Abstract:
A piezo-electric speaker ensures a uniform sound in a broad band and can easily reproduce a signal of large amplitude or sound. A piezo-electric speaker has a piezo-electric member to generate a vibration according to an electric signal applied thereto. A piezo-electric vibration plate converts the vibration to a sound. The piezo-electric vibration plate is positioned closely to the piezo-electric member. The piezo-electric vibration plate is divided into parts of any configuration and is connected to the piezo-electric member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to Japanese Patent Application Nos. 2001-272907 filed Sep. 10, 2001 and 2002-215376 filed Jul. 24, 2002, which applications are herein expressly incorporated by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a piezo-electric speaker having a piezo-electric member. 
   BACKGROUND OF THE INVENTION 
   A piezo-electric speaker  40  of the prior art has, as shown in  FIG. 10 , has a completely round piezo-electric member  41  generating a vibration according to an electric signal applied thereto. A piezo-electric vibration plate  42  is adhered to the piezo-electric member  41  to convert the vibration to a sound. The piezo-electric member  41  and the piezo-electric vibration plate are adhered to each other with the centers of them being aligned. 
   However in the piezo-electric speaker  40  of the prior art, since the piezo-electric vibration plate  42  is made of a metallic plate-shaped member with less stretchability, no-vibrating portions are caused on the piezo-electric vibration plate  42  by a distortion such as creases generated during vibration. This makes it difficult to ensure a uniform sound in a broad band. 
   Since the diameter of the piezo-electric vibration plate  42  is limited, a large distortion of the piezo-electric vibration plate is caused when a signal of large sound is applied and therefore it is difficult to reproduce a clear sound. In addition, since the number of resonance point is limited, the sound pressure would be remarkably increased or reduced at particular frequencies corresponding to resonance points. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a piezo-electric speaker which can ensure a uniform sound in a broad band and can easily reproduce a signal of large amplitude or sound. 
   According to one preferred embodiment of the present invention, a piezo-electric speaker comprises a piezo-electric member for generating a vibration according to an electric signal applied thereto. A piezo-electric vibration plate converts the vibration to a sound while being closely contacted to the piezo-electric member. The piezo-electric vibration plate is divided into parts of any configuration and is connected to the piezo-electric member. 
   According to this embodiment, since the piezo-electric vibration plate is divided into parts of any configuration, the distortion cannot be easily caused when the vibration plate vibrates and thus it is possible to ensure a uniform sound in a broad band and to easily reproducing a signal of large amplitude or sound. 
   According to another preferred embodiment of the present invention, a piezo-electric speaker comprises a piezo-electric member for generating a vibration according to an electric signal applied thereto. A piezo-electric vibration plate converts the vibration to a sound while being closely contacted to the piezo-electric member. The piezo-electric vibration plate is divided into several parts by dividing slits that extend from a position near the center of the piezo-electric vibration plate to the periphery. 
   According to this embodiment, since the piezo-electric vibration plate is divided by dividing slits, the distortion cannot be easily caused when the vibration plate vibrates. The vibration can be efficiently propagated from the center of the piezo-electric member to the periphery. Thus it is possible to ensure a uniform sound in a broad band and to easily reproducing a signal of large amplitude or sound. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention will be described with reference to the accompanied drawings in which; 
       FIGS. 1(   a ) and ( b ) are, respectively, a front elevation view and a cross section view of one preferred embodiment of the piezo-electric speaker of the present invention; and  FIGS. 1  ( c )˜( f ) are front elevation views of other preferred embodiments of the piezo-electric speakers of the present invention; 
       FIGS. 2(   a )˜( d ) are front elevation views of preferred embodiments of oval piezo-electric speakers of the present invention; 
       FIGS. 3(   a )˜( f ) are front elevation views of preferred embodiments of the piezo-electric vibrating plates of the piezo-electric speakers of the present invention; 
       FIG. 4  is a front elevation view of a polygonal piezo-electric speaker of the present invention; 
       FIG. 5  is a front elevation view of a piezo-electric speaker having eccentric arcs of which radii gradually increasing of the present invention; 
       FIG. 6  is a front elevation view of another embodiment of the piezo-electric speaker having eccentric arcs of which radii gradually increasing of the present invention; 
       FIG. 7  is a graph showing the sound pressure characteristics: 
       FIG. 8  is a front elevation view showing a method for mounting the piezo-electric speaker; 
       FIG. 9(   a ) is an exploded view of a speaker having a reinforcing plate, and  FIG. 9(   b ) is a cross section view of the speaker of  FIG. 9(   a ); and 
       FIG. 10(   a ) is a front elevation view of a piezo-electric speaker of the prior art, and  FIG. 10(   b ) is a cross section view of the speaker of  FIG. 10(   a ). 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   A piezo-electric speaker  1  shown in  FIGS. 1˜8  is connected to audio instruments such as CD players or MD players generally used in homes for producing a sound. The piezo-electric speaker  1  comprises a piezo-electric member  5  and piezo-electric vibration plate  10  as shown in  FIGS. 1(   a ) and ( b ). The piezo-electric member  5  is formed as a disc of piezo-electric ceramic generating the mechanical distortion based upon the application of electric signals. The piezo-electric vibration plate  10  is a metallic disc having a larger area than that that of the piezo-electric member  5 . The piezo-electric vibration plate  10  is formed with dividing slits  10   a  radially extending from the periphery toward the center of the vibration plate  10 . In the embodiments in which both the piezo-electric member  5  and the piezo-electric vibration plate  10  are formed as complete circles, the vibration centers of them are positioned at the center of the circular configuration. 
   The piezo-electric member  5  is adhered to the piezo-electric vibration plate  10  at the center. Thus, the piezo-electric vibration plate  10  can convert the mechanical distortion of the piezo-electric member  5  to the acoustic vibration. The materials of the piezo-electric vibration plate  10  include iron, copper, brass, stainless steel (SUS), titanium etc. as a metallic family, carbon graphite etc. as a carbon family, polyimide etc. as a resin family, or compound materials in which boron etc. are vapor deposited on the surfaces of said materials, and any other materials being able to propagate the acoustic vibration. 
   In the piezo-electric speaker  1  shown in  FIG. 1(   a ), since the piezo-electric vibration plate  10  is divided by dividing slits  10   a  which extend from the center of vibration of the piezo-electric member  5  to the periphery of the vibration plate  10 , the distortion cannot be easily generated because it is absorbed by the dividing slits  10   a  when the vibration plate  10  is vibrated. In addition, since the vibration is efficiently propagated from the center of the piezo-electric member  5  to the periphery of the vibration plate  10 , it is possible to ensure a uniform sound pressure in a broad band. 
   The material of the piezo-electric member  5  is not limited to the piezo-electric ceramic and may be any material having a piezo-electric property such as a piezo-electric polymer membrane or piezo-electric composite material. The configuration of the piezo-electric member  5  and the piezo-electric vibration plate  10  is not limited to a circle and any other configuration may be adopted, which will be hereinafter described. The function and the material of the piezo-electric member and the piezo-electric vibration plate of embodiments hereinafter described are same as those of the piezo-electric member  5  and the piezo-electric vibration plate  10 . 
   A piezo-electric vibration plate  11  shown in  FIG. 1(   c ) is divided to eight parts equally separated along lines passing through its center and is adhered to the piezo-electric member  5  so that slits  11   a  are formed between two adjacent parts. In the piezo-electric speaker  1   a , since the piezo-electric vibration plate  11  is radially divided to several parts by dividing slits  11   a , which extend from the center of vibration toward the periphery of the vibration plate  11 , the distortion cannot be easily generated in the vibration plate  11  when it vibrates. Thus, it is possible to ensure a uniform sound pressure in a broad frequency band and to easily reproduce a large acoustic signal. 
   A piezo-electric speaker  1   b  shown in  FIG. 1(   d ) is substantially same as that of  FIG. 1(   a ) except that the dividing slits are formed by curved lines not straight lines. A piezo-electric speaker  1   c  shown in  FIG. 1(   e ) is substantially same as that of  FIG. 1(   a ) except that the dividing slits are formed by radially extending parabolas not straight lines. The speakers  1   b  and  1   c  of  FIG. 1(   d ) and ( e ) have functions and effects similar to those of the speaker  1  of  FIG. 1(   a ). 
   In a piezo-electric speaker  1   d  shown in  FIG. 1(   f ), a piezo-electric vibration plate  14  is divided into a plurality of parts each having any appropriate configuration which are adhered to the piezo-electric member  5  so that gaps  14   a  are formed therebetween. Since the vibration plate  14  is divided into parts, each having any appropriate configuration, the distortion cannot be easily generated in the vibration plate  14  when it vibrates. Thus, it is possible to ensure a uniform sound pressure in a broad frequency band and to easily reproduce a large acoustic signal. 
   In four piezo-electric speakers  2   a ˜ 2   d  shown in  FIG. 2 , both a piezo electric member  6  and piezo-electric vibration plate  15 ˜ 18  have an oval configuration. The piezo-electric member  6  of  FIG. 2(   a ) is positioned at a position slightly shifted toward the right from the center of the oval vibration plate  15  on the major axis thereof and adhered thereto. The piezo-electric vibration plate  15  is formed with a plurality of dividing slits  15   a  that extend toward the center of the piezo-electric member  6  (i.e. the center of vibration) from near the periphery of the piezo-electric member  6  to the periphery of the piezo-electric vibration plate  15 . 
   A piezo-electric speaker  2   b  shown in  FIG. 2(   b ) is similar to that shown in  FIG. 2(   a ). Accordingly, both a piezo electric member  6  and a piezo-electric vibration plate  16  have an oval configuration. However the piezo-electric member  6  of  FIG. 2(   b ) is positioned at a position slightly shifted toward the left from the center of the oval vibration plate  16  on the major axis thereof and adhered thereto. The piezo-electric vibration plate  16  is also formed with a plurality of dividing slits  16   a  that extend toward the center of the piezo-electric member  6  (i.e. the center of vibration) from near the periphery of the piezo-electric member  6  to the periphery of the piezo-electric vibration plate  16 . 
   A piezo-electric speaker  2   c  shown in  FIG. 2(   c ) is similar to that shown in  FIG. 2(   a ) except that dividing slits  17   a  are curved lines not straight lines. A piezo-electric speaker  2   d  shown in  FIG. 2(   d ) is also similar to that shown in  FIG. 2(   b ) except that dividing slits  18   a  are curved lines not straight lines. In the piezo-electric speakers  2   a ˜ 2   d  shown in  FIG. 2 , the peripheries of the piezo-electric vibration plate  15 ˜ 18  are eccentric relative to the center of vibration and thus the lengths of the vibration plates  15 ˜ 18  from the center of vibration to the peripheries thereof are not constant. Accordingly, these speakers  2   a ˜ 2   d  have many number of resonance points and thus it is possible to ensure a uniform sound pressure in a broad frequency band without causing remarkable increase or decrease of the sound pressure at particular frequencies. 
     FIG. 3  shows examples of six speakers  3   a ˜ 3   f  in which piezo-electric member  5 ,  7  and  8  have circular configurations and the peripheries of the piezo-electric vibration plate are curved. In a piezo-electric speaker  3   a  shown in  FIG. 3(   a ), the periphery of a piezo-electric vibration plate  21  is formed by several circular arcs of complete round and straight lines like a wind wheel arranged so that the pointed portions of several semi-circular pieces are directed to the outside. In a speaker  3   b  shown in  FIG. 3(   b ), the piezo-electric vibration plate is formed by four quadrants  22   a ˜ 22   d  of different radii connected to each other via curved connections. In a speaker  3   c  shown in  FIG. 3(   c ), the piezo-electric vibration plate  23  is formed by four oval pieces connected at their apexes to each other to form an “X” arrangement. In a speaker  3   d  shown in  FIG. 3(   d ), piezo-electric vibration plate is formed by several (five in the illustrated example) different oval pieces  24   a ˜ 24   e  arranged as a petal. In the examples of  FIGS. 3(   c ) and ( d ), either one of oval pieces may be changed to circular pieces. 
   A piezo-electric vibration plate  25  of a piezo-electric speaker  3   e  shown in  FIG. 3(   e ) is formed by four largest quadrants divided at a position shifted from the center of a circle. That is the periphery of the vibration plate  25  is formed by four circular arcs of complete round of the same radius. The four quadrants are connected to each other via dividing slits  25   a . A piezo-electric vibration plate  26  of the piezo-electric speaker  3   f  shown in  FIG. 3(   f ) is formed by two ovals connected to each other so that their major axes are aligned. 
   In any one of the piezo-electric speakers  3   a ˜ 3   f , since the distance from the center of vibration to the periphery of the vibration plate is not constant, they have a number of resonance points and thus it is possible to ensure a uniform sound pressure in a broad frequency band without causing remarkable increase or decrease of the sound pressure at particular frequencies, and also to ensure a uniform sound pressure in a broad frequency band. 
     FIG. 4  shows a piezo-electric speaker  20  in which both a piezo-electric member  9  and a piezo-electric vibration plate  27  are formed by polygons. Although a regular octagon is shown in the illustrated example, any other polygon may be used and any combination of the polygon and the circular arc (circular arc of complete round or eccentric circular arc) may also be used. Also in this speaker  20 , since the distance from the center of vibration to the periphery of the vibration plate is not constant, it has a number of resonance points and thus it is possible to ensure a uniform sound pressure in a broad frequency band without causing remarkable increase or decrease of the sound pressure at particular frequencies, and also to ensure a uniform sound pressure in a broad frequency band. 
   In the piezo-electric speaker  30   a  shown in  FIG. 5 , the periphery of the piezo-electric vibration plate is formed by radially dividing several parts  31   a ˜ 31   i  and an auxiliary movable region  31   j . The parts  31   a ˜ 31   i  are adhered to a piezo-electric member  35  and the radii of these parts  31   a ˜ 31   i  gradually increase from a shortest radius  31   n  to a longest radius  31   m . A predetermined depression angle is formed by a line connecting the outer ends of the longest radius  31   m  and the shortest radius  31   n . The auxiliary movable region  31   j  is defined by the longest radius  31   m , the shortest radii  31   n  and the line connecting the outer ends of these radius  31   m  and  31   n.    
   Since there is a large difference of radius between the parts  31   a  and  31   i  of the piezo-electric vibration plate, if no auxiliary movable region to smoothly connect the periphery is present between them, undesirable vibration or distortion would be generated during the vibration of the piezo-electric vibration plate. In the embodiment of the piezo-electric speaker  30   a  shown in  FIG. 5 , the periphery of the auxiliary movable region i.e. the part  31   j  is formed by a straight line and that of the speaker  30   b  shown in  FIG. 6  is formed by a curved line. 
   In the piezo-electric speakers  30   a  and  30   b , since the peripheries of the parts  31   a ˜ 31   j  and  32   a ˜ 32   j  gradually increase and the lines connecting, respectively, the outer ends of the longest radius  31   m  and  32   m  and the shortest radius  31   n  and  32   n  form the predetermined depression angle, it is possible to ensure a uniform sound pressure in a broad frequency band without causing remarkable increase or decrease of the sound pressure at particular frequencies, and also to ensure a uniform sound pressure in a broad frequency band. 
     FIG. 7  is a graph showing the sound pressure obtained by driving the piezo-electric speaker  30   b  shown in  FIG. 6 . The specifications of the speaker  30   b  are as follows. The piezoelectric member  36  is made of piezo-electric ceramics, the diameter is about 50 mm, and the thickness is about 0.18 mm. The piezo-electric vibration plates  32   a ˜ 32   j  are made of SUS, the longest radius  32   m  is about 60 mm from the center of the piezo-electric member  36 , and the shortest radius  32   n  is about 30 mm from the center of the piezo-electric member  36 . Although the piezo-electric speaker  30   b  is very large as compared with that of the prior art, the periphery of the piezo-electric vibration plates  32   a ˜ 32   i  are formed by the eccentric circular arcs in which the radii gradually increase and the line connecting the outer ends of the longest radius  31   m  and the shortest radius  31   n  forms the predetermined depression angle and the auxiliary movable region. Thus the distance from the center of vibration to the periphery of the vibration plate is not constant. Accordingly, the speaker has a number of resonance points and thus it is possible to ensure a uniform sound pressure in a broad frequency band without causing remarkable increase or decrease of the sound pressure at particular frequencies. 
     FIG. 8  shows a method for mounting the piezo-electric speaker  30   b  of  FIG. 6  to a speaker box means. Supporting plates  33   a ˜ 33   j  with vibration propagating ability, are respectively adhered to each of the divided piezo-electric vibration plates  32   a ˜ 32   j . These supporting plates  33   a ˜ 33   j  connect the piezo-electric vibration plates  32   a ˜ 32   j  to a suitable box means. The supporting plates  33   a ˜ 33   j  may be made of materials with a high elasticity and a high sound propagating velocity such as titanium, carbon graphite, beryllium etc. When the piezo-electric vibration plates  32   a ˜ 32   j  are supported on the box means, via the supporting plates  33   a ˜ 33   j , the vibrations of the piezo-electric vibration plates  32   a ˜ 32   j  can be independently propagated to the box means and thus it is possible to ensure a uniform sound pressure in a broad frequency band. 
   In the piezo-electric vibrating plate formed by the divided parts as shown in  FIGS. 1˜8 , for example, in the piezo-electric speaker  30   b  in  FIG. 6 , it is possible to use materials with a different modulus of elasticity in the respective piezo-electric vibration plates  32   a ˜ 32   j . In this specification, the modulus of elasticity means the modulus of longitudinal elasticity (Young&#39;s modulus). The higher the modulus of elasticity, the higher the propagatable frequency (resonance point). Of course, it is possible to ensure a uniform sound pressure in a broad frequency band by the piezo-electric speaker  30   b  using a material of same modulus of elasticity in the piezo-electric vibration plates  32   a ˜ 32   j . However it is possible to change the material of any part of the piezo-electric vibration plates having a radius influencing the reproducing of frequency to the other material having a different modulus of elasticity so as to adjust the part to obtain a further uniformed sound pressure. This makes it possible to further finely adjust the sound pressure due to the change of the resonance point of the piezo-electric vibration plates  32   a ˜ 32   j . In this case, the modulus of elasticity is appropriately selected in accordance with the change of the sound pressure. By forming the piezo-electric vibration plate with divided parts having different moduli of elasticity, it is possible to adjust the depression or projection of sound pressure at a particular frequency and thus to further easily ensure a uniform sound pressure in a broad frequency. 
   Since the piezo-electric member is very thin piezo-electric ceramics, cracks form in it due to the distortion of the piezo-electric vibration plate generated by application of a signal causing an enormous vibration. In such a case, it is possible to prevent the generation of cracks at the divided portions of the piezo-electric vibration plates by providing a reinforcing plate  39  as shown in  FIG. 9 . 
   More particularly as shown in  FIG. 9 , the reinforcing plate  39  has substantially the same configuration as that of a piezo-electric member  37  and is arranged between the piezo-electric member  37  and piezo-electric vibration plates  38   a ˜ 38   f  and adhered to them. The reinforcing plate  39  is formed of material with acoustic vibration propagating ability and rigidity sufficient to prevent the generation of cracks of the piezo-electric member  37  due to the vibration of the piezo-electric vibration plates. The reinforcing plate  39  may be formed of metal similar to the piezo-electric vibration plates  38   a ˜ 38   f , or formed of synthetic resin or carbon family material if they have necessary rigidity to prevent the generation of the cracks. The configuration of the reinforcing plate  39  is preferably the same as that of the piezo-electric member  37 , however, it may be larger than that of the latter. The provision of dividing slits  39   a  in the reinforcing plate  39  that extend along the dividing slits  38   g  makes it possible to reduce loss of vibration propagation and to ensure a uniform sound pressure in a broad frequency. 
   The present invention has been described with reference to the preferred embodiment. Obviously, modifications and alternations will occur to those of ordinary skill in the art upon reading and understanding the preceding detailed description. It is intended that the present invention be construed as including all such alternations and modifications insofar as they come within the scope of the appended claims or the equivalents thereof.