JPS626784Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a directional microphone unit that is housed in an outer case and constitutes a directional microphone.This invention allows the velocity component of a sound wave to pass smoothly and has improved directivity characteristics. It was invented for the purpose of obtaining a microphone.

As illustrated in the vertical cross-sectional view of FIG. 1, a conventional directional microphone unit has a diaphragm 5 sandwiched between a front cover 2 having a sound hole 1 and a frame 4 at the front end of a case 3, and generates vibrations. A pole piece 7 whose tips are close to the inner and outer surfaces of a coil 6 fixed to the back surface of the plate 5 and a magnetically conductive ring 8 are connected by an annular magnet 9 and a magnetically conductive plate 11 having a through hole 10 formed in the inner edge of the case 3. The rear part of the case 3 is closed with an inner lid 13 having a through hole 12 and an outer lid 15 having a through hole 14 to form a rear chamber 16 between the inner and outer lids 13 and 15.The side of the case 3 has through holes 17, 1
8, and each through hole 12, 14, 1
7 and 18 are pasted with cloth to provide acoustic resistance.
A cylindrical passage 19 is formed between the pole piece 7, the magnetically conductive ring 8, and the annular magnet 9, and a cylindrical passage 19 is formed between the case 3, the magnetically conductive ring 8, and the annular magnet 9 on the outer periphery of the back surface of the diaphragm 5. A communicating cylindrical passage 20 is formed.

In a directional microphone, sound waves are introduced into the case through holes 17 and 18 on the side of the case in order to provide directivity, and the velocity components of these sound waves are applied to the back of the diaphragm 5, but the position at which this is applied is the same as the vibration. It is most effective to use the dome portion 5a at the center of the plate 5. In the above conventional structure, the through holes 17, 18
The velocity component of the sound wave that entered the case from the passage 20
In order to reach the back surface of the dome part 5a through the diaphragm 5, the pole piece 7 and the coil 6 are passed through the inner space of the periphery of the diaphragm 5, pass through a minute gap between the magnetic conduction ring 8 and the coil 6, and exit to the front end of the passage 19. Because the velocity component has to exit to the back surface of the dome part 5a through a small gap between the diaphragm and the dome part 5a, the velocity component cannot effectively act on the dome part 5a of the diaphragm due to the inertance and acoustic resistance of both the small gaps. It was not possible to make the directivity sufficiently good.

The present invention improves the above points.

2 and 3 show an embodiment of the directional microphone unit according to the present invention, in which a magnetically conductive ring 8 and an annular magnet 9 are shown.
radial passages 2 in the annular magnet 9 at the contact surface with
1 was formed. The passage 21 may be formed only on the front surface of the annular magnet 9 as shown in FIG. . The rest of the structure is the same as that of the conventional example shown in FIG. 1, so the same reference numerals are given and the explanation will be omitted.

Since the directional microphone unit of the present invention is constructed in this way, the through holes 17 and 1 on the side of the case are
The velocity component of the sound wave entering the passage 20 from the diaphragm 8 enters the passage 19 through the passage 21, passes through only the minute gap between the pole piece 7 and the coil 6, and reaches the back surface of the dome portion 5a of the diaphragm. That is, since it is not necessary to pass through the minute gap between the magnetically conductive ring 8 and the coil 6, inertance and acoustic resistance can be reduced accordingly.

Figure 4 shows the acoustic equivalent circuit when rear case A is attached to the directional microphone unit according to the present invention, where p is sound pressure, m is inertance, r is acoustic resistance, c is acoustic capacitance, and saphix is Each part of FIG. 5 is shown. Since the acoustic resistance r ₂ of the passage 21 is significantly smaller than the acoustic resistance r ₁ between the magnetic conductive ring 8 and the coil 6, the inertance m ₁ ,
In parallel with acoustic resistance r ₁ is inertance m ₂ , acoustic resistance r ₂
Due to the existence of , the influence of acoustic resistance r ₁ can be ignored. Note that if such a passage 21 is formed, the effective magnetic flux acting on the coil 6 will be reduced, but since the passage 21 does not need to be significantly large, the effect 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, and the solid lines indicate the characteristics of the microphone unit of the present invention,
The dotted line shows the conventional structure, where A is the sensitivity in the 0° direction (front), B is the sensitivity in the 90° direction (side), C is the sensitivity in the 180° direction (backward) on the vertical axis, and the horizontal axis is the frequency. This is what was shown. In this example, it can be seen that the directivity is improved in the approximate frequency range of 1000 to 5000.

As described above, the present invention has an annular magnet 9 and a magnetically conductive ring 8.
By forming a passage 21 with low acoustic resistance between the diaphragm and the dome part 5 at the center of the diaphragm, the velocity components of the sound waves entering the case from the side holes 17 and 18 are
Directivity is improved by increasing the effect on a.

In an internal magnet type microphone in which a magnet is placed inside the coil and a yoke is placed outside the coil, providing a passage in the yoke to communicate between the inside and outside is disclosed in Japanese Utility Model Publication No. 46-6871 and Japanese Patent Application Laid-Open No. 55-96796. As stated in the publication, it is difficult to form a through hole in the annular magnet in an external magnet type microphone such as the present invention in which a pole piece is placed inside the coil and the coil is surrounded by an annular magnet. be. This idea is
Passage 21 when press molding ferrite powder
This was done with the focus on the fact that forming a passageway would be easy, and it could be easily implemented with simple machining, and would be highly effective in improving the directivity of the microphone unit.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view illustrating a conventional directional microphone unit, Fig. 2 and the following exemplify the directional micro unit according to the present invention, Fig. 2 is a longitudinal sectional view, and Fig. 3 is a perspective view of an annular magnet. , FIG. 4 is an equivalent circuit diagram, FIG. 5 is a longitudinal sectional view of the microphone unit showing the symbols in the equivalent circuit diagram, and FIG. 6 is a characteristic curve shown in comparison with a conventional microphone unit. 1: Sound hole, 2: Front cover, 3: Case, 4:
Frame, 5: Diaphragm, 5a: Dome part, 6: Coil,
7: Pole piece, 8: Magnetically conductive ring, 9: Annular magnet,
10, 12, 14, 17, 18: Through hole, 11: Magnetic conductive plate, 13: Inner lid, 15: Outer lid, 16: Rear chamber, 1
9, 20, 21: Passage.

Claims (1)

[Scope of utility model registration request] A coil 6 fixed to the back of the diaphragm 5 surrounding the dome portion 5a is sandwiched between a pole piece 7 surrounded by a case 3 across a passage 20 and a magnetically conductive ring 8 with a small gap between them. Pole piece 7 to passage 1
A magnetically conductive plate 1 having a through hole 10 connects the annular magnet 9 surrounding the pole piece 7 and the annular magnet 9.
In the directional microphone unit connected at 1, a radial passage 21 is formed in the annular magnet 9 made by press-molding powdered ferrite during molding, and a passage 19 between the pole piece 7 and the annular magnet 9 is formed. A directional microphone unit characterized in that a channel 20 is connected to a passage 20 inside the case.