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JP2008294178

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DESCRIPTION JP2008294178
An electro-acoustic transducer for obtaining a high voltage audio signal, and a condenser
headphone driven by the electro-acoustic transducer are provided. An electroacoustic transducer
includes a giant magnetostrictive member, a first piezoelectric element and a second piezoelectric
element disposed at each end of the magnetostrictive member, a first piezoelectric element, a
giant magnetostrictive member, and a second piezoelectric element. And a magnetic field
generation unit 3 disposed around the giant magnetostrictive member 2 and generating a
magnetic field oriented along the displacement direction of the giant magnetostrictive member 2
according to the audio signal, The first piezoelectric element 4 and the second piezoelectric
element 5 are disposed such that the polarities thereof face each other, and both ends of the first
piezoelectric element 4 or the second piezoelectric element 5 are output portions 11 and 12. The
output units 11 and 12 are connected to the fixed electrodes 22 and 23 of the condenser type
headphone unit provided with the diaphragm 21 and the fixed electrodes 22 and 23 opposed
thereto, respectively, to form a condenser headphone 20. [Selected figure] Figure 2
Electro-acoustic transducer and condenser headphone
[0001]
The present invention relates to an electro-acoustic transducer and a condenser headphone using
the electro-acoustic transducer, and more specifically, a low-voltage audio signal is converted
into a high-voltage audio signal without using a step-up transformer. The present invention
relates to a technology for generating sound by vibrating a diaphragm by changing a capacitor
capacity between a diaphragm in a unit and a pair of fixed electrodes facing each other across
the diaphragm in accordance with an audio signal.
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[0002]
In order to drive a capacitor type speaker or a piezoelectric type speaker, a high drive voltage is
required.
For example, the condenser headphone is driven by applying an audio signal of a high voltage of
about 100 V effective between the diaphragm and the fixed electrode facing each other.
However, since a normal audio signal is a signal of a relatively low voltage, it is necessary to
boost the audio signal level to a high voltage of about 100 V effective value.
[0003]
Generally, in order to boost the voltage of the audio signal to a high voltage of about 100 V
effective, it is necessary to increase the transformation ratio, for example, 1:70, and a step-up
transformer with a high transformation ratio is used. In addition, it is desirable that the power
amplifier for driving the speaker is as inexpensive as possible. Therefore, a boosting transformer
with a high transformation ratio is connected to the power amplifier so that sound is output from
the speaker.
[0004]
Condenser headphones using a step-up transformer, for example, have a structure as shown in
FIG. 4 and are connected as shown. In FIG. 4, the condenser headphone 50 includes a condenser
type headphone unit configured of one diaphragm 51 and a pair of fixed electrodes 52 and 53
disposed on both sides of the diaphragm 51. The diaphragm 51 is circular, and its peripheral
portion is supported by the diaphragm support 54. In FIG. 4, the diaphragm 51 and the fixed
electrodes 52 and 53 are shown in a longitudinal cross section. The pair of fixed electrodes 52
and 53 is disposed with a predetermined gap with respect to the diaphragm 51. The diaphragm
51 and the fixed electrodes 52 and 53 are incorporated in a unit case (not shown) so as to
maintain the relative positional relationship as described above. In addition, a signal source 55
for an audio signal and a boosting transformer 56 for boosting the audio signal output from the
signal source 55 are provided. The audio signal boosted by the step-up transformer 56 is applied
to the fixed electrode 52 by the first lead wire 58 from one output terminal of the step-up
transformer 56, and the fixed electrode by the second lead wire 59 from the other output
terminal. 53 is applied. Further, in FIG. 4, a battery 57 is connected as a power source for
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applying a polarization voltage to the diaphragm 51. However, in the case where the condenser
type headphone unit is an electret type, there is no need to apply a polarization voltage, so there
is no need to connect the battery 57.
[0005]
However, the frequency of the audio signal is about 20 Hz to 20 kHz, and when the audio signal
in such a frequency band is boosted using the step-up transformer with a large transformation
ratio as described above, there is a problem that the frequency response is degraded. In addition,
since a transformer with a large transformation ratio becomes large and heavy, it becomes a
factor that hinders downsizing and weight reduction of headphones.
[0006]
Therefore, a technique has been proposed in which a high voltage is generated by using a
piezoelectric element without using a step-up transformer (see, for example, Patent Document 1).
However, the one described in the above-mentioned Patent Document 1 relates to a high voltage
generating circuit which prevents a decrease in boosting efficiency due to a temperature change,
and as intended by the present invention, a high voltage audio signal of low voltage is high. It
does not relate to an electroacoustic transducer that boosts to a voltage.
[0007]
Unexamined-Japanese-Patent No. 5-252734
[0008]
The present invention has been made in view of the above circumstances, and provides an
electroacoustic transducer that can obtain a high voltage audio signal without using a step-up
transformer, and a condenser headphone using the electroacoustic transducer. Intended to be
provided.
[0009]
An electro-acoustic transducer according to the present invention comprises: a giant
magnetostrictive member displaced according to a change in a magnetic field; a first piezoelectric
element and a second piezoelectric element disposed at each end of the giant magnetostrictive
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member in the displacement direction; A single piezoelectric element, the super magnetostrictive
member, a support member for assembling and holding the second piezoelectric element in
series, and the super magnetostrictive member disposed around the super magnetostrictive
member according to the supply of a drive current based on an audio signal A magnetic field
generation unit for generating a magnetic field oriented in the direction of displacement of the
first piezoelectric element and the second piezoelectric element, and the first piezoelectric
element and the second piezoelectric element are arranged to face each other The main feature is
that both ends of the piezoelectric element are output parts.
[0010]
Further, in the condenser headphone according to the present invention, the condenser
capacitance between the electroacoustic transducer, the diaphragm, and a pair of fixed electrodes
disposed opposite to each other with the diaphragm interposed therebetween is changed
according to the audio signal. A condenser type headphone unit that vibrates the diaphragm to
generate sound, and the output part of the electro-acoustic transducer is connected to a fixed
electrode of the condenser type headphone unit, respectively, and corresponding to an audio
signal A signal voltage generated by a piezoelectric element of an electroacoustic transducer is
applied to a fixed electrode of the condenser type headphone unit.
[0011]
According to the electro-acoustic transducer of the present invention, when the magnetic field
generation unit generates a magnetic field in response to the supply of the drive current based
on the audio signal, the giant magnetostrictive member is displaced according to the fluctuation
of the magnetic field, and mechanical stress Occur.
This mechanical stress is transmitted to the first piezoelectric element and the second
piezoelectric element disposed at each end in the displacement direction of the giant
magnetostrictive member, which are assembled and held in series by the support member, and
the first piezoelectric element and the second piezoelectric element The piezoelectric elements
generate high voltage signals respectively corresponding to the audio signals.
And this high voltage sound signal can be outputted from the output part of the first piezoelectric
element or the second piezoelectric element.
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Therefore, the low voltage audio signal input to the magnetic field generation unit is converted to
mechanical stress by the magnetostrictive member, and the mechanical stress is further
converted to high voltage audio signal by the piezoelectric element and output from the output
unit It will be.
Therefore, it is possible to provide an electroacoustic transducer capable of obtaining a high
voltage audio signal without using a step-up transformer.
[0012]
Further, according to the condenser headphone of the present invention, the high voltage sound
signal outputted from the output part of the electroacoustic transducer is applied to a pair of
fixed electrodes constituting the condenser type headphone unit, and the diaphragm is It vibrates
according to the voice signal, is converted to voice, and is output. The high voltage audio signal
output from the electroacoustic transducer is input to the condenser type headphone unit to
drive the condenser headphone. Therefore, unlike the conventional condenser headphones, it is
not necessary to use a step-up transformer with a high transformation ratio, and it is possible to
provide the condenser headphones which can obtain a high voltage audio signal. Moreover, since
this condenser headphone does not use a step-up transformer, it can be made compact and
lightweight.
[0013]
Hereinafter, embodiments of an electro-acoustic transducer according to the present invention
and a condenser headphone using the electro-acoustic transducer will be described with
reference to the drawings. FIG. 1 is a structural view and a connection diagram schematically
showing an embodiment of an electroacoustic transducer according to the present invention. The
electroacoustic transducer 10 of the present invention includes the support member 1, the giant
magnetostrictive member 2, and the first piezoelectric element 4 and the second piezoelectric
element 5.
[0014]
The support member 1 is a support member that assembles and holds the first piezoelectric
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element 4, the giant magnetostrictive member 2, and the second piezoelectric element 5 in series,
and is made of a rigid body such as metal. In FIG. 1, the support member 1 is a fixing bolt
(hereinafter, denoted by reference numeral 1) inserted through the central holes of the giant
magnetostrictive member 2 and the piezoelectric elements 4 and 5. And the nut 9 is screwed in
from the tip side. The first piezoelectric element 4, the giant magnetostrictive member 2, and the
second piezoelectric element 5 are fastened in a mechanically joined state by fastening means
including the fixing bolt 1 and the nut 9. Therefore, the giant magnetostrictive member 2, the
giant magnetostrictive member 2, and the second piezoelectric element 5 are elastically
supported by the tension (resistance) of the fixing bolt 1. Moreover, the coupling of the
mechanical vibration system becomes dense, and the conversion efficiency becomes high.
Moreover, since it is fastened by the tension of the fixing bolt 1, it is equivalent to positioning the
giant magnetostrictive member 2 between so-called Langevin type piezoelectric electrons, and
the giant magnetostrictive member that was necessary when used alone as a giant
magnetostrictive member There is no need for a coil spring to support the Further, both end
portions where the first piezoelectric element 4, the giant magnetostrictive member 2 and the
second piezoelectric element 5 are assembled in series, that is, the head of the fixing bolt 1, the
nut 9 and the first and second piezoelectric elements Washers 7 and 8 intervene between them.
The first piezoelectric element 4, the giant magnetostrictive member 2, and the second
piezoelectric element 5 are stably supported by the washers 7 and 8.
[0015]
The giant magnetostrictive member 2 is a giant magnetostrictive element (hereinafter referred to
as symbol 2) that has the property of being displaced (stretched) according to the variation of the
magnetic field. ) Is the material. The giant magnetostrictive element 2 is an element made of, for
example, a single crystal alloy mainly composed of terbium, dysprosium, iron, etc. When a
magnetic field is applied from the outside, the direction of the external magnetic field is applied
by the Joule effect. It has the property of causing a change in dimension extending along the axis,
and the property of causing a change in the amount of magnetization due to a billy effect when
subjected to external stress to cause compressive deformation. In addition, the giant
magnetostrictive element 2 is made of powder metallurgy and has extremely high mechanical
strength such as compressive strength of 600 × 10 <6> (Pa) and tensile strength of 20 × 10
<6> (Pa). In addition, Young's modulus is also extremely high at 2.0 × 10 <6> (N / m <2>). As
described above, since the giant magnetostrictive member is formed of an element having high
mechanical strength, it is not broken even if stress is applied. Moreover, since the Young's
modulus is high, it is possible to secure the response to high frequency.
[0016]
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In FIG. 1, the giant magnetostrictive element 2 is in the shape of a circular cylinder having a
central hole, and the fixing bolt 1 is inserted inside (in the center). As described above, since the
giant magnetostrictive element 2 is an annular body, it is efficiently and easily supported by the
fixing bolt 1.
[0017]
The magnetic field generation unit 3 is disposed around the giant magnetostrictive member 2 at
intervals, and generates a magnetic field in a direction along the displacement direction of the
giant magnetostrictive member 2 according to the supply of the drive current based on the audio
signal , Symbol 3 shows. )とする。 In FIG. 1, the coil 3 is wound an appropriate number of
times with the giant magnetostrictive element 2 as a core. The coil 3 may be wound around a
bobbin, and the super magnetostrictive element 2 may be inserted into the center hole of the
bobbin. A signal source 6 is connected to the coil 3, and an audio signal is input from the signal
source 6. The voltage level of the audio signal input to the coil 3 is a low voltage signal level
equivalent to the voltage level input to a commercially available headphone. The coil 3 can be
driven by an ordinary audio amplifier.
[0018]
The first piezoelectric element 4 and the second piezoelectric element 5 output an electrical
signal according to the amount of strain by the piezoelectric effect when mechanical strain
occurs, and are arranged at each end of the giant magnetostrictive element 2 in the displacement
direction It is done. The first piezoelectric element 4 and the second piezoelectric element 5 are
disposed such that the polarities thereof face each other as shown by the arrows in FIG. Further,
the first piezoelectric element 4 and the second piezoelectric element 5 have a cylindrical shape
having the same diameter as the giant magnetostrictive element 2 having an annular body
having a central hole, and the fixing bolt 1 is inserted inside (center) There is. Therefore, the
giant magnetostrictive element 2 assembled in series, and the first piezoelectric element 4 and
the second piezoelectric element 5 have a continuous cylindrical shape. As described above, the
first piezoelectric element 4 and the second piezoelectric element 5 are efficiently and easily
supported by the fixing bolt 1 by being annular members.
[0019]
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It is desirable that the first piezoelectric element 4 and the second piezoelectric element 5 be
configured in a stack shape in which a plurality of layers are stacked. By laminating a plurality of
piezoelectric elements, they are electrically connected in series, and a high voltage can be
generated from both ends of each of the laminated piezoelectric elements. Further, output
terminals are provided at both ends of each of the stacked piezoelectric elements. In FIG. 1, the
first terminal portion 14A is disposed on one end side of the first piezoelectric element 4, and the
second terminal portion 14B is disposed on the other end side. On the other hand, the third
terminal portion 15A is disposed on one end side of the second piezoelectric element 5, and the
fourth terminal portion 15B is disposed on the other end side. That is, the first terminal portion
14A is disposed between the washer 7 and one end side of the first piezoelectric element 4, and
the second terminal portion 14B is located between the other end side of the first piezoelectric
element 4 and the super magnetostrictive element 2. It is arranged. On the other hand, the fourth
terminal portion 15B is disposed between the giant magnetostrictive element 2 and the other end
of the second piezoelectric element 5, and the third terminal 15A is disposed between the one
end of the second piezoelectric element 5 and the washer 8. It is arranged. Therefore, from each
terminal part of the both ends in the 1st piezoelectric element 4 and the 2nd piezoelectric
element 5, the output voltage of each laminated piezoelectric element is added and it outputs.
[0020]
Further, the first terminal portion 14A of the first piezoelectric element 4 and the third terminal
portion 15A of the second piezoelectric element 5 are connected to each other to form a first
output portion 11. On the other hand, the second terminal portion 14 B of the first piezoelectric
element 4 and the fourth terminal portion 15 B of the second piezoelectric element are
connected to each other to form a second output portion 12. Signals are output from these
output units 11 and 12. Although the first piezoelectric element 4 and the second piezoelectric
element 5 are connected in parallel in the illustrated example, they may be connected in series.
[0021]
In the electroacoustic transducer 10 configured as described above, when an audio signal is
input from the signal source 6 to the coil 3, a magnetic field corresponding to the audio signal is
generated in the coil 2, and the magnetostrictive element 2 has its magnetostriction It tries to
expand and contract corresponding to the magnetic field by the action. The dimensional change
of the giant magnetostrictive element 2 due to the external magnetic field is referred to as the
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Joule effect. Since the giant magnetostrictive element 2 is joined in series with the piezoelectric
element 4 and held between the fixing bolts 1, dimensional change is limited, and mechanical
stress is generated inside the giant magnetostrictive element 2. This stress is transmitted
(applied) to the first piezoelectric element 4 and the second piezoelectric element 5 disposed at
each end of the giant magnetostrictive element 2 in the displacement direction, and is applied to
both ends of the first piezoelectric element 4 and the second piezoelectric element 5. A high
voltage signal corresponding to the stress, that is, corresponding to the audio signal is generated.
Therefore, a low voltage signal can be converted to a high voltage signal.
[0022]
By using the above-described electroacoustic transducer 10, it is possible to configure a
condenser headphone which needs to be driven by a high voltage audio signal. FIG. 2 is a
structural view and a connection diagram schematically showing an embodiment of a condenser
headphone using the electroacoustic transducer according to the present invention. In FIG. 2, in
the condenser headphone 20, the condenser capacitance between the electro-acoustic transducer
10, the diaphragm 21 and a pair of fixed electrodes 22 and 23 opposed to both surfaces of the
diaphragm 21 is changed according to the audio signal. And the condenser type headphone unit
that vibrates the diaphragm 21 to generate sound. In addition, the condenser headphone 20
connects the output parts 11 and 12 of the electroacoustic transducer 10 to the fixed electrodes
22 and 23 of the condenser type headphone unit, respectively, and corresponds to the audio
signal. Signal voltages generated by the one piezoelectric element 4 and the second piezoelectric
element 5 are applied to the fixed electrodes 22 and 23 of the condenser type headphone unit.
[0023]
By inputting the high voltage sound signal generated by the first piezoelectric element 4 and the
second piezoelectric element 5 to the condenser type headphone unit, the condenser type
headphone unit can be driven. The embodiment shown in FIG. 2 does not merely input high
voltage audio signals respectively generated by the first piezoelectric element 4 and the second
piezoelectric element 5 to the condenser type headphone unit, but more efficiently the condenser
type headphone unit In order to be able to drive, the structure of the condenser type headphone
unit, the structure of the first piezoelectric element 4 and the structure of the second
piezoelectric element 5, and the electrical connection are further devised. This will be explained
concretely.
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[0024]
As seen in a condenser microphone, a condenser type headphone unit is mainly composed of a
diaphragm made of a thin film that vibrates according to a voice, and a fixed electrode disposed
opposite to the diaphragm with a predetermined gap. When a capacitor is formed by the
diaphragm and the fixed electrode and the voltage applied between the diaphragm and the fixed
electrode is changed, the diaphragm vibrates according to the change of the voltage, and a sound
is generated.
[0025]
In the embodiment shown in FIG. 2, the configuration of the condenser type headphone unit
includes a diaphragm 21 and a pair of fixed electrodes 22 and 23 disposed on both sides of the
diaphragm 21. The diaphragm 21 is circular, and its peripheral portion is supported by the
diaphragm support 24. In FIG. 2, the diaphragm 21 and the fixed electrodes 22 and 23 are
shown in a longitudinal cross section. The pair of fixed electrodes 22 and 23 is disposed with a
predetermined gap with respect to the diaphragm 21. The diaphragm 21 and the fixed electrodes
22 and 23 are incorporated in a unit case (not shown) so as to maintain the relative positional
relationship as described above.
[0026]
The first output 11 of the electroacoustic transducer 10 is electrically connected to the fixed
electrode 22, while the second output 12 is electrically connected to the fixed electrode 23. In
this example, the first output unit 11 is a positive pole, and the second output unit 12 is a
negative pole.
[0027]
In the condenser headphone 20 configured as described above, when an audio signal is input
from the signal source 6 to the coil 3, a magnetic field corresponding to the audio signal is
generated in the coil 2, and the giant magnetostrictive element 2 has its magnetostrictive effect.
Try to displace (stretch) in response to the magnetic field. The giant magnetostrictive element 2
is joined in series with the first piezoelectric element 4 and the second piezoelectric element 5
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disposed at each end in the displacement direction, and the dimensional change is limited
because the element is held by the fixing bolt 1. Mechanical stress is generated inside the giant
magnetostrictive element 2. This stress is transmitted from the giant magnetostrictive element 2
to the first piezoelectric element 4 and the second piezoelectric element 5, and both ends of the
first piezoelectric element 4 and the second piezoelectric element 5 are consequently high
corresponding to the above-mentioned audio signal. A signal of voltage is generated. Then, by
applying the high voltage signal to the fixed electrodes 22 and 23 constituting the condenser
type headphone unit, the diaphragm 21 is vibrated corresponding to the above audio signal, and
the condenser headphone is converted by the converted high AC signal. 20 can be driven to emit
an acoustic wave from the diaphragm 21.
[0028]
As described above, the condenser type headphone unit includes the diaphragm 21 and the pair
of fixed electrodes 22 and 23 disposed opposite to each other with the diaphragm 21 interposed
therebetween, and the first terminal portion 14A of the first piezoelectric element 4 And the third
terminal portion 15A of the second piezoelectric element 5 are connected to each other and the
first output portion 11 is connected to the fixed electrode 22, and the second terminal portion
14B of the first piezoelectric element 4 and the second piezoelectric element The second output
portion 12 formed by bonding the fourth terminal portion 15B of the element to each other is
connected to the fixed electrode 23. Therefore, the audio signal is boosted to a high voltage by
the boosting means comprising the giant magnetostrictive element 2 and the first piezoelectric
element 4 and the second piezoelectric element 5 and applied to the pair of fixed electrodes 22
and 23, and the diaphragm 21 is fixed It drives with both the capacitor | condenser structure
comprised with the electrode 22, and the capacitor | condenser structure comprised with the
fixed electrode 23. FIG. Thus, since the diaphragm 21 is efficiently driven by the fixed electrodes
22 and 23 sandwiching the diaphragm 21, sound waves with sufficiently high sound pressure
can be output.
[0029]
Thus, even if the audio signal input from the signal source 6 is a general low voltage signal, it is
boosted to a high voltage by the magnetostrictive element 2 and the first piezoelectric element 4
and the second piezoelectric element 5, It is not necessary to use a step-up transformer with a
high transformation ratio as in conventional condenser type headphones, and a compact and
lightweight condenser headphone can be obtained.
[0030]
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11
In addition, by using the electro-acoustic transducer 10 according to the present invention, it is
possible to realize a voltage variable oscillator (VCO) which can change the oscillation frequency
by the input voltage.
FIG. 3 is a structural view and a connection diagram schematically showing an embodiment of a
voltage variable oscillator using the electro-acoustic transducer according to the present
invention. In FIG. 3, the voltage variable oscillator 30 includes an oscillation circuit connected to
the coil 3 and configured of a capacitor division circuit and a transistor. Therefore, when the first
output unit 11 and the second output unit 12 are respectively used as signal input units, and
signal voltages are applied from the first output unit 11 and the second output unit 12 to the
first piezoelectric element 4 and the second piezoelectric element 5 According to the signal
voltage, the first piezoelectric element 4 and the second piezoelectric element 5 tend to expand
and contract, and stress is applied to the giant magnetostrictive element 2. Since the giant
magnetostrictive element 2 has a property that the inductance changes in accordance with the
applied stress, the oscillation frequency of the above-mentioned oscillation circuit can be
changed by the change of the inductance.
[0031]
FIG. 1 is a structural view and a connection diagram schematically showing an embodiment of an
electroacoustic transducer according to the present invention. FIG. 1 is a structural view and a
connection diagram schematically showing an embodiment of a condenser headphone using an
electroacoustic transducer according to the present invention. FIG. 1 is a structural view and a
connection diagram schematically showing an embodiment of a voltage variable oscillator using
an electro-acoustic transducer according to the present invention. FIG. 1 is a structural view and
a connection diagram schematically showing an embodiment of a conventional electroacoustic
transducer.
Explanation of sign
[0032]
Reference Signs List 1 fixed bolt (support member) 2 super magnetostrictive member (super
magnetostrictive element) 3 magnetic field generating unit (coil) 4 first piezoelectric element
(piezoelectric element stack) 5 second piezoelectric element (piezoelectric element stack) 6 signal
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source 7, 8 washer 9 nut 10 electroacoustic transducer 11 first output section 12 second output
section 14A first terminal section 14B second terminal section 15A third terminal section 15B
fourth terminal section 20 condenser headphone 21 diaphragm 22, 23 fixed electrode 24
vibration Plate support
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