for vibrating air, and a support system for supporting the diaphragm. A cone-type speaker device (for the bass reproduction, full-range reproduction, etc.) and a dome-type speaker (for the treble reproduction) are known generally as a speaker device with the above-described configuration. 
     JP 2005-123779 A discloses a technique for improving fluctuations in a sound pressure frequency response, especially in a treble part, by providing thick parts having different thicknesses at several locations on a cone-type diaphragm. 
     JP 60 (1985)-47597 A discloses a technique of making a cone-type diaphragm gradually thinner from the center to the outer circumferential side for reducing the weight of the diaphragm. 
     Thus, the conventional speaker device is able to reproduce music with good sound quality by improving the diaphragm. 
     However, as described in Non-Patent Document 1 (“Speaker System” written by Takeo Yamamoto, Radio Technology, published in 1977), when vibrations having frequencies from the midrange (about 2 kHz) to the treble (about 20 kHz) are applied on a common diaphragm for a cone-type speaker device, separate vibrations sometimes occur, which worsens the quality of output sounds. Specifically, since the strength of the conventional diaphragm on the outer circumferential side is not sufficient, separate vibrations in a circumferential direction occur on the outer circumferential side when midrange signals are input. Further, since the strength of the conventional diaphragm on the inner circumferential side is not sufficient, separate vibrations in the circumferential direction occur on the inner circumferential side when treble signals are input. Moreover, in specific frequencies in the midrange and the treble, separate vibrations in a radiation direction sometimes occur. Because of these influences, in the conventional speaker device, there has been a problem that large peaks and dips occur in the sound pressure frequency response and fluctuations occur in sounds. Note here that “separate vibration” refers to the motion by which the diaphragm vibrates while bending. 
     Further, the thick parts of the diaphragm disclosed in JP 2005-123779 A have a uniform length, and parts other than the thick parts are made gradually thinner from the outer circumferential side to the inner circumferential side. With this configuration, although fluctuations in the sound pressure frequency response are reduced, the decrease in the strength of the diaphragm on the inner circumferential side reduces the sound pressure in the treble. Therefore, such a configuration is not suitable for enlarging a reproduction band in the treble. 
     SUMMARY 
     A diaphragm disclosed in the present application is a diaphragm provided with a plurality of thick portions radially from an inner circumferential side to an outer circumferential side, wherein the thick portions are composed of at least two kinds of thick portions having different lengths in a radiation direction and formed to be gradually thinner in the radiation direction from the inner circumferential side to the outer circumferential side. 
     A speaker device disclosed in the present application is a speaker device including: a magnet; a moving coil that is displaceable in a first direction based on an input current and magnetic flux generated by the magnet; and a diaphragm that is displaceable in the first direction together with the moving coil, wherein the diaphragm is provided with a plurality of thick portions radially from an inner circumferential side to an outer circumferential side, and the thick portions are composed of at least two kinds of thick portions having different lengths in a radiation direction and formed to be gradually thinner in the radiation direction from the inner circumferential side to the outer circumferential side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a speaker device according to the present embodiment. 
         FIG. 2  is a cross-sectional view of the speaker device according to the present embodiment. 
         FIG. 3  is a plan view showing an exemplary diaphragm according to the present embodiment. 
         FIG. 4  is a cross-sectional view of a long thick portion in the diaphragm. 
         FIG. 5  is a cross-sectional view of a short thick portion in the diaphragm. 
         FIG. 6  is a plan view showing a modification example of the diaphragm. 
         FIG. 7  is a plan view showing a modification example of the diaphragm. 
         FIG. 8  is a graph showing a frequency response of the speaker device according to the present embodiment. 
         FIG. 9  is a plan view showing an exemplary diaphragm according to the present embodiment. 
         FIG. 10  is a plan view showing a diaphragm of a conventional speaker device. 
         FIG. 11  is a graph showing a frequency response of the conventional speaker device. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     (Embodiment) 
     [1. Configuration of the Speaker Device] 
       FIG. 1  is a perspective view of a speaker device according to the present embodiment.  FIG. 2  is a cross-sectional view taken along a line Z-Z in  FIG. 1 . 
     A speaker device  100  is provided with a voice coil  101 , a diaphragm  102 , a dust cap  103 , an edge member  104 , a damper member  105 , a magnet  106 , a top plate  107 , a bottom plate  108  and a frame  109 . 
     The voice coil  101  is supported by the bottom plate  108  so as to be displaceable in a direction indicated by an arrow A or B. The voice coil  101  has a winding portion, which is arranged in a magnetic field of the magnet  106 . The diaphragm  102  is fixed to one end portion of the voice coil  101 . The voice coil  101  has a terminal  101   a . When a current (sound signal) is applied to the voice coil  101  from the outside through the terminal  101   a , an electromagnetic force is caused between magnetic flux generated by the voice coil  101  and the magnet  106 , thereby causing the voice coil  101  to be displaced in the direction indicated by the arrow A or B. When an alternating current is input to the terminal  101   a , the voice coil  101  is displaced (vibrates) back and forth in the directions indicated by the arrows A and B in accordance with the direction of the alternating current. 
     The diaphragm  102  is formed in a substantially cone shape. Since the diaphragm  102  is fixed to the voice coil  101 , the diaphragm  102  is displaced (vibrates) in the direction indicated by the arrow A or B in accordance with the displacement (vibration) of the voice coil  101 . The displacement (vibration) of the diaphragm  102  in the direction indicated by the arrow A or B vibrates the ambient air, whereby sound waves are emitted in the air. Although the material is not limited, the diaphragm  102  can be formed of a resin, pulp, metal, glass fiber, etc. In the present embodiment, the diaphragm  102  is formed of polypropylene mixed with mica. Although in the present embodiment the diaphragm  102  has a cone shape including a perfect circle, it may have a cone shape including an ellipse or a pyramid shape. Further, a dashed line C shown in  FIG. 2  is a centerline of the speaker device or the diaphragm  102 . In each member provided in the speaker device, the side close to the centerline C is defined as “inner circumferential side” and the side away from the centerline C is defined as “outer circumferential side”. For example, “inner circumferential side” of the diaphragm  102  includes an end portion on the side close to the centerline C and its vicinity, and “outer circumferential side” of the diaphragm  102  includes an end portion on the side away from the centerline C and its vicinity. 
     The dust cap  103  is a member formed in a part-spherical shape using a resin, metal, etc. The dust cap  103  is fixed on the inner circumferential side of the diaphragm  102  for stabilizing the vibration of the diaphragm  102 , and blocks an opening formed on the inner circumferential side of the diaphragm  102  for preventing the intrusion of foreign substances from the outside. Note here that the material and the shape of the dust cap  103  described herein are merely examples. 
     The edge member  104  is a member formed in a ring shape using a resin, etc. The inner circumferential side of the edge member  104  is fixed to the diaphragm  102  and the outer circumferential side thereof is fixed to the frame  109 . In order not to prevent the desired displacement (vibration) of the diaphragm  102 , the edge member  104  preferably is formed of a flexible material. The edge member  104  stabilizes the vibration of the diaphragm  102 . Note here that the material and the shape of the edge member  104  described herein are merely examples. 
     The damper member  105  is a member formed in a pleated disc shape using a resin, etc. The inner circumferential side of the damper member  105  is fixed to the voice coil  101  and the outer circumferential side thereof is fixed to the frame  109 . In order not to prevent the desired displacement (vibration) of the diaphragm  102 , the damper member  105  preferably is formed of a flexible material. The damper member  105  stabilizes the vibration of the diaphragm  102 . Note here that the material and the shape of the damper member  105  described herein are merely examples. 
     The magnet  106  is fixed to the bottom plate  108 . It is preferable to use a permanent magnet such as a ferrite magnet and a neodymium magnet as the magnet  106 . The magnet  106  is formed in a ring shape. A part of the voice coil  101  and a part of the bottom plate  108  are arranged in the opening on the inner circumferential side. 
     The top plate  107  is fixed to the magnet  106 . 
     The bottom plate  108  is arranged in the lowermost part of the speaker device  100 , and a columnar protrusion  108   a  formed in the center on the inner circumferential side supports the voice coil  101 . 
     The frame  109  fixes the diaphragm  102  and a drive system composed of the magnet  106 , top plate  107  and bottom plate  108 . 
     In the speaker device  100  shown in  FIGS. 1 and 2 , when an alternating current (sound signal) is input to the terminal  101   a , an electromagnetic force is caused based on the input alternating current and the magnetic flux generated by the magnet  106 , thereby causing the voice coil  101  to be displaced in the directions indicated by the arrows A and B. Since the diaphragm  102  is fixed to the voice coil  101 , the diaphragm  102  is displaced in the directions indicated by the arrows A and B in accordance with the displacement of the voice coil  101 . The displacement of the diaphragm  102  in the directions indicated by the arrows A and B vibrates the air around the diaphragm  102 , whereby sounds are emitted. In other words, by vibrating air, the diaphragm  102  emits sound waves in the air. 
     [2. Configuration of the Diaphragm  102 ] 
       FIG. 3  is a plan view of the diaphragm  102 .  FIG. 4  is a cross-sectional view taken along a line X-X in  FIG. 3 .  FIG. 5  is a cross-sectional view taken along a line Y-Y in  FIG. 3 . 
     The diaphragm  102  includes a thin portion  110 , long thick portions  111  and short thick portions  112 . 
     The thickness of the thin portion  110  is uniform. The thin portion  110  is provided mainly on the outer circumferential side of the diaphragm  102 . 
     As shown in  FIG. 3 , the long thick portions  111  are formed in a radiation direction (radially) from the centerline C of the diaphragm  102 . Although in the present embodiment four long thick portions  111  are provided at equal intervals, the number and the interval dimension are not limited to the configuration of the present embodiment. A length L 1  of the long thick portion  111  from the inner circumferential side to the outer circumferential side is longer than a length L 11  of the short thick portion  112  from the inner circumferential side to the outer circumferential side. As shown in  FIG. 4 , the long thick portion  111  is formed on a surface  102   a  of the diaphragm  102 . A thickness T 1  of the long thick portion  111  is made gradually thinner from the inner circumferential side to the outer circumferential side. The thickness of the long thick portion  111  on the outer circumferential side is the same as a thickness T 2  of the thin portion  110 . Note here that the length L 1  and the thickness T 1  of the long thick portion  111  can be determined arbitrarily depending on a desired frequency response and specifications of other members. 
     As shown in  FIG. 3 , the short thick portions  112  are formed in the radiation direction (radially) from the centerline C of the diaphragm  102 . Although in the present embodiment four short thick portions  112  are provided at equal intervals, the number and the interval dimension are not limited to the configuration of the present embodiment. As shown in  FIG. 5 , the short thick portion  112  is formed on the surface  102   a  of the diaphragm  102 . A thickness T 11  of the short thick portion  112  is made gradually thinner from the inner circumferential side to the outer circumferential side. The thickness of the short thick portion  112  on the outer circumferential side is the same as the thickness T 2  of the thin portion  110 . Note here that the length L 11  and the thickness T 11  of the short thick portion  112  can be determined arbitrarily depending on a desired frequency response and specifications of other members. 
     Note here that “gradually thinner” described in the present specification is not limited to the configuration in which the thickness of the diaphragm  102  is made continuously smaller from the inner circumferential side to the outer circumferential side as shown  FIG. 4 , and includes a configuration in which the thickness of the diaphragm  102  is made stepwise smaller from the inner circumferential side to the outer circumferential side (step-like configuration). 
     Further, in the present embodiment, the long thick portions  111  and the short thick portions  112  are formed on the surface  102   a  of the diaphragm  102 , but the same effect can be obtained even if they are formed on a back face  102   b  (back side of the surface  102   a ) of the diaphragm  102 . Further, the same effect can be obtained even if one of the long thick portion  111  and the short thick portion  112  is formed on the surface  102   a  of the diaphragm  102 , and the other is formed on the back face  102   b  of the diaphragm  102 . 
     Further, although in the present embodiment the long thick portions  111  and the short thick portions  112  respectively are formed at four locations, there is no limitation to the number as long as they are formed at least at one location. 
     Further, although in the present embodiment the number of each of the long thick portions  111  and the short thick portions  112  is an even number, it may be an odd number. For example, as shown in  FIG. 6 , two long thick portions  111  and one short thick portion  112  may be formed. Incidentally,  FIG. 6  is a plan view showing a modification example of the diaphragm  102 . 
     Further, in the present embodiment, the long thick portions  111  and the short thick portions  112  may be arranged symmetrically with respect to a line segment passing through the centerline C, or may be arranged asymmetrically. 
     Further, the long thick portion  111  and the short thick portion  112  can be set arbitrarily in accordance with the size or the material of the diaphragm  102 . For example, as shown in  FIG. 7 , the long thick portion  111  may be composed of a first long thick portion  111   a  and a second long thick portion  111   b  shorter than the first long thick portion  111   a . Incidentally,  FIG. 7  is a plan view showing a modification example of the diaphragm  102 . 
     Further, in the configuration shown in  FIG. 3 , the long thick portions  111  are extended close to an end portion of the diaphragm  102  on the outer circumferential side, but may be formed to reach the end portion. 
     Hereinafter, the motion of the diaphragm  102  in the present embodiment will be described. 
     The diaphragm  102  of the present embodiment is mechanically reinforced from the inner circumferential side to the outer circumferential side by having the long thick portions  111  from the inner circumferential side to the outer circumferential side. In other words, the long thick portions  111  enhance the strength of the diaphragm  102 . With this configuration, it is possible to reduce separate vibrations occurring on the outer circumferential side of the diaphragm  102 . 
     Further, the inner circumferential side of the diaphragm  102  is mechanically reinforced by having the short thick portions  112 . In other words, the short thick portions  112  enhance the strength of the diaphragm  102 . With this configuration, it is possible to reduce separate vibrations occurring on the inner circumferential side of the diaphragm  102 . 
     Further, since the long thick portions  111  and the short thick portions  112  of the diaphragm  102  are formed to be gradually thinner from the inner circumferential side to the outer circumferential side, the strength on the inner circumferential side and the strength on the outer circumferential side are different from each other. With this configuration, it is possible to reduce separate vibrations occurring in the radiation direction in the diaphragm  102 . 
     Since the diaphragm  102  of the present embodiment has the long thick portions  111  and the short thick portions  112  that are made gradually thinner from the inner circumferential side to the outer circumferential side, it is possible to reduce separate vibrations occurring on the outer circumferential side, the inner circumferential side and in the radiation direction. 
       FIG. 8  is a graph showing the frequency response of the speaker device  100  of the present embodiment.  FIG. 9  is a plan view of the diaphragm  102  in the speaker device  100  having the frequency response shown in  FIG. 8 . The diaphragm  102  shown in  FIG. 9  is formed of polypropylene mixed with mica. An outermost diameter R 1  of the diaphragm  102  shown in  FIG. 9  is set at 47.0 mm. A distance R 2  between the end portions of the opposed long thick portions  111  is set at 42.0 mm. A distance R 3  between the end portions of the opposed short thick portions  112  is set at 33.0 mm. A distance R 4  is set at 25.0 mm between opposed root portions between the long thick portion  111  and the short thick portion  112 . A width W 1  of a tip portion of the long thick portion  111  is set at 5.1 mm. A width W 2  of a root portion of the long thick portion  111  is set at 8.0 mm. A width W 3  of a tip portion of the short thick portion  112  is set at 5.1 mm. A width W 4  of a root portion of the short thick portion  112  is set at 8.0 mm. The thickness T 1  (see  FIG. 4 ), which is the thickest part in the long thick portion  111 , is set at 0.35 mm. The thickness T 11  (see  FIG. 5 ), which is the thickest part in the short thick portion  112 , is set at 0.35 mm. The thickness T 2  of the thin portion  110  (see  FIGS. 4 and 5 ) is set at 0.2 mm. Note here that the above-described dimensions are examples. 
     Meanwhile,  FIG. 10  is a plan view of a diaphragm  202  not provided with long thick portions and short thick portions. The diaphragm  202  is formed entirely of a thin portion  210  having a uniform thickness. An outermost diameter R 11  of the diaphragm  202  is set at 47.0 mm.  FIG. 11  is a graph showing the frequency response of a speaker device to which the diaphragm  202  shown in  FIG. 10  is mounted. 
     In the speaker device provided with the diaphragm  202  shown in  FIG. 10 , separate vibrations occur in the diaphragm  202  in the band between the midrange (about 2 kHz) and the treble (about 20 kHz) as shown in  FIG. 11 , whereby large peaks and dips occur. On the other hand, in the speaker device provided with the diaphragm  102  shown in  FIG. 9 , separate vibrations are reduced in the band between the midrange and the treble as shown in  FIG. 8 , whereby peaks and dips of the sound pressure are reduced. 
     In other words, since the diaphragm  102  of the present embodiment is provided with the long thick portions  111 , the strength of the diaphragm  102  on the outer circumferential side is improved, whereby separate vibrations occurring in the circumferential direction on the outer circumferential side can be reduced. Therefore, it is possible to improve the midrange frequency response. Further, since the diaphragm  102  of the present embodiment is provided with the short thick portions  112 , the strength of the diaphragm  102  on the inner circumferential side is improved, whereby separate vibrations occurring in the circumferential direction on the inner circumferential side can be reduced. Therefore, it is possible to improve the treble frequency response. Further, since the long thick portions  111  and the short thick portions  112  of the diaphragm  102  of the present embodiment are formed to be gradually thinner from the inner circumferential side to the outer circumferential side, separate vibrations occurring in the radiation direction of the diaphragm  102  can be reduced. Therefore, it is possible to improve the midrange and the treble frequency responses. 
     [3. Effects of Embodiment, Etc] 
     In the present embodiment, the strength of the diaphragm  102  is enhanced by providing the long thick portions  111  and the short thick portions  112  to the diaphragm  102 , whereby separate vibrations owing to the deformation of the diaphragm  102  can be reduced. Therefore, it is possible to stabilize the motion of the diaphragm  102  when generating sounds, which makes it possible to reduce fluctuations in the sound pressure of the speaker device. 
     Further, in the present embodiment, since the inner circumferential side of the diaphragm  102  is thicker than the outer circumferential side, the strength of the diaphragm  102  on the inner circumferential side is enhanced, whereby separate vibrations owing to the deformation of the diaphragm  102  on the inner circumferential side can be reduced. Therefore, it is possible to increase the sound pressure in the treble of the speaker device, which makes it possible to broaden the band on the treble side. 
     Further, in the present embodiment, since the diaphragm  102  is formed of a resin, the manufacture is easy using a molding method such as an injection molding. Therefore, the diaphragm  102  of the present embodiment is well-suited for mass production. 
     Further, in the long thick portion  111  and the short thick portion  112 , since the width of the tip portion is smaller than the width of the root portion, an area between the tip portion and the root portion functions as a draft at the time of removing the diaphragm  102  from a die. Therefore, it is possible easily to remove the diaphragm  102  immediately after the molding from a die. 
     In the diaphragm  102  of the present embodiment, although the width W 1  of the tip portion of the long thick portion  111  is smaller than the width W 2  of the root portion thereof as shown in  FIG. 9 , the width W 1  and the width W 2  may have the same dimension. Moreover, although the width W 3  of the tip portion of the short thick portion  112  is smaller than the width W 4  of the root portion thereof, the width W 3  and the width W 4  may have the same dimension. 
     Further, in the present embodiment, although the long thick portions  111  and the short thick portions  112  are formed on the surface  102   a  of the diaphragm  102 , the long thick portions  111  and the short thick portions  112  can be obscured by forming them on the back face  102   b . That is, when the diaphragm  102  is mounted to the speaker device  100 , the surface  102   a  is exposed to the outside. Therefore, forming the long thick portions  111  and the short thick portions  112  on the back face  102   b  is preferable for obscuring these thick portions. 
     Further, the present embodiment relates to a speaker device capable of reducing fluctuations in the sound pressure frequency response while broadening the reproduction band in the treble by providing a partially thick configuration to the diaphragm, and offers a speaker capable of reproducing sounds faithfully in accordance with input signals. Therefore, the speaker device of the present embodiment can be adapted not only to household audio devices, but also to a wide range of uses, such as in-car speakers, speakers for personal computers, professional-use speakers, etc. 
     The magnet  106  in the present embodiment is an example of the magnet. The voice coil  101  in the present embodiment is an example of the moving coil. The diaphragm  102  in the present embodiment is an example of the diaphragm. The long thick portion  111  and the short thick portion  112  in the present embodiment are examples of a plurality of thick portions. The long thick portion  111  is an example of the first thick portion. The short thick portion  112  is an example of the second thick portion. The displacement directions (directions indicated by the arrows A and B in  FIG. 2 ) of the voice coil  101  and the diaphragm  102  in the present embodiment are examples of the displacement directions (predetermined directions) of the moving coil and the diaphragm. 
     The disclosure of the present application is useful for a diaphragm and a speaker device. 
     The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.