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JPS5521679

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DESCRIPTION JPS5521679
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a conventional directional
microphone, FIG. 3 is a block diagram of a directional microphone according to an embodiment
of the present invention, and FIGS. FIG. 6 is a characteristic view of the microphone, and FIG. 6 is
a plan view of the main part. 11 иииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииии
Damping material.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a directional
microphone with improved specification characteristics and less variation in assembly and
stabilization. Heretofore, in an electrostatic microphone and a self-polarizing electrostatic
microphone having uni-directionality and biphasic directivity, a circuit (phase-shifting circuit)
which appropriately changes the phase shift together with the inlet where the sound f enters
from the front of the microphone ) Is set behind the back air chamber, and the desired
characteristics are set by performing synthesis with those coming in through the same circuit
from the rear. By the way, as shown in FIGS. 1 and 2, the phase shift circuits' -21 and -2 are
formed in a portion surrounded by the insulator 2 supporting the fixed electrode 1 and the phase
shift plate 4. Here, in FIG. 1, a spacer 3 forming a 50 to 100 ?m interval is provided between the
insulator 2 and the phase shift plate 4 to utilize the acoustic resistance for the thin fluid layer
between the intervals. However, in order to stably obtain directivity in this configuration,
uniformity of the thickness of the spacer 3 and flatness of the insulator 2 and the phase shift
plate 4 are required. Therefore, the insulator 2 and the phase shift plate 4 need to be flatwrapped using a ceramic substrate. The same effect can be obtained by inserting the damping
material 6 made of non-woven fabric or cotton cloth instead of the spacer 3 as shown in FIG. 2 in
order to eliminate such high precision requirements. However, this configuration has two
disadvantages as described below. First, four to eight 0.3.phi. To 1.phi. Through holes 8a are
provided coaxially on the insulator 2 in order to transmit the braking resistance of the braking
material 6, and this is used in the phase shift plate 4 at the corresponding position. Also, the
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through hole 7a is provided. In this case, the relative position of the through holes 7a is kept
constant by a jig or the like so as to have a constant angle coaxially. However, even if the air gap
entering the damping member 6 is kept constant, the damping member 6 generally has a large
variation in coarse density depending on thickness and location, and it is difficult to obtain a
constant directivity without adjustment. Therefore, after assembling, it is necessary to fill the
holes after the adhesive, which requires a lot of man-hours. Second, since the through holes 7a of
the phase shift plate 4 to be the acoustic terminals 5 from the back side are coaxially provided at
regular intervals, the phase shift circuit in the high frequency band (82 to 2 oKHz at 5) The
phases of the sound waves passing through are irregular, and it becomes impossible to obtain the
desired directivity. For example, in FIG. 4, curve a is the frequency characteristic of the
microphone and b is the characteristic of the acoustic signal passing through the phase shift
circuit. The present invention eliminates the above-mentioned conventional drawbacks, and will
be described below along with its embodiments.
In FIG. 3, reference numeral 11 denotes a fixed electrode integrally provided with a terminal 15,
and 12) an insulator 13 provided with a large number of through holes 12a is provided with a
through hole 13a at a position opposed to the L4 distribution hole 12a. The plane is shown in
FIG. 6 with a phase plate. 14 is a damping material. As described above, by providing the through
holes 12a and 13a linearly (by providing a large number of Cs, the resistance value per unit area
of the damping material 14 is increased to increase the equivalent cross-sectional area, so that
the thickness of the damping material 6 is increased. The variation due to the density is reduced,
and adjustment is not required. Further, by distributing the spacings of the holes of the acoustic
terminal surface formed by the through holes 13a to be smaller than the wavelength at the high
frequency, it becomes possible to improve the directivity so as to secure good directivity in the
high frequency band. . In FIG. 5, a is the frequency characteristic of the microphone, and b is the
characteristic of the acoustic signal passing through the conversion circuit.
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