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JP2017073712

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DESCRIPTION JP2017073712
Abstract: [Problem] To make it possible to switch the impedance terminating the front end of an
acoustic tube so as to obtain characteristics suitable for the use situation. An acoustic tube 2
having an opening 21 at its front end and a side sound wave introduction hole 22 formed in a
part of the tube wall along the axial direction is provided, and a microphone unit 3 is provided at
the rear end of the acoustic tube 2. A narrow-directional microphone is mounted, and has a
bottomed cylindrical inner pipe 4 in which an acoustic absorption member 42 is stuffed into the
sound pipe 2 at one end with an opening 41 at one end, the inner pipe 4 An inner pipe opening
41 is disposed in the acoustic pipe 2 so as to face the acoustic pipe opening 21. Preferably, the
cross sectional area of the inner pipe 4 is approximately equal to the cross sectional area
between the acoustic pipe 2 and the inner pipe 4 The acoustic tube 2 is provided with shutters
24 and 43 which are identical with each other and open and close the acoustic tube opening 21
and the inner tube opening 41, and the shutter 24 and 43 appropriately switches the impedance
terminating the front end of the acoustic tube 2 Open or close the front end of the To enable end.
[Selected figure] Figure 1
Narrow directional microphone
[0001]
The present invention relates to a narrow directional microphone having an acoustic tube used to
pick up sound from a sound source located relatively far away, and more specifically, to switch
the impedance terminating the front end of the acoustic tube The present invention relates to a
narrow directional microphone that can have characteristics suitable for use conditions.
[0002]
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1
In a narrow directional microphone, narrow directivity is obtained by attaching a relatively long
acoustic tube to a unidirectional microphone unit, but the directional frequency response differs
depending on the impedance loaded on the front end of the acoustic tube It has been known.
Non-Patent Document 1 introduces the respective characteristics of the case where the front end
of the acoustic tube is opened, closed, or terminated with an appropriate impedance.
[0003]
Although the acoustic tube basically has, for example, a slit-like side acoustic wave introduction
hole formed along the axial direction in a part of the tube wall, many narrow directional
microphones The front end is open.
[0004]
According to this, even if the acoustic tubes have the same length, narrow directivity higher than
that in which the front end is closed can be obtained.
On the other hand, when the front end of the acoustic tube is closed, the acoustic center in the
acoustic tube is approximately at the center in the longitudinal direction of the acoustic tube, so
narrow directivity and sensitivity are better than those with the front end open. Although
inferior, wind noise has superior characteristics to those with an open front end.
[0005]
Non-Patent Document 1 describes that by appropriately designing the termination impedance to
be loaded on the front end of the acoustic tube, directivity higher than that obtained by opening
the front end of the acoustic tube can be obtained. As a related technique, in the superdirective
microphone described in Patent Document 1, the front end of the acoustic tube has the same
diameter as that of the acoustic tube, and has a sound-absorbing material packed therein and a
non-porous second acoustic wave having no sound introducing hole. I try to connect the tube.
[0006]
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2
According to this, the reflected energy in the acoustic tube is absorbed by the sound absorbing
material in the second acoustic tube, so that the directivity is further enhanced. Since the
acoustic tube is connected, the microphone becomes larger accordingly.
In particular, in order to obtain excellent directivity characteristics down to the low frequency
range, there is a problem that the microphone becomes larger because it is necessary to make
the second acoustic tube longer.
[0007]
Unexamined-Japanese-Patent No. 6-178380
[0008]
Akio Mizoguchi: November, 1977 Proceedings of the Acoustical Society of Japan "A Note on
Acoustic Tubes for Line Microphones"
[0009]
Therefore, an object of the present invention is to make it possible to switch the impedance for
terminating the front end of an acoustic tube in a narrow directional microphone using an
acoustic tube without adding another acoustic tube having a sound absorbing material at the
front end of the acoustic tube. , To be able to obtain the characteristic suitable for the use
situation.
[0010]
In order to solve the above-mentioned problems, the present invention is an acoustic tube which
is a cylindrical shape having a predetermined length having an opening at its front end, and in
which a side acoustic wave introducing hole is formed in a part of the tube wall In the narrow
directional microphone having the microphone unit mounted at the rear end of the acoustic tube,
the bottomed cylindrical inner tube having an opening and an acoustic absorption material
packed therein at the one end thereof. And the inner pipe is disposed in the acoustic pipe with
the inner pipe opening directed to the acoustic pipe opening side, and a first shutter for opening
and closing the acoustic pipe opening, and the inner pipe opening And a second shutter that
opens and closes the unit.
[0011]
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In the present invention, the cross-sectional area of the inner tube is preferably substantially the
same as the cross-sectional area between the acoustic tube and the inner tube.
[0012]
Preferably, the inner pipe is disposed coaxially with the acoustic pipe via a predetermined
support means.
[0013]
According to the present invention, a bottomed cylindrical inner tube having a sound absorbing
material packed therein is provided in an acoustic tube having an opening at the front end and a
side acoustic wave introducing hole provided in the tube wall. Preferably, the cross-sectional area
of the inner tube is substantially the same as the cross-sectional area between the acoustic tube
and the inner tube, and the coaxial tube is housed coaxially with the acoustic tube so that the
opening faces the opening of the acoustic tube In addition, by providing the first shutter and the
second shutter at the acoustic pipe opening and the inner pipe opening, respectively, the first
and second shutters are closed as a first mode of use, and the acoustic pipe is closed. If both the
opening and the inner pipe opening are closed, as with the sound pipe whose front end is closed,
the side sound wave introduction hole becomes the main sound terminal, there is little wind
noise, and the narrow directivity of a relatively wide sound collection angle In the second mode
of use, the first shutter is opened to open the acoustic tube opening. If the second shutter is
closed and the inner pipe opening is closed, the sound pipe opening becomes the main sound
terminal as in the case of an acoustic pipe whose front end is opened, narrow narrow directivity
with raised low frequency response As a third mode of use, if the first shutter is closed to close
the acoustic pipe opening and the second shutter is opened to open the inner pipe opening, the
side sound wave introduction hole becomes the main acoustic terminal. Since the front end of the
acoustic tube (the connection between the acoustic tube and the inner tube) is terminated with
an appropriate impedance, sensitivity and low frequency response are reduced, but wind noise is
small and good narrow directivity is obtained. Be
[0014]
Moreover, since the inner pipe which comprises termination | terminus impedance is
accommodated in an acoustic pipe, it does not become large either.
In addition, since the cross-sectional area of the inner pipe is substantially the same as the crosssectional area between the acoustic pipe and the inner pipe, the impedance matching at the
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connection portion between the acoustic pipe and the inner pipe is also good.
[0015]
FIG. 1 is an external perspective view showing a partially disassembled narrow directional
microphone according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view taken along the line AA of FIG.
Sectional drawing along the BB line of FIG.
The perspective view which shows the support tool of an inner pipe.
The principal part expanded sectional view which shows the structure of the operation part of a
1st and 2nd shutter.
The typical sectional view showing the 1st usage condition of the above-mentioned narrow
directivity microphone.
Typical sectional drawing which shows the 2nd usage aspect of the said narrow directivity
microphone. The typical sectional view showing the 3rd usage condition of the above-mentioned
narrow directivity microphone.
[0016]
Next, embodiments of the present invention will be described with reference to FIGS. 1 to 8, but
the present invention is not limited thereto.
[0017]
First, referring to FIGS. 1 to 3, as a basic configuration, narrow directional microphone 1
according to this embodiment includes an acoustic tube 2 for obtaining narrow directivity and a
microphone unit 3 .
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[0018]
The acoustic tube 2 is formed of a cylindrical body having a predetermined axial length, and has
an opening 21 at its front end (the side directed to the sound source during sound collection) 2a,
and its rear end 2b is open.
Side sound introduction holes 22 are provided in a part of the tube wall 20 b of the acoustic tube
2.
[0019]
In this embodiment, the side acoustic wave introducing holes 22 are formed in a slit shape
continuous along the axial direction of the acoustic tube 2 and are disposed at two locations
facing each other at 180 degrees, and each of them is made of non-woven fabric or the like The
acoustic resistance material 23 is covered.
The side sound wave introduction holes 22 may not be continuous slit holes, but may be, for
example, a collection of a plurality of sound holes arranged in a line along the axial direction of
the acoustic tube 2.
[0020]
The microphone unit 3 is attached to the rear end 2 b of the acoustic tube 2 in a unidirectional
manner. In the case of a narrow directional microphone, an electrostatic type is generally used
for the microphone unit 3, but an electrodynamic type may be used.
[0021]
The narrow directional microphone 1 includes an inner pipe 4 in an acoustic pipe 2. The inner
pipe 4 is formed of a bottomed cylindrical body having an opening 41 at one end, and a sound
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absorbing material 42 made of glass fiber or the like is packed therein. The inner pipe 4 is made
of synthetic resin or metal and has no sound wave introducing portion other than the opening
41.
[0022]
The inner pipe 4 is housed in the acoustic pipe 2 with its opening 41 directed to the opening 21
side of the acoustic pipe 2 as an acoustic pipe for forming a termination impedance, but the
cross-sectional area S1 of the inner pipe 4 is , And the cross-sectional area S2 between the
acoustic pipe 2 and the inner pipe 4. In other words, assuming that the cross-sectional area of
the acoustic tube 2 is S, S1 = S2 = S / 2. This is to match the termination impedance at the
connection connecting the acoustic tube 2 and the inner tube 4.
[0023]
The inner pipe 4 may be disposed non-coaxially to the acoustic pipe 2, ie, at a biased position in
contact with a portion of the inner surface of the acoustic pipe 2, but, for example, via the inner
pipe support member 5 shown in FIG. It is preferable that the sound tube 2 be disposed in a
double tube coaxial with the sound tube 2.
[0024]
The inner pipe support member 5 has a first ring 51 fitted to the outer peripheral surface of the
inner pipe 4, a second ring 52 fitted to the inner peripheral surface of the acoustic pipe 2, and a
second ring relative to the first ring 51. A plurality of (three in this case, three evenly spaced)
spokes 53 coaxially connecting 52 are provided, and they are attached to at least two places on
the front and back of the inner pipe 4.
[0025]
According to the present invention, the first shutter 24 for opening and closing the opening 21 of
the acoustic tube 2 and the second shutter 43 for opening and closing the opening 41 of the
inner tube 4 in order to switch the termination impedance of the front end 2a of the acoustic
tube 2 Prepare.
Both the first shutter 24 and the second shutter 43 are made of a sound insulating material such
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as synthetic resin.
[0026]
The axial length of the inner pipe 4 and the distance (interval) between the opening 21 of the
acoustic pipe 2 and the opening 41 of the inner pipe 4 are arbitrarily determined in
consideration of the wavelength of the sound wave to be collected, etc. You may
[0027]
Referring to FIG. 5, according to this embodiment, the first shutter 24 includes operating rods
24a and 24a at positions facing each other by 180 degrees.
The operating rods 24 a, 24 a are attached substantially orthogonal to the first shutter 24, and
are drawn to the front of the acoustic tube 2 through the front wall 20 a around the opening 21.
[0028]
According to this, by pinching the operating rods 24a and 24a with a finger and pushing it into
the acoustic tube 2, the first shutter 24 moves in the right direction in FIG. 5, and the opening 21
of the acoustic tube 2 is opened. The front end will be open.
Further, by pulling the operating rods 24a, 24a, the first shutter 24 moves in the left direction in
FIG. 5, and the opening 21 of the acoustic tube 2 is closed to close the front end.
[0029]
The second shutter 43 is also provided with operating rods 43a and 43a at positions facing each
other by 180 degrees. In this case, each end of the operating rods 43a and 43a penetrates the
tube wall 20b of the acoustic tube 2 It is extended in the radial direction of the second shutter
43.
[0030]
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Corresponding to this, on the tube wall 20b side of the acoustic tube 2, slits 44, 44 through
which respective end portions of the operation rods 43a, 43a penetrate are provided along the
axial direction.
According to this, the second shutter 43 can be moved to the position where the opening 41 of
the inner pipe 4 is closed and the position where the opening 41 of the inner pipe 4 is opened
via the operation rods 43a, 43a.
[0031]
In order to prevent sound from entering the acoustic tube 2 from the slits 44, 44, it is preferable
to attach sound shielding covers 45, 45 having a larger width and length than the slits 44 to the
operation rods 43a, 43a. In addition, it is preferable to provide an engagement means for holding
the shutters 24 and 43 with an appropriate engagement force at the closed position and the
open position. Furthermore, if the space in the acoustic tube 2 permits, the shutters 24 and 43
may be butterfly valves.
[0032]
Next, switching of the characteristics of the narrow directional microphone 1 according to this
embodiment will be described with reference to FIGS. 6 to 8. In these drawings, the operation
members (operation rods 24a and 43a) of the shutters 24 and 43 are not shown for the
convenience of drawing.
[0033]
First, as a first mode of use, as shown in FIG. 6, the opening 21 of the acoustic tube 2 is closed by
the first shutter 24 to close the front end (at this time, the opening 41 of the inner tube 4 is also
used as the second shutter 43). In this case, the side sound wave introduction hole 22 becomes a
main sound terminal, and there is little wind noise, and a narrow directivity of a relatively wide
sound collection angle can be obtained.
[0034]
Next, as a second mode of use, as shown in FIG. 7, with the opening 41 of the inner tube 4 closed
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by the second shutter 43, the first shutter 24 is opened to open the acoustic tube 2 opening 21.
By opening the opening, the opening 21 of the sound tube 2 becomes a main sound terminal as
in the case of the sound tube whose front end is opened, and a narrow narrow directivity in
which the low frequency response is raised can be obtained.
[0035]
Furthermore, as a third mode of use, as shown in FIG. 8, with the opening 21 of the acoustic tube
2 closed by the first shutter 24, the second shutter 43 is opened to open the opening 41 of the
inner tube 4. By opening it, the side sound wave introduction hole 22 becomes the main acoustic
terminal, and the front end of the acoustic tube 2 (the connection portion between the acoustic
tube 2 and the inner tube 4) is terminated with an appropriate impedance. Although the
frequency response is reduced, wind noise is small and good narrow directivity can be obtained.
[0036]
As described above, according to the present invention, the acoustic pipe including the sound
absorbing material constituting the termination impedance is disposed as the inner pipe in the
original acoustic pipe, and the front end opening (sound inlet) of the acoustic pipe and the inner
pipe By providing the opening and closing shutters respectively with the opening of the sound
tube, the impedance for terminating the front end of the sound tube is appropriately switched
without enlarging the sound tube, and the front end of the sound tube is opened, closed or
terminated with an appropriate impedance. can do.
[0037]
Reference Signs List 1 narrow directivity microphone 2 acoustic tube 2a front end 2b rear end
20a front wall 20b tube wall 21 opening 22 side acoustic wave introduction hole 23 acoustic
resistance material 24 first shutter 24a operation rod 3 microphone unit 4 inner tube 41
opening 42 sound absorption Material 43 First shutter 43a Operation rod 44 Slit 45 Sound
insulation cover 5 Inner tube support member
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