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JPS57191190

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DESCRIPTION JPS57191190
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view illustrating a
conventional directional microphone unit, FIG. 2 and the subsequent figures exemplify a fingerdirectional microphone unit according to the present invention, and FIG. 2 is a longitudinal
sectional view 3 is a perspective view of an annular magnet, FIG. 4 is an equivalent circuit
diagram, FIG. 5 is a longitudinal sectional view of a microphone unit showing the reference
numerals in the equivalent circuit diagram, and FIG. 6 is shown in comparison with a
conventional microphone unit Characteristic curve. 1: Sound hole 2: Front cover 3: Case 4: Frame
5: Diaphragm 5a: dome portion 6: Coil 7: pole piece 8: magnetic conductive ring 9: annular
magnet 10. 12, 14, 17, 18: through hole, 11: magnetic guide plate, 13: inner lid, 15: outer lid, 16:
rear chamber, 19. 20, 21: passage.
DETAILED DESCRIPTION OF THE INVENTION This invention relates to a directional microphone
unit <1)> 1oo47y9 'unit which is housed in an outer cover and constitutes a directional
microphone, and can smoothly pass the velocity component of the sound wave, It is a device
aimed at obtaining a directional microphone with improved characteristics. In the conventional
directional microphone unit, the diaphragm 5 is held between the front cover 2 having the sound
hole 1 and the frame 4 at the front end of the case 3 as illustrated in the longitudinal sectional
view of FIG. The pole piece 7 with its tip close to the inner and outer side surfaces of the coil 6
fixed to the back surface of the plate 5, the magnetically conductive ring 8, the annular magnet 9,
the magnetically conductive plate 1 with the through hole 10 formed in the inner edge A rear
chamber 16 is formed between the inner and outer lids 13.15 by connecting and closing with an
inner lid 13 having a through hole 12 and an outer lid 15 having a through hole 14. A throughhole 17.18 is formed in each of the through-holes 12.14.17.18, and a cloth serving as an acoustic
resistance is attached to each through-hole 12.14.17.18. A cylindrical passage 19 is formed
between the pole piece 7 and the magnetically conductive ring 8 and the annular magnet 9, and
on the back outer periphery of the diaphragm 5 between the case 3 and the magnetically
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conductive ring 8 and the annular magnet 9. Cylindrical C2> +11 (11 passages 20 are formed). In
the directional microphone, in order to provide directivity, a sound wave is introduced into the
case from the through hole 17.18 on the side of the case, and the velocity component of this
sound wave is applied to the back of the diaphragm 5, but this position is added 7 '. In the case of
the dome portion 5a at the center of the diaphragm 5, the most effective effect is obtained. In the
above-described conventional structure, the velocity component of the sound wave entering the
case from the through hole 17.18 passes through the passage 20 and reaches the back surface of
the dome portion 5a. Since both the small gap between the ring 8 and the coil 6 has to go out to
the front end of the passage 19 and then the small gap between the pole piece 7 and the coil 6 to
go out to the back of the dome part 5a Because of the inertance and the acoustic resistance, the
velocity component can not be effectively acted on the dome portion 5a of the diaphragm, and
the directivity can not be made sufficiently good. The present invention is an improvement of the
above points. FIGS. 2 to 3 show an embodiment of the directional microphone C3) 11 # 102 unit
according to the present invention, in which radial passages 21 are formed in the annular
magnet 9 at the contact surface between the magnetically conductive ring 8 and the annular
magnet 9. It is. The passage 21 may be formed only on the front surface of the annular magnet 9
as shown in FIG. 3 showing this embodiment, but may be formed on the back surface of the
magnetically conductive ring 8 or on both sides 2 You can also.
The other structure is the same as that of the conventional example shown in FIG. Since the
directional microphone unit of the present invention is configured as described above, the
velocity component of the sound wave entering the passage 20 from the through hole 17.18 on
the side of the nurse passes through the passage 21 and enters the passage 19 and Only through
the minute gap with the coil 6, it reaches the back of the dome portion 5a of the diaphragm.
Since it is not necessary to pass through the minute gap between the magnetic ring 8 and the coil
6, the inertance and the acoustic resistance can be reduced accordingly. Fig. 4 shows the circuit
when the rear couss A is attached to the directional microphone (4) li 103 unit according to the
present invention, etc., where P is sound pressure, m is inertance 1, / r is acoustic resistance, 0
indicates the acoustic capacity, and the suffix indicates that in each part of FIG. Since the acoustic
resistance r of the passage 21 is significantly smaller than the acoustic resistance rl between the
magnet guide ring 8 and the coil 6, the presence of the inertance m2 and the acoustic resistance
r in parallel with the inertance m + and the acoustic resistance r1 The influence of the resistance
r0 is negligible. In addition, if such a passage 21 is formed, the effective magnetic flux acting on
the coil 6 is reduced, but since the passage 21 does not have to be made extremely large, the
influence of the reduction in magnetic flux is negligible. FIG. 6 illustrates the characteristics of
the microphone unit of the present invention provided with the passage 21 and the conventional
microphone unit without the passage 21, the solid line showing the present invention, the dotted
line showing the conventional structure, A +! The sensitivity to the 0 ° direction (front), B is the
sensitivity to the 90 ° direction (side), C is the sensitivity to 180 ° (rear) (5) 11.04 effect-) 1
The frequency is shown on the horizontal axis. In this example, it can be seen that the directivity
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is improved in the range of 1000 to 5000 of the approximate frequency. As described above,
according to the present invention, by forming the passage 21 with small acoustic resistance
between the annular magnet 9 and the magnetically conductive ring 8, the velocity component of
the sound wave entering the case from the side through hole 17.18. The action on the dome
portion 5a at the center of the diaphragm is enlarged to improve the directivity, and it can be
easily implemented by a simple work, and the effect of improving the directivity of the
microphone unit is large.
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