JPH0241995Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to the structure of a moving coil microphone in electroacoustic equipment.

[Conventional technology]

Generally, a moving coil type microphone has a moving coil 24 held by an edge 26 in a magnetic gap of a magnetic circuit consisting of a magnet 21, a yoke 22, and a plate 23, as shown in FIG.
A vibration plate 25 is bonded to the upper end of the movable coil to constitute a vibration system.

In omnidirectional or unidirectional moving coil microphones, in order to control the vibration system with resistance, the yoke 2 is located behind the moving coil, that is, inside the magnetic circuit.
A braking acoustic resistor 27 made of felt or the like is inserted between the yoke 2 and the magnet 21, and a case 28 is installed on the back of the yoke 22 in order to sufficiently increase the braking effect.
A back air chamber 29 is formed, and a ventilation hole 221 is formed in the bottom surface of the yoke 22 so that the back air chamber 29 and the back surface of the vibration system communicate with each other.

[Problem to be solved]

However, in conventional microphones, the magnet 21 and yoke 2 are used to make the magnetic circuit smaller.
Since the dimension between the two inner walls is small and the total area of the ventilation hole 221 cannot be increased, a sufficient damping effect cannot be obtained and the frequency characteristics tend to deteriorate.
In order to eliminate this drawback, if the total number of ventilation holes 221 is increased, the magnetic resistance of the yoke will increase, the air gap magnetic flux density will decrease, and the microphone sensitivity will decrease, so it is not recommended to increase the number of ventilation holes 221 beyond a certain limit. Therefore, there was a problem in that the effects of the acoustic resistor and the rear air chamber were limited.

The purpose of this idea is to eliminate the problems of the conventional method described above, and to improve the communication between the vibration system and the rear air chamber, increase the damping effect of the acoustic resistor, and improve the frequency characteristics by creating a magnetic circuit. Regarding structure.

[Means for solving problems]

FIG. 1 shows the configuration of a basic embodiment of the microphone of the present invention.

It has a vibration system in which a moving coil 5 is bonded to the lower surface of a diaphragm 4 having an edge 7 on its outer periphery, and a magnetic circuit consisting of a magnet 1, a yoke 2, and a plate 3. A vibration system is held by the edge 7 so as to be located in the magnetic gap 6 formed by the plate 3, forming a microphone unit. The microphone unit is attached to the front end of the case 12, and the rear end of the case forms a back air chamber 9 at the rear of the microphone unit.

In the gap between the magnet 1 and the yoke 2 of the magnetic circuit, an acoustic resistor 11 made of felt or the like is inserted for controlling the vibration system.

The yoke 2 of the magnetic circuit is provided with a protrusion 8 having a smaller diameter than the magnet 1 at the bottom, and a plurality of ventilation holes 10 communicating with the rear air chamber 9 are bored at the bottom between the protrusion 8 and the side wall of the yoke 2. It is set up. The first
Since the figure illustrates a unidirectional microphone, the yoke 2 and the case 12 are connected to each other, and an introduction hole 13 for delayed sound waves to be applied to the back of the diaphragm is bored, and at the same time, a damping body 14 for delayed sound waves is installed. has been done.

[Effect]

In the microphone unit having the above structure, even though the yoke 2 and the magnet 1 have the same diameter as the conventional one, the width of the perforated part of the ventilation hole 10 that communicates the back side of the vibration system and the back air chamber 9 is widened. The effective area of the pores can be increased, the flow of the acoustic medium to the back air chamber 9 is improved, the damping effect on the vibration system is increased, and the frequency characteristics are improved.

〔Example〕

Figures 3a and 3b show other embodiments of the present invention,
By making the ventilation hole 31 into an oval shape or fan shape along the radial direction of the microphone unit, the area of the ventilation hole can be further increased without narrowing the effective path of the magnetic field lines, and the acoustic resistance effect of the rear air chamber can be reduced. It is possible to make it larger. Furthermore, behind the magnet 32, the magnet 32 and the yoke 33 are connected.
By interposing the auxiliary plate 34 between the auxiliary plate 34 and the bottom part, a shunt circuit for magnetic lines of force is formed, which compensates for the increase in magnetic resistance due to a decrease in the adhesive area between the magnet 32 and the yoke 33, and has the effect of preventing an excessive decrease. It is effective to make the size of the auxiliary plate 34 larger than the diameter of the magnet 32 as long as the area of the gap between it and the inner surface of the yoke 33 does not become smaller than the area of the ventilation hole.

〔effect〕

Figure 4 shows the frequency characteristics of the microphone of the present invention. 41 is the characteristic in the front direction, and 42 is the characteristic in the 180° direction.
Figures 43 and 44 show the frequency characteristics of the conventional microphone in the front and 180° directions, respectively.

It is clear that the damping effect is superior because the peak due to vibration system resonance at 3.5KHz has been lowered compared to the conventional model, and the directivity around 3KHz has also been improved. Furthermore, in terms of microphone manufacturing, enlarging the vent hole has advantages not found in conventional products in terms of mold design and mold life.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the moving coil microphone of the present invention, Figure 2 is a cross-sectional view of a conventional microphone, and Figures 3a and b are cross-sectional views of a unit according to another embodiment of the present invention, with a partial cutaway. The front view and FIG. 4 are frequency characteristic diagrams of the present invention and a conventional microphone. 1 is magnet, 2 is yoke, 3 is plate,
4 is a diaphragm, 5 is a moving coil, 6 is a magnetic gap, 7
8 is an edge, 8 is a protrusion, 9 is a rear air chamber, 10 is a ventilation hole, 11 is an acoustic resistor, and 12 is a case.

Claims (1)

[Scope of utility model registration request] The moving coil 5 glued to the bottom surface of the diaphragm 4 is
It is held by an edge 7 so as to be located inside a magnetic gap 6 of an internal magnet type magnetic circuit consisting of a magnet 1, a yoke 2, and a plate 3, and an acoustic resistor 11 inserted between the magnet 1 and the yoke 2. In a moving coil microphone having a structure in which a rear air chamber 9 is formed by covering a transducer unit with a case 12, a protrusion 8 having a diameter smaller than that of the magnet 1 is provided at the bottom of the yoke 2, and the protrusion 8 and the yoke 2 are connected to each other. A moving coil type microphone characterized in that a plurality of ventilation holes 10 communicating with the rear air chamber 9 are provided at the bottom of the yoke 2 between the side wall and the yoke 2.