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JP2003153387

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2003153387
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
flat speaker, and more particularly to a flat speaker using a piezoelectric element.
[0002]
2. Description of the Related Art Conventionally, cone type dynamic speakers, horn type dynamic
speakers, etc. are known as a speaker device for converting an audio signal into an acoustic
output.
[0003]
For example, a cone-type dynamic speaker includes a diaphragm formed in a conical shape, a
driver unit for driving the diaphragm, a frame for supporting the outer peripheral edge of the
diaphragm, and a cabinet or the like that accommodates these members. It is comprised by the
member.
The driver unit is constituted by members such as a voice coil, a pole, a plate, a magnet, a damper
and a center cap.
[0004]
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The diaphragm used in the cone type dynamic speaker is formed of a material which is light in
weight and has a large internal loss to have the above-described conical shape as a basic shape,
and a driver unit is disposed at the central portion thereof. Generally, the thickness of the
diaphragm is gradually reduced from the inner peripheral portion toward the outer peripheral
portion, and the outer peripheral edge portion is supported by the frame over the entire
circumference through arrows. The frame is a member that couples the diaphragm and the driver
unit and also surrounds the diaphragm to provide its protective function. The frame is generally
formed with a notch window so that the diaphragm is not affected by the reaction due to its
vibration operation. The arrows act to hold the outer peripheral edge of the diaphragm and to
prevent contact with the mounting portion of the cabinet when the diaphragm vibrates.
[0005]
On the other hand, the horn type dynamic speaker is such that the vibration sound of the
diaphragm driven by the voice coil is enlarged and emitted by the horn, and the above-mentioned
cone type is the basic configuration other than having the horn. It is considered equivalent to a
dynamic speaker. That is, also in the horn type dynamic speaker, the magnet, the pole integrally
assembled at the tip thereof, the yoke surrounding the periphery of the pole, and the plate
having the opening facing the pole and assembled to the yoke The driver unit is configured, and
the diaphragm is vibrated by the driver unit.
[0006]
The diaphragm used in the horn type dynamic speaker is formed to have a spherical shape by a
light metal such as aluminum or a synthetic resin. The diaphragm is connected to the plate at its
outer peripheral edge so as to face the pole by closing the opening. The diaphragm is smaller
than the diaphragm of the above-described cone type dynamic speaker, and mechanical
resonance is large because the resonance of the vibration system may be in a substantially
central region of the reproduction band. Therefore, the diaphragm is coupled to the plate without
the damper, and its periphery is vibrated by the driver unit. In other words, also in the horn type
dynamic speaker, the diaphragm thereof is supported with its outer peripheral portion fixed as in
the diaphragm of the cone type dynamic speaker.
[0007]
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In the meantime, many attempts have been made to realize a so-called flat (panel) type speaker
device which is thin without requiring a box or the like and can be installed at an arbitrary
position. However, none of these attempts have led to the realization of an ideal panel-type
speaker device due to technical limitations, acoustic performance limitations, etc.
[0008]
In the conventional speaker device, it is generally considered that when the reproduction input
signal is supplied, the diaphragm acts as a piston by the driver unit to obtain output
reproduction. Therefore, also in the panel type speaker device, an attempt has been made to
manufacture a high precision flat diaphragm which operates in the same manner as the
diaphragm of the above-mentioned conventional speaker device by the electromagnetic drive
method or electrostatic drive method. . For example, in the electrostatic drive type diaphragm,
the outer peripheral portion is supported with a predetermined tension, and when a driving force
is given from the driver unit, waves are generated concentrically and continuously from the
driving position. Such diaphragms must solve various problems resulting from large area piston
motion that results in sound concentration and uncontrollable vibrations by operating as a large
single phase diaphragm.
[0009]
On the other hand, as a panel type speaker device, a speaker device having a panel structure in
which a diaphragm is driven by a driver unit based on bending wave theory has been proposed.
[0010]
In a panel type speaker device based on bending wave theory, a diaphragm having a rigid panel
structure with relatively large mechanical rigidity is used.
The diaphragm generates a complicated vibration mode over the entire surface when a driving
force is applied from the driver unit. The vibration mode is the most complex and densely-packed
waveform structure uniformly distributed over the operating frequency range of the flat panel
(diaphragm). This panel-type speaker device is characterized by the analysis of the physical
characteristics of bending waves with respect to a flat panel (diaphragm) of finite size, the
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velocity-frequency characteristics of the waves, and the driving point impedance characteristics.
[0011]
In the panel type speaker device based on this bending wave theory, a flat panel of bending
rigidity whose parameter is optimized according to the assumed application is used, and
generally, to secure a bending mode of maximum density from the flat panel. The driver unit
drives near the center point of the flat panel. Flat panels have been demonstrated by
mathematical modeling tools with specific aspect ratios that give uniform mode density by finite
element analysis. Also, in the case of a flat panel, the feed position of the driving force for
achieving the best mode uniformity is determined by Fourier type analysis. And, in the flat panel,
although the Fourier type analysis causes some loss in the high frequency band, it is also possible
to drive a panel with a larger area. A flat panel is expressed by a bending stiffness equation that
approximates the bending equation of a more general static beam by taking the zero frequency
limit of the wave function.
[0012]
The panel-type speaker device based on such bending wave theory is a factor that defines the
bending operation of the flat panel, that is, area density, bending rigidity, geometric dimensions
(outer dimension), surface area, position of driving point, and drive unit. The parameter, the
shear module of the core, the internal loss, or the parameter of the supporting method of the
panel are set by being optimally set.
[0013]
By the way, there is a piezoelectric speaker that utilizes a piezoelectric phenomenon such as a
piezoelectric ceramic other than the above dynamic speaker, but this is mainly used as a
notification buzzer of an electronic device or a speaker of a small device such as a mobile phone.
Is only used slightly for tweeters that sound highs in speaker systems such as mini components.
[0014]
The reason is that, since the piezoelectric speaker can not obtain sufficient sound pressure and
the reproduction band is not wide, only limited applications such as small sound and narrow
band can be used.
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For example, FIG. 9 is a semi-logarithmic graph showing an example of the acoustic
characteristics under the conditions of a measurement distance of 1 m and an input voltage of 10
V constant for a single piezoelectric speaker, the sound pressure level (dB) on the vertical axis
and the frequency f on the horizontal axis 50 Hz to 40000 Hz).
[0015]
As apparent from FIG. 9, the piezoelectric speaker has a small sound pressure in the low
frequency range, and in the range of 1 kHz or more, wide dips with sharp undulations continue
repeatedly, and such as a dynamic speaker required for audio equipment as a whole. Flat
acoustic characteristics over the whole area can not be expected at all.
Originally, a piezoelectric vibrator can not be expected to have a large size due to its structure,
and is a piezoelectric vibrator using a circular diaphragm, and its diameter is at most about 4 cm
to 5 cm.
[0016]
Although the piezoelectric speaker has the disadvantages as described above, the conventional
dynamic speaker is (a) thin and simple in structure, (b) can be driven with a low voltage, and (c)
has good electrical-acoustic conversion efficiency. It has superior features compared to
[0017]
By the way, the efficiency (electro-acoustic conversion efficiency) of a dynamic speaker for
general audio equipment is said to be at most about 3 to 5%.
That is, the efficiency of the speaker, which indicates how much of the electrical energy applied
to the input terminal of the speaker has been converted to acoustic energy, is extremely low, the
thermal energy through the electrical resistance of the voice coil, the kinetic energy of the
vibrating member, the support system The energy of deformation, the heat energy through
mechanical resistance, etc. is wasted.
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[0018]
In this respect, it is well known that energy saving of electric products is strongly demanded in
the electric industry including the audio industry, and the reduction of power consumption in
audio devices such as players and amplifiers has been remarkably advanced, but It is the present
condition that the speaker which consumes is not progressing lately. In particular, in the dynamic
cone speaker, devices such as means for increasing the magnetic flux of the magnetic circuit,
means for winding the voice coil as much as possible in the magnetic gap, and means for
increasing the diaphragm area are adopted. Close to Therefore, there is a strong demand for
development of efficient speakers for audio equipment.
[0019]
In this respect, the above-mentioned piezoelectric speaker generally has a large impedance and
high electro-acoustic conversion efficiency, and if this piezoelectric speaker can be adopted as a
speaker for an audio device entirely, the demand for low power consumption is sufficiently
satisfied. Will be able to
[0020]
At this time, problems of the piezoelectric speaker to be solved are (a) improvement of acoustic
characteristics and (b) improvement of sound pressure.
[0021]
The present invention has been made to solve the above-described problems, and is a
piezoelectric speaker that is excellent in acoustic characteristics and has an improved sound
pressure, and a flat speaker that is light in weight and achieves low power consumption. The
purpose is to provide
[0022]
SUMMARY OF THE INVENTION The present invention has been made to achieve the above
object, and the invention according to claim 1 comprises a frame 1 provided with an opening 1a,
and the frame 1 The diaphragm 2 made of a foamed sheet-like elastic body having an opening 2a
smaller than the opening 1a provided on the surface of the opening 1a side, and the diaphragm
so as to cover the opening 2a on the opening 1a side 2, a piezoelectric element unit 3 disposed in
contact with the weight 2, a weight 4 fixed to a central portion of the piezoelectric element unit 3
disposed on the opening 1a side, and the piezoelectric element on the opening 1a side It is
characterized in that it comprises a divided vibration control plate 5 which is disposed so as to
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surround the unit 3 and the weight 4 and be in contact with the diaphragm 2.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present
invention will be described below with reference to the attached drawings.
The embodiments described below are preferable specific examples of the present invention, and
therefore, various technically preferable limitations are given. However, the scope of the present
invention particularly limits the present invention in the following description. As long as there is
no statement of the effect, it is not limited to these modes.
[0024]
FIG. 1 is a plan view of an embodiment of the flat speaker according to the present invention,
FIG. 2 is a side view thereof, FIG. 3 is a rear view thereof, and FIG. 4 is an acoustic characteristic
of the flat speaker according to the present invention. FIG. 5 is an explanatory view showing the
acoustic characteristics of the flat speaker according to the present invention, and FIG. 6 is a view
showing the difference between the frequency characteristics with and without the divided
vibration control plate in FIG. It is a frequency characteristic figure to represent.
[0025]
The flat speaker 10 as shown in FIGS. 1 to 3 according to the present embodiment includes a
frame 1 provided with an opening 1 a substantially at the center, and the opening attached to the
surface of the opening 1 a of the frame 1. A diaphragm 2 made of a lightweight foamed sheetlike elastic loss material having an opening 2a smaller than the portion 1a, and one side (rear
surface) of the diaphragm 2 on the side of the opening 1a and covering the opening 2a A
piezoelectric element unit 3 as a sounding body fixed to 2b, a weight 4 fixed near the center of
the piezoelectric element unit 3 disposed on the opening 1a side, and a weight 4 on the opening
1a side A through hole 5a larger in diameter than the piezoelectric element unit 3 is provided in
the central portion to surround the piezoelectric element unit 3 and the weight 4 and by the
radial divided vibration control plate 5 fixed so as to be in contact with the diaphragm 2 It is
roughly configured.
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Reference numeral 6 denotes an adjustment weight fixed to the tip of the radial divided vibration
control plate 5 described above.
[0026]
Next, each component described above will be described below.
First, the vibrating body constituting the flat speaker 10 described above is a sounding body
utilizing the piezoelectric phenomenon of a piezoelectric element (an electrostriction
phenomenon that causes deformation distortion when an electric field is applied), and mainly as
a piezoelectric element, a ferroelectric ceramic A piezoelectric ceramic excellent in mechanical
strength such as lead zirconate titanate (PZT) or barium titanate is typically used, but a Rochelle
salt crystal or polyvinyl difluoride (PVDF) of an organic piezoelectric material may be used.
[0027]
In this piezoelectric element, the piezoelectric material is formed as a piezoelectric element unit 3
having a multilayer bimorph configuration.
As described above, the multilayer bimorph configuration of the piezoelectric element unit 3
improves the drive capability as the driver unit, and can perform electromechanical conversion to
a wide frequency band, so that the sound pressure can be increased and the timbre can be
increased. It will be good.
[0028]
Further, as the diaphragm 2, as described above, the one having the opening 2a in the
approximate center and using a lightweight foamed sheet elastic loss material (PET is better)
formed in a rectangular panel shape is used.
The diaphragm 2 has a sound output surface on the main surface 7 side to be described later,
and a back surface side (a side on which the diaphragm 2 of the frame 1 is not attached) 8 is a
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driven surface. The pressure is increased and the tone is also good.
[0029]
Next, the weight 4 disposed in the vicinity of the center of the back surface 3a of the
piezoelectric element unit 3 is, for example, a metal piece (lead or the like) with a weight of 20 g,
and fixed to the back surface of the piezoelectric element unit 3 by means such as an adhesive.
Be done.
[0030]
The radial divided vibration control plate 5 is fixed to the back surface 2b of the diaphragm 2
made of the above-described light weight foamed sheet-like elastic loss material and provided
with a through hole 5a having a diameter larger than that of the piezoelectric element unit 3
substantially at the center. The division vibration control plate 5 is a material that is light and
elastic, has a suitable loss, and has a high expansion ratio so as to ensure a certain level of
strength, for example, polystyrene foam. Composed of
In this example, the hole diameter of the substantially central portion was Φ75, the thickness
was 10 mm, the short side length was 240 mm, and the longitudinal length was 320 mm.
[0031]
As described above, by actively utilizing the divided vibration, the surface (main surface) side 7
and the back surface (the driven surface) side of the vibrating body (the side on which the
diaphragm 2 of the frame 1 is not attached) 8 Since the sound interferes with each other, it is
possible to correct the lowered bass, so that a powerful volume feeling can be obtained. The
resonance frequency is determined by the length of the radiation portion of the radial divided
vibration control plate 5 and the adjustment weight 6 fixed to the tip. In this embodiment, by
providing the radial divided vibration control plate 5 in this manner, the reproduction zone can
be expanded.
[0032]
Although not shown in the figure as the state where the signal input terminal is connected to the
piezoelectric element unit 3 of FIGS. 1 to 3 described above, it is of course configured as such.
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[0033]
In the flat speaker 10 configured as described above, for example, when a digital audio signal is
supplied to the piezoelectric element unit 3 through an input terminal (not shown), the
electrostriction characteristic of the piezoelectric element constituting the piezoelectric element
unit 3 described above Thus, the diaphragm 2 is driven, and the emission surface 7 of the
diaphragm 2 emits the reproduction output.
That is, a partial bending operation is generated in the diaphragm 2 with the substantially central
portion of the radiation surface 7 which is the main surface of the diaphragm 2 joined and fixed
to the piezoelectric element unit 3 as a driving point. An electroacoustic conversion system in
which
[0034]
Next, in the flat speaker 10 according to the present embodiment having the above-described
configuration, acoustic characteristics under a constant condition as a measurement distance of 1
m and an input voltage of 5 V will be described with reference to the overall explanatory view of
FIG. As apparent from FIG. 4, according to the configuration of the present embodiment, it can be
seen that substantially flat characteristics are obtained in the band of 70 Hz to 20 KHz. Further,
as apparent from the lower side of FIG. 4, since the impedance is high, the power consumption at
the time of reproducing the music source is about 1⁄5 of the conventional power saving.
[0035]
FIG. 5 is an explanatory view showing acoustic characteristics of the flat speaker according to the
present invention under the same conditions as FIG. 4 described above. In FIG. 5, a PET foam
sheet elastic loss material is used as the diaphragm 2, and a weight of a metal piece (such as
lead) having a weight of 20 g is added near the center of the piezoelectric unit 3 and the
diaphragm The radial divided vibration control plate 5 is fixed to the back surface of the second
case 2. As apparent from FIG. 5, according to the configuration of the present embodiment, the
sound pressure and distortion characteristics are excellent, and can be used as a speaker for
high-band audio.
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[0036]
FIG. 6 is a frequency characteristic diagram showing the difference in frequency characteristics
between the case where the divided vibration control plate 5 is added and the case where the
divided vibration control plate 5 is not added in FIG. It can be seen that there is a marked
difference in the range characteristics, demonstrating the superiority of the configuration of this
embodiment.
[0037]
Further, the superiority of the configuration of the present embodiment will be described with
reference to other embodiments.
FIG. 7 is a piezoelectric speaker using a general PET foam sheet material as the diaphragm 2, and
shows the acoustic characteristics when the piezoelectric unit 3 is attached to the center of the
diaphragm 2. As shown in FIG. In this case, no weight 4 is added to the piezoelectric unit 3. As
apparent from FIG. 7, the ups and downs in sound pressure are severe, and it can not be adopted
for audio use. The acoustic characteristics of FIG. 7 are obtained under the same conditions as
those of FIG. 4 described above.
[0038]
FIG. 8 shows the acoustic characteristics when 20 g of the weight 4 is added to the piezoelectric
unit 3 in FIG. As apparent from FIG. 8, it is understood that the characteristic of 300 Hz or more
has no ups and downs and the characteristic is improved. However, the characteristic of 300 Hz
or less drops sharply, and narrow bands can be seen.
[0039]
The invention according to the present invention is a vibration comprising a frame provided with
an opening and a foam sheet-like elastic body having an opening smaller than the opening
provided on the opening side surface of the frame. It is fixed to a plate, a piezoelectric element
unit disposed on the opening side and in contact with the diaphragm so as to cover the opening,
and a central part of the piezoelectric element unit disposed on the opening side Improvement of
acoustic characteristics and sound by comprising a weight and a divided vibration control plate
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disposed on the opening side, surrounding the piezoelectric element unit and the periphery of
the weight, and arranged to be in contact with the diaphragm. While being able to aim at
pressure improvement, the flat speaker for efficient sound equipments with which power saving
was attained is obtained.
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