A piezoelectric transducer is formed by fixedly laying a second oscillating plate over a first oscillating plate to which a piezoelectric oscillating assembly having a piezoelectric oscillating element is adhered, so as to define an acoustically sealed space. And, as the first oscillating plate oscillates by being driven by the oscillation of the piezoelectric oscillating assembly, the second oscillating plate oscillates by being driven thereby by way of the sealed space. Due to the shifting of the resonance frequencies of the piezoelectric oscillating assembly and the first and the second oscillating plates, and also due to the restriction of the oscillation by the sealed space, a wide frequency property is obtained, making this piezoelectric transducer particularly suitable for use as a speaker or as a microphone.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a piezoelectric transducer using a 
piezoelectric oscillating element as its driving means, and in particular 
relates to an improvement of such a piezoelectric transducer which is 
suitable for use as a piezoelectric loudspeaker, a piezoelectric 
microphone, a piezoelectric buzzer, and so on. 
2. Description of the Prior Art 
Conventionally, a piezoelectric transducer of this type has had a structure 
such as shown in longitudinal sectional view in FIG. 20 of the 
accompanying drawings. 
Specifically, in this structure, a step portion 3 is formed at a 
longitudinally central portion of the interior of a tubular case 1 which 
has an open end, and a piezoelectric oscillating assembly 9 which is 
formed by adhering a piezoelectric oscillating element 5 (made of a per se 
known type of piezoelectric material) onto a surface of an 
electroconductive plate 7 of a circular shape is attached by its circular 
edge portion to the step portion 3 with elastic adhesive 11. Further, a 
sound emitting hole 13 is formed in the end surface of the case 1 which is 
not open, and a circuit board 15 having a drive circuit (which is not 
shown in the drawing) for driving the piezoelectric oscillating element 5 
is mounted in the open end surface of the case 1, with wires which are 
also not shown in the figure being provided for electrically connecting 
the piezoelectric oscillating element 5 to said circuit board 15. 
According to such a structure for a piezoelectric electro-acoustic 
transducer, when the piezoelectric oscillating element 5 is driven by the 
drive circuit, the piezoelectric oscillating assembly 9 is caused to 
oscillate by way of the oscillation of the piezoelectric oscillating 
element 5, and this causes the production of sound in the air filling the 
chamber 17 defined on the side of the piezoelectric oscillating assembly 9 
towards the closed end of the casing 1 and the sound emitting hole 13, and 
this sound is thence emitted to the outside mainly through the sound 
emitting hole 13. Such a sound has frequency characteristics in which the 
sound level is high near the characteristic resonance frequency A of the 
piezoelectric oscillating assembly 9 and also near the characteristic 
resonance freqency B of the acoustic space or chamber 17. Such a frequency 
characteristic is exemplarily shown in FIG. 21 of the accompanying 
drawings as a graph of sound intensity against frequency. 
Because the characterisic resonance frequency B may be changed by varying 
the shape and the volume of the acoustic space 17 by adjusting the shape 
of the case 1 and of the sound emitting hole 13, thus by bring the 
resonance frequency B of the chamber 17 near to the characteristic 
resonance frequency A of the piezoelectric oscillating assembly 9 it is 
conventionally considered to be possible to broaden the frequency range of 
high sound pressure level. 
However, according to such a structure for a piezoelectric transducer, the 
adjustable factors are limited to the shape and the dimensions of the 
piezoelectric oscillating assembly 9 and of the case 1, and the 
characteristic resonance frequencies A and B are relatively steep and are 
few in number (i.e., two), and thus, even when the characteristic 
resonance frequency B is varied, it is not possible to broaden the 
frequency range of high sound pressure level, and further it is difficult 
to obtain a favorable sound pressure level over a wide frequency range. 
Therefore, such a piezoelectric transducer is suitable for driving air, 
i.e. for producing a sound, at a certain substantially constant frequency, 
as in the case of a piezoelectric buzzer, but when it is to be driven by a 
signal the frequency of which varies over a wide range, as in the case of 
a loudspeaker, it is difficult to obtain a favorable sound pressure and to 
get crisp reproduction over a wide frequency range, and the reproduced 
sound tends to have a squeaky tone. 
Moreover, because such a piezoelectric transducer has the above described 
structure in which the piezoelectric oscillating assembly 9 is secured 
within the tubular case 1, it is hard to make its configuration compact, 
and in particular it is hard to make said structure in particular low 
profiled (by which is meant short in longitudinal extent), while 
broadening its frequency range at the same time. 
SUMMARY OF THE INVENTION 
Accordingly, it is the primary object of the present invention to provide a 
piezoelectric transducer which has a wide frequency range property by 
using a simple structure. 
It is a further object of the present invention to provide such a 
piezoelectric transducer which is both compact and low profiled, and which 
is built from a piezoelectric oscillating element and an oscillating 
plate, with the possibility of eliminating the requirement for a casing. 
It is a further object of the present invention to provide such a 
piezoelectric transducer which is suitable for use as a loudspeaker or a 
microphone. 
According to the most general aspect of the present invention, these and 
other objects are accomplished by a piezoelectric transducer comprising: 
(a) a piezoelectric oscillating assembly comprising a piezoelectric 
oscillating element comprising a thin piezoelectric plate and electrodes 
attached to the opposing surfaces of the thin piezoelectric plate; (b) a 
first oscillating plate, which is greater in diameter than the 
piezoelectric oscillating assembly, to which the piezoelectric oscillating 
assembly is adhered; and (c) a second oscillating plate, which is laid 
over the first oscillating plate with the edges thereof substantially 
sealed together so as to define an acoustically sealed space therebetween; 
(d) a support portion being defined by the aforethe laid over and sealed 
together portions of the first and the second oscillating plates, the edge 
portion of the support portion being defined by at least the edge portion 
of the first or the second oscillating plate. 
According to such a structure according to the present invention, as will 
be explained hereinafter, it becomes possible to obtain a relatively wide 
frequency range property, and when such a piezoelectric transducer is used 
as a loudspeaker (for instance) it can reproduce a crisp sound and a 
favorable sound pressure level over a wide frequency range, while further 
achieving great simplicity and remarkable compactness, and in particular 
being of a low profiled structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with reference to the preferred 
embodiments thereof, and with reference to the appended drawings. FIG. 1 
relates to the first preferred embodiment, and shows, in longitudinal 
sectional view, a piezoelectric transducer incorporating a piezoelectric 
oscillating assembly 19 which is formed by adhering a piezoelectric 
oscillating element 25, having a pair of circular disk shaped electrodes 
23 (only one is shown in the drawings) fitted on the opposing plane 
circular surfaces of a piezoelectric plate 21 also of a circular disk 
shape, to an electroconductive plate 27 which is likewise of a circular 
disk shape and is greater in diameter than the piezoelectric oscillating 
element 25, in such a manner that one of said electrodes (the one which is 
not shown) comes in contact therewith. This piezoelectric oscillating 
assembly 19 is shown in perspective view in FIG. 2. 
This piezoelectric oscillating assembly 19 is adhered to the internal 
bottom surface of a depression 31 formed in a central portion of a first 
oscillating plate 29 of a circular shape which is greater in diameter than 
the piezoelectric oscillating assembly 19 and is made of a thin plastic 
film having a thickness of the order of 0.1 mm for instance. This 
depression 31 is shaped like a frustrum of a cone with a wide apical 
angle, and diverges towards its open end, and a surrounding edge portion 
of the first oscillating plate 29 forms a flange 33 around the edge of the 
depression 31. The general outer configuration of this first oscillating 
plate 29 is shown in perspective view in FIG. 3. 
A second oscillating plate 35 which is likewise circular in shape and is 
likewise made of a thin plastic film is attached over the first 
oscillating plate 29 so as to cover the depression 31, and is fixedly 
secured to the aforementioned flange 33 of said first oscillating plate 
29. As a result, the depression 31 of the first oscillating plate 29 is 
sealed and defines a substantially sealed space 37 between the first and 
second oscillating plates 29 and 31. 
The first oscillating plate 29 is provided with an insertion hole 39 which 
communicates the substantially sealed space 37 with the outside. Through 
this insertion hole 39, a pair of lead wires 41, 43 extending from the 
electroconductive plate 27 and from the one of the electrodes 23 of the 
piezoelectric oscillating element 25 not contacted to said 
electroconductive plate 27 (the one which is visible in FIG. 2) are 
passed, and are led out to the outside as shown in FIG. 3 and in the 
sectional view of FIG. 4, and these lead wires 41 and 43 are connected to 
a drive circuit which is not shown in the drawings. 
The inner diameter of this insertion hole 39 is equal to or slightly 
greater than the combined diameter of the lead wires 41 and 43, and a very 
small gap (or gaps) 45 is defined between the internal wall of the 
insertion hole 39 and the lead wires 41 and 43. This gap 45 effectively 
acoustically seals the sealed space 37 when the piezoelectric oscillating 
assembly 29 is being driven as explained hereinbelow, and on the other 
hand functions as a small but effective communication hole for relieving 
the sealed state of the space 37 by communicating with the outside so as 
to equalize the pressure in said space 37 with the exterior atmospheric 
pressure. 
This piezoelectric transducer is used with its support portion 47 which is 
constituted by the superposed sandwich assembly of the flange 33 of the 
first oscillating plate 29 and the second oscillating plate 35 being 
directly mounted over a depression formed in case or chassis 49 for 
electrical equipment or the like. 
And, when a drive signal is applied by the drive circuit (not shown) 
between the shown electrode 23 of the piezoelectric oscillating element 25 
and the electroconductive plate 27, then the piezoelectric oscillating 
element 25 undergoes a bending oscillation and by way of the thus produced 
overall oscillation of the piezoelectric oscillating assembly 19 the first 
oscillating plate 29 also oscillates. 
Since the acoustic sealed space 37 defined by the first and the second 
oscillating plates 29 and 35 is defined on the upper side in FIG. 1 of the 
piezoelectric oscillating assembly 19, the second oscillating plate 35 
oscillates following after the oscillation of first oscillating plate 29. 
In this case, since it is not likely that the characteristic resonance 
frequencies of the piezoelectric oscillating assembly 19 and of the first 
and the second oscillating plates 29 and 35 should be in agreement, the 
characteristic resonance frequencies are increased in number as compared 
with the case of the prior art discussed hereinbefore and illustrated in 
FIGS. 20 and 21. Further, since the acoustically sealed space 37 functions 
so as to slightly reduce the sound pressure levels of the piezoelectric 
oscillating assembly 19 and of the first and the second oscillating plates 
29 and 35 at their characteristic resonance frequencies, thereby the 
frequency property is in a manner of speaking leveled out over a wider 
range; and, since the characteristic resonance frequencies may be easily 
varied by changing the thicknesses and the shapes of the piezoelectric 
oscillating assembly 19 and of the first and the second oscillating plates 
29 and 35, it can be satisfactorily ensured that the frequency property is 
appropriate. 
Therefore the overall frequency characteristics can come closer to a flat 
state, as schematically shown by the broken line in FIG. 21, and, even 
when the piezoelectric oscillating element 25 is used as a piezoelectric 
speaker and a drive signal which varies over a wide frequency range is 
supplied thereto, it is possible to obtain a practical and usable sound 
pressure level over a relatively wide frequency range, and the reproduced 
sound is crisper. 
Since the second oscillating plate 35 is directly adhered to the first 
oscillating plate 29 which is in turn adhered to the piezoelectric 
oscillating assembly 19 which is itself of a plate shape, as compared to 
the above discussed prior art the structure is simplified and is made more 
compact, and in particular is made more low profiled. For instance, one 
can make a piezoelectric speaker having a thickness of from 1.5 mm to 2 mm 
using as material for the first and the second oscillating plates 29 and 
35 pieces of a plate material having a thickness of about 0.1 mm and a 
diameter of about 30 mm, and using a piezoelectric oscillating assembly 19 
having a thickness of about 0.1 mm and a diameter of about 20 mm. 
Furthermore, since the piezoelectric oscillating assembly 19 is located 
inside the sealed space 37, said piezoelectric oscillating assembly 19 is 
kept isolated and protected from the influences of moisture and dust from 
outside, and its operational property can remain stable over an extended 
service life. 
When the piezoelectric oscillating assembly 19 is not being driven, the 
sealed space 37 is kept at substantially atmospheric pressure by the gap 
39 communicating said space 37 with the outside. Therefore, even when the 
piezoelectric transducer is placed in an environment where the pressure 
fluctuates, for instance during transportation, the sealed space 37 will 
not be caused to expand or contract by such atmospheric pressure 
fluctuations, and the first and the second oscillating plates 29 and 35 
will not be subjected to changes in shape or to damage by pressure 
differential between the atmosphere and the gas in the space 37. 
In the above described piezoelectric oscillating assembly 19, the 
electroconductive plate 27 is not indispensable, but it is also possible 
to build a structure therefor using only the piezoelectric oscillating 
element 25, and further it becomes possible to obtain an even greater 
sound pressure by adhering a pair of piezoelectric oscillating bodies on 
both surfaces of the first oscillating plate 29 so as to achieve a 
bimorphic structure. The first and the second oscillating plates 29 and 35 
may be implemented by using materials suitable for making an oscillating 
cone for a loudspeaker such as paper. 
The piezoelectric transducer of this invention may have lead wire 
structures for connecting the piezoelectric oscillating element 25 to a 
drive circuit other than the lead wires 41 and 43 described above. 
For instance, as shown in the sectional view of FIG. 6 and the perspective 
view of FIG. 7, the first oscillating plate 29, which is adhered to the 
piezoelectric oscillating assembly 19, may be provided with a lead pattern 
51 (instead of using the separate lead wires 41 and 43) extending from the 
vicinity of the piezoelectric oscillating assembly 19 to the flange 33, 
said pattern 51 being formed by photoetching or some other conventional 
method, and the piezoelectric oscillating assembly 19 may be connected to 
this lead pattern 51 by a connecting lead wire structure. 
According to a piezoelectric transducer of this modified structure, the 
productivity of assembly labor is increased, because the labor required 
for pulling the lead wires 41 and 43 through the insertion hole 39 may be 
eliminated. Further, as shown in the sectional view of FIG. 8, the lead 
pattern 51 generally protrudes from the surface of the first oscillating 
plate 29, and a gap 53 is generated in the vicinity of the flange portion 
33 of the first oscillating plate 29 in the area surrounded by the lead 
pattern 51 and the first and the second oscillating plates 29 and 35. This 
gap 53 functions as the communication hole, like the gap 53 of the first 
structure for the transducer as shown in FIGS. 1 through 5. 
Although such a structure is not particularly shown in the drawings, in the 
piezoelectric transducer of FIG. 1, the lead wires 41 and 43 may be led 
out from the laid over portion of the flange 33 of the first oscillating 
plate 29 and the second oscillating plate 35 by defining a communication 
hole thereby. And, as another alternative, the insertion hole may be 
formed in the second oscillating plate 35, and it is also possible to 
define such an insertion hole by piercing the first or the second 
oscillating plate 29 or 35 with a fine wire. 
FIGS. 9 and 10 are longitudinal sectional views, similar to FIG. 1 for the 
first embodiment, showing the second and the third preferred embodiments 
of the piezoelectric transducer of the present invention. 
According to the piezoelectric transducer shown in FIG. 9, as opposed to 
the first embodiment shown in FIG. 1, the piezoelectric oscillating 
assembly 19 is adhered over the flat and circular disk shaped first 
oscillating plate 55, and the piezoelectric oscillating assembly 19 is 
then covered by laying the second oscillating plate 59 having the 
depression 57 formed in it over said first oscillating plate 55 with a 
sealed space 61 being thereby defined between the first oscillating plate 
55 and the second oscillating plate 59. 
Thus, according to the piezoelectric transducer of this invention, the 
sealed space 61 may be formed either by using the second oscillating plate 
59 having the depression 57 or by using the first and the second 
oscillating plates both having depressions. Essentially, it suffices if 
the first and the second oscillating plates are laid over each other, i.e. 
are sandwiched together, so as to define a sealed space on the front 
surface, the rear surface, or both the surfaces of the piezoelectric 
oscillating assembly 19. 
In the piezoelectric transducer shown in FIG. 10, the sealed space 37 is 
divided in layers further by the third and the fourth oscillating plates 
63 and 65, this embodiment otherwise having the same structure as that 
shown in FIG. 1. In this case, the sealed space 37 is located on the rear 
surface side of the piezoelectric oscillating assembly 19. 
According to such a piezoelectric transducer, since the third and the 
fourth oscillating plates 63 and 65 having different characteristic 
resonance frequencies are added to the characteristic curve, in addition 
to the first and the second oscillating plates 29 and 35, the overall 
frequency property of the piezoelectric transducer as a whole may be made 
even more flat than that which is obtained with the FIG. 1 construction. 
In order to assure the proper oscillation of the second oscillating plate 
35, it is preferable to form sound emitting holes 67 and 69 in the third 
and the fourth oscillating plates 63 and 65 and to offset the relative 
position of the sound emitting holes 67 and 69. These holes, as in the 
previously described embodiments, serve for equalizing the pressures in 
the chambers defined between the various oscillating plates. 
FIG. 11 shows the fourth preferred embodiment of the piezoelectric 
transducer of the present invention. 
This embodiment is similar to the first preferred embodiment shown in FIG. 
1, except for the fact that the portion defining the depression 31 in the 
first oscillating plate 29 is provided with a plurality of protrusions 
protruding to the outside from the sealed space 37, i.e. a large number of 
outwardly bent dot portions 71 in a distributed relationship. These 
protruding bent portions 71 may be formed by pressing the first 
oscillating plate 29 with a tip of a wire without piercing it, and the 
wire may be applied from the outside to the sealed space 37, or pressure 
from both sides may be combined. 
According to such a piezoelectric transducer, since the number of resonance 
points of the first oscillating plate 29 is increased as compared to the 
FIG. 1 case in which no bent portions 71 are formed, the frequency 
property may be made more flat as compared to that of the structure shown 
in FIG. 1. Since the resonance points produced in the characteristic curve 
of the first oscillating plate 29 change as the positions, the number, and 
the spacing of the protruding bent portions 71 formed in said first 
oscillating plate 29 are varied, the adjustment of the overall frequency 
property is possible with the use of these bent portions 71. 
FIGS. 12 and 13 show variations of the piezoelectric transducer of FIG. 11. 
According to the piezoelectric transducer shown in FIG. 12, bent portions 
73a, 73b with wave shaped cross sections are formed in the portions of the 
first and the second oscillating plates 29 and 35 defining the sealed 
space 37 by forming annular concentric wrinkles therein. 
According to such a piezoelectric transducer of this invention, since not 
only are the bent portions 73a formed in the first oscillating plate 29 
but also the other bent portions 73b are formed in the second oscillating 
plate 35, thereby the number of resonance points in the characteristic 
curves of each of the first and the second oscillating plates 29 and 35 
are drastically increased, and an even more flat frequency property 
becomes readily possible. 
As for the bent portions, as an alternative to the annular shapes therefor 
shown in FIG. 12, they may be constituted by spiral shaped bent portions 
75 formed in the first oscillating plate 29 in the form of curved wrinkles 
facing away from the piezoelectric oscillating assembly 19 as shown in 
FIG. 13 (only the first oscillating plate 29 is shown in this figure) and 
FIG. 14 (the piezoelectric oscillating assembly 19 is not shown in this 
FIG. 14). The bent portions may also consist of spirals facing the 
piezoelectric oscillating assembly 19, although this alternative concept 
is not shown in the drawings. Thus, the objects of this invention may be 
achieved, no matter whether the bent portions are protrusions or wrinkles, 
as long as they are formed in the portions of the first and the second 
oscillating plates 29 and 35 which define the sealed space 37. 
FIG. 15 shows the fifth preferred embodiment of the piezoelectric 
transducer of the present invention. 
The structure of this embodiment is similar to that of the first preferred 
embodiment shown in FIG. 1, except that the outer part of the laid over 
portions of the flange 33 of the first oscillating plate 29 and the second 
oscillating plate 35 is made as a somwhat thick support portion 83 for 
mounting the piezoelectric transducer as a whole to a chassis 49 for 
electronic or electrical equipment, and the somewhat inward portion of the 
second oscillating plate 35 in the vicinity of this support portion 83 is 
provided with an annular groove 77, which thins out this portion of the 
second oscillating plate 35. 
Thus, the portions of the first and the second oscillating plates 29 and 35 
which extend beyond the groove 77 are increased in thickness and define 
annular thick portions 79 and 81 which are to be mounted onto the chassis 
49. 
According to such a structure for the piezoelectric transducer, since the 
support portion 83 is increased in thickness and on its inward side the 
groove 77 is provided, the oscillation produced in the first and the 
second oscillating plates 29 and 35 is prevented from being transmitted to 
the outer edge portion of the support portion 83 or the edge portions of 
the first and the second oscillating plates 29 and 35, and therefore even 
when the thick portions 79 and 81 are fixedly secured to the chassis 49 
the proper free oscillation of the first and the second oscillating plates 
29 and 35 is assured. In other words, the change in the thickness of the 
first and the second oscillating plates 29 and 35 (including the groove 
77) functions as a transmission preventing portion 85 which prevents 
oscillations produced either in the combination of first and the second 
oscillating plates 29 and 35 or in the chassis 49 from being transmitted 
to the other one thereof. The groove 77 functions as part of the 
transmission preventing portion but is not indispensable. 
As a result, according to such a piezoelectric transducer of this 
structure, in particular, the sound pressure in low frequency range, for 
instance from 400 to 500 Hz, is increased as compared to the case of the 
first preferred embodiment shown in FIG. 1. Furthermore, because of the 
presence of the transmission preventing portion 85, even when the 
electrical equipment to which the piezoelectric transducer is attached is 
changed, the frequency properties of the piezoelectric transducer is not 
substantially altered; in other words, the frequency properties of said 
piezoelectric transducer by itself in the unmounted condition, and in the 
mounted condition, are not different from each other to any appreciable 
degree. 
The transmission preventing portion 85 which restricts the transmission of 
oscillation may be formed, as an alternative to varying the thickness of 
the support portion 83 constituted by portions of the first and second 
oscillating plates 29 and 35, by forming bent portions in the support 
portion 83 of the piezoelectric transducer, as shown in FIGS. 16 to 18. 
In other words, in the FIG. 16 structure, the flange 87 of the first 
oscillating plate 29 forms a support portion 83 which extends beyond the 
second oscillating plate 35 and thence forms a step portion 89 by rising 
up in a cranked shape (in cross sectional view; actually this shape is an 
annular step shape), whereby the transmission preventing portion 85 is 
formed. 
On the other hand, in the FIG. 17 structure, the flange 91 of the first 
oscillating plate 29 extending beyond the second oscillating plate 35 is 
provided with an annular bent crease portion 93 having a U-shaped cross 
section, and this bent crease portion 93 constitutes the transmission 
preventing portion 85. 
In the FIG. 18 structure, by contrast, the second oscillating plate 95 
forms a support portion 83 extending beyond the flange 33 of the first 
oscillating plate 29, and an annular wave shaped bent portion 97 is formed 
in the second oscillating plate 95 so as to define the transmission 
preventing portion 85 so that the annular edge portion beyond the bent 
portion 97 may be fixedly attached to the chassis 49. 
It should be noted that, further, the support portions 47 and 83 in the 
above described piezoelectric transducers according to this invention may 
not be formed over the whole peripheral length, but may be formed 
partially therein. 
As a structure for fixedly supporting the piezoelectric transducer of this 
invention onto the chassis 49 of electronic equipment and so on, when an 
oscillating piece 99 is extended from the chassis 49, and the support 
portion 47 of a piezoelectric transducer such as for example the one shown 
in FIG. 1 is fixedly placed on the oscillating piece 99, as schematically 
shown in FIG. 19, not only the piezoelectric oscillating assembly 19 but 
also the oscillating piece 99 oscillates, whereby the oscillating range is 
expanded from the range B provided only by the piezoelectric transducer to 
the range indicated by C which includes the aforementioned oscillating 
piece 99, and the sound pressure in the high frequency range is slightly 
restrained, while the sound pressure in the low frequency range is raised. 
Furthermore, since the sound pressure in the low frequency range may be 
increased without increasing the size of the piezoelectric oscillating 
assembly 19, the cost of the piezoelectric oscillating assembly 19 is not 
increased. 
Because generally the impact and the oscillation which may be applied to 
the chassis are not the same as those of the piezoelectric oscillating 
assembly 19, even when such impacts and oscillations are applied to the 
chassis 49 the oscillating piece 99 absorbs such impacts and oscillations 
by preventing the transmission thereof to the piezoelectric oscillating 
assembly 19, thereby reducing the possibility of unfavorable influence on 
the oscillation of the piezoelectric oscillating assembly 19. 
The piezoelectric transducer may be fixedly supported not only by fixedly 
placing the support portion 47 onto the oscillating piece 99 of the 
chassis 49 but also by interposingly securing the oscillating piece 99. 
Because in the application of the piezoelectric transducer of this 
invention the frequency properties of the piezoelectric transducer as it 
is mounted include the properties of the acoustic space defined between 
the second oscillating plate 35 and the electronic equipment to which the 
piezoelectric transducer is mounted, the second oscillating plate 35 may 
be considered to be functioning as a plane sound source with respect to 
the outside. Therefore, the structure of the electronic equipment, 
particularly the structure of the case or the chassis to which the 
piezoelectric transducer is to be mounted, may be arbitrary. 
The above described piezoelectric transducer according to this invention 
has been described in an exemplary fashion by considering the case of a 
piezoelectirc loudspeaker for the convenience of description, but the 
present invention in fact may be applied not only to a piezoelectric 
speaker but also to a piezoelectric microphone, a piezoelectric buzzer, 
and so on. When a piezoelectric transducer according to the present 
invention is to be used as a piezoelectric microphone, in the structure 
shown in FIG. 1, the first oscillating plate 29 oscillates by being driven 
by the oscillation of the second oscillating plate 35, and an electrical 
output signal is outputted from the piezoelectric oscillating assembly 19. 
Although the present invention has been shown and described with reference 
to the preferred embodiments thereof, and in terms of the illustrative 
drawings, it should not be considered as limited thereby, since various 
possible modifications, omissions, and alterations could be conceived of 
by one skilled in the art to the form and the content of any particular 
embodiment, without departing from the scope of the present invention. 
Therefore it is desired that the scope of the present invention should be 
defined solely by the scope of the appened claims, which follow.