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DESCRIPTION JP2014175807

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DESCRIPTION JP2014175807
PROBLEM TO BE SOLVED: To suppress a standing wave generated in a chamber in an acoustic
device having a chamber like a tweeter. SOLUTION: Open tubes 21 and 22 are provided in a
chamber 20 of a tweeter. The open tube 21 has open ends 21a and 21b at both ends, and the
open tube 22 has open ends 22a and 22b at both ends. The open end 21 a of the open tube 21
communicates the cavity in the open tube 21 with the cavity in the chamber 20 near the closed
end of the chamber 20, and the open end 21 b of the open tube 21 is a cavity in the open tube
21 in the middle of the chamber 20. In communication with the cavity in the chamber 20. The
same applies to the open pipe 22. The open tubes 21 and 22 have the same tube length as the
chamber 20. The distance between the position of the open ends 21a and 22a and the position of
the open ends 21b and 22b in the lengthwise direction of the chamber 20 is half the length of
the chamber 20. In the chamber 20, the open ends 21 a and 22 a are covered with the sound
absorbing material 23, and the open ends 21 b and 22 b are also covered by the sound
absorbing material 23. [Selected figure] Figure 1
Sound equipment
[0001]
The present invention relates to a technique for suppressing standing waves using tube
resonance.
[0002]
In a space surrounded by walls in an acoustic device etc., when a sound wave of natural
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frequency is emitted in the space, a standing wave is generated due to the reciprocation of the
sound wave between the wall faces of the space, which adversely affects its acoustic
characteristics It has been known.
Patent documents 1 to 3 disclose a technique for suppressing a standing wave in a speaker
which is one of the acoustic devices. The speaker device disclosed in Patent Document 1 includes
a speaker unit, a cabinet including the speaker unit, and a Helmholtz resonator provided inside
the cabinet. In this speaker device, its neck length L and cavity volume V are designed such that
the Helmholtz resonator resonates at the same frequency as the standing wave generated in the
cabinet. According to this speaker device, when a standing wave is generated in the cabinet, the
Helmholtz resonator exhibits a resonance phenomenon, and the standing wave is attenuated by
this resonance phenomenon. The speaker device disclosed in Patent Document 2 includes a
speaker unit, a cabinet incorporating the same, and an acoustic pipe (closed pipe) having an open
end and a closed end. The acoustic tube of this speaker device has a tube length L which is 1/4
of the lowest resonance mode of the standing wave generated in the cabinet. The acoustic tube is
housed in the cabinet in a posture in which the position of the open end is close to the position of
the antinode (node of particle velocity) of the sound pressure of the standing wave in the cabinet.
In this speaker device, when a standing wave (a standing wave having a wavelength of 4 times
the tube length L) is generated in the cabinet, a resonance wave is generated in the acoustic pipe.
The resonance wave has a node of sound pressure (antinode of particle velocity) at the open end
of the acoustic tube and has an antinode (node of particle velocity) of the closed end. Therefore,
according to this speaker device, the bias of the sound pressure distribution in the cabinet is
alleviated, and the standing wave in the cabinet is attenuated. Patent Document 3 also discloses
the same technology as Patent Document 2.
[0003]
Patent No. 2606447 gazette Patent No. 3763682 gazette JP, 2008-131199, A
[0004]
By the way, there is a speaker apparatus for high frequency reproduction called a tweeter, which
is configured to have a chamber which is a closed tube for expanding a reproduction sound
range behind a driver as a vibration source.
In this type of chamber-equipped tweeter, a standing wave is likely to be generated in a closed
space surrounded by the driver and the chamber, which causes a large peak dip in the radiation
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characteristics of the tweeter, which causes the sound quality to be degraded. It had become. As
means for solving this problem, it is conceivable to arrange the above-mentioned Helmholtz
resonator, acoustic tube or the like in the chamber of the tweeter. However, since the chamber of
the tweeter is a very thin tube, it is difficult to arrange a Helmholtz resonator, an acoustic tube or
the like inside the chamber. For this reason, conventionally, no effective means for improving the
radiation characteristics of the tweeter has been provided.
[0005]
The present invention has been made in view of such problems, and an object of the present
invention is to provide a technical means for suppressing standing waves generated in a chamber
in an acoustic device having a chamber such as a tweeter. Do.
[0006]
The present invention relates to a tube including a cavity facing behind a vibration unit
generating acoustic vibration, and an open tube communicating with the tube via the first and
second open ends, the constant tube generating in the tube An open tube having a tube length
which is an integral multiple of substantially half wavelength of a standing wave, and the first
open end is disposed at a position of a substantially antinode of a standing wave generated in the
tube. To provide an acoustic device.
[0007]
According to the present invention, when a standing wave is generated in the tube by the
vibration of the vibrating portion, a standing wave which can not coexist with the standing wave
is generated in the open tube, so the standing wave generated in the space is reduced. Ru.
[0008]
In a preferred embodiment, the second open end is disposed at a position substantially at a node
of a standing wave generated in the tube.
[0009]
In another preferred embodiment, the first and second open ends are located at positions
separated by an odd multiple of about a quarter wavelength of the standing wave in the direction
of the tube axis of the tube.
[0010]
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In another preferred embodiment, the second open end is disposed at a position substantially
antinode to a standing wave generated in the tube.
[0011]
In another preferred embodiment, all or a part of one or both open ends of the first and second
open ends are covered with a breathable sound absorbing material.
[0012]
It is a figure which shows the 3-way speaker which is an example of application object of this
invention, and its tweeter.
It is a figure which shows the acoustic characteristic of a chamber | room tweeter.
It is a figure which shows the structure of the tweeter which is one Embodiment of the audio
equipment by this invention.
It is a figure explaining suppression operation of a standing wave in the embodiment.
It is a figure which shows the effect of the embodiment.
It is a figure which shows the 1st example of the chamber with an open pipe which can be used
for the embodiment.
It is a figure which shows the 2nd example of the chamber with an open pipe.
It is a figure which shows the 3rd example of the chamber with an open pipe. It is a figure which
shows the 4th example of the chamber with an open pipe.
[0013]
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Hereinafter, embodiments of the present invention will be described with reference to the
drawings. FIG. 1A is a perspective view showing a configuration of a 3-way speaker including a
tweeter to which the present invention is applied. As shown in FIG. 1A, this 3-way speaker is
obtained by attaching a woofer 101, a squawker 102 and a tweeter 103 to the front of a cabinet
100. FIG. 1B is a side view showing the configuration of the tweeter 103. As shown in FIG. 1B,
the tweeter 103 has a driver 10 that vibrates by an electric signal supplied from an amplifier (not
shown), and a chamber 20 that includes a space facing the back of the driver 10. Here, the
chamber 20 is a closed tube in which the opposite end of the driver 10 is a closed end.
[0014]
FIG. 2 is a diagram showing frequency characteristics of the sound pressure level SPL of the
tweeter 103 and the electric impedance Imp. In the tweeter 103, the chamber 20 is provided to
expand the reproduction range. However, when the chamber 20 is provided in the tweeter 103, a
standing wave is easily generated in the closed space surrounded by the driver 10 and the
chamber 20. In FIG. 1B, the sound pressure waveform of the lowest order (basic mode) of the
standing waves generated in the closed space surrounded by the driver 10 and the chamber 20
is illustrated by a broken line. Thus, the sound pressure waveform of the standing wave in the
fundamental mode is antinode at the driver 10 and the closed end 20 a of the chamber 20 and is
node at the central position of the chamber 20. In the closed space surrounded by the driver 10
and the chamber 20, in addition to the basic mode shown, a high-order standing wave having a
sound pressure antinode at the closed end 20a of the driver 10 and the chamber 20 is generated
Do. Therefore, a large peak dip occurs in the sound pressure level SPL emitted by the tweeter
103 and the electrical impedance Imp of the tweeter 103, which causes the quality of the sound
to be degraded. An object of the present invention is to suppress a standing wave generated in a
closed space surrounded by the driver 10 and the chamber 20.
[0015]
FIG. 3 is a side view showing the configuration of a tweeter which is an embodiment of the
acoustic device according to the present invention. As shown in the drawing, in the tweeter
according to the present embodiment, the open tubes 21 and 22 are connected to the chamber
20. Here, the open tube 21 is a hollow tube whose both ends are open ends 21a and 21b, and
the open end 21a is open at a wall surface near the closed end of the chamber 20, and the open
end 21b is approximately the chamber 20 It is open at the central wall. The space in the open
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tube 21 is in communication with the space in the chamber 20 via the open ends 21a and 21b.
Similarly, the open tube 22 is a hollow tube having open ends 22 a and 22 b at both ends, and
the open end 22 a is open at the wall near the closed end of the chamber 20, and the open end
22 b is substantially at the center of the chamber 20. It is open at the wall of The space in the
open tube 22 is in communication with the space in the chamber 20 via the open ends 22a and
22b. The open tubes 21 and 22 have a pipe length equal to that of the chamber 20. Although
two open tubes 21 and 22 are used in this example, one open tube may be used, or three or more
open tubes may be used. In the chamber 20, the sound absorbing material 23, which is a
breathable sound absorbing material, is disposed in the area near the open ends 21a and 22a
and the area near the open ends 21b and 22b. More specifically, in this example, in the chamber
20, the entire area of both open ends of the two open ends 21a and 21b of the open pipe 21 is
covered with a sound absorbing material, and the two open ends of the open pipe 22 are The
entire area of the open ends of both 22a and 22b is covered by the sound absorbing material.
[0016]
The first feature of this embodiment lies in the open tubes 21 and 22. In the present
embodiment, the open tubes 21 and 22 have the following effects. When an electrical signal from
an amplifier (not shown) is given, the driver 10 emits an acoustic wave both forward and
backward. Then, the sound waves emitted backward by the driver 10 propagate in the space in
the chamber 20. In the sound wave emitted by the driver 10, a component having the same
frequency as the natural frequency of the space in the chamber 20 reciprocates between the
driver 10 and the closed end of the chamber 20 in the chamber 20. In this way, a plurality of
sound waves that reciprocate together are standing with a wavelength λ k = 2 L / k (k = 1, 2...)
Times 2 / k (k = 1, 2...) Times the tube length L of the chamber 20 Waves SWk (k = 1, 2...) Are
generated.
[0017]
FIGS. 4A to 4E illustrate the sound pressure waveforms of the first to fifth standing waves SWk (k
= 1 to 5) generated in the chamber 20 in this manner. As illustrated, the sound pressure
waveform of these standing waves is a sound pressure waveform having an antinode near the
closed end of the chamber 20. Then, among the sound pressure waveforms of the standing
waves, the sound pressure waveforms of the first, third, and fifth standing waves SW1, SW3, and
SW5 are sound pressure waveforms having nodes near the center of the chamber 20. On the
other hand, the open tubes 21 and 22 have a tube length L equal to that of the chamber 20, that
is, a tube length L = k / 2 (k = 1, 2,...) Times the wavelength of the standing wave SWk (k = 1, 2. It
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has kλ k / 2. Therefore, in the process of propagating standing tubes SW1, SW3, SW5 from
open ends 21b and 22b through open tubes 21 and 22, respectively, a phase delay of (k / 2) ×
2π is given, and open ends 21a and 22a. To reach each. Therefore, nodes of the sound pressure
waveform are generated near the open ends 21 a and 22 a in the chamber 20. As a result, in the
chamber 20, the standing waves SW1, SW3, and SW5 are suppressed.
[0018]
Also, focusing on the sound pressure component of the second standing wave SW 2 generated in
the chamber 20, in the vicinity of the center of the chamber 20, the sound pressure of the
antiphase with the antinode of the sound pressure generated at the closed end of the chamber 20
A belly develops. Then, in the process of propagating the open tubes 21 and 22 from the open
ends 21b and 22b, the standing wave SW2 is given a phase delay of 2π and reaches the open
ends 21a and 22a, respectively. That is, in the vicinity of the closed end of the chamber 20, the
antinodes and antinodes of the sound pressure waveform of the standing wave SW2 generated in
the chamber 20 reach via the open tubes 21 and 22. As a result, the standing wave SW2 in the
chamber 20 is suppressed.
[0019]
Also, focusing on the sound pressure component of the fourth order standing wave SW 4
generated in the chamber 20, in the vicinity of the center of the chamber 20, the antinode of the
sound pressure in phase with the antinode of the sound pressure generated at the closed end of
the chamber 20 Occurs. Then, in the process of propagating the open tubes 21 and 22 from the
open ends 21 b and 22 b, the standing wave SW 4 is given a phase delay of 4π and reaches the
open ends 21 a and 22 a respectively. Therefore, the suppression of the fourth standing wave
SW4 is not performed in the chamber 20.
[0020]
As described above, in the present embodiment, by connecting the open tubes 21 and 22 to the
chamber 20, it is possible to suppress all the standing waves except the fourth among the first to
fifth standing waves. In this example, since the antinodes of the sound pressure of various
standing waves to be suppressed are located at the center of the chamber 20, the open ends 21b
and 22b are provided at the center of the chamber 20. However, when the antinode of the sound
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pressure of the standing wave to be suppressed is generated at a position other than the center
of the chamber 20, the open ends 21b and 22b may be provided at that position.
[0021]
The second feature of this embodiment is the arrangement position of the sound absorbing
material 23. The sound absorbing material 23 disposed in the area near the open ends 21a and
22a and the area near the open ends 21b and 22b in the chamber 20 has the following effects.
First, since these two regions are boundary regions between the chamber 20 and the open tubes
21 and 22, they are regions where the flow velocity of the air flow is high, and in the region
where sound energy tends to be concentrated in the chamber 20. is there. Therefore, by
arranging the sound absorbing material 23 in these areas, the energy of the sound in the
chamber 20 can be efficiently deprived. As such, the sound absorbing material 23 disposed in the
boundary region between the chamber 20 and the open tubes 21 and 22 has an effect of
efficiently depriving the standing waves in the chamber 20 of the energy of sound.
[0022]
The inventors of the present application carried out a simulation to confirm the effects of the
present embodiment. That is, the sound pressure level of the sound radiated from the tweeter
and the electrical impedance of the driver when the frequency of the test signal given to the
driver of the tweeter was changed were determined by simulation. FIG. 5 shows the result of this
simulation. In FIG. 5, the sound pressure level SPL1 and the electrical impedance Imp1 of the
radiated sound of the tweeter when the sound absorbing material is filled in the entire region of
the chamber 20 in the conventional tweeter (see FIG. 1B), and the present embodiment The
sound pressure level SPL2 and the electrical impedance Imp2 of the radiated sound of the
tweeter (see FIG. 3) according to FIG. In the conventional example, a large peak dip due to a
standing wave generated in the chamber 20 is generated in the sound pressure level SPL of the
tweeter and the frequency characteristic of the electrical impedance Imp (see FIG. 2) when no
sound absorbing material is used. The Looking at the frequency characteristics of the sound
pressure level SPL1 of the radiated sound of the tweeter and the electrical impedance Imp1
according to this embodiment, this peak dip is significantly suppressed. Also in the conventional
tweeter (see FIG. 1B), even when the sound absorbing material is filled in the entire area of the
chamber 20, the peak dip of the sound pressure level SPL1 of the radiated sound of the tweeter
and the electrical impedance Imp1 as in the present embodiment. It can be suppressed. However,
in the tweeter according to the present embodiment, the sound absorbing material 23 which is
about 1/3 of the entire area in the chamber 20 is not disposed. Nevertheless, in the present
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embodiment, an improvement effect of the acoustic characteristics is obtained which is almost
the same as when the sound absorbing material 23 is filled in the entire area in the chamber 20
of the conventional tweeter.
[0023]
As described above, according to the present embodiment, since the open tubes 21 and 22 are
provided in the chamber 20 of the tweeter, the standing waves generated in the chamber 20 can
be suppressed, and the acoustic characteristics of the tweeter can be improved. Further,
according to the present embodiment, since the sound absorbing material is filled only in the
boundary region with the open tubes 21 and 22 in the chamber 20, the sound absorbing
material is more than in the case where the sound absorbing material is filled in the entire region
in the chamber 20. The amount can be reduced, the cost can be reduced, and the adverse effects
caused by the use of a large amount of sound absorbing material can be avoided. That is, when
the sound absorbing material is filled in the whole area in the chamber 20, the components other
than the standing waves generated in the chamber 20 are also attenuated, which results in
adversely affecting the acoustic characteristics of the tweeter. This adverse effect can be avoided
by filling the sound absorbing material only in the boundary region with the inner open tubes 21
and 22.
[0024]
Next, specific examples of the open-tubed chamber usable in the present embodiment will be
described. 6 (A) and 6 (B) show a first example of the open-tube chamber, and FIG. 6 (A) is a side
view of the open-tube chamber, and FIG. 6 (B) is the open-tube chamber. It is the figure which
looked at the longitudinal cross-section of the chamber from the diagonal direction. As shown,
the open-tubular chamber of this first example has flat wings 25 and 26 protruding to the left
and right of the cylindrical chamber 20. Further, a through hole 25 n is provided in the wing
portion 25 through the open end 25 a in the vicinity of the closed end of the chamber 20 and
reaching the open end 25 b in the middle of the chamber 20. Further, a through hole 26 n is
provided in the wing portion 26 through the open end 26 a near the closed end of the chamber
20 and reaching the open end 26 b in the middle of the chamber 20. The wing 25 provided with
the through hole 25 n and the wing 26 provided with the through hole 26 n play a role as an
open pipe. The length of each of the through holes 25 n and 26 n is 1/2 of the wavelength of the
lowest one of the standing waves to be suppressed. Further, the distance between the positions of
the open ends 25a and 26a and the positions of the open ends 25b and 26b in the lengthwise
direction of the chamber 20 is 1⁄4 of the wavelength of the lowest one of the standing waves to
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be suppressed. .
[0025]
FIG. 7 is a perspective view showing a second example of the open tube chamber. As shown, the
second example of the open-tubular chamber surrounds the cylindrical chamber 20 and has a
spiral open tube 27 provided along the axial direction of the chamber 20. There is. The lower end
27 a and the upper end 27 b of the spiral open tube 27 are connected to a position near the
closed end on the side surface of the chamber 20 and to an intermediate position of the chamber
20. Then, on the side surface of the chamber 20, in the vicinity of the lower end 27a and the
upper end 27b of the open tube 27, two open ends (not shown) that respectively connect the
cavity in the open tube 27 to the cavity in the chamber 20 It is provided. The length of the open
tube 27 is 1/2 of the wavelength of the lowest order standing wave to be suppressed. Further,
the distance between the position of the lower end 27a of the open tube 27 and the position of
the upper end 27b in the lengthwise direction of the chamber 20 is 1⁄4 of the wavelength of the
lowest one of the standing waves to be suppressed.
[0026]
FIG. 8 is a perspective view showing a third example of the open tube chamber. As shown, the
third example of the open-tubular chamber has two open tubes 28 and 29 connected to the left
and right sides of the cylindrical chamber 20. The lower end 28 a and the upper end 28 b of the
open tube 28 are connected to a position near the closed end on the side of the chamber 20 and
to a position halfway the chamber 20. Similarly, the lower end 29 a and the upper end 29 b of
the open tube 29 are connected to a position near the closed end on the side surface of the
chamber 20 and to an intermediate position of the chamber 20. The open tube 28 extends
laterally from the upper end 28b and then travels downward while drawing a wave that
reciprocates in the lateral direction, and extends laterally to the lower end 28a. The same applies
to the open pipe 29. Then, on the side surface of the chamber 20, in the vicinity of the lower end
28a and the upper end 28b of the open tube 28, two open ends (not shown) for respectively
connecting the cavity in the open tube 28 to the cavity in the chamber 20 It is provided. The
same applies to the open pipe 29. The length of each of the open tubes 28 and 29 is 1/2 of the
wavelength of the lowest one of the standing waves to be suppressed. Further, the distance
between the positions of the lower ends 28a and 29a of the open tubes 28 and 29 and the
positions of the upper ends 28b and 29b in the lengthwise direction of the chamber 20 is one of
the wavelengths of the lowest one of standing waves to be suppressed. / 4.
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[0027]
FIG. 9 is a perspective view showing a fourth example of the open tube chamber. As shown in the
drawing, the open-tube chamber of this fourth example has two open tubes 30 and 31 connected
to the left and right sides of the cylindrical chamber 20. The lower end 30 a and the upper end
30 b of the open tube 30 are connected to a position near the closed end on the side surface of
the chamber 20 and an intermediate position of the chamber 20. Similarly, the lower end 31 a
and the upper end 31 b of the open tube 31 are connected to a position near the closed end on
the side surface of the chamber 20 and to an intermediate position of the chamber 20. The open
tube 30 extends laterally from the upper end 30b and then extends downward, looping once,
extends downward again, extends laterally and extends to the lower end 30a. The same applies to
the open pipe 31. Then, on the side surface of the chamber 20, in the vicinity of the lower end
30a of the open tube 30 and in the vicinity of the upper end 30b, two open ends (not shown)
that respectively connect the cavity in the open tube 30 to the cavity in the chamber 20 It is
provided. The same applies to the open pipe 31. The length of each of the open tubes 30 and 31
is 1/2 of the wavelength of the lowest one of the standing waves to be suppressed. Further, the
distance between the positions of the lower ends 30a and 31a of the open tubes 30 and 31 and
the positions of the upper ends 30b and 31b in the lengthwise direction of the chamber 20 is
one of the wavelengths of the lowest one of the standing waves to be suppressed. / 4.
[0028]
According to the first to fourth examples described above, each open end of the open tube having
an appropriate tube length according to the wavelength of the standing wave to be suppressed is
provided at an appropriate position in the chamber. The standing wave generated in the chamber
can be suppressed to improve the acoustic characteristics of the tweeter. Moreover, although
illustration is abbreviate | omitted, the unnecessary standing wave in a chamber can be
efficiently reduced by arrange | positioning a sound absorbing material in the boundary area |
region with the open pipe in a chamber.
[0029]
<Other Embodiments> While one embodiment of the present invention has been described
above, other embodiments can be considered in the present invention.
[0030]
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(1) In the above embodiment, in the chamber, all of the two open ends of the open tubes are
covered with the breathable sound absorbing material.
However, if sufficient standing wave damping effect can be obtained, a part of both open ends of
the two open ends of the open tube, a part of all open ends or one open end of one open end may
be ventilated. It may be covered with a sound absorbing material.
[0031]
(2) In the said embodiment, this invention was applied to the tweeter. However, the scope of
application of the present invention is not limited to a speaker such as a tweeter. For example,
the present invention may be applied to a motorcycle muffler or the like.
[0032]
(3) In the above embodiment, the length of the open tube connected to the chamber is set to 2/1
of the wavelength of the lowest one of the standing waves to be suppressed. However, the tube
length of this open tube does not necessarily have to be exactly 2/1 of the wavelength of the
lowest one of the standing waves to be suppressed strictly, and may be an integral multiple of
approximately 1⁄2 of the same wavelength . Also in this case, the same effect as the above
embodiment can be obtained.
[0033]
(4) In the above embodiment, the positions of the two open ends of the open tube connected to
the chamber are separated along the tube axis direction of the chamber by 1/4 of the wavelength
of the lowest one of the standing waves to be suppressed. I let it go. However, the two open ends
do not necessarily have to be exactly separated by 1⁄4 of the same wavelength, and may be
separated by an odd multiple of approximately 1⁄4 of the same wavelength. Also in this case, the
same effect as the above embodiment can be obtained.
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[0034]
DESCRIPTION OF SYMBOLS 10 ... Driver, 20 ... Chamber, 21, 22, 27, 28, 29, 30, 31 ... Open pipe,
21a, 21b, 22a, 22b, 25a, 25b, 26a, 26b, 27a, 28b, 29a, 29b, 30a , 30b, 31a, 31b ... opening end,
23 ... sound absorbing material, 25, 26 ... wing portion, 25n, 26n ... through hole.
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