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Description of the Invention A compact electromagnetic electroacoustic transducer 1 comprising
at least a diaphragm, at least a diaphragm, a movable iron fixed to the diaphragm, a magnet, a
drive coil, a magnetic core, and a stator A small electromagnetic electro-acoustic transducer
characterized by having a yoke between an iron piece and the magnet. 2. The small
electromagnetic electro-acoustic transducer according to claim 1, wherein the movable iron piece
is located on the magnetic core side of the diaphragm, and one end face of the yoke is positioned
so as to surround the outer periphery of the movable iron piece.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement
of the magnetic circuit of a miniature electromagnetic electroacoustic transducer. An object of
the present invention is to provide a small electromagnetic electro-acoustic transducer which can
be used for a wrist watch, a small electronic desk calculator, a micro radio and the like. The
structure of a conventional compact electromagnetic electroacoustic transducer is shown in FIG.
1 is a diaphragm, 2 is a movable iron piece, 3 is a magnet, 4 is a drive coil, 5 is a coil frame, 6 is a
magnetic core, 7 is a stator, 8 is a case, 9 is a coil terminal, and 10 is a cover. The operation
principle of the electromagnetic type electroacoustic transducer will be described. A magnetic
circuit is formed by the magnet 3, the stator 7, the magnetic core 6, the movable iron piece 2 and
their air gaps. The magnetic flux passing through the magnetic circuit generates a suction force
between the movable iron 2, the magnetic core 6 and the magnet 3, and the diaphragm 1 bends
and stabilizes to a position where the force balances with the recovery force of the deflection of
the diaphragm 1. When current flows through the drive coil 4 in this state, a magnetomotive
force is generated to change the magnetic flux passing through the magnetic circuit, and the
attractive force changes, so the amount of deflection of the diaphragm 1 changes. Therefore, by
passing a drive current such as an audio current to the drive coil 4, the diaphragm 1 can be
vibrated to generate a sound. Conversely, the voltage can be generated in the drive coil 4 by
vibrating the diaphragm 1 by voice or the like. Since this converter is reversible as described in
EndPage: 1, only the electro-acoustic conversion will be described below. The generated sound
pressure is proportional to the square of the diaphragm diameter and the amplitude. It is known
that the amplitude is proportional to the amount of change in attractive force, which is also
proportional to the magnetomotive force of the magnet and the magnetomotive force (current О
number of turns) of the drive coil, and inversely proportional to the square of the magnetic
resistance of the magnetic circuit . In the conventional small electromagnetic electroacoustic
transducer shown in FIG. 1, the gap between the magnet 3 and the movable iron piece 2 has a
large magnetic resistance. Therefore, it is necessary to enlarge the magnet 3 to increase the
magnetomotive force, the cost of the magnet increases, and the magnetic leakage to the outside
increases, and in particular, when used as a watch, it attracts magnetic objects such as iron
powder, etc. If there is a mechanical watch, there is a drawback such as causing rounding or
stopping of the rate. In the case where a large diaphragm diameter is permitted as shown in FIG.
2, the magnetic resistance can be reduced if the movable iron piece 12 reaches the top of the
magnet 13 with a large diameter, but if it is small, the movable iron piece If the value of x is
increased, the elastic support portion of the diaphragm is reduced to make the amplitude difficult
to obtain, and the sound pressure is reduced. As mentioned above, since the sound pressure is
proportional to the square of the diameter of the diaphragm, in the case of an ultra-compact
watch such as a watch, it is necessary to increase the amplitude and obtain the pressure, so It
gets bigger.
The present invention eliminates such a drawback, and its structure is shown in FIG. 31 is a yoke.
In order to reduce the magnetic resistance of the air gap between the magnet 23 and the
movable iron piece 22, a yoke 31 of a magnetic material provided with one end face on the
magnet 26 and the other end face surrounding the outer periphery of the movable iron piece 22
It is. As a material, pure iron having a high saturation magnetic flux density is preferable. The
yoke 31 exerts an effect even when the movable iron piece 2 is positioned on the opposite side of
the magnetic core 6 of the diaphragm 1 as shown in FIG. 1, but in particular as shown in FIG. If
the yoke 3.1 is used by disposing the yoke 21 on the side of the core 26 of the plate 21, the gap
between the movable iron 22 and the yoke 31 will not change even if the diaphragm 21 vibrates
and the movable iron 22 is displaced. And the magnetic resistance can be significantly reduced.
Furthermore, the change in magnetic resistance due to vibration is small, and the frequency
characteristics are improved. By providing the yoke 31, the magnetic resistance of the magnetic
circuit is reduced, so that the magnet can be made smaller (and the supermagnetic force can be
reduced, the magnetic leakage is reduced, and the cost is also reduced. In addition, since the
efficiency can be improved, the size can be reduced, and the power consumption can be reduced.
As described above, according to the present invention, a small electromagnetic type
electroacoustic transducer with small magnetic leakage and power consumption can be obtained,
which can be used for a small electronic device such as a wristwatch, and the effect thereof is
extremely large.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a conventional small
electromagnetic electro-acoustic transducer, FIG. 2 is a cross-sectional view of a conventional
relatively large electromagnetic electro-acoustic transducer, and FIG. It is a sectional view of an
electromagnetic type electroacoustic transducer. 1.11, 21 ... Diaphragm 2.12, 22 и Addiction и
Movable iron piece 3.15; 23 и и и Magnet 5-4.14, 24 и и и Drive coil 5.15, 25 и и и и и Coil frame 6.15,
26 иии Magnetic core 7.17, 27 и и и Stator 8, 18. 28 и и и Case 9.19, 29 и fist и coil terminal 10.20. и и и и
cover 31 и и и more than the yoke 6-EndPage: 2 Figure 3 EndPage: ?
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