JPS6110396

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DESCRIPTION JPS6110396
[0001]
FIELD OF THE INVENTION The present invention relates to dynamic microphones. Prior Art
Configuration and Its Problem FIG. 1 shows a conventional omnidirectional dynamic microphone.
The configuration of this conventional example will be described below with reference to FIG. In
FIG. 1, 1 is a pole piece, 2 is a magnet, 3 is a yoke, and they are concentrically coupled to form a
magnetic circuit. A voice coil 5 is coupled to the diaphragm 4, and the voice coil 5 is inserted into
an air gap formed by the pole piece 1 and the yoke 3, and the diaphragm 4 is coupled to the case
6. Reference numeral 7 denotes an acoustic resistance material, which is coupled to the case 6. 8
is a back room. Next, the operation of the conventional example will be described. FIG. 2 shows
an equivalent circuit of the prior art. ここで、rQ、mo。 so is the mechanical resistance, mass
and stiffness of the vibration system, and Sl is the stiffness of the air chamber 9, M, and R. The
mass of the acoustic resistance material 7 and the acoustic resistance Sb are the stiffness of the
back air chamber 8. P is the input sound pressure, and Vm is the vibration velocity of the
vibration system. In this equivalent circuit, when the sound pressure P of the diaphragm 4 is
applied, it vibrates at the velocity Vm, and the voice coil 5 inserted in the gap also vibrates at the
same velocity. The output of the microphone is E = B / Vm, and an output E proportional to the
vibration velocity Vm is obtained. Here, B is the magnetic flux density of the air gap, l! Is the wire
length of the voice coil 5. In this conventional example, resonance occurs due to the stiffness S of
the air chamber 9, a large peak appears in the frequency characteristic, and there is a problem
that the sound quality is deteriorated. In order to damp this resonance, attenuate the peak and
obtain a flat frequency characteristic, it is necessary to add a resistive material or the like in the
air chamber 9, but in this case the shape becomes complicated, and conversely There is a
problem that the variation is increased and the control becomes difficult. -In the case of a normal
nondirectional dynamic microphone with a case 6 diameter of 20 to 30 mm, the air chamber 9 is
about 1 cc, the back air chamber 8 is 10 to 20 cc, and the peak frequency of the above frequency
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characteristic is 2,000 Hz It occurs in ˜ 3,000 cities. SUMMARY OF THE INVENTION The object
of the present invention is to eliminate the problems of the prior art described above, and it is an
object of the present invention to provide an excellent dynamic microphone which can easily
obtain flat frequency characteristics with a simple configuration. . SUMMARY OF THE
INVENTION In order to achieve the above object, the present invention accommodates a voice
coil, a diaphragm, a magnet, and a first air chamber in a first case, and a first acoustic resistance
member is inserted into the first air chamber. The second air chamber is connected via the
second air chamber, and the back air chamber is connected to the second air chamber via the
second acoustic resistance material, and the frequency characteristic of the output is effectively
flat. It has the advantage of being able to
Description of the Embodiments One embodiment of the present invention will be described with
reference to the drawings. In FIG. 3, 11 is a pole piece, 12 is a magnet, and 13 is a yoke, which
are concentrically coupled to form a magnetic circuit. A voice coil 15 is coupled to the diaphragm
14, and the voice coil 15 is inserted into an air gap formed by the pole piece 11 and the yoke 13.
The diaphragm 14 is coupled to the first case 16 There is. Reference numeral 17 denotes a first
acoustic resistance material, and the first acoustic resistance material 17 is coupled to close a
hole 16 a formed in the first case 16. A second case 20 forms a second air chamber 18.
Reference numeral 21 denotes a second acoustic resistance material, and the second acoustic
resistance material 21 is coupled to close a hole 20 a formed in the second case 20. 22 is a back
room. Next, the operation of the above embodiment will be described. FIG. 4 shows an equivalent
circuit of the above embodiment. ここで、ro。 mQ and SQ are mechanical resistance, mass
and stiffness of the vibration system, and S1 is stiffness of the first air chamber 19. M,,, R, are the
mass of the first acoustic resistance material 17 and the acoustic 2 ball resistance. S2 is the
stiffness of the second air chamber 18, M2. R is the mass and acoustic resistance of the second
acoustic resistance material 21, and Sb is the stiffness of the back air chamber 22. P is the input
sound pressure, and Vm is the vibration velocity of the vibration system. In this equivalent
circuit, when the sound pressure P is applied to the diaphragm 14, the diaphragm 14 vibrates at
a velocity Vm, and the voice coil 15 inserted in the gap also vibrates at a velocity Vm. The output
of the microphone is E = BJVm, and an output E proportional to the vibration velocity Vm is
obtained. Here, B is the magnetic flux density of the air gap, and l is the wire length of the voice
coil. In the present embodiment, the first case 16 is 20 to 30 mm, and the first air chamber 19 is
about 1 cc. The back air chamber 22 is 10-20 CC. The second air chamber 18 is 1 to 3 cc. Since
the stiffness S of the second air chamber 18 is connected in parallel to the stiffness S of the first
air chamber 19 via the first acoustic resistance member 17 and the value is small, the stiffness Sb
of the back air chamber 22 and the Since the entire stiffness S2 of the second air chamber 18 is
increased in frequency, only the stiffness S2 of the second air chamber 18 contributes. The peak
appearing at 200 (H1z to 3000) 1z is due to the stiffness S1 of the first air chamber 19, and
since the stiffness S2 of the second air chamber 18 is coupled in parallel with the stiffness S1, a
plurality of resonance modes are provided. It is divided, and the noise due to resonance is
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attenuated, and flat frequency characteristics are obtained.
FIG. 5 shows the frequency characteristics when the volume of the second air chamber 18 is 2 cc
in this embodiment. In FIG. 5, the broken line is the conventional example, and the solid line is
the embodiment. In this embodiment, the peak at 2000 Hz is attenuated to provide a flat
frequency characteristic. The present embodiment is configured as described above, and the
following effects can be obtained. (A) Flat frequency characteristics can be easily obtained. (B) It
is possible to easily provide an omnidirectional dynamic microphone at low cost, since it is
possible to easily share the part-1 designed for a unidirectional microphone. According to the
experiment, the volumes of the first air chamber, the second air chamber, and the back air
chamber are 1 to 3 times as large as the first air chamber, and the back air chamber is the first
air space. It is desirable to make the room several times to several tens of times. According to the
present invention, as is apparent from the above embodiment, the voice coil, the diaphragm, the
magnet, and the first air chamber are accommodated in the first case, and the first acoustic
resistance is applied to the first air chamber. Since the second air chamber is connected via the
material and the back air chamber is connected to the second air chamber via the second
acoustic resistance material, the effect of flattening the frequency characteristic of the output is
Have.
[0002]
Brief description of the drawings
[0003]
1 is a cross-sectional view of a conventional nondirectional dynamic microphone, FIG. 2 is an
equivalent circuit diagram of a conventional nondirectional dynamic microphone, and FIG. 3 is a
nondirectional dynamic microphone according to an embodiment of the present invention FIG. 4
is an equivalent circuit diagram 1 of the nondirectional dynamic microphone in the above
embodiment. FIG. 5 is a frequency characteristic diagram of the output of the nondirectional
dynamic microphone according to the above embodiment.
11 ... pole piece 12 ... magnet 13 yoke 14 diaphragm 15 voice coil 16 first case 17 first acoustic
resistance material 18 second air Chamber 19 first air chamber 20 second case 21 second
acoustic resistance material 22 back air chamber. Name of Agent Attorney Nakao Toshio Other 1
person Figure 1 @ 2 Figure 3 Figure 4
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