Patent Publication Number: US-2005129261-A1

Title: Electronic instrument

Description:
FIELD OF THE INVENTION  
      The present invention relates to piezoelectric sounding bodies (such as piezoelectric type speakers) functioning as acoustically transducing electronic parts of buzzers or speakers, and relates to an improvement of electronic instruments such as portable telephones utilizing such piezoelectric speakers.  
     BACKGROUND OF THE INVENTION  
      Acoustically transducing electronic parts used in portable telephones include a dynamic type making use of electromagnetic induction, and a piezoelectric type making use of piezoelectric phenomena. In the acoustically transducing electronic part of the dynamic type, as one embodiment shown in  FIG. 11A , a circular diaphragm  900  formed with a resin such as PET (polyethyleneterephthalate) is supported by a cylindrical coil  902  whose back side is a driving source and that inside is arranged with a magnet  904 . The magnet  904  is respectively furnished on opposite sides with yokes  906 ,  908  so as to form a magnetic path. The coil  902  is transverse with the magnetic path held between the yokes  906 ,  908 . The outside yoke  908  is supported in, for example, a metal case  910 , and the diaphragm  900  is put on a surface with a cover  914  having sound issuing holes  912 , with the cover  914  being secured to the case  910 . When the coil  902  is supplied with sound signals, the coil  902  vibrates vertically in response to the signals, this vibration is transmitted to the diaphragm  900 , so that an air-vibration occurs to output sounds from the sound issuing holes  912 .  
      The acoustically transducing electronic part of the piezoelectric type has, as one embodiment shown in  FIG. 11B , a diaphragm  920  with a piezoelectric element  922  attached on one side and supported on the circumference of the diaphragm  920  by a ring-shaped case  924 . The shown embodiment is an example of a bimorph type where the piezoelectric elements  922  are attached to the front and back sides of the diaphragm  920 . The case  924  is provided with a cover (not shown), if needed.  
      When the piezoelectric element  922  is supplied with a sound signal, the piezoelectric element  922  expands and contracts in a radial direction, and the diaphragm  920  bends, so that the air-vibration occurs to generate sounds. Since phases of the air-vibration occurring on the front and back sides of the diaphragm  920  are different by 180 degrees, either one of the front or back sides of the diaphragm  920  is sealed with the case  924  and the cover so as to form an acoustic space.  
      These acoustically transducing electronic parts are mounted within the casing of an electronic instrument. For example, such a structure is employed which attaches the acoustically transducing electronic parts on the inside of the casing of the portable telephone to issue sounds from holes formed in the casing.  FIG. 11C  shows one embodiment of mounting the piezoelectric sounding body  926  shown in  FIG. 11B  installed in the inside of the casing  930 . Then an appropriate cushioning material  932  is interposed between the case  924  of the piezoelectric sounding body  926  and the casing  930 , and those are adhered closely. The casing  930  is formed with the sound issuing hole(s)  934  from which the sounds are outputted outside. It is also possible to use a waveguide pipe and dispose the piezoelectric sounding body at a position separate from the sound issuing hole.  
      By the way, since the acoustically transducing electronic parts of the above mentioned dynamic type are complicated in structure and have a large number of parts including coils  902 , a certain thickness must be secured. Further, in a case of a narrow space, those parts are influenced by air viscosity, and therefore a certain capacity of the casing is necessary. But since the diaphragm  900  is driven by vertical movement of the coil  902  within magnetic flux, the diameter of the diaphragm  900  can be reduced. Vibrational energy owned by the diaphragm itself is small, and is not significantly influenced by vibration of the case  910  and the characteristics of the parts.  
      On the other hand, the acoustically transducing electronic parts of the piezoelectric type are simple in structure, less in number, and possible to be lightened. But since a stretching movement of the piezoelectric element  922  is converted into concave/convex curving movement of the diaphragm  920 , amplitude depends on the diameter of the diaphragm  920 . Accordingly, for increased sound pressure, the diameter of the diaphragm must be enlarged. In addition, the acoustically transducing electronic part of the piezoelectric type easily becomes irregular in frequency characteristics due to resonance phenomena, and is difficult to produce flat frequency characteristics. When mounted to a portable telephone, since the vibrational energy owned by the piezoelectric sounding body itself is large and conformity of mechanical impedance with the case is good, the vibration easily transmits to the case  924  when mounted, and proper vibration different from the vibration produced inherently by the piezoelectric sounding body occurs by the vibration of the case  924 .  
     SUMMARY OF THE INVENTION  
      The above and other features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is views showing a structure of an embodiment 1 of the invention;  
       FIG. 2  is a graph showing a characteristic of the sound pressure frequency of the embodiment 1;  
       FIG. 3  is a view showing the relationship between the structures and the characteristics in a plurality of samples using the piezoelectric sounding body;  
       FIG. 4  is a view showing the relationship between the structures and the characteristics in a plurality of the samples using an acoustic transducer of the dynamic type;  
       FIG. 5  is views of the cross sections and the plans of the samples when changing the contacting areas between the piezoelectric sounding body and the mass parts;  
       FIG. 6  is the graph showing the sound pressure frequency characteristics when changing the contacting areas between the piezoelectric sounding body and the mass part;  
       FIG. 7  is the graph showing the relationship between an air-chamber and the area of the piezoelectric sounding body;  
       FIG. 8  is a major cross sectional view showing the structure of the embodiment 2 of the invention;  
       FIG. 9  is major views showing the structures of the embodiment 3 of the invention;  
       FIG. 10  is the major views showing the structures of the embodiment 3 of the invention; and  
       FIG. 11  is the views showing the structures of the piezoelectric sounding body and the attaching structures in the conventional electronic instruments. 
    
    
     DETAILED DESCRIPTION AND MOST PREFERRED EMBODIMENTS  
      The present invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, substantial numbers of the herein shown and described embodiments have been made, tested and used, and all have performed in an eminently satisfactory manner.  
     (1) Embodiment 1  
      At first, referring to FIGS.  1  to  7 , the embodiment 1 of the invention will be explained.  FIG. 1A  shows the whole structure of the embodiment 1, and a cross section seen in a direction of arrows along #1-#1 of  FIG. 1A  is shown in  FIG. 1B . Enlarged vibrating parts of  FIG. 1B  are shown in  FIG. 1C .  
      In these views, as to the electronic instrument  10 , various electronic parts are housed in the casing  12 , and a mass part (mass body)  14  among the parts is shown. The mass part  14  may, for example, comprise such parts having comparatively large mass, for example, a liquid crystal display of the portable telephone or a battery box holding a charging battery. It may be an assembly of several parts. The piezoelectric sounding body  20  is mounted at a back side of the mass part  14  (the inside of the casing  12  of the mass part  14 ) via a ring shaped cushioning material or a spacer  16 . Specifically, the piezoelectric sounding body  20  may be closely adhered to the mass part  14  with the cushioning material  16  of thickness being 0.4 mm and an inner diameter being 20 mm provided with adhesive layers on both main faces. As shown  FIG. 1B , the piezoelectric sounding body  20  may only partially overlap the mass part  14 , and a part not overlapping with the mass part  14  is provided with a partition  18  of 2.5 mm in height. The thickness of the cushioning material  16  is preferably 0.1 to 1.0 mm, and the height of the partition  18  is set by deducting the thickness of the wall of the casing  12  from the thickness of the mass part  15 , preferably 1.0 to 5.0 mm.  
      As shown in  FIG. 1C , the piezoelectric elements  24 ,  26  are attached on the front and back sides of the circular diaphragm  22  formed with a metallic material such as a phosphor bronze or 42-alloy, or a resin material such as polyethylene-terephthalate (PET). In one embodiment, the diameter of the diaphragm made of the phosphor bronze is 23 mm and the thickness is 30 μm. The piezoelectric element  24  is structured in that electrodes  24 B,  24 C such as of Ni, Pd, or Ag are formed on the front and back sides of the piezoelectric sheet  24 A of the piezoelectric ceramics such as lead titanate zirconate (PZT). The piezoelectric element  26  is similarly structured in that the electrodes  26 B,  26 C are formed on the front and back sides of the piezoelectric sheet  26 A of the piezoelectric ceramics such as PZT. The diaphragm  22  may serve as the electrodes  24 C,  26 C. The diaphragm  22  is secured by a silicone-type adhesive at its circumference in the center in height of a ring-shaped case  27  of the 0.7 mm height having an inner shoulder. For the case  27 , a metallic material such as a stainless steel, or a resin material such as polyethyleneterephthalate (PET) or acrylonitrile butadiene styrene (ABS) may be used. The illustrated embodiment is a bimorph type, and there is also a unimorph type having only one of the piezoelectric elements  24 ,  26 .  
      Basic movements of such a structured piezoelectric sounding body  20  are similar to those of the above mentioned conventional techniques. When the piezoelectric elements  24 ,  26  are applied with sound signals, one of the piezoelectric elements  24 ,  25  extends in the radial direction and the other shrinks in the same direction, so that the diaphragm  22  is bent to vibrate the air and issue the sound.  
      Returning to  FIGS. 1A  and B, a main air-chamber  29  is air tightly-formed with the above mentioned mass part  14 , piezoelectric sounding body  20 , and partition  18 , and a sound issuing hole  28  is formed in the casing  12  within the main air-chamber  29 . Specifically, the capacity of the space defined at the inside of the inner diameter of the ring shaped cushioning material  16  is 126 mm 3 , the capacity of interior space surrounded by the partition  18  and the mass part  14  is 192 mm 3 , and the capacity of the main air-chamber at this time is 318 mm 3 . As mentioned above, the sound is issued by bending of the diaphragm  22 , and the issued sound is outputted in the direction of the front and back sides (up and down in  FIG. 1B ) of the piezoelectric sounding body  20 . The sounds outputted into the main air-chamber  29  from the outside (the side of the piezoelectric element  24 ) are outputted outside of the casing  12  from the sound issuing hole  28 . The sounds outputted into a sub air-chamber  30  inside of the casing  12  from the backside (the side of the piezoelectric element  26 ) of the piezoelectric sounding body  20  remain within the casing  12 . This prevents the mixing of both of the sounds since the phases of the air vibration occurring at the inside and outside of the diaphragm  22  are different 180 degrees. Electronic components or other parts may be present in the main air-chamber  29  or the sub air-chamber  30 .  
      In this embodiment, the piezoelectric sounding body  20  is mounted at the back edge of the mass part  14  within the casing  12  of the electronic instrument  10 . Therefore, in comparison with the prior art of mounting the piezoelectric sounding body  20  in the casing  12  (which is thinner than the mass part  14 ), vibration generated from the piezoelectric sounding body  20  interferes with the mass part  14 , so that transmission of vibration to the casing  12  is restrained, and since the space between the front and back sides of the piezoelectric sounding body  20  is served as the air-chamber, the sound pressure characteristic is made flat. In the present invention, the thickness of the casing  12  is meant the thickness (t b ) of the wall of the casing, while the thickness of the mass part  14  is meant the total thickness (t a ) of the material under the sounding body  20 . The piezoelectric speaker is meant the sounding body which uses the piezoelectric element. Embodiments of the invention have a wide frequency band and flat frequency-sound pressure characteristic in the frequency band of 1 to 3 KHz, and is used in a free sound field.  
       FIG. 2  shows a measured sound pressure frequency characteristics. In  FIG. 2 , the graph GA is the characteristic of the present embodiment, and the graph GB is the characteristic of the above mentioned prior art. A vertical axis is the sound pressure (dB), and a lateral axis is the frequency (Hz). As is apparent by comparing graphs GA and GB, the graph GA shows better flatness in the frequency range from 1 to 10 kHz. The graph GA shows that the sound pressure varies in the range of 80 to 98 dB, while the graph GB shows that the sound pressure varies in the range of 80 to 105 dB, and irregularities of the characteristics are large.  
      If the resonance frequency of vibration associated with the mass part  14  is out of the audio-frequency range (ordinarily, around 300 to 4000 Hz), influences to the sound by the vibration of the mass part  14  is reduced. Assuming that the mass of the mass part  14  is M a , the area (the whole area of the face with which the piezoelectric sounding body  20  overlaps) is S, and the thickness is t a , the resonance frequency f o  owned by the mass part  14  is expressed with 
 
 f   o α{square root}( S/ma )={square root}(( t   a   2   ·E )/( S   2 ·ρ))=( t   a   /S )·{square root}( E/ρ )   (1) 
 
 Herein, E is the Young&#39;s modulus of the mass part  14 , ρ is the density of the mass part  14 , M a =S·t a ·ρ. “{square root}(S/ma)” expresses “(S/ma) 1/2 ”. To make the resonance frequency f o  larger than the audio-frequency range, it is sufficient to make the thickness t a  of the mass part  14  large or make the area S small. 
 
      Furthermore, if the frequency of the sound outputted from the piezoelectric sounding body  20  is low, since the vibrating amplitude of the mass part  14  is in inverse proportion to its stiffness S f , the amplitude is 
 
Amplitudeα1/ S   f   =S /( t   a   3   ·E )   (2) 
 
 When the frequency of the sound is high, since the vibrating amplitude of the mass part  14  is in inverse proportion to its mass M a , 
 
Amplitudeα1/ M   a =1/( S·t   a ·ρ)   (3) 
 
 Accordingly, in either case, by making the thickness t a  of the mass part  14  large, which will mean the mass M a  of the mass part will also be large, it is possible to restrain the amplitude. By the way, from the above mentioned formula (2), 
 
 S   f =( t   a   3   ·E )/ S    (4) 
 
      Taking the above mentioned points into consideration, the following conclusions can be made:  
      1) Desirably, the thickness t a  of the mass part  14  is large, but it is good that the thickness t b  of the casing  12  is small (on a premise of having a desired strength) from the viewpoint of making the electronic instrument  10  light in weight. Accordingly, the relation between the thickness t a  of the mass part  14  and the thickness t b  of the casing  12  is desirably t a &gt;t b . For example, assuming that a lithium ion (Li-Ion) battery is the mass part  14  and a casing of the portable telephone is the casing  12 , if the thickness t a  of the lithium ion battery is 6 mm and the thickness t b  of the wall of the casing  12  is 1 mm, it is possible to obtain a good sound pressure characteristic while restraining the vibration of the casing  12  by mounting the piezoelectric sounding body  20  on the lithium ion battery.  
      2) It is good that the mass M a  of the mass part  14  is large, but it is good that the mass M c  of the piezoelectric sounding body  20  is small from the viewpoint of making the electronic instrument  10  light in weight. Accordingly, the mass M a  of the mass part  14  and the mass M c  of the piezoelectric sounding body  20  is desirably M a &gt;M c . For example, assuming that the piezoelectric sounding body mounted on the portable telephone is 0.6 g and the lithium ion battery is 18 g, it is possible to obtain a good sound pressure characteristic while restraining the vibration of the casing  12  by mounting the piezoelectric sounding body  20  on the lithium ion battery.  
      Next, referring to  FIG. 3 , as to the samples made by way of trial, the characteristics will be compared. In  FIG. 3 , the sample A is an example of directly attaching the piezoelectric sounding body  20  on the mass part  14 , in which the cushioning materials  32  are held between the piezoelectric sounding body  20  and the casing  12  of the electronic instrument. The sample B is an example of attaching the cushioning materials  16  between the piezoelectric sounding body  20  of the sample A and the mass part  14 . The sample C is an example of arranging the piezoelectric sounding body  20  and the mass part  14  such that they partially overlap, and at the same time the backside of the piezoelectric sounding body  20  contacts the casing  12 . The sample D is the present embodiment. The sample E is an example of attaching the piezoelectric sounding body  20  to the casing  12  via the cushioning materials  34 , and corresponds to the above mentioned prior art.  
      Measuring the scales and the characteristics of the electronic instruments of these samples A to E, the results shown in  FIG. 3  have been obtained. At first, comparing from the viewpoint of the thicknesses and the areas, in the samples A, B, the thicknesses are fairly large. The samples A, B do not meet the requirements of making the recent electronic instrument thin such as the portable telephone while maintaining good audio characteristics. On the other hand, in the sample E, although the thickness is small, the area is large, and the vibration restraining effect of the invention cannot be brought about. Thus, from the viewpoints of the thickness and the area, the sample C or D is suitable. Comparing from the viewpoints of regenerative frequency zones and the sound pressure, in the samples B and D, the regenerative zones are wide as 1 to 4 kHz, and the sound pressure is high as 90 dB. Therefore, putting the above points together, it is seen that the structure as the sample D of the present embodiment is good, because of the smallest and thinnest type and the good characteristics, where (in the sample D) the piezoelectric sounding body  20  is disposed as overlapping with the mass part  14 , and the sound is outputted in the direction of the mass part  14 . In the sample D, since the mass part has the back area to a certain extent, this is useful to the piezoelectric acoustically transducing electronic part necessitating the diameter of the diaphragm of the piezoelectric sounding body.  
      In these mounting methods, the capacity of the casing for mounting the piezoelectric acoustically transducing electronic parts is made narrow so as to increase viscous resistance of the air, so that resonance can be restrained, and the methods can contribute to making the electronic instrument thin.  
      Next, for reference, comparing the same characteristics as to the samples P to T attaching the acoustic transducer  36  of the dynamic type instead of the piezoelectric sounding body  20 , the results are as in  FIG. 4 . The results of  FIG. 4  are compared with those of  FIG. 3 . Although the regenerative frequency zone and the sound pressure are almost the same, the thicknesses of the dynamic type of  FIG. 4  is generally larger. This is because the thickness of the acoustic transducer itself of the dynamic type reaches, for example, around 3.2 mm. Even if the acoustic transducer  36  is mounted on the mass part  14  as the sample S, the thickness of the casing  12  is quite large. Also the structure of the sample T requires a very large area.  
      Comparing merits and demerits in case of using the piezoelectric sounding body and using the acoustic transducer of the dynamic type, the results are as in Table 1.  
                           TABLE 1                                      Mass Parts Present   Mass Parts Absent                                                     Characteristics       Capacity       Characteristics       Capacity               of sound   Vibration   of   Area of   of sound   Vibration   of   Area of       Systems   pressure   of casing   casing   casing   pressure   of casing   casing   casing               Dynamic   No influences   No   Large   Necessary   No influences   No   Large   Necessary       type       influences               influences       Piezoelectric   No influences   No   Small   No   Irregularities   Influences   Small   Large       type       influences       influences                  
 
      As shown in Table 1, when mounting the piezoelectric sounding body on the mass part of the casing, it is possible to produce a small-sized and thin electronic instrument with excellent sound pressure characteristics as compared to the acoustic transducer of the dynamic type.  
      A next consideration will be made to the overlapping condition of the piezoelectric sounding body  20  and the mass part  14 , that is, the proportion of the contacting area between the piezoelectric sounding body  20  and the mass part  14  (directly or via the cushioning material).  FIGS. 5A  to  5 D respectively show the conditions in cross section and plan when changing the proportion of the contacting areas. In  FIG. 5A , the proportion of the area of contact between the piezoelectric sounding body  20  and the mass part  14  is 98%, almost overlapping. The area of contact in  FIG. 5B  is 50%, that of  FIG. 5C  is 30%, and that of  FIG. 5D  is 10%. Each of the figures shows no cushioning material, although such material may be utilized as shown in  FIG. 1 .  
      Measuring the sound pressure frequency characteristics as to the samples of the respective embodiments, the results are as shown in  FIG. 6 . The vertical axis of  FIG. 6  is the sound pressure (dB), and the lateral axis is the frequency (Hz). The graphs GE to GH correspond to the rates of 98%, 50%, 30%, and 10% of the above mentioned contacting areas. As shown in the graphs of  FIG. 6 , the graph GE being 98% of the area of contact and the graph GF being 50% of the area of contact show the good flatness. The graph GG being 30% of the area of contact certainly shows the flattening effect of the sound pressure characteristic, but irregularities are more prominent than those of the graphs GE or GF. Further, the graph GH in which the area of contact is 10% is similar to the graph GB of the prior art scarcely shows the flattening effect. Considering these measuring results, when the rate of the area of contact between the piezoelectric sounding body  20  and the mass part  14  based on the whole contacting area between the part of the piezoelectric sounding body  20  attaching directly or via the cushioning material is 30% or more, the flattening effect of the sound pressure characteristic is recognized, and when it is more than 50%, good flattening characteristic are available.  
      Referring to  FIG. 7 , the relation between the area of the piezoelectric sounding body  20  and the capacity (volume) of the sub air-chamber  30  is considered. When the capacity of the back of the piezoelectric sounding body  20 , that is, the capacity of the sub air-chamber  30  is constant or less, the air in the air chamber becomes viscosity resistant, giving influences to vibration of the diaphragm  22  so that the vibration is restrained. The degree of influence is different in dependence on the size (area) of the diaphragm  22 , and the larger is the area, the easier to receive the influences of the capacity of the air chamber (the limited capacity is large).  FIG. 7  shows the relation between the area of the diaphragm  22  of the piezoelectric sounding body  20  and the capacity of the sub air-chamber  30 . The graph GJ shows changing of the influenced area (the capacity where the sound pressure characteristic decreases under 3 dB), while the graph GK shows the allowed area (the capacity where changing of the sound pressure characteristic is under 1 dB). As shown in these graphs, the larger the area of the diaphragm  22  is, the more the influenced area and the allowed area increase. Therefore, the scale of the capacity of the sub air-chamber  30  may be determined from this information. Incidentally, since the piezoelectric sounding body  20  can be adjusted in the characteristics by the sound issuing hole  28  at the front face, the sound pressure characteristics are the same even if the capacity of the sub air-chamber  30  is infinite, as far as being more than the allowed capacity,.  
     (2) Embodiment 2  
      In reference to  FIG. 8 , the embodiment 2 of the invention will be explained. The electronic instrument  50  of this embodiment is similar to the embodiment 1 in that the piezoelectric sounding body  20  is positioned on the back of the mass part  14  and mounted, but different in that the sound issuing hole  58  is formed on the front and back sides of the casing  12 . In this embodiment, at the backside of the piezoelectric sounding body  20 , a curved partition  52  is provided between the piezoelectric sounding body  20  and the casing  12 , and the interior space of this partition  52  continues to the surface of the piezoelectric sounding body  20 . Further, at the other end of the piezoelectric sounding body, a sub air-chamber  54  is defined, and the sub air-chamber  54  and the main air-chamber  56  are divided by the partition  52 . The main air-chamber  56  communicates with the front and back sides of the casing  12 , each provided with the respective sound issuing holes  58 .  
      If the respective sound issuing holes  58  are provided in the front and back sides of the piezoelectric sounding body  20  for issuing the sound, since the sounds from the surface and from the rear side are at anti-phase, a canceling effect occurs, and the sound pressure goes down. But, the present embodiment can make the most of the area and the thickness of the mounted casing  12  as the above mentioned embodiment, and the sounds of the inside and outside of the casing  12  are at equi-phase, and the sound pressure is not reduced due to the anti-phase.  
     (3) Embodiment 3  
      In reference to  FIGS. 9 and 10 , an embodiment 3 of the invention will be explained. The embodiment shown in  FIG. 9A  is in some ways similar to the above mentioned embodiment 1, comprising the piezoelectric sounding body  20 , the cushioning material  16  and partition  18 . The example shown in  FIG. 9B  unifies the partition  18 A and the mass part  14  as one body. The example shown in  FIG. 9C  unifies the cushioning material and the partition  18 B as one body.  FIG. 9D  installs the piezoelectric sounding bodies  20 L,  20 R at left and right ends of the mass part  14  respectively via the cushioning materials  16 L,  16 R and the partitions  18 L,  18 R, for example, so as to reproduce the sounds of 2 channels such as a stereo. The example shown in  FIG. 9E  installs the piezoelectric sounding body  20  at the corner of the mass part  14  via the cushioning material  16  and the partition  18 C. The example shown in  FIG. 9F  provides in advance a cutout  14 B for the piezoelectric sounding body in the mass part  14 A so as to house the piezoelectric sounding body  20  and the cushioning material  16  there.  
      The example shown in  FIG. 10A  makes use of a plate frame  60  having a circular projection at the end thereof. The plate frame may be made of ABS or acrylic. The circular projection of the plate frame  60  has an opening  62  for receiving and supporting the diaphragm  22  having the piezoelectric element  24  (or the piezoelectric elements  24  and  26 ). Then, the plate frame  60  is closely adhered and secured on the upper face of the mass part  14  via an adhesive material such as double-coated tape, and the partition  18  is installed as in the above mentioned embodiment for defining the main air-chamber. By closely adhering the plate frame  60  to the mass part  14 , the mass and the thickness of the mass part  14  substantially increase, so that a further improvement may be expected in restraining vibration of the casing, or flattening the sound pressure characteristic. It is also sufficient to provide a difference  64  in level in the inside of the opening  62  so as to support the diaphragm  22  by this difference  64  in level. This embodiment may be assumed as extending the case  27  of the above mentioned piezoelectric sounding body  20  to be plate shape.  
      The example shown in  FIG. 10B  uses a printed wiring substrate  70  of such as a glass epoxy as the plate frame  60  of  FIG. 10A . The printed wiring substrate  70  is mounted on one side with electronic parts  72  as a resistor, capacitor, coil, or semi-conductor, with which various kinds of electronic circuits are formed as the piezoelectric sounding body driving circuits such as a boosting circuit or an amplifying circuit. On the other side of the printed wiring substrate  70 , the electronic parts  74  are mounted. The opening  62  is formed at an end of the printed wiring substrate  70 . The present embodiment secures the printed wiring substrate  70  to the mass part  14 , such that the end part provided with the electronic parts of the printed wiring substrate  70  projects beyond the edge of the mass part  14 , that is, the position shown with a dotted line is in line with the end of the mass part  14 . According to this embodiment, the substantial mass and thickness of the mass part  14  increase by mounting the electronic parts  72 ,  74 , and the further improvement may be expected.  
      The example shown in  FIG. 10C  provides a conductive electrode  82  in a thin printed wiring substrate  80  as a flexible substrate and directly adheres the piezoelectric element  24 . In the present embodiment, the printed wiring substrate  80  works as the diaphragm. Such a printed wiring substrate  80  is closely fixed to the upper face of the mass part  14 , interposing a spacer  84  formed by an elastic substance in the piezoelectric element  24 . Further, the partition plate  18  is provided for defining the main air-chamber. Also in this embodiment, the printed wiring substrate  80  is secured to the mass part  14  such that the position shown with the dotted line is in line with the end of the mass part  14 . According to this example, since the printed wiring substrate  80  is thin, the improvement is not so much effected as the above embodiment as to the thickness of the mass part  14 , but the structure of the piezoelectric sounding body is simplified and formed as one of the electronic parts on the flexible substrate, and an advantage is brought about as simplifying the mounting.  
      The present invention includes many embodiments, and various modifications are available on the basis of the above mentioned disclosure. For example, the followings may be included. P 1) The materials, shapes or dimensions shown in the above embodiments are only examples, and designs may be modified to exhibit similar characteristics. The structure of the piezoelectric sounding body may be either of unimorph and bimorph. The acoustic element itself has a structure alternately laminated with a piezoelectric layer and an electrode layer, and the number of laminated layers, the connecting pattern of the internal electrode, or the drawer structure may be appropriately changed as needed.  
      2) As the casing, so far as being structured for securing, protecting or sealing parts within the electronic instrument, it is not necessarily outermost. The mass part is typically thicker and heavier than the casing, and is often formed on an extension of the casing. The resonance frequency is in proportion with thickness, and also from this viewpoint, the mass part is usually thickest. The mass part has the suitable examples in the liquid crystal display, battery, or part mounting printed circuit substrate. Further, the spaces for installing the piezoelectric sounding body are assumed between the display means and the protective cover, a stroke space under a key board, or between the wall of a battery chamber and battery case.  
      3) The piezoelectric sounding body may be attached to the mass part by adhesive or pressure. The cushioning material or the spacer may be provided. The electronic parts are present in the main air-chamber or the sub air-chamber. The sub air-chamber may be one part of plural spaces in the casing partitioned by the partition wall.  
      4) The above mentioned embodiments may be combined, for example, as combining the embodiments of  FIGS. 9A , B, C, E, F and of  FIG. 10A  to C and the embodiment of  FIG. 9D .  
      5) As preferably applied examples of the invention, there are many kinds of electronic instruments such as the portable telephone, portable information terminals (PDA), voiceless coder, or PC (personal computer).  
      As above explained, according to the invention, it is possible to restrain vibration of the casing, efficiently drive the piezoelectric sounding body itself, and flatten the sound pressure characteristic within the electronic instrument requiring the miniaturized type, light weight, and thin type in the electronic instrument, in particular the portable telephone.  
      As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.