JPH0534795

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DESCRIPTION JPH0534795
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
narrow directional microphone, and more particularly to the reduction of wind noise in a narrow
directional microphone in which an acoustic tube is fitted to a microphone unit.
[0002]
2. Description of the Related Art Various types of narrow directional microphones, called line
microphones or the like in which the directivity is narrowed by fitting one end of an acoustic
tube to the tip of a microphone unit, have been provided conventionally. An example of a
conventional narrow directional microphone will be described with reference to FIG. 6. The
narrow directional microphone 1 has a microphone unit 4 having a front acoustic terminal 2 and
a rear acoustic terminal 3 and openings 5 for a plurality of acoustic resistances on its peripheral
surface. And the acoustic pipe 6 in which One end of the acoustic tube 6 is fitted to the front
acoustic terminal 2 side of the microphone unit 4, and the rear acoustic terminal 3 side of the
microphone unit 4 is positioned in a free sound field. On the outer peripheral surface of the
acoustic tube 6, an acoustic resistance material 7 made of non-woven fabric such as felt or nylon
mesh is provided. An outer tube 9 having an inner diameter larger than the outer diameter of the
acoustic resistance material 7 and having a plurality of through holes 8 formed therein is fitted
to the outer peripheral surfaces of the microphone unit 4 and the acoustic tube 6. The
microphone unit 4 is supported in the outer tube 9 by a fixing ring 10.
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[0003]
On the other hand, in the microphone, a pressure difference is generated by wind before and
after the diaphragm of the microphone unit, and this pressure difference becomes wind noise.
The wind noise increases in the order of the nondirectional microphone, the unidirectional
microphone, and the narrow directional microphone as described above. The wind noise of the
narrow directional microphone is large because one end of the acoustic tube 6 is directly and
completely connected to the front acoustic terminal 2 of the microphone unit 4. The tip 11 of the
front end becomes the sound inlet of the front acoustic terminal 2, the distance to the rear
acoustic terminal 3 becomes long, a very large pressure difference occurs, and as a result, a large
wind noise is generated in the bass region .
[0004]
In order to improve such a defect, for example, in Japanese Patent Application Laid-Open No. 62118698, the outer peripheral surface of the microphone unit is spaced from the inner peripheral
surface of the acoustic pipe in the rear end of the acoustic pipe. It has been proposed to position
and form a passage between the front and rear acoustic terminals to reduce the pressure
differential due to wind. With this structure, even if there is a pressure difference between the
front acoustic terminal and the rear acoustic terminal, the air on the high pressure side can be
made to flow to the low pressure side, thereby reducing the pressure difference and reducing
wind noise. about
[0005]
However, positioning the microphone unit with a gap in the acoustic pipe is suitable for the case
where the outer diameter of the microphone is large, since the acoustic pipe also becomes large
accordingly. However, if it is desired to make the outer diameter of the microphone extremely
thin, for example, 8 mm in diameter, it is necessary to use a very small microphone unit of a
much smaller diameter. As the microphone unit becomes smaller and its performance degrades,
it becomes extremely difficult to obtain the desired performance.
[0006]
Therefore, an object of the present invention is to provide a narrow directional microphone
which reduces the wind noise by reducing the pressure difference between the front acoustic
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terminal and the rear acoustic terminal without increasing the outer diameter.
[0007]
SUMMARY OF THE INVENTION The narrow directional microphone according to the present
invention comprises an outer casing whose one end is fitted to one end of the acoustic tube, and
an acoustic tube fitted in one end of the acoustic tube. A unit holder having a front portion with
an outer diameter smaller than the outer diameter and a rear portion formed with an outer
diameter larger than the inner diameter of the acoustic tube fitted in the outer casing; And a
notch for communicating the gap formed by the outer diameter of the unit holder with the inner
diameter of the outer casing and the outer diameter of the rear portion of the unit holder. There
is.
[0008]
With this arrangement, the gap between the inner diameter of the acoustic tube and the outer
diameter of the unit holder, the gap between the inner diameter of the notch of the acoustic tube
and the outer case of the outer casing and the outer diameter of the rear of the unit holder Since
the high pressure side air can flow into the low pressure side even if there is a pressure
difference between the front acoustic terminal and the rear acoustic terminal, the pressure
difference Can be reduced to reduce wind noise.
Furthermore, since the leak path is formed in the outer casing, when obtaining a microphone of a
desired outer diameter, it is possible to use a microphone unit having a diameter substantially
equal to the outer diameter.
[0009]
DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will be described with
reference to an embodiment shown in the drawings. As shown in FIG. 2, the narrow directional
microphone 21 is made of an acoustic tube 22 made of metal such as aluminum. The rear end of
the acoustic tube 22 is fitted with one end of a substantially cylindrical outer casing 23 whose
inner circumferential surface is in close contact with the outer circumferential surface of the
acoustic tube 22.
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The outer casing 23 accommodates the microphone unit in its inside, and is made of metal such
as aluminum similarly to the acoustic tube 22, and an opening 24 serving as a rear acoustic
terminal on the other end side has a predetermined interval in the circumferential direction. A
plurality of these are provided. The other end of the outer casing 23 is similarly fitted with one
end of a grip case 25 having a cylindrical shape. As shown in detail in FIG. 3, a substantially arcshaped notch 26 is formed at the end of the acoustic tube 22 on the outer casing 23 side.
[0010]
A substantially cylindrical unit holder 28 for accommodating the microphone unit 27 therein is
fitted in the outer casing 23. The unit holder 28 includes a rear cylindrical portion 29
accommodating the microphone unit 27 and a front cylindrical portion 30 extending from the
sound collecting side of the microphone unit 27 into the acoustic tube 22. In order to fit the rear
cylindrical portion 29 into the outer casing 23, the outer diameter thereof is slightly smaller than
the inner diameter of the outer casing 23, and rattling of the microphone unit 27 caused by the
gap covers the opening 24. The end of the wire mesh 31 inserted into the outer casing 23 is
prevented by being interposed in this gap, and the air permeability of this gap is secured. The
front cylindrical portion 30 side end of the rear cylindrical portion 29 is positioned to abut on
the end edge of the acoustic tube 22. The outer diameter of the front cylindrical portion 30 is
smaller than the outer diameter of the rear cylindrical portion 29, thereby creating a gap
between the inner peripheral surface of the acoustic tube 22 and the outer peripheral surface of
the rear cylindrical portion 29. The notch 26 communicates with the gap between the outer
diameter of the rear cylindrical portion 29 and the inner diameter of the outer casing 23.
[0011]
While the sound collecting side of the microphone unit 27 is the front acoustic terminal in the
middle frequency band and above, the tip of the acoustic tube 22 is the front acoustic terminal in
the low frequency band as in the prior art, and the rear acoustic The distance between the
terminal and the opening 24 of the outer casing 23 is long, and a very large pressure difference
is generated between the two. However, as described above, from the gap between the inner
peripheral surface of the acoustic tube 22 and the outer peripheral surface of the rear cylindrical
portion 29 of the unit holder 28, the outer diameter of the rear cylindrical portion 29 and the
outer casing 23 pass through the notch 26 of the acoustic tube 22. A leak passage of air
communicating with the gap between the inner diameters of the two is formed, and even if there
is a pressure difference between the front acoustic terminal and the rear acoustic terminal, the
high pressure air can flow into the low pressure side. Because the pressure difference is reduced,
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wind noise can be reduced. Furthermore, since this air leakage passage does not have a factor
that increases the appearance of the acoustic tube 22, the unit holder 28, and the outer casing
23, the overall downsizing can be achieved without degrading the performance of the
microphone.
[0012]
FIG. 5 shows the wind noise characteristics of the conventional narrow directional microphone
shown in FIG. 6, and FIG. 4 shows the wind noise characteristics of the narrow directional
microphone of the embodiment described above. It was found from this measurement that the
improvement was about 4 dB.
[0013]
As described above, according to the narrow directional microphone of the present invention, the
outer casing has one end fitted to one end of the acoustic tube, and the acoustic tube fitted in one
end of the acoustic tube. The unit holder has a front portion with an outer diameter smaller than
the outer diameter and a rear portion formed with an outer diameter larger than the inner
diameter of the acoustic tube fitted in the outer casing, and a notch is formed at one end of the
acoustic tube As it is formed, air leaks from the gap between the inner diameter of the acoustic
tube and the outer diameter of the unit holder to the gap between the notch of the acoustic tube
and the inner diameter of the outer casing and the outer diameter of the rear of the unit holder
Even if there is a passage and there is a pressure difference between the front and rear acoustic
terminals, the high pressure air can flow into the low pressure side, so the pressure difference
becomes smaller and wind noise is reduced. It can be reduced.
Furthermore, since this leak path is formed in the outer casing, it is possible to use a unit having
an outer diameter approximately equal to the outer diameter of the acoustic tube, so that the
performance of the microphone is not degraded.
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