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JP2009232176

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DESCRIPTION JP2009232176
[Problem] Even when the volume of the back air chamber is small, sound collection at a low
frequency (low frequency range) is enabled by equivalently lowering the acoustic impedance of
the back air chamber. SOLUTION: A microphone unit 20 including a diaphragm 21 with a voice
coil 21a and a magnetic circuit 22 having a magnetic gap, and the microphone unit 20 supported
at one end side, and a back surface of the diaphragm 21 via an acoustic resistance material 26
inside. In the dynamic microphone including the microphone case 10 having the back air
chamber 12a provided on the side, the sub microphone unit 40 is provided separately from the
microphone unit 20, and an applied voltage is applied between the acoustic resistance material
26 and the back air chamber 12a. Accordingly, a membrane plate 50 made of a piezoelectric
element that is curved and deformed toward the back air chamber 12a is provided, and the
membrane plate 50 is driven by an audio signal (voltage signal) output from the sub microphone
unit 40. Make the acoustic impedance of [Selected figure] Figure 1
ダイナミックマイクロホン
[0001]
The present invention relates to a dynamic microphone, and more specifically, to lower the
acoustic impedance of the back air chamber provided on the back side of the diaphragm
equivalently when the pressure on the front side of the diaphragm increases. It relates to the
technology that makes it possible to pick up sound.
[0002]
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1
First, the general configuration of the dynamic microphone will be described with reference to
FIG.
Since a dynamic microphone is mainly used for vocals and speech, it has a cylindrical
microphone case 10 as a grip. Usually, the microphone case 10 is made of metal such as brass
alloy.
[0003]
In this example, the middle cylinder 12 is coaxially held in the microphone case 10 via the shock
mount member 11 made of a rubber elastic material, and the microphone unit 20 is supported
on one end side of the middle cylinder 12.
[0004]
The microphone unit 20 includes a diaphragm 21 having a voice coil 21 a and a magnetic circuit
22.
The diaphragm 21 has a center dome and a sub dome formed around it, and the voice coil 21a is
attached to the boundary between the center dome and the sub dome via an adhesive.
[0005]
The magnetic circuit 22 is disposed on the other pole side of a magnet 22a magnetized in the
thickness direction, a bottomed cylindrical yoke 22b disposed on one pole side of the magnet
22a, and a bottomed cylindrical yoke 22b. A magnetic gap is formed between the yoke 22b and
the center pole piece 22c, including the center pole piece 22c.
[0006]
The diaphragm 21 and the magnetic circuit 22 are assembled on one end side of the unit holder
23 in a state where the voice coil 21a is disposed in the magnetic gap so as to be able to vibrate.
On the diaphragm 21, a resonator 24 having a front acoustic terminal 24a is placed.
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2
[0007]
Further, in the case of unidirectionality, the unit holder 23 is provided with a rear acoustic
terminal 23 a communicating with the back surface of the diaphragm 21. Both the front acoustic
terminal 24a and the rear acoustic terminal 23a are holes through which sound waves pass.
[0008]
At the other end of the unit holder 23, a cap 25 having a sound hole 25a covered with the
acoustic resistance material 26 is fitted. As a result, a back air chamber 12 a communicating with
the back side of the diaphragm 21 via the acoustic resistance material 26 is formed inside the
middle cylinder 12.
[0009]
A protective cover 27 made of a metal mesh for protecting the microphone unit 20 from a drop
impact or the like is attached to one end of the microphone case 10, and an output connector 30
is attached to the other end of the microphone case 10.
[0010]
By the way, a unidirectional dynamic microphone has both mass control properties and
resistance control properties.
In contrast, omnidirectional dynamic microphones are resistance control. The driving force of the
nondirectional component is obtained by the pressure difference between the front side (sound
receiving side) of the diaphragm 21 and the back air chamber 12a present on the back side, and
the acoustic resistance of the acoustic resistance material 26 It is controlled.
[0011]
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FIG. 5 shows an acoustic equivalent circuit of a unidirectional dynamic microphone. P1 is a front
sound source, P2 is a rear sound source, m0, s0 are the mass and stiffness of the diaphragm 21,
r1 is the acoustic resistance of the acoustic resistance member 26, s1 is the stiffness of the back
air chamber 12a, and m1 is the mass of the back air chamber 12a is there.
[0012]
In the dynamic microphone, the size (volume) of the back air chamber 12a has a great influence
on the frequency band of sound collection. For example, if the back air chamber 12a is small, the
impedance of the back air chamber 12a is high at low frequencies.
[0013]
Therefore, in the dynamic microphone intended to pick up sound up to the low frequency range,
the volume of the back air chamber 12a is increased in both unidirectionality and
nondirectionality, and the impedance of the back air chamber 12a is designed to be low. There is.
[0014]
However, increasing the volume of the back air chamber 12a interferes with the design of other
parts.
In particular, in a microphone in which an electronic circuit is mounted in the microphone case
10 serving as a grip unit like a wireless microphone, the volume of the back air chamber 12a can
not be sufficiently secured.
[0015]
In addition, although the invention which can make the volume of a back air chamber variable
according to a model is described in patent document 1 according to a model, this is a movable
partition plate in the back air chamber of the decided fixed volume. Because the back air
chamber is divided into two by the movable partition plate, the volume of the back air chamber
itself can not be further increased.
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[0016]
Japanese Patent Application Laid-Open No. 62-197
[0017]
Therefore, it is an object of the present invention to enable sound collection at low frequencies
(bass frequency range) by equivalently lowering the acoustic impedance of the back air chamber
even when the volume of the back air chamber is small. It is in.
[0018]
In order to solve the above problems, the present invention supports a microphone unit including
a diaphragm having a voice coil and a magnetic circuit having a magnetic gap in which the voice
coil is disposed so as to be able to vibrate; A dynamic microphone including a microphone case
having a back air chamber provided on the back side of the diaphragm via an acoustic resistance
material inside, a secondary microphone unit that receives an acoustic wave arriving at the
microphone unit and outputs an audio signal A membrane plate comprising a piezoelectric
element is provided between the acoustic resistance material and the back air chamber, and is
bent and deformed toward the back air chamber according to the applied voltage, and the
membrane plate is the sub microphone It is characterized in that it is driven by an audio signal
output from the unit.
[0019]
In the present invention, a nondirectional microphone unit is preferably used as the sub
microphone unit.
[0020]
Among non-directional microphone units, electret condenser microphone units and piezoelectric
microphone units that do not require a power source are particularly preferable, but when
batteries are built in like wireless microphones, power is supplied by wire. If it is a microphone, a
condenser microphone unit may be used.
[0021]
According to the present invention, the microphone unit is provided with the secondary
microphone unit that receives the sound wave arriving to the microphone unit and outputs the
audio signal, and is directed between the acoustic resistance material and the back air chamber
toward the back air chamber according to the applied voltage A membrane plate made of a
piezoelectric element that bends and deforms is provided, and as the pressure on the front side
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of the diaphragm rises, an audio signal output from the secondary microphone unit is applied to
the membrane plate, whereby the membrane plate is back air Since it operates to compress the
chamber and the acoustic impedance of the back air chamber becomes equivalently low, even if
the back air chamber is small, it is possible to pick up a low frequency (low frequency range).
[0022]
Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.
FIG. 1 is a sectional view showing a dynamic microphone according to a first embodiment of the
present invention, FIG. 2 is a sectional view showing a dynamic microphone according to a
second embodiment of the present invention, and FIG. 3 is a dynamic microphone according to
each of the above embodiments. It is an acoustic equivalent circuit schematic.
The same reference numerals are used for the same components as the conventional example
described in FIG.
[0023]
First, a first embodiment shown in FIG. 1 will be described.
The dynamic microphone includes a cylindrical microphone case 10 used as a grip made of a
metal material such as brass alloy.
[0024]
Also in this embodiment, the middle cylinder 12 is coaxially held in the microphone case 10 via
the shock mount member 11 made of a rubber elastic material, and the microphone unit 20 is
supported on one end side of the middle cylinder 12 .
[0025]
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The microphone unit 20 includes a diaphragm 21 having a voice coil 21 a and a magnetic circuit
22.
The diaphragm 21 is made of a synthetic resin film and has a center dome and a sub dome
formed around it, and a voice coil 21a is attached to the boundary between the center dome and
the sub dome through an adhesive.
[0026]
The magnetic circuit 22 is disposed on a disc-like magnet 22a magnetized in the thickness
direction, a bottomed cylindrical yoke 22b disposed on one pole side of the magnet 22a, and the
other pole side of the magnet 22a. A magnetic gap is formed between the yoke 22b and the
center pole piece 22c, including the center pole piece 22c.
[0027]
The diaphragm 21 and the magnetic circuit 22 are assembled on one end side of the unit holder
23 in a state where the voice coil 21a is disposed in the magnetic gap so as to be able to vibrate.
On the diaphragm 21, a resonator 24 having a front acoustic terminal 24a is placed.
[0028]
Since the dynamic microphone according to this embodiment is unidirectional, the unit holder 23
is provided with a rear acoustic terminal 23 a communicating with the rear surface of the
diaphragm 21.
Both the front acoustic terminal 24a and the rear acoustic terminal 23a are holes through which
sound waves pass.
[0029]
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At the other end side of the unit holder 23, a cap 25 having a sound hole 25a covered with the
acoustic resistance material 26 is fitted.
The microphone unit 20 is supported by the middle cylinder 12 by inserting the other end side
of the unit holder 23 into the middle cylinder 12.
[0030]
A protective cover 27 made of a metal mesh is attached to one end of the microphone case 10
for protecting the microphone unit 20 from a drop impact or the like, and an output connector
30 is attached to the other end of the microphone case 10. ing.
[0031]
In the present invention, the sub microphone unit 40 is provided separately from the above
microphone unit 20.
The secondary microphone unit 40 is preferably disposed on the resonator 24, and receives
sound waves arriving from the sound source (not shown) to the microphone unit 20.
[0032]
For the secondary microphone unit 40, preferably a nondirectional microphone unit is used.
In the first embodiment, a nondirectional electret condenser microphone unit 41 is used as the
sub microphone unit 40.
[0033]
Also in the present invention, the back air chamber 12 a is provided in the middle cylinder 12,
but in this embodiment, the inside of the middle cylinder 12 is the partition plate 13 in order to
store electronic circuit parts and the like not shown in the middle cylinder 12. The volume of the
back air chamber 12a is considerably smaller than that of the prior art.
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[0034]
In this way, at low frequencies, the acoustic impedance of the back air chamber 12a becomes
high, which hinders sound collection in the low frequency range.
In order to solve this point, in the present invention, a film plate 50 made of a piezoelectric
element is provided between the acoustic resistance material 26 and the back air chamber 12a.
The membrane plate 50 has its periphery fixed to the inner cylinder 12 on the inner wall surface
by fixing means such as an adhesive.
[0035]
The piezoelectric element deforms in accordance with the applied voltage, but in the present
invention, the central portion of the film plate 50 is designed to be curved and deformed toward
the back air chamber 12a when a voltage is applied.
[0036]
In the first embodiment, the audio signal (voltage signal) output from the electret condenser
microphone unit 41 as the sub microphone unit 40 is amplified in a predetermined manner by
the amplifier 41 a and applied to the membrane plate 50.
[0037]
When the pressure on the front surface side (the sound receiving surface side) of the diaphragm
21 is increased by the sound wave coming from the sound source (not shown), the level of the
voltage signal output from the electret condenser microphone unit 41 becomes high. Bends
toward the back air chamber 12a to compress the back air chamber 12a.
Along with this, the pressure on the back side of the diaphragm 21 is relatively lowered.
[0038]
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As a result, the acoustic impedance of the back air chamber 12a operates to be equivalently
reduced, and even when the volume of the back air chamber 12a is small, it is possible to pick up
a low frequency sound.
[0039]
Next, a second embodiment shown in FIG. 2 will be described.
The second embodiment is different from the first embodiment in that the piezoelectric
microphone unit 42 is used as the sub microphone unit 40, and the other configuration may be
the same as the first embodiment. , The description is omitted.
[0040]
In the case of the piezoelectric microphone unit 42, an electromotive voltage is generated by
deformation of the diaphragm made of piezoelectric elements by sound waves, so the output
terminal is directly connected to the film plate 50 through the two lead wires 42a and 42b. be
able to.
In some cases, it may be via a voltage amplifier.
[0041]
The operation is the same as the first embodiment, and when the pressure on the front side (the
sound receiving surface side) of the diaphragm 21 is increased by the sound wave coming from
the sound source (not shown), a voltage proportional to that is outputted from the piezoelectric
microphone unit 42 Be done.
[0042]
As a result, the central portion of the membrane plate 50 is curved and deformed toward the
back air chamber 12a, and the back air chamber 12a is compressed, and the pressure on the
back side of the diaphragm 21 is relatively lowered accordingly. It operates as if the acoustic
impedance of the air chamber 12a becomes equivalently small, and even when the volume of the
back air chamber 12a is small, it is possible to pick up a low frequency sound.
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[0043]
FIG. 3 shows an acoustic equivalent circuit of the dynamic microphone according to the present
invention described in the first embodiment and the second embodiment.
[0044]
P1 is a front sound source, P2 is a rear sound source, m0, s0 are the mass and stiffness of the
diaphragm 21, r1 is the acoustic resistance of the acoustic resistance member 26, s1 is the
stiffness of the back air chamber 12a, and m1 is the mass of the back air chamber 12a However,
in the case of the present invention, since the acoustic impedance of the back air chamber 12a
can be made equivalently small, the stiffness s1 of the back air chamber 12a is represented by a
variable capacitor.
[0045]
In the case of the secondary microphone unit 40 in the first and second embodiments, although
it is preferable in that it does not require the drive power source in particular, it is preferable to
incorporate a battery as in a wireless microphone or In the case of a microphone to which power
is supplied, a condenser microphone unit requiring a polarized power supply can also be used as
the secondary microphone unit 40.
[0046]
In the above embodiment, the back air chamber 12a is provided in the middle cylinder 12
disposed in the microphone case 10. In this case, the middle cylinder 12 is included in the
microphone case 10 as a component thereof. The back air chamber 12 a may be substantially
provided in the microphone case 10.
[0047]
FIG. 1 is a cross-sectional view showing a dynamic microphone according to a first embodiment
of the present invention.
Sectional drawing which shows the dynamic microphone concerning 2nd Embodiment of this
invention.
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The acoustic equivalent circuit schematic in the dynamic microphone concerning each said
embodiment.
Sectional drawing which shows the general structure of a dynamic microphone as a prior art
example.
The acoustic equivalent circuit schematic in the dynamic microphone concerning the abovementioned conventional example.
Explanation of sign
[0048]
DESCRIPTION OF SYMBOLS 10 microphone case 12 middle cylinder 12a back air chamber 20
microphone unit 21 diaphragm 21a voice coil 22 magnetic circuit 23 unit case 26 acoustic
resistance material 30 output connector 40 sub microphone unit 41 electret condenser
microphone unit 42 piezoelectric microphone unit 50 from piezoelectric element Membrane
plate
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