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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an external perspective view of a conventional
line microphone, FIG. 2A is a partial longitudinal sectional view of the same, FIG. 2B is a cross
sectional view of the line portion, and FIG. FIG. 4 is a plan view of a line of a conventional line
microphone, FIG. 5 is a diagram of the frequency directivity characteristic of the line, and FIG. Is
a plan view of a line in an embodiment of the present invention, FIG. 7 is a frequency directivity
characteristic view of the line, and FIG. 8 is a cross-sectional view of the line. DESCRIPTION OF
SYMBOLS 1 ... line part, 2 ... main-body part, 4 ... microphone unit, 5 ... line, 6 ... hole, 7 ...
resistance surface cloth, m ... parallel arrangement range.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a line microphone
and aims to improve the characteristics. Line microphones are used in cases where
superdirective microphones are desired to improve S / N with ambient noise such as far-edge
noise. FIG. 1 shows an example of the appearance of the prior art, in which (1) shows a line
portion, (2) shows a main body M, and j3 + shows a built-in position of the microphone unit. FIG.
2 IAI is a partial longitudinal sectional view of FIG. 1, and FIG. In the figure, the f41 id micro-bon
unit, (5) is an acoustic capillary (hereinafter referred to as a line), and 16+ is a hole of a few
orchids provided in the line (5). There is also a rule that a single slit is provided instead of the
plurality of eleven holes (6). (7) shows a thin grombite bonded to a hole + 61 [line 51] as a hole i
61 t-11, and a thin rubber sheet attached to a portion other than the hole + Li 1 of the line (5).
The principle of operation of the above-mentioned sbt line microphone is fully understood. Since
the line + 5 + VC number of holes (61 or slip (2 I + (I '1-7 r) is provided, the phase difference of
human incident waves from the hole (6) or each part of the slit is The direction changes
depending on the direction, and since tlj 伜 f is in the microphone unit (4), directivity can be
written by the phase difference \. In this case, when the acoustic impedance of the hole + 61 or
the slit is smaller than the acoustic impedance seen from the hole (6) or the slit on the unit (4)
side of the line + 51,- Since the sound wave comes out of the hole 161 or the slit from the
reexamination line (51, the phase is largely disturbed, and the directivity deteriorates. In order to
prevent this, it is necessary to increase the acoustic impedance of the r hole (6) or the slit, and
the above-mentioned resistive heavy cloth (7) is stuck. In the line microphone configured as
described above, in order to obtain superdirectivity, it is assumed that the hole (6) is a circular
hole and the resistance surface portion of a constant resistance is quadruple. It is necessary to
take the relationship between (81 and the line length (l, as shown in FIG. 8). That is, the area of
the unit 1 (the hole 1 in 411111 is small (resistance is large), and the area of the end of the wing
1 is large dance (the fence pile is small). (3) Tree 44 # FIG. 4 is a plan view of the conventional
line +5), and FIG. 5 shows its frequency directivity (in the case of a line length of about 801 and a
tube inner diameter 14 14 m). As seen from this characteristic, the directivity characteristic (180
° to 4S) is degraded at about 8 KHz or more.
This is considered to be due to the standing wave of the line (5) inner diameter. The present
invention eliminates the above-mentioned drawbacks and provides a rational line microphone
with a good directional characteristic, and a description will be given on that day. First, as is well
known, standing waves are considered to occur at frequencies of λ / 8 to λ / 4 or more of the
inner diameter of the tube. λ is the wavelength. In other words, in the case of FIG. 5, since it is
the inside diameter holder 14M, it can be understood that about 8 to (iKH2 or more) from f = x,
and that it is 11 to 111 cycles. tel is quick. Generally speaking, W standing waves are considered
to be easily generated by the microphone unit + 41Ill with large resistance, but according to real
-I #, the effective length of the line is based on the end of the line as the circle mantissa becomes
higher Gradually shorter, +1-found that 坤 1 <. つまり1. The standing wave due to the sash in
the area is considered to be due to the vicinity of the line end (4)-"stone end side, so the inner
product of the hole or slit in this vicinity is increased, and the hole area ratio to the inner surface
of the pipe is increased. If the size is increased, this characteristic deterioration can be prevented.
In addition, since the standing wave is generated at a frequency of 7878 to λ / 4 or more of the
tube diameter, the line portion involved in the standing wave is considered to be approximately 4
to 8 times the tube diameter from the tip, φ 14 w , The tip is about 55-IIIMI. The present
invention has been made based on the above-described improvement method, and one
embodiment of the present invention will be described below with reference to FIGS. FIG. 6
shows a plan view of line (5). In the line microphone of the present invention, the turtle portion
of the line (5) is the same as that shown in FIGS. In the line (5), a plurality of 11 holes (6a) are
transposed in parallel in two rows in the tube axis direction in the distal end side portion, that is,
the distant 1I 111 portion facing the microphone unit (4) A plurality of holes (6b) are provided
on the near side 4) with respect to each other). Holes (6a, 6b) consist of holes. The range fml of
parallel distribution of holes (6a) is 2 to the length of 4 to 8 times the diameter of the tube from
the end of the line 151, and it is 2 but it may or may not be this arrangement . Moreover,
although two or more parallel two holes (6a) are used in this embodiment, eight or more holes
may be provided. The central position of the hole (6a) of the two rows i arranged parallel to each
other (the section of the line 151 so that the sheep 81 n 1 It is considered to be a distant place.
FIG. 7 receives an example of the frequency directivity characteristic of the line microphone
which has filled the entire line (5) shown in FIG. It is a rim base with a line length of about RO 葎
and an internal diameter of m 14 m. As can be seen, the index inertia is improved at about 3 KHz
or higher. Of course, it is necessary to consider to increase the wiping resistance per + p about
the hole + 61 K to be in between villages 11 ah. For example, the resistance VC of a round hole is
proportional to 1 / (pore diameter) 4 and when it is necessary to set 2 · 11 to 1 ···················· 1 From
the above, the pore diameter is 1 / σ-084 (cultivation) t6 +-. Also, the order of the holes (6) of
both rows arranged in parallel I! As in the present embodiment, if the positions are 90 ° apart
from each other, the reflection of the constant 11 with respect to the inner surface of the line
+51 is reduced, so that the standing # can be eliminated with high efficiency <RI. In the above
embodiment, the positions @ of the holes (6) in both rows arranged in parallel 1 are provided
adjacent to U, but the holes 1610 in both rows are misaligned and arranged in a thousand hour
shape It is also good. The above practical example shows the case where the holes (6) are cast.
15 = The same applies to the case where the plurality of holes 1610 V in each row are provided
with a dwelling slit in the H direction in the pipe An effect is obtained. As described above,
according to the present invention, it is possible to provide a massive line microphone that can
prevent the deterioration of the directivity characteristics due to the standing wave of the f inner