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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
directional microphone, and in particular, can combine four bi-directional microphones to follow
the movement of a target sound source (including a sound source to be captured and a noise
source to be excluded). The present invention relates to an analog variable directional
microphone as described above. (Prior Art) Directional microphones are used to filter out
ambient noise and capture only the target sound. There are various types of directional
microphones, for example, the one shown in FIG. 3 arranges two nondirectional microphones 1.2
at a distance of @d, and the output of the microphone 2 is a delay unit 3 The difference between
the outputs of the two microphones 1.2 is calculated by the adder 4 and taken out from the
terminal 5 as an output. This type of microphone is called a primary pressure gradient type
unidirectional microphone, and the directivity characteristic is as shown in the basic
characteristic diagram of FIG. Further, as shown in FIG. 5, the delay devices 10 to 13 and the gain
adjusters 14 to 17 are respectively connected to the four nondirectional microphones 6 to 9, and
the output signal from the gain adjuster 14.17 is A microphone having directivity as shown in
the basic characteristic diagram of FIG. 6 can be obtained by using the difference between the
summed signal and the summed signal output from the regulator 15.16 as the output. it can. This
microphone is called a secondary pressure gradient type directional microphone. The two
nondirectional microphones in this case can be replaced by one bidirectional microphone having
the characteristics as shown in the basic characteristic diagram of FIG. 7, so as shown in FIG. By
combining the bidirectional microphones 18.19 and providing the delayers 2o and 21 and the
gain adjusters 22.23 respectively, directional microphones similar to those of FIG. 5 can be
obtained. FIG. 9 schematically shows a specific structure of a bi-directional microphone, in which
an electret diaphragm 27, a porous back electrode 28, and an acoustic resistance cloth 29 are
provided in a case 26 having an opening 24. 25 on the front and back. Thus, the pressure due to
the sound wave coming from the lateral direction of the case can be weakened to obtain bidirectional characteristics as shown in FIG. (Problems to be Solved by the Invention) The
conventional directional microphone as described above has a fixed direction of directivity, and
when the position of the sound source changes, the microphone is manually moved in the
direction of the sound source. The direction had to be corrected, and the microphone itself could
not follow the moving sound source. The same is true when attempting to weaken the sensitivity
to the signal from the direction of the noise source. (Means for Solving the Problems) The
present invention uses four bi-directional microphones, and is provided with a delay device, a
gain regulator, a power comparator, and a control device, so that the sound source We have
obtained a directional microphone that can follow the movement of the sound source, the noise
source to be excluded).
That is, a delay unit and a gain adjuster are respectively connected to four bi-directional
microphones equally spaced on one circumference, and two microphones at both ends of one
diameter on the circumference The difference between the output of one of the microphones and
the output of the other microphone through the above delay unit and gain adjuster is added to
obtain four output differences, and these four output differences are output to the four terminals
of the changeover switch. While connecting, this output difference is input to the power
comparator, and the controller driven by the power comparator switches the changeover switch
so as to obtain the maximum output to capture the target sound or eliminate the noise. The
above problem is solved by obtaining a directional microphone which automatically follows a
target sound source. (Operation) One of four bi-directional microphones (located at each end of
two orthogonal diameters) equally spaced on one circumference. By adding a delay and a gain
adjuster to one of the two bidirectional microphones, the two microphones act as microphones
having a second-order pressure gradient type directivity as shown in FIG. . If two each of four bidirectional microphones are placed at both ends of one diameter as described above, and the two
diameters are orthogonally compared and their outputs are compared, it is possible to know the
large sound source direction of the output by the comparator it can. Therefore, the moving sound
source can be automatically made to follow by comparing the four outputs and switching the
switch by the control device to always capture the sound in the direction of the large output.
(Embodiment) FIG. 1 schematically shows the structure of a directional microphone which
follows a target sound source according to the present invention. The four bi-directional
microphones A, B, C, and D are framed by positioning the two microphones A, C, and B% D at
both ends of the orthogonal diameter of one circle as shown in FIG. It is attached to the body 31.
Each of the microphones A to D is connected to an analog phase shifter 32 to 35 which is a delay
unit, an electronic volume 36 to 39 which is a gain adjuster, and an adder 40 to 43 of the
outputs of the microphones facing each other in diameter. It is connected to four terminals,
selected by this switch, connected to the output terminal 47 through the amplifier 45 and the
equalizer 46, and the output is taken out. The outputs of the respective microphones passing
through the adders 40 to 43 are branched and input to the power comparator 49 through the
changeover switch 48, and the output of the comparator 49 is manually input to the controller
50. The changeover switch 48 always repeats the switching operation as in the radar to
alternately transmit the outputs of the summers 40 to 43 connected to the respective contacts to
the power comparator 49.
The controller 50 drives this switch to connect the changeover switch 44 to the largest terminal
of the microphone output. With such a configuration, the directional microphone constituted by
the bidirectional microphones A to D eliminates noise around the target sound source and
collects the target sound with a sharp directivity, while the target sound source moves. Even if
this is followed, the changeover switch 44 can be switched to always collect the target sound.
Also, if there is a large noise source, the power comparator 49 senses the microphone output
that minimizes the noise automatically by following this, and connects the terminal of the output
switch 44 to the amplifier 45. By operating the controller 50 as described above, it is possible to
reduce noise in the captured sound (the target sound is contained therein). According to the
present invention, the sound source moves by comparing the strength of the target sound
captured by the four bidirectional microphones to know the direction of the sound source and
driving the changeover switch to extract the largest microphone output. Even then, it can
automatically follow this to capture the target sound or reduce noise.
Brief description of the drawings
FIG. 1 is a diagram schematically showing the configuration of the microphone of the present
invention, FIG. 2 is a schematic diagram showing the arrangement of four bi-directional
microphones, FIG. 3 and the following are prior art, and FIG. FIG. 4 is a schematic diagram
showing a configuration for obtaining a primary pressure gradient type directional microphone
by this nondirectional microphone, FIG. 4 is a basic directional characteristic diagram obtained
by this, and FIG. 5 is two by the four nondirectional microphones. A schematic diagram showing
the configuration for obtaining the next pressure gradient type directional microphone, FIG. 6 is
its basic directional characteristic diagram, FIG. 7 is a basic directional characteristic diagram,
and FIG. 8 is a secondary pressure by two bi-directional microphones FIG. 9 is a schematic view
showing a configuration for obtaining a gradient type microphone, and FIG. 9 is a schematic view
showing an example of the structure of a bi-directional microphone.
A, B, C, D: Bi-directional microphone, 1.2: Non-directional microphone, 3: Delay, 4: Adder, 5:
Output terminal, 6.7. 8.9: Non-directional microphone , delay device,
gain regulator, 18.19: bi-directional microphone, 20.21: delay device, 22.23: gain regulator, 24.
Reference numeral 25: aperture, 26: case, 27: electret diaphragm, 28: back electrode, 29:
acoustic resistance cloth, 31: frame, analog phaser, Electronic volume, summing device, 44: changeover switch, 45: amplifier, 46: equalizer, 47: output
terminal, 48: changeover switch, 49: power comparator, 50: controller.