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JPS6126394

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DESCRIPTION JPS6126394
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
microphone device having donut directivity suitable for meetings and the like. Prior Art
Configuration and Its Problem FIG. 1 shows a conventional microphone device. The configuration
of this conventional example will be described below with reference to FIG. In FIG. 1, 1 is a bidirectional microphone; In the Y-Y 'axis direction, 2 indicates a nondirectional microphone, 3
indicates a differential circuit, and is configured to obtain an output difference between the
microphones 1 and 2. Next, the operation of the above conventional example will be described. 2
'1'i' FIG. 1 'is an external cover diagram illustrating the operation of the microphone device in
FIG. In the figure, reference numeral 1 'denotes a cover turn of the microphone 1 and a cover
turn of the 2' microphone 2. In FIG. 1, since the output difference of each of the microphones 1
and 2 is obtained, an output cover such as 3 'is obtained. This is an output coverage on a certain
vertical plane, but since the outputs of each of the microphones 1, 2 are equivalent in all vertical
planes, all the patterns 8 'of the differential output are also equivalent. In the vertical plane of In
other words, it is a donut directional microphone device. In addition to the configuration of the
conventional example, it is also possible to arrange two single directional microphones coaxially
in opposite directions with respect to the duplex 9 of the bidirectional microphone 1 and obtain
the output difference. A donut directional microphone is extremely suitable for conferences and
the like because the horizontal pattern is non-directional and the sound in the direction of the
vertical axis which is not necessary is hard to spread. However, in the above conventional
configuration, a plurality of microphones must be used in combination in a predetermined
relationship, so that the circuit configuration is complicated and many characteristics are
obtained in order to obtain appropriate characteristics. The adjustment function was required,
and there were various problems L in terms of operability. SUMMARY OF THE INVENTION The
present invention eliminates the drawbacks of the prior art and provides an excellent donut
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directional microphone device that can obtain appropriate characteristics with a simple
configuration and that requires little preparation function. The purpose is to Configuration of the
Invention In order to achieve the above object, the present invention uses an acoustic tube and
mounts a single differential microphone so that the front portion of the vibrating film faces
outward substantially at the center of the acoustic tube. It is configured to effectively obtain the
desired directivity by utilizing the sound path of the above. Description of the Embodiments The
configuration of an embodiment of the present invention will be described below with reference
to the drawings.
FIG. 3 is an external view of an embodiment of the microphone device according to the present
invention. In FIG. 3, 4 is a differential microphone that enables introduction of sound from the
front and back of the diaphragm, and 5 is an aperture at both ends. It is an acoustic tube of
length L, which is the end 5 ', and several differential microphones 4 are shown near its center.
FIG. 4 is a partially enlarged cross-sectional view of the vicinity of the attachment of the
differential microphone 4 in FIG. In the figure, 4 'indicates the position of the diaphragm, 4a
indicates the front of the diaphragm 4', 4b indicates the back of the diaphragm 4 ', and 6
indicates the output lead of the differential microphone 4. That is, several examples of the
differential microphones 4 are formed in the through holes formed near the center of the
acoustic tube 5 so that the front part 4a of the diaphragm 4 'is on the outside, with respect to the
front part 4a of the diaphragm 4'. Is configured by direct sound being applied, and the acoustic
tube 5 is configured to act as an acoustic path for the back 4b. Next, the operation of the above
embodiment will be described. FIG. 5 is an operation explanatory view for explaining the
operation, in which t is the distance between the open end 5 'of the acoustic tube 5 and the
differential microphone 4, O is the introduction angle of sound, Po is Σjwt Indicates the sound
pressure applied to the front 4 a of the differential microphone 4. In the figure, since Sin (90 ° 90) = cosθ'-fi +, the sound pressure applied to the back 4bK of the differential microphone 4
from the Y direction is -c, ω-2πf, and C: the velocity of sound p00j (wt + kl Cose '-kl) (21)
Similarly, the sound pressure applied to the back part 4b from the VCY' direction becomes Po j j
(wt-kl ° 0 ° θ-1) (3). Therefore, the synthetic sound pressure PT applied to the differential
microphone 4 is 5 in the following equation. In the equation (4), the first item is the sound
pressure applied to the front portion 4a of the differential microphone 4, which indicates that it
is nondirectional. And the second item is the sound pressure applied to the back 4b through the
sound pipe 5, and the sound pressure from each direction of 9, Y-Y'1 紬 becomes uni-directional
()--- Each differential output indicates that it is synthetically bi-directional. In other words, 0
indicates that the conventional microphone device shown in FIG. 2 has a directivity pattern
similar to that of the conventional microphone device. It can be seen that the sound pressure PT
& sought equation (4) is a directivity pattern of donut directivity. FIG. 6 shows an example of
frequency characteristics in the case of L = 40 cm and L = 20 crn. From the same figure, it is
apparent that the reproduction band of the horizontal pattern (0 °) is equal to or higher than
the frequency at which λ is almost L-H (λ: wavelength of sound wave).
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This is due to the tube resonance of the acoustic tube 5. The characteristic in the 90 ° direction
shown by a dotted line in the figure is a donut directivity as shown in the figure. In the case of
FIG. 6, the resonance of the Takumi acoustic tube 5 is affected by λ as described above, and
particularly at a frequency of L-2, the resonance Q becomes high, and deterioration of the
frequency characteristics of the reproduction band is observed. FIG. 7 is a cross-sectional view of
an essential part of another embodiment in which measures for preventing deterioration of the
frequency characteristic are taken, and the acoustic resistance material 7 is attached near the
open end 5 'of the acoustic pipe 5. ing. As described above, when the acoustic resistance material
7 is attached in the vicinity of the opening 5 ', as shown in FIG. 81, the Q of resonance drops
appropriately, and the deterioration of the frequency characteristics can be minimized. The
resonance Q can be sufficiently reduced by reducing the diameter of the acoustic tube 5 or in the
case of FIG. 6, a frequency characteristic graph about three times the frequency of L-2 The dip
occurs and the deterioration of the frequency characteristic is observed. This cause is considered
to be due to the phase of the sound from each aperture end 5 '. As a countermeasure, as shown
in FIG. 9, the mounting position of the differential microphone 4 is from the vicinity of the center
Y-Y'. They may be slightly offset in any direction along the axis d, and the distances to the
respective open ends 5 'may be made different from each other and made asymmetric. In this
way, the frequency characteristics as shown in FIG. 10 can be obtained, and the tip near the
frequency about three times the L-100 frequency shown in FIG. 6 can be greatly improved. FIG.
11 shows still another embodiment, in which a plurality of sound holes 8 are provided between
the mounting position of the differential microphone 4 and the open end 5 'of the acoustic tube
5. . However, in this case as well, the same effect as that of the embodiment shown in FIG. 9 can
be obtained. That is, in the embodiment shown in FIG. 11, a frequency characteristic as shown in
FIG. 12 can be obtained, and in the same manner as the embodiment shown in FIG. The dip in the
vicinity can be greatly improved. If the sound from the front part 4a of the differential
microphone 4 is eliminated by providing an appropriate air chamber from K, it can be a simple
bi-directional microphone (Y-Y 'axis direction) is there. And, by taking out the output
differentially using this and a unidirectional microphone, it is possible to obtain an MS (MAIN 5
IDE) microphone having a binaural effect. Also, if the open end 5 'of the acoustic tube 5 is set to
one direction only, it can be a simple unidirectional microphone, and in this case, the sound
incident from the front portion 4a of the differential microphone 4 is moderate. If an air chamber
is provided and eliminated, it is possible to reverse the directionality of its unidirectionality.
According to the present invention, as is apparent from the above embodiments, the differential
microphone is attached to the central portion of the acoustic tube so that the front portion of the
diaphragm is directed outward, and the acoustic path to the back of the diaphragm is constituted
by all the above-mentioned acoustic tubes It can be easily configured with only an acoustic tube
and a differential microphone, and can easily obtain excellent frequency characteristics, and does
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not require many adjustment functions etc. It is extremely advantageous.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a block diagram of a conventional microphone device, FIG. 2 is a schematic diagram
showing the operation of the microphone device, and FIG. 3 is an external view showing the
configuration of an embodiment of the microphone device of the present invention. 4 is an
enlarged sectional view of the main part, FIG. 5 is an operation explanatory view of the same
embodiment, FIG. 6 is a frequency characteristic view of the present embodiment, and FIG. 7 is
an enlarged sectional view of the main part of the other embodiment. 8 is a frequency
characteristic diagram of the embodiment, FIG. 9 is an external view showing the configuration of
still another embodiment, FIG. 10 is a frequency characteristic diagram of the embodiment, and
FIG. FIG. 12 is an external view showing the configuration of one embodiment, and FIG. 12 is a
frequency characteristic diagram of the same embodiment.
4- · Differential micro-bon 5 · · Acoustic tube 5 '· · · Open end 7 · · · Acoustic resistance material.
Name of agent Attorney Nakao Toshio has 1 person Fig. 1 (qo ')] Y Fig. 5' Fig. 6 Circulating fluid
number (Hz) Fig. 7 Evening 'Fig. 8 Frequency (Hz) Fig. 9 Fig. 10 O Fig. 11 Fig. 12
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