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JPH0613298

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DESCRIPTION JPH0613298
[0001]
Industrial Applicability] The present invention is an external magnet for a speaker which forms
an annular magnetic air gap for enhancing the magnetic performance of the main magnet by
mounting a combination of the main magnet and a cancel magnet for preventing a leakage flux.
Type magnetic circuit. 2. Description of the Related Art In general, the external magnet type
magnetic circuit of this type of magnetically shielded speaker is used for canceling as shown in
FIG. 3 in the conventional external magnet type magnetic circuit (45) as shown in FIG. In some
cases, a magnet (26) is added and used, or the shapes of constituent materials such as the yoke,
plate, and pole are changed to make it magnetic-proof and to improve its magnetic performance.
This is a circle in which a thick main magnet (21) having an annular thickness is placed on the
lower plate (23) of the soft iron center pole (24) and placed on the magnet (21). A voice coil (7)
wound around a voice coil bobbin (7a) is formed in an annular magnetic gap (16) formed by the
center hole of the annular top plate (25) and the tip of the center pole (24). The voice coil bobbin
(7a) is suspended at a tip of a diaphragm (10) which is suspended and held by a damper (8)
pasted and fixed to the frame (9), and stuck and supported to the outer edge of the frame (9).
The tip of) is glued. When a speaker using such a speaker magnetic circuit (45) is incorporated
close to a CRT for a television receiver or the like, the leakage flux from the magnetic circuit
(.phi.L) is generally used. The external shape is required to be small, and the magnetic shielding
effect can be expected, but there is a problem of the external shape being too high. More
recently, small-sized CRT devices and the like have increased, and the leakage flux (φ L) leaking
from the speaker is required to have a value of approximately 5 × 10 −4 Tesla or less.
Therefore, the external magnetic type magnetic circuit using the ring-shaped ferrite magnet (21)
in the conventional main magnet to such a strict demand significantly increases the magnetic
leakage, and another means for preventing it. Not only does it require a large magnetic force and
its mechanism, or a magnetic shielding cover, etc., and the magnetic shielding effect can not be
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said to be sufficient to increase the cost, and its shape becomes bulky, making it impossible to
incorporate it in a narrow place The Therefore, when the leakage flux (.phi.L) in the vicinity of
the bottom of the conventional magnetic circuit (35), (45) becomes a problem, a magnetic circuit
with a cancel magnet (26) as shown in FIG. 35), but in such an external magnet type magnetic
circuit with a cancel magnet (26), the main magnet (21) and the cancel magnet (26) have
approximately the same size, and two magnets ( 21) and (26) are disposed so as to overlap in the
longitudinal direction, so that the shape is bulky and there is a problem that the shape is
disadvantageous in shape.
In particular, when the leakage flux near the bottom of the magnetic circuit is a problem, a
magnetic shielding cover is required to cover the entire magnetic circuit, which is
disadvantageous in terms of shape and size. In addition, in such a magnetic circuit (35), the main
magnet (21) and the cancel magnet (26) of the main magnetic path need to be magnets having
the same degree of magnetic performance, which is disadvantageous in cost. There was also a
problem that The present invention solves such a problem and reduces the leakage magnetic flux
of the main magnet (21) by the cancel magnet without concentrating the cost and concentrating
on the magnetic air gaps (6, 16). It is an object of the present invention to provide a speaker
magnetic circuit which can be made thin and thin. Therefore, in the conventional magnetic circuit
(45) of the prior art shown in FIG. 4, since there is only one magnet (21), it is difficult to control
the leakage flux, and the performance is considerably increased. There was a problem that the
improvement of was not recognized. In addition, such an external magnet type magnetic circuit
(45) requires an extra large magnet volume, is inconvenient to handle, and is expensive, so the
present invention can be used for such a conventional type. In order to solve the problem that
the external magnet type magnetic circuit (45) had, the inventor simulated the magnetic flux
distribution in the magnetic path for the external magnetic type magnetic circuit, and the leakage
of the external magnet type magnetic circuit (45) was , It was found that the magnetic path at the
outer periphery of the magnetic circuit and the magnetic flux density in the vicinity of the outer
periphery in the lower plate (23) are small, and that deleting this part does not greatly affect the
performance of the magnetic circuit. A cancellation magnet (2) is disposed in the removed
portion (4a) of this magnetic circuit so that the leakage flux on the outside surface of the
magnetic gap (5), in particular the outer surface of the magnet (21) can be controlled and used
effectively. Facilitates concentration of the magnetic flux into the magnetic air gap (5) by It aims
to improve the flux density, it is intended to provide a magnetic circuit which can increase the
use efficiency of the magnet. The constitution of the present invention for achieving the object
will be described with reference to FIGS. 1 and 2 corresponding to the embodiments. 1) is placed
on the lower plate (4a) of the center pole (4), and the center hole (3c) of the upper plate (3)
placed on the magnet (1), and the center pole (4) A notch (4b) provided by cutting out the lower
outer corner of the lower plate (4a) of the external magnetic circuit (6) incorporating and
forming an annular magnetic gap (5) with the head The speaker external magnet is configured
such that the main and cancel magnets (1) and (2) are magnetized in opposite directions by
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fitting a ring-shaped cancel magnet (2) such as, for example, a flare light magnet. Type magnetic
circuit.
In the invention 2, the ferrite main annular ring magnet (1) is placed on the lower plate (4a) of
the center pole (4), and the center hole of the upper plate (3) placed on the magnet (1) (3c) and
the head of the center pole (4), the outer bottom lower corner angle of the lower plate (4a) of the
external magnetic circuit (6) incorporating and forming an annular magnetic gap (5) A ringshaped cancel magnet (2) of a rare earth magnet such as an Nd-Fe-B magnet is fitted to a
cutaway portion (4b) provided by cutting out a part, and both main and cancel magnets (1), It is
an external magnet type magnetic circuit for speakers of a configuration in which (2) is
magnetized in opposite directions. Since the present invention is configured as described above,
the present invention uses the cancel magnet (2) disposed in the magnetic path to make the main
magnet (1) among the leakage flux of the magnetic gap (5). The magnetic flux can be
concentrated in the magnetic gap (5) in the magnetic path by controlling the leakage flux outside
the magnetic flux path, and the effective utilization rate of the magnet can be improved. (5) It is
possible to facilitate concentration of magnetic flux toward the inside, and to realize
improvement in magnetic flux density. When a rare earth magnet (1) is used as a cancel magnet,
the rare earth magnet has a large energy product, high performance can be maintained whether
the thickness is thick or thin, and the degree of freedom in the shape in the thickness direction is
high. Even when incorporated in the magnetic circuit (6), it is possible to make it thin in shape,
and because of its large energy product, it has the strength of the magnetic force sufficient to
balance the magnetic force of the main magnet (1) even if it is small. And without increasing the
bulk of the shape of the magnetic circuit (6) and minimizing the cost increase to effectively
prevent the leakage flux and significantly increase the magnetic flux density of the magnetic gap
(5). It is useful as a speaker magnetic circuit (6) that requires low magnetic leakage. DETAILED
DESCRIPTION OF THE PREFERRED EMBODIMENT A magnetic circuit for a speaker is prepared
by making the magnetic flux density in the annular magnetic gap (5) formed as large as possible,
and the magnetic flux (.phi.L) leaking to the outside of the gap as small as possible. Maximizing
the effective utilization rate of (1) is the key to the design of the magnetic circuit. However, when
the magnet is one main magnet (1), a large amount of leakage magnetism leaks to the outside of
the magnet (1) from the outer surface of the magnet (1). Therefore, it is effective to apply an
external force in the direction of bending the entire magnetic path in the direction of the
magnetic gap (5) to concentrate the magnetic flux (φL) leaking to the outside to the magnetic
gap (5).
The present invention applies a magnetic force in the reverse direction from the outside to the
magnetic field of the main magnet (1) using the cancel magnet (2) to leak magnetic flux (φ L)
leaking from the outer surface of the main magnet (1) 1) Apply an external force so as to pass
through the inside, prevent it from leaking out of the magnet (1), and push it toward the
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magnetic gap (5) to increase the magnetic flux density in the magnetic gap (5) Thus, the
magnetomotive force of the magnets (1) and (2) is effectively utilized. An embodiment of the
present invention will be described below based on the drawings. 1 and 2 are cross-sectional
views of an embodiment of the present invention, wherein FIG. 1 shows the whole, and FIG. 2
shows an enlarged half-section of the main part thereof. In the invention 1, (1) is a main annular
ring magnet, and is incorporated in the external magnetic type magnetic circuit (6), and a notch
(4b) at the lower corner of the lower plate (4a) of the magnetic circuit (6). , And an annular
cancel magnet (2) is fitted in the notch (4b). In this way, the thin part of the lower plate (4a) is
sandwiched between the main and cancel magnets (1) and (2), and both magnets (1) and (2) are
magnetized in opposite directions. It is an external-magnet-type magnetic circuit for a speaker. In
particular, in the case of the ferrite magnet, for example, the cancel magnet (2) is fitted to the
notch (4b) of the lower plate (4a) even if the thickness is increased compared to the rare earth
magnet, In the invention 2, the thickness of the whole speaker can be formed thin (1) is a main
annular ring magnet and is incorporated in the external magnetic type magnetic circuit (6), and
the lower plate of the magnetic circuit (6) A notch (4b) is provided at the lower corner of the
outer edge of 4a), and an annular cancel magnet (2) is fitted in the notch (4b). In this way, the
thin part of the lower plate (4b) is sandwiched between the main and cancel magnets (1) and (2),
and both magnets (1) and (2) are magnetized in opposite directions. It is an external-magnet-type
magnetic circuit for a speaker. In particular, in the case of the rare earth cancel magnet (2), for
example, an Nd-Fe-B magnet (neody magnet), since the magnetomotive force can be sufficiently
exhibited even if the magnetic characteristics are thin, the thickness of the entire speaker is
particularly It can be formed thin (it may be the thickness of the conventional lower plate (4a)).
Although the embodiments considered to be representative of the present invention have been
described above, the present invention is not necessarily limited to only the structure of these
embodiments, and includes the above-described components according to the present invention,
and In order to achieve the purpose mentioned above, the present invention can be suitably
modified and implemented within the range having the effects mentioned below.
As is apparent from the above description, according to the present invention, by the cancel
magnet (2) disposed in the magnetic path, the magnet (1) of the leakage flux (.phi.L) not passing
through the magnetic gap (5). Can be controlled to improve the effective utilization of the
magnets (1) and (2), and the magnetic flux can be easily concentrated toward the inside of the
magnetic gap (5). As a result, it is possible to expect a remarkable effect in practical use that
makes it possible to expect an effect that the magnetic flux density can be improved while
realizing an improvement in the magnetic flux density. FIG. 8 is a distribution diagram of leakage
flux showing a conventional external magnet type (dotted line) without the cancel magnet (2) and
the first and second embodiments of the present invention (solid line) with the cancel magnet (2)
mounted. . The first embodiment is a case where the toroidal ring magnet for cancellation (2) is a
ferrite magnet, and the second embodiment is a case where the toroidal ring magnet for
cancellation is a rare earth magnet. In the magnetic flux density of FIG. 5, Example 1 is about
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2.8%, Example 2 is about 7.0%, and the leakage flux of FIG. 6 is about 6%, and Example 2 is about
37%. In the leakage flux of FIG. 7, Example 1 is reduced by about 16.6%, Example 2 is reduced by
about 36.6%, and the leakage flux of FIG. 8 is about 24.2%. Example 2 shows a difference of
approximately 62.1% decrease. Thus, the present invention is particularly useful as a speaker
magnetic circuit (6) which is required to have a low level of magnetic leakage and to have a low
height.
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