JP2016012756

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DESCRIPTION JP2016012756
An object of the present invention is to provide a dynamic microphone capable of preventing a
wall surface forming a back air chamber from having a specific resonance frequency and
effectively preventing a standing wave from being generated in the back air chamber. A dynamic
microphone unit 15 includes a diaphragm 17 having a voice coil 16 and a magnetic circuit 18
having a magnetic gap in which the voice coil 16 is disposed so as to be able to vibrate, and the
dynamic microphone unit 15 is connected. A bottomed casing 13 forming a back air chamber 14
communicating with the back surface of the diaphragm 17, and the pressure-sensitively disposed
in the casing 13 as the distance from the dynamic microphone unit 15 increases An acoustic
resistor 27 made of metal fiber is provided with a recess 28 gradually decreasing. [Selected
figure] Figure 1
Dynamic microphone and back air chamber molding method
[0001]
The present invention relates to a dynamic microphone in which an air chamber formed in the
back of a dynamic microphone unit is improved and a method of forming the back air chamber.
[0002]
It is known that omnidirectional dynamic microphones operate with resistance control, and
unidirectional dynamic microphones operate with mass control and resistance control.
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Resistance control of the dynamic microphone is realized by providing an acoustic resistance
disposed in the immediate vicinity of the rear of the diaphragm and a back air chamber in which
sound waves do not enter behind the acoustic resistance. The acoustic resistance is at the
entrance of the back air chamber, and when the volume of the back air chamber is extremely
large, the impedance seen from the air chamber to the air chamber is almost acoustic resistance.
[0003]
However, if the volume of the back air chamber is small, the stiffness of the air chamber is
present, so that in the low region the impedance of the air chamber operates in series with the
acoustic resistance. Therefore, if the back air chamber is designed to be small, the frequency
response in the low range is reduced, and the directivity in the low range is also changed. In
reality, it is impossible to increase the volume of the back air chamber infinitely, and in particular
in a hand-held dynamic microphone, the volume of the back air chamber is more restricted.
[0004]
On the other hand, when any part of the wall forming the back air chamber vibrates, a sound
wave generated as the volume of the air chamber fluctuates reaches the diaphragm through the
aforementioned acoustic resistance. Therefore, when a part of the wall of the air chamber
vibrates, the directional frequency response of the microphone is degraded in the vicinity of the
resonance frequency.
[0005]
In addition, when a bottomed pipe-like air chamber is used, a standing wave is generated in the
longitudinal direction. This is generated by the sound wave entering the air chamber through the
aforementioned acoustic resistance. For this purpose, means is generally employed to insert a
sponge or the like having a small acoustic resistance into the air chamber to prevent the
generation of the standing wave. However, in this case, since the acoustic resistance inserted into
the air chamber is connected in series equivalent to the acoustic resistance for realizing the
resistance control described above, the acoustic resistance for suppressing the generation of
standing waves is the minimum necessary. It is necessary to keep it in range.
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[0006]
Patent Document 1 proposes a dynamic microphone having a configuration in which the opening
cross-sectional area of the back air chamber is set to be smaller as the distance from the
diaphragm increases. According to the dynamic microphone disclosed in Patent Document 1, the
microphone grip (grip case) and the back air chamber housed in the microphone grip are formed
so that the opening cross-sectional area decreases toward the rear end side. And thereby
configured to suppress the occurrence of standing waves in the microphone grip and in the back
air chamber.
[0007]
Patent No. 3882268
[0008]
According to the dynamic microphone disclosed in Patent Document 1 described above, if the
shape of the outer wall of the back air chamber and the shape in the microphone grip do not
substantially match, the volume in the microphone grip as shown in FIG. It can not be used.
That is, as described above, it is desirable to set the volume of the back air chamber as large as
possible. In the dynamic microphone disclosed in Patent Document 1, for example, in order to
form a conical back air chamber, There is a problem that the volume is limited.
[0009]
Therefore, the present invention can utilize the volume in the grip case effectively to design the
back air chamber large, and prevent the wall surface forming the back air chamber from having a
specific resonance frequency, and further, the back It is an object of the present invention to
provide a dynamic microphone and a method of forming a back air chamber that can effectively
prevent standing waves from being generated in the air chamber.
[0010]
A dynamic microphone according to the present invention, which has been made to achieve the
above-mentioned problems, includes a dynamic microphone unit including a diaphragm provided
with a voice coil and a magnetic circuit provided with a magnetic gap in which the voice coil is
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vibratably disposed. A bottomed casing connected to the dynamic microphone unit and forming a
back air chamber communicating with the back surface of the diaphragm, and crimped and
disposed in the casing, the opening being opened as it is separated from the dynamic microphone
unit And an acoustic resistor made of a metal fiber provided with a depression whose area
gradually decreases.
[0011]
In this case, aluminum fibers are preferably used as the metal fibers.
Further, it is also possible to adopt a configuration in which a plurality of depressions whose
opening area gradually decreases as the distance from the dynamic microphone unit increases.
In addition, it is desirable that the metal fibers crimped and disposed in the housing be disposed
in close contact with the inner surface of the housing without a gap.
[0012]
The housing forming the back air chamber can use a grip case for supporting the dynamic
microphone unit. Moreover, the structure which accommodated the housing ¦ casing which
forms a back ¦ bag air chamber in the grip case which supports the said microphone unit can
also be employ ¦ adopted suitably.
[0013]
On the other hand, in the method of forming the back air chamber communicating with the back
surface of the diaphragm of the dynamic microphone unit according to the present invention, a
predetermined amount of metal fiber is provided in a bottomed housing provided with an
opening communicating with the back surface of the diaphragm. And inserting a rod member
having a projection whose outer diameter decreases toward the tip end from the opening of the
housing, and the metal fiber in the housing corresponds to the projection of the rod By providing
a step of forming a recess by plastic deformation and a step of pulling out the rod member from
the opening of the housing, a housing of an acoustic resistor made of metal fiber having a recess
whose opening area gradually decreases It is possible to obtain a back air chamber provided at
the inner bottom of the
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[0014]
In this case, in the step of forming a recess corresponding to the protrusion of the rod member in
the metal fiber by plastic deformation, it is desirable to closely adhere the metal fiber to the inner
surface of the housing without a gap; Aluminum fibers can be suitably used.
[0015]
According to the dynamic microphone of the above-described configuration and the method of
forming the back air chamber thereof, metal fibers represented by, for example, aluminum fibers
are introduced into the bottomed housing, and the metal fibers have an outer diameter toward
the tip The rod member having the projection to be reduced is pushed into the bottomed housing
to undergo plastic deformation.
Therefore, the metal fiber is formed as an acoustic resistor having a recess whose opening area
gradually decreases as the distance from the dynamic microphone unit is increased.
[0016]
Further, when the metal fiber is pushed into the bottomed housing by the rod member, the metal
fiber is pressured by the rod member and crimped into the housing.
Thus, the metal fiber is fixed in close contact with the inner surface of the housing without a gap.
[0017]
Since the shape of the recess formed in the acoustic resistor made of metal fiber is configured
such that its opening area gradually decreases with distance from the dynamic microphone unit,
the acoustic resistance thereof is also moved away from the dynamic microphone unit as well. It
is therefore made to increase. This makes it possible to effectively prevent the generation of
standing waves in the back air chamber.
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[0018]
Further, since the metal fiber is crimped in the housing constituting the back air chamber and is
housed in a state in close contact with the inner surface of the housing without gaps, the metal
fiber suppresses free vibration of the wall surface constituting the housing. It is possible to
provide a dynamic microphone that effectively prevents the wall surface of the back air chamber
from having a specific resonant frequency.
[0019]
FIG. 1 is a central cross-sectional view showing an entire configuration of a dynamic microphone
according to the present invention.
It is process drawing explaining the shaping ¦ molding method in the case of shape ¦ molding the
back air chamber in the dynamic microphone shown in FIG. It is a center sectional view showing
the whole composition of the dynamic microphone of other composition concerning the present
invention.
[0020]
A dynamic microphone according to the present invention will be described based on the
embodiment shown in the drawings. FIG. 1 shows the first embodiment, and in the example
shown in FIG. 1, a cylindrical grip case 11 formed of, for example, a brass alloy is used mainly for
vocals and speech. It is equipped. In the grip case 11, a bottomed casing 13 made of, for
example, an aluminum material is coaxially attached to the grip case 11 via a shock mount
member 12 made of a rubber elastic body. The bottomed casing 13 constitutes the back air
chamber 14 of the dynamic microphone unit as described later.
[0021]
A dynamic microphone unit 15 is attached to the front end of the housing 13. As is well known,
the dynamic microphone unit 15 includes a diaphragm 17 having a voice coil 16 and a magnetic
circuit 18 having a magnetic gap in which the voice coil 16 is disposed so as to be able to vibrate.
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The peripheral side surface of the yoke which comprises the circuit 18 is attached in the state
fitted in the unit holder 19 formed cylindrically.
[0022]
At the rear end portion of the unit holder 19, the cap member 21 accommodating the acoustic
resistor 20 and having a sound hole 21a formed at the center portion is fitted and attached. The
rear surface of the diaphragm 17 constituting the dynamic microphone unit 15 is in
communication with the back air chamber 14 in the housing 13 through the acoustic resistor 20
and the sound hole 21a. A resonator 22 is attached to the front end of the unit holder 19 so as to
cover the diaphragm 17.
[0023]
A protective cover 24 provided with a metal mesh is attached to the front end of the grip case 11
so as to cover the dynamic microphone unit 15. An output connector 25 is attached to the rear
end of the grip case 11.
[0024]
In addition, in this embodiment, the acoustic resistor 27 made of metal fiber (in this embodiment,
aluminum fiber) is accommodated in the bottomed housing 13 forming the back air chamber 14.
In the example shown in FIG. 1, a recess 28 whose opening area gradually decreases as it goes
away from the microphone unit 15 is formed in the central portion of the acoustic resistor 27.
The acoustic resistor 27 made of metal fibers accommodated in the bottomed housing 13 will be
described in detail with reference to FIG.
[0025]
FIG. 2 illustrates a method of molding the acoustic resistor 27 by metal fibers. The metal fiber
used for this is disclosed in, for example, Japanese Patent No. 3856790, and an aluminum fiber
having a wire diameter of 50 to 100 μm can be suitably used. This aluminum fiber can be
obtained, for example, by injecting aluminum in a molten state from the nozzle injection holes
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into the atmosphere and rapidly solidifying it. That is, the aluminum fibers thus obtained are
provided, for example, in the same manner as cotton fibers, in a state in which aluminum long
fibers are in a non-compressed state and have a predetermined surface density.
[0026]
In order to form the acoustic resistor 27 in the back air chamber 14 using this aluminum fiber, as
shown in FIG. 2A, the bottomed casing 13 constituting the back air chamber 14 is previously
made A defined amount of aluminum fibers (indicated by the same reference numeral 27 as the
acoustic resistor). ) Is injected. In this state, the aluminum fiber 27 is in a non-compressed state,
and an appropriate gap 31 exists with the inner surface of the housing 13.
[0027]
Subsequently, the rod member 33 provided with the projection 33 a whose outer diameter
decreases toward the tip end is inserted from the opening 13 a of the housing 13. The rod
member 33 is formed of, for example, a brass alloy, and the outer diameter of the rod member
33 is set to be slightly smaller than the inner diameter of the housing 13 as shown in FIG. 2 (B).
[0028]
The projection 33a of the rod member 33 is formed in a substantially conical shape in this
example, and the aluminum fiber 27 introduced into the housing 13 is subjected to a pressure
drop of the rod member 33 to be under the housing 13 It is pushed to the bottom 13b side and is
subjected to the compression action. As a result, a recess 28 corresponding to the projection 33 a
of the rod member 33 is formed by plastic deformation at the central portion of the aluminum
fiber 27 in the housing 13.
[0029]
At the same time, the aluminum fibers 27 in the housing 13 are pressure-bonded to the inside of
the housing 13 under pressure from the rod member 33 to be plastically deformed, and the
aluminum fibers 27 are separated from the inner surface of the housing 13 It is fixed in the state
where it is not in close contact and functions as an acoustic resistor.
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[0030]
FIG. 2C shows a state in which the rod member 33 is pulled out from the inside of the housing
13, and the inner bottom portion of the housing 13 has an aluminum fiber having a recess 28
whose opening area gradually decreases in the central portion. An acoustic resistor 27 is fixed to
the lower bottom inner surface of the housing 13 in close contact with no gap.
In the acoustic resistor 27 made of aluminum fibers formed by the above-described process, the
fiber density on the opening side of the housing 13 is coarse, while the fiber density on the lower
bottom side of the housing 13 is high. It is set to the density distribution. In addition, the said
density distribution can acquire the same effect, even if the whole is substantially uniform. The
housing 13 accommodating the acoustic resistor 27 shown in FIG. 2C is attached so that the
opening 13a side communicates with the back surface of the diaphragm 17 of the dynamic
microphone unit 15, as shown in FIG.
[0031]
Therefore, according to the dynamic microphone shown in FIG. 1, the conical recess 28 formed
in the acoustic resistor 27 made of aluminum fiber works to effectively prevent the generation of
standing waves in the back air chamber 14. Do. As a result, it is possible to provide a dynamic
microphone that is not affected by standing waves in the back air chamber 14.
[0032]
Further, since the acoustic resistor 27 made of aluminum fiber is housed in the housing 13
constituting the back air chamber 14 in close contact with the inner surface of the lower bottom
portion of the housing, the aluminum fiber is used as the housing 13. It is possible to suppress
the free vibration of the wall surface that composes the wall surface of the back air chamber 14
from having a specific resonance frequency. This can also reliably prevent degradation of the
directional frequency response of the microphone at the resonance frequency of the wall surface
in the back air chamber 14.
[0033]
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FIG. 3 shows a second embodiment of a dynamic microphone according to the present invention.
In the embodiment shown in FIG. 3, the grip case 11 is used as a housing in place of the housing
13 forming the back air chamber 14 shown in FIG. Therefore, in FIG. 3, portions that perform the
same functions as those of the dynamic microphone shown in FIG. 1 are denoted by the same
reference numerals, and detailed descriptions thereof will be omitted.
[0034]
In the example shown in FIG. 3, since the grip case 11 is used as the housing 13 forming the
back air chamber 14, the seal covering the output connector 25 attached to the rear end of the
grip case 11 from the inside A member 29 is disposed at the lower bottom of the grip case 11.
And the method of forming the acoustic resistor 27 which has the hollow 28 in the grip case 11
using aluminum fiber is the same as that of the example shown in FIG. Therefore, also in the
example shown in FIG. 3, the same function and effect as the dynamic microphone shown in FIG.
1 can be obtained.
[0035]
In addition, according to the second example of the dynamic microphone shown in FIG. 3, since
the back air chamber 14 is formed by using the grip case 11, the back air chamber effectively
utilizing the volume of the grip case 11 And can contribute to the improvement of the low
frequency characteristic of the dynamic microphone.
[0036]
In the embodiment described above, the acoustic resistor 27 made of metal fiber is formed in a
form in which one conical recess 28 is formed in the central part, but this is a recess in which the
opening area gradually decreases. The same effect can be obtained even in the configuration
including a plurality of.
As described above, in the case where the acoustic resistor 27 is provided with a plurality of
depressions 28 whose opening area gradually decreases, a plurality of, for example, conical
projections 33a at the tip end instead of the rod member 33 shown in FIG. By using the rod
members 33 provided individually, a plurality of depressions 28 can be similarly formed in the
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acoustic resistor 27 by plastic deformation.
[0037]
Further, in the embodiment described above, an example in which aluminum fibers are used as
the metal fibers is shown, but for example, as shown in FIG. Other metal fibers can be used as
well.
[0038]
11 grip case 12 shock mount member 13 housing 13a opening 13b lower bottom 14 back air
chamber 15 dynamic microphone unit 16 voice coil 17 diaphragm 18 magnetic circuit 19 unit
holder 20 acoustic resistor 21 cap member 21a sound hole 22 resonator 24 protection Cover 25
Output connector 27 Acoustic resistor (metal fiber) 28 Recess 29 Sealing member 31 Clearance
33 Rod member 33a Protrusion
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