JPH10126885

Patent Translate
Powered by EPO and Google
Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JPH10126885
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric sound generator which obtains desired frequency characteristics by utilizing
resonance of a front air chamber and a rear air chamber.
[0002]
2. Description of the Related Art In a piezoelectric sounding device for obtaining desired
frequency characteristics by utilizing resonance of a front air chamber and a rear air chamber, a
resonance frequency based on the vibration of a piezoelectric vibrator and a resonance obtained
from the front air chamber The resonance obtained from the air chamber overlaps to determine
the frequency characteristic. The piezoelectric vibrator is configured by joining a piezoelectric
ceramic element to a plate-like metal diaphragm, and the peripheral portion of the metal
diaphragm of the piezoelectric vibrator is supported by the insulating case. As schematically
shown in FIG. 11, the front air chamber 103 is formed on one side of the piezoelectric vibrator
102 supported by the insulating case 101, and the rear air chamber 104 is on the other side of
the piezoelectric vibrator 102. Is formed. Generally, as shown in FIG. 11, the interior of the
insulating case 101 is often partitioned by the piezoelectric vibrator 102 to form both the front
air chamber 103 and the rear air chamber 104. However, the inside of the electronic device is In
some cases, both the front air chamber and the rear air chamber may be formed only when the
case of the electronic device and the insulation case of the piezoelectric speaker are combined.
04-05-2019
1
[0003]
The frequency characteristic (sound pressure-frequency) obtained by the vibration of the
piezoelectric vibrator 102 has a peak P1 of the primary resonance frequency and a peak P2 of
the secondary resonance frequency, as shown in FIG. When the diameter of the piezoelectric
diaphragm is large (for example, in the case of 20 mm), the resonance obtained from the front air
chamber 103 is such that the sound pressure peak is generated in the frequency region higher
than the secondary resonance frequency in FIG. The area of the hole 105 is set, and the area of
the sound emission hole 106 is set so that the resonance obtained from the back air chamber
104 has a peak of sound pressure in a frequency region lower than the secondary resonance
frequency. Then, the frequency characteristic obtained only from the piezoelectric vibrator 102
and the resonance from the front air chamber 103 and the rear air chamber 104 overlap, and the
frequency characteristic of the piezoelectric sound generator is determined.
[0004]
For example, FIG. 13 shows the reception frequency characteristics of the handset standard
established by the Japan Telecommunications Machinery Manufacturers Association for
telephone call quality. When a piezoelectric speaker is used for the handset of the telephone, it is
required to satisfy this reception frequency characteristic. According to this standard, when the
sound pressure at 1000 Hz is 0 dB, the frequency characteristic of the receiver falls within the
allowable range between the allowable limit (lower limit) D and the allowable limit (upper limit) C
in the frequency range of 300 Hz to 3400 Hz. You are asking to enter. However, the smaller the
diameter of the piezoelectric vibrator (piezoelectric diaphragm), the higher the secondary
resonance frequency tends to be. Therefore, if the diameter of the piezoelectric vibrator, that is,
the diameter of the metal diaphragm is reduced according to the demand for miniaturization, the
secondary resonance frequency becomes 3400 Hz or more, and as a result, the frequency
characteristic of the piezoelectric speaker is high. The sound pressure in the frequency domain is
reduced and does not meet the aforementioned standard. Then, although it tried to raise the
sound pressure of the area ¦ region where the frequency is high by adjusting the number or the
dimension of the sound emission hole of a front air chamber or a back air chamber, a sufficient
result could not be obtained.
[0005]
An object of the present invention is to provide a piezoelectric speaker capable of adjusting
frequency characteristics in a high frequency region.
04-05-2019
2
[0006]
Another object of the present invention is to provide a piezoelectric sound generator capable of
adjusting frequency characteristics in a high frequency region when the diameter size of the
piezoelectric vibrator is reduced.
[0007]
Another object of the present invention is to provide a piezoelectric speaker capable of adjusting
frequency characteristics in a high frequency region by adjusting a secondary resonance
frequency.
[0008]
Another object of the present invention is to provide a piezoelectric sound generator capable of
preventing a decrease in sound pressure when a mass member is attached to a piezoelectric
vibrator using an adhesive in order to adjust a secondary resonance frequency. is there.
[0009]
Another object of the present invention is to provide a piezoelectric speaker capable of
effectively adjusting a secondary resonance frequency by attaching a mass member to a
piezoelectric vibrator.
[0010]
SUMMARY OF THE INVENTION A piezoelectric sounding device to which the present invention is
to be improved comprises a peripheral portion of a metal diaphragm of a piezoelectric vibrator in
which a piezoelectric ceramic element is joined to a plate-shaped metal diaphragm. A front air
chamber is formed on one side of the piezoelectric vibrator supported by the insulating case and
supported by the insulation case, and a rear air chamber is formed on the other side of the
piezoelectric vibrator. There is.
[0011]
In the present invention, a mass member for adjusting the resonance frequency is attached to the
central portion of the metal diaphragm to adjust the frequency characteristic.
04-05-2019
3
In the present invention, the frequency characteristic in the high frequency region is improved by
attaching the mass member to the metal diaphragm and moving the secondary resonance
frequency to the low frequency side.
In the present invention, in particular, the diameter of the metal diaphragm is so small that the
secondary resonance frequency obtained from the configuration of only the piezoelectric vibrator
is higher than a predetermined upper limit frequency (for example, the diameter of the metal
diaphragm is 14 mm or less In the case of) is effective.
As described above, when the diameter of the metal diaphragm is large to a certain extent, the
frequency characteristics can be easily adjusted by adjusting the number and size of the sound
emission holes.
However, as the diameter of the metal diaphragm becomes smaller, it is difficult to improve the
reduction in sound pressure in a high frequency region only by adjusting the number and size of
the sound emission holes.
Therefore, the inventor considers to improve or adjust the sound pressure drop by changing the
secondary resonance frequency that is causing the sound pressure drop in the high frequency
region (by shifting to a lower frequency). The
[0012]
The primary resonance frequency (f) of the diaphragm can be expressed by the equation f = (1 /
2π) (1 / mc) 1/2.
Here, m is equivalent mass and C is compliance. The secondary resonant frequency appears
accompanying this primary resonant frequency. The equivalent mass is not the mass of the
diaphragm itself but a mass that actually participates in the vibration when it vibrates, and the
equivalent mass changes depending on the support structure or support condition of the
diaphragm. The compliance C is a constant indicating the softness of the vibrating body, and as C
becomes larger, it means that the diaphragm is softer. In order to lower the secondary resonance
frequency (shift to the lower frequency side), m or C may be increased. However, even if C is
increased, if C is increased too much, it is impossible to support or maintain the shape of the
04-05-2019
4
diaphragm. In reality, the thickness of the metal diaphragm of the piezoelectric vibrator is
reduced to almost the limit, and it is impossible to further increase the C (softness) of the metal
diaphragm. Therefore, the inventor considered lowering the secondary resonance frequency by
increasing m (equivalent mass). A simple way to increase m (equivalent mass) is to increase the
metal diaphragm thickness by increasing the metal diaphragm thickness. However, if m is
increased in this way, C will be decreased, and as a result, it is difficult to lower the secondary
resonance frequency. Therefore, in the present invention, m (equivalent mass) is increased by
attaching the mass member to the piezoelectric vibrator. In the present invention, in order to
increase m (equivalent mass) most effectively with a light and small mass member, the mass
member is disposed at the central portion of the piezoelectric vibrator. If the mass member is not
disposed at the central portion, the mass of the mass member is heavy, and as a result, the size of
the mass member is increased, and the C of the diaphragm is decreased. If you place it in the
center of the case, you will not have this problem.
[0013]
According to the present invention, the equivalent mass is increased by arranging the mass
member at the central portion of the piezoelectric vibrator, and the secondary resonance
frequency is shifted to the lower frequency side, so that the sound pressure in the frequency
domain having high frequency characteristics. Thus, it is possible to adjust the frequency
characteristic in the high frequency region by preventing the decrease of
[0014]
Although the shape of the mass member is arbitrary, it is preferable to make the mass member
into a plate shape for thinning.
Since the metal diaphragm is usually in the form of a disk, it is ideal that the mass member is also
in the shape of a disk and disposed substantially concentric with the metal diaphragm. In this
way, the mass characteristics and mass of the mass member can be minimized to adjust the
frequency characteristics. Specifically, the frequency characteristics are adjusted by adjusting the
secondary resonance frequency obtained from the piezoelectric vibrator by setting the mass and
shape and size of the mass member, but it is obtained from the piezoelectric vibrator to which
the mass member is attached. By setting the mass and shape of the mass member such that the
secondary resonance frequency to be obtained approaches a predetermined upper limit
frequency, it is possible to minimize the mass of the mass member and effectively adjust the
frequency characteristics. The predetermined upper limit frequency is the upper limit of the
frequency which requires a sound pressure equal to or higher than a predetermined value which
04-05-2019
5
is naturally determined according to the application. In the case of adjusting the frequency
characteristic so as to conform to the above-mentioned standard of the reception frequency
characteristic of the communication equipment industry association, the upper limit frequency of
3400 Hz is the predetermined upper limit frequency. Therefore, in this case, the mass and shape
of the mass member may be set so that the secondary resonance frequency approaches 3400 Hz.
And, it goes without saying that the adjustment by the number and the size of the sound emission
holes is used in combination so that the resonance frequency of the front air chamber becomes
slightly lower than the upper limit frequency.
[0015]
When the mass member is bonded onto the piezoelectric ceramic element of the piezoelectric
vibrator, a silicone rubber adhesive having elasticity in a cured state is used as the adhesive. This
is to prevent the mass member from separating the deformation of the piezoelectric vibrator. If
an adhesive that exhibits little elasticity after curing is used as the adhesive, the movement or
deformation of the piezoelectric ceramic element may be separated due to the presence of the
mass member, and sufficient vibration may not occur to reduce the sound pressure. is there. The
same applies to the case where a mass member is bonded to the center of the surface opposite to
the surface of the metal diaphragm to which the piezoelectric ceramic element is bonded, and
also in this case, an adhesive having elasticity in a cured state as an adhesive. When used, there is
an effect that the compliance of the metal diaphragm can be prevented from being reduced. In
particular, when the mass member is bonded to the surface opposite to the surface of the metal
diaphragm to which the piezoelectric ceramic element is bonded, the thickness dimension of the
case on which the piezoelectric ceramic element is disposed can be reduced.
[0016]
Preferably, the peripheral portion of the metal diaphragm is supported on the insulating case by
a support structure which does not substantially reduce the substantial diameter of the metal
diaphragm. This is because if the substantial diameter of the metal diaphragm is substantially
reduced, it is necessary to further increase the equivalent mass of the mass member by that
amount.
[0017]
04-05-2019
6
The mass member is preferably as soft as possible so as to minimize the compliance of the metal
diaphragm. However, in order to obtain a certain amount of mass, a metal plate is used by all
means, but in that case, it is preferable to use an inexpensive one such as an iron-nickel alloy etc.
and having as large a specific gravity as possible.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of
the present invention will be described in detail with reference to the drawings. FIG. 1 is a
schematic partial cross-sectional view of a handset of a mobile phone in which a piezoelectric
speaker (or piezoelectric speaker) according to an embodiment of the present invention is
disposed, and FIG. 2 is an embodiment of the present invention used in FIG. FIG. 7 is a schematic
cross-sectional view of an example piezoelectric transducer. In addition, in FIG. 2, in order to
make an understanding easy, the thickness of each part is exaggerated and drawn.
[0019]
The telephone receiver of this telephone has a structure in which a piezoelectric transducer 2
which is combined with the housing 1 to constitute a piezoelectric sound generator is attached to
the housing 1 as shown in FIG. The housing 1 has a fitting portion (projecting portion) 4 for
attaching the piezoelectric transducer integrally with an inner wall portion of the housing main
body 3. The protrusion 4 has a cylindrical shape, and has a notch 4 a into which the positioning
projection half 7 f of the piezoelectric transducer 2 is fitted. Further, in the housing main body 3,
one or more sound emitting holes 3 a are formed in an inner portion surrounded by the
projecting portion 4. A ring-shaped spacer 5 is disposed on the inner periphery of the protrusion
4. The end of the front case 6 of the piezoelectric transducer 2 is fitted to the projection 4 via the
ring spacer 5 in a state where the positioning projection half 7f and the notch 4a are fitted.
Specifically, the piezoelectric transducer is arranged such that the opening 6c of the front case 6
faces the sound emission holes 3a formed in the housing body 3, that is, the opening 6c is
covered by the wall of the housing body 3 2 is fitted to the projection 4. In this state, a front air
chamber R1 is formed between the wall of the housing body 3 and the piezoelectric vibrator 8 of
the piezoelectric transducer 2.
[0020]
04-05-2019
7
As shown in detail in FIG. 2, the piezoelectric transducer 2 is divided into two parts, in which a
back side case 7 constituting a second case half is fitted to a front side case 6 constituting a first
case half. A storage case (insulation case) is provided, and in the storage case, a piezoelectric
vibrator 8 that vibrates according to an electric signal is stored. In the present embodiment, in
order to prevent air leakage from the fitting portion of the front case 6 and the rear case 7, the
fitting portion is joined by welding or the like. As shown in detail in FIGS. 2 and 3A to 3C, the
front side case 6 includes a bottom wall 6a and a peripheral wall 6b extending from the outer
circumference so as to surround the outer circumference of the bottom wall 6a. And is integrally
molded of an insulating resin material made of glass-containing PPO resin. 3A to 3C are a plan
view, a cross-sectional view, and a back view of the front case 6. The bottom wall 6a is formed
with a circular opening 6c that partially exposes the metal diaphragm 8a of the piezoelectric
vibrator 8. The diameter of the opening 6c is made small to the extent that the finger does not
touch the metal diaphragm 8a at the time of the assembly work of the telephone, and is made
large to the extent that resonance does not occur. A positioning projection half portion 6d having
a rectangular parallelepiped shape is integrally provided on an outer peripheral portion of the
bottom wall portion 6a. The peripheral wall 6b has a substantially cylindrical shape having a
notch 6e. The notch 6e is formed at a position corresponding to the positioning projection half
6d. Further, the notch 6e is for forming a gap for leading out the lead wires 10a and 10b in a
state in which the back case 7 is fitted to the front side case 6, and finally the inside thereof is a
sealant It is sealed by 11. On the inner wall of the peripheral wall 6b, an annular rib 6f extending
continuously in the circumferential direction is integrally formed at a position near the opening
6c. An inclined surface, that is, a first tapered portion 6g is formed on the outer surface of the
inner wall portion of the rib 6f. The first tapered portion 6g is formed in such a direction as to
expand radially outward (that is, to increase in diameter) as it is separated from the opening 6c.
[0021]
As shown in detail in FIGS. 2 and 4 (A) to (C), the back side case 7 constituting the second case
half part has a disk-like bottom wall 7a and an edge of the bottom wall 7a. It has a peripheral
wall 7b rising from the bottom wall 7a so as to leave 7a1 and is integrally formed of an
insulating resin made of PPO resin with glass like the front side case 6. 4A to 4C are a plan view,
a cross-sectional view, and a back view of the back case 7. The bottom wall 7a is formed with a
leakage hole 7c. The leakage hole 7c is formed at the center of the bottom wall 7a, and a
damping cloth 9 is joined to the opening at one end of the leakage hole 7c located inside the
back case 7 so as to cover the leakage hole 7c. It is pasted (Figure 2). A reinforcing rib 7d is
formed on the inner surface of the bottom wall 7a facing the front case 6. The reinforcing ribs 7d
are formed in a lattice shape and have a shape and a size that can enhance the strength of the
back case 7. A positioning projection half 7f is formed on the outer periphery of the bottom wall
7a. The positioning projection half 7f is composed of two rectangular parallelepiped projecting
04-05-2019
8
pieces 7f1 and 7f2 and a plate 7f3 continuous with the bottom wall 7a. With the back case 7
fitted to the front case 6, the positioning projection half 6d of the front case 6 is engaged with
the positioning projection half 7f while being sandwiched between the projecting pieces 7f1 and
7f2. When the back side case 7 is fitted to the front side case 6, a gap through which the lead
wires 10a and 10b are led out from the piezoelectric transducer 2 is formed between the
positioning projection half portion 6d and the plate portion 7f3. Ru. The plate-like portion 7f3
can be easily taken out of the lead wires 10a and 10b and can be injected with a sealant, and can
enhance the attachment strength of the projecting pieces 7f1 and 7f2 to the bottom wall 7a. The
notch 7f4 is formed.
[0022]
The peripheral wall 7b has a substantially cylindrical shape having a notch 7g. The notch 7g is
formed at a position corresponding to the positioning projection half 7f. The notch 7g forms a
gap for leading out the lead wires 10a and 10b in a state where the back case 7 is fitted to the
front side case 6, and a sealing agent 11 made of a silicone rubber adhesive is formed therein. Is
filled. An inclined surface, that is, a second tapered portion 7h is formed on the outer surface of
the inner wall portion of the peripheral wall portion 7b. Similar to the first tapered portion 6g of
the front case 6, the second tapered portion 7h is formed so as to expand (that is, increase in
diameter) radially outward as it is separated from the bottom wall 7a.
[0023]
In the insulating case, as shown in FIG. 2, the peripheral wall portions 6b and 7b of the front case
6 and the rear case 7 are fitted so that the end face 6b1 of the peripheral wall 6b contacts the
edge 7a1 of the rear case 7. It is configured. Thus, in the state in which the peripheral wall
portions 6b and 7b are fitted to each other, the groove G is formed in the inner wall portion of
the peripheral wall of the insulating case. The groove G is opened inside the insulating case
(toward the center), ie, spreads toward the center and extends along the peripheral wall of the
insulating case, and the peripheral portion of the metal diaphragm 8a of the piezoelectric
vibrator 8 The cross-sectional shape for receiving The shapes (or the shapes of the first and
second tapered portions) of the inner wall portions of the peripheral wall portions 6 b and 7 b
are respectively configured to form such a groove portion G.
[0024]
04-05-2019
9
In the piezoelectric vibrator 8, as shown in the schematic views of FIGS. 5A and 5B, the first
electrode portion 8a1 is left on the outer peripheral portion of the plate-like metal diaphragm 8a
and the metal diaphragm 8a. The piezoelectric ceramic element 8b is provided on the metal
diaphragm 8a, and the mass member 8c is provided on the piezoelectric ceramic element 8b. FIG.
5A is a schematic cross-sectional view of the piezoelectric vibrator 8, and FIG. 5B is a schematic
plan view of the piezoelectric vibrator 8. The metal diaphragm 8a is formed of a circular metal
plate made of iron and nickel alloy and having a thickness of 0.03 mm and a diameter of 14 mm.
The piezoelectric ceramic element 8b is composed of a piezoelectric ceramic 8b1 and a bonding
electrode layer 8b2 and a non-bonding electrode layer 8b3 respectively provided on both sides
of the piezoelectric ceramic 8b1, and has a thickness of 0.05 mm and a diameter of 11.3 mm.
have. The bonding electrode layer 8b2 is bonded to the metal diaphragm 8a so as to be
electrically connected. Lead wires 10a and 10b are respectively connected to the first electrode
portion 8a1 and the non-junction electrode layer 8b3 by soldering, and the piezoelectric vibrator
8 is provided between the first electrode portion 8a1 and the non-junction electrode layer 8b3.
Vibrate in response to the electrical signal being
[0025]
The mass member 8c is formed of a circular metal plate made of iron and nickel alloy and having
a thickness of 0.1 mm and a diameter of 5.6 mm. The mass member 8c is not formed by an
adhesive so as to be disposed substantially concentrically with the metal diaphragm 8a. It is
bonded to the bonding electrode layer 8b3. The adhesive used to bond the mass member 8c is
preferably one that has elasticity in a cured state so that the mass member 8c does not separate
the deformation of the piezoelectric vibrator 8. In this example, a silicone rubber adhesive is
used. Agent was used. The mass member 8c plays a role of adjusting the secondary resonance
frequency of the piezoelectric vibrator 8 to adjust the frequency characteristic of the
piezoelectric sound generator, and sets the secondary resonance frequency obtained from the
piezoelectric vibrator 8 to the predetermined upper limit frequency. It has a mass and shape that
can be set. In this example, by setting the diameter of the metal diaphragm 8a to 14 mm, the
secondary resonance frequency of the piezoelectric vibrator 8 which has become 4000 Hz
becomes 3400 Hz (the upper limit frequency of the standard defined by the Communication
Machinery Manufacturers Association) The mass of the mass member 8c was set to 20 mg.
[0026]
The piezoelectric vibrator 8 is fixed to the first and second tapered portions (wall portions
surrounding the groove portion G) 6g and 7h such that the mass member 8c faces the inner side
(rear side case 7 side) of the storage case (Figure 2).
04-05-2019
10
[0027]
When assembled in the above configuration, the contact state between the peripheral portion of
the metal diaphragm 8a and the first and second tapered portions 6g and 7h may be any of the
states shown in FIGS. It is in a state of
This is based on the processing accuracy of the insulating case and the metal diaphragm and the
dimensional error caused by the expansion and contraction of the material. In design, the
dimensions of each part are determined so as to be in the state of FIG.
[0028]
In the contact state shown in FIG. 6, the peripheral portion of the metal diaphragm 8a is received
in the groove portion G so as to form a slight gap with the groove portion G, and in the contact
state shown in FIGS. The peripheral portion of the metal diaphragm 8a is in contact with the
groove G and is received by the groove G. In the example shown in FIG. 7, the enlarged end
portion 6g1 of the first tapered portion 6g of the front side case 6 and the enlarged end portion
7h1 of the second tapered portion 7h of the rear case 7 correspond to the metal diaphragm 8a. A
contact inner wall portion 6h continuous with the first tapered portion 6g of the peripheral wall
6b is exposed between the end 6g1 and the end 7h1 which is separated by the thickness. In the
example shown in FIG. 8, the enlarged end portion 6g1 of the first tapered portion 6g of the front
case 6 and the enlarged end portion 7h1 of the second tapered portion 7h of the rear case 7 are
in contact with each other. Actually, since the metal diaphragm 8a is metal and the tapered
portion is formed of resin, the corner of the metal diaphragm 8a bites into the tapered portion.
[0029]
In the contact state shown in FIG. 6, between the peripheral portion of the metal diaphragm 8a
and the inner wall 6g of the first case half 6 and the inner wall 7h of the second case half 7, a
metal diaphragm is used. An airtight seal portion (insulating resin melting and curing portion) K
is formed to block communication between a space located on the front side (front air chamber
R1) and a space located on the back side (rear air chamber R2). In the contact state shown in
FIGS. 6 and 7, communication between the front air chamber R1 and the rear air chamber R2 is
04-05-2019
11
blocked between the peripheral portion of the metal diaphragm 8a and the inner wall 6g of the
first case half 6. An airtight seal portion (insulating resin melt-hardened portion) K is formed. The
hermetic seal portion K is formed by dissolving the wall portion of the first tapered portion 6g
with a solvent (for example, dichloromethane) that dissolves the PPO resin of the first tapered
portion 6g and then evaporating the solvent to disappear.
[0030]
Next, the piezoelectric transducer of the present embodiment and the piezoelectric transducer of
the comparative example having the same structure as that of the present embodiment without
the mass member 8c are manufactured, and each piezoelectric transducer is mounted on the
housing 1 as shown in FIG. It attached and comprised the piezoelectric sound generator, and
investigated the frequency characteristic. FIG. 9 shows the relationship between the sound
pressure of each piezoelectric sound generator and the frequency of the piezoelectric vibrator. In
the figure, A, A1 and A2 indicate the characteristic curves of the piezoelectric speaker according
to the present invention, the peak of the primary resonance and the peak of the secondary
resonance, and B, B1 and B2 indicate the characteristic curves of the piezoelectric speaker of the
comparative example, The peak of primary resonance and the peak of secondary resonance are
shown. From this figure, it can be seen that in the piezoelectric sound generator of the
comparative example, the secondary resonance frequency exceeds the upper limit (3400 Hz) of
the standard established by the Communication Machine Industry Association. On the other
hand, in the piezoelectric speaker of the present invention provided with the mass member 8c, it
can be seen that the secondary resonance frequency can be 3400 Hz.
[0031]
In FIG. 10, the sensitivity of each piezoelectric sound generator, the frequency of the
piezoelectric sound generator (the primary and secondary resonance frequencies based on
vibration, the resonance obtained from the front air chamber, and the resonance from the rear
air chamber overlap And the allowable range of the receiver's frequency characteristics defined
by the Communications Equipment Manufacturers Association. In this figure, A and B show the
characteristic curves of the piezoelectric sounders of the present invention and the comparative
example, and C and D show upper and lower tolerance limits. From this figure, in the
piezoelectric sound generator of the comparative example, since the secondary resonance
frequency exceeds 3400 Hz, the frequency of the piezoelectric sound generator falls below the
lower limit of allowable frequency in the frequency range of 300 to 3400 Hz, while the mass
member 8c In the piezoelectric speaker according to the present invention provided with the
04-05-2019
12
above, it is understood that the frequency of the piezoelectric speaker can be within the
allowable range because the secondary resonance frequency approaches 3400 Hz.
[0032]
In the present embodiment, although the mass member is bonded onto the piezoelectric ceramic
element of the piezoelectric vibrator, the mass member is placed at the center of the surface
opposite to the surface of the metal diaphragm to which the piezoelectric ceramic element is
bonded. It may be joined. Also in this case, when an adhesive having elasticity in a cured state is
used as the adhesive, it is possible to suppress the reduction in the compliance of the metal
diaphragm. Further, by thus bonding the mass member and arranging the piezoelectric ceramic
element on the rear air chamber side and arranging the mass member on the front air chamber
side, the thickness of the mass member is increased and the diameter of the mass member is
reduced. It is possible to suppress the reduction in compliance.
[0033]
Further, in the present embodiment, the hermetic seal portion K is formed using a solvent or an
adhesive, but the hermetic seal portion may not necessarily be formed.
[0034]
According to the present invention, the equivalent mass is increased by arranging the mass
member at the central portion of the piezoelectric vibrator, and the secondary resonance
frequency is shifted to the lower frequency side, so that the frequency characteristic is high. It is
possible to adjust the frequency characteristic in a high frequency region by preventing a drop in
sound pressure in the frequency region.
Therefore, it is possible to reduce the diameter of the piezoelectric vibrator and miniaturize the
piezoelectric sound generator while maintaining the desired sound quality.
[0035]
Brief description of the drawings
04-05-2019
13
[0036]
FIG. 1 is a schematic partial cross-sectional view of a handset of a mobile phone in which a
piezoelectric speaker according to an embodiment of the present invention is disposed.
[0037]
FIG. 2 is a schematic cross-sectional view of an example of a piezoelectric transducer used in the
embodiment of the present invention.
[0038]
3 (A) to 3 (C) are a plan view, a cross-sectional view, and a back view of the front side case used
for the piezoelectric transducer of FIG.
[0039]
4 (A) to 4 (C) are a plan view, a cross-sectional view and a back view of the back side case used
for the piezoelectric transducer of FIG. 2.
[0040]
5A and 5B are a cross-sectional view and a plan view of a piezoelectric vibrator used in an
example of the embodiment of the present invention.
[0041]
FIG. 6 is an enlarged view of a fixed portion of the piezoelectric vibrator and the first and second
tapered portions.
[0042]
FIG. 7 is an enlarged view of another fixed portion of the piezoelectric vibrator and the first and
second tapered portions.
[0043]
FIG. 8 is an enlarged view of still another fixed portion of the piezoelectric vibrator and the first
and second tapered portions.
[0044]
04-05-2019
14
FIG. 9 is a diagram showing the relationship between sound pressure and frequency of each
piezoelectric sound generator.
[0045]
Fig. 10 Relationship between sensitivity and frequency of each piezoelectric sound generator
(frequency at which primary resonance frequency and secondary resonance frequency based on
vibration, resonance obtained from the front air chamber and resonance obtained from the rear
air chamber overlap) FIG.
[0046]
FIG. 11 is a schematic partial cross-sectional view of a conventional piezoelectric speaker.
[0047]
FIG. 12 is a diagram showing the relationship between sound pressure and frequency of a
conventional piezoelectric transducer.
[0048]
FIG. 13 is a diagram showing a standard reference of the receiving frequency characteristic of
the receiver set by the Communication Machine Industry Association.
[0049]
Explanation of sign
[0050]
2 Piezoelectric Transducer 6 Front Case (First Case Half) 6a Bottom Wall 6b Peripheral Wall 6c
Opening 6g First Taper 7 Back Case (Second Case Half) 7a Bottom Wall 7b Peripheral Wall 7h
Second tapered portion 8 Piezoelectric vibrator 8a Metal diaphragm 8b Piezoelectric ceramic
element 8c Mass member G Groove portion K Air tight seal portion (insulation resin melting and
curing portion)
04-05-2019
15