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DESCRIPTION JPH0613297

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DESCRIPTION JPH0613297
[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, as shown in FIG. 4, the
external magnet type magnetic circuit of this type of magnetic shield type speaker generally uses
a magnet (21) larger than other speakers, or FIG. As shown in the figure, there is a magnetic
shield type and advanced magnetic performance by adding and using a canceling magnet (26) or
changing the shape of constituent materials such as yoke, plate and pole. 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 end 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. A
speaker using such a speaker magnetic circuit (25) is generally used in the case where it is
incorporated close to a CRT for a television receiver or the like. The external shape is required to
be small, and the magnetic shielding effect can be expected, but the problem of the external
shape is too high. Furthermore, small CRT devices etc. are increasing recently, and leakage flux
leaking from the speaker (φ L 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 said to be sufficient to increase the cost, and its shape becomes bulky, making it
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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 , And the magnetic flux density in the
vicinity of the outer peripheral portion in the plate (25) is small, and even if this portion is
deleted, the performance of the magnetic circuit is not greatly influenced. By positioning the
cancellation magnet (2) in the removed portion (3a) to control the leakage flux outside the
magnetic gap (5) for effective use, it is directed into the magnetic gap (5) The purpose is to
facilitate the concentration of magnetic flux and to improve the magnetic 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 of the upper plate (3) placed on the magnet (1), and the head
of the center pole (3) In the external magnetic type magnetic circuit (6), in which the magnetic
gap (5) is formed by incorporating them, in the cutout (3a) provided by cutting out the outer
upper corner of the upper plate (3) For example, it is an external magnet type magnetic circuit
for a speaker in which a cancel magnet (2) such as a flare light magnet is fitted to magnetize both
the main and cancel magnets (1) and (2) in opposite directions. .
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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) And the
top plate (3) of the external magnet type magnetic circuit (6) incorporating and forming a
magnetic gap (5) between the head of the center pole (3) and the magnetic pole (5). An annular
ring of, for example, a cancel magnet (2) of a rare earth magnet such as an Nd-Fe-B magnet is
fitted to the provided notch (3a), and both the main and cancel magnets (1) and (2) It is a speaker
external magnet type magnetic circuit configured to be magnetized in the reverse direction. Since
the present invention is configured as described above, the present invention controls the
leakage flux of the magnetic gap (5) by means of the cancel magnet (2) disposed in the magnetic
path to In the inside, the flow direction of the magnetic flux can be concentrated to the magnetic
gap (5), and the effective utilization rate of the magnet can be improved, and the magnetic flux
can be easily concentrated toward the inside of the magnetic gap (5). It is possible to realize an
improvement in the magnetic flux density. In addition, when the rare earth magnet (1) is used as
the cancel magnet, the shape is originally thin, and the shape can be thinned even when
incorporated in the magnetic circuit (6), and the energy product is large. Even if it is small in size,
it has the strength of the magnetic force sufficiently balanced to the magnetic force of the main
magnet (1), does not increase the bulk of the shape of the magnetic circuit (6), and minimizes the
cost increase. While effectively preventing the leakage flux, the magnetic flux density of the
magnetic gap (5) can be remarkably increased, and it is useful as a speaker magnetic circuit (6)
which requires a low level 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 a force in the direction of bending the entire
magnetic path in the direction of the magnetic gap (5) to concentrate the magnetic flux (φ L)
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 main magnet (1) toward the
magnetic gap (5) The magnetic flux density in the magnetic gap (5) is increased by pressing the
magnetic gap (5) to effectively utilize the magnetomotive force of the magnets (1) and (2).
Hereinafter, an embodiment of the present invention will be described based on the drawings. 1
and 2 are cross-sectional views of one embodiment of the present invention, wherein FIG. 1 is the
whole, and FIG. 2 is an enlarged half-sectional view 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 (3a) is formed in the upper edge of the upper plate (3) of the magnetic
circuit (6). ), And an annular cancel magnet (2) is fitted in the notch (3a). In this way, a speaker
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having a configuration in which the upper plate (3) is sandwiched between the main and cancel
magnets (1) and (2), and the magnets (1) and (2) are magnetized in opposite directions. It is an
external magnet type magnetic circuit. In particular, in the case of the ferrite magnet, for
example, the cancel magnet (2) can sufficiently exhibit the magnetomotive force even if the
magnetic property is thin, so that the thickness of the entire speaker can be thin (in Invention 2 )
Is a main annular ring magnet, and is incorporated in the external magnet type magnetic circuit
(6), and a notch (3a) is provided in the outer upper corner of the top plate (3) of the magnetic
circuit (6) An annular cancel magnet (2) is fitted to the part (3a). In this way, a speaker having a
configuration in which the upper plate (3) is sandwiched between the main and cancel magnets
(1) and (2), and the magnets (1) and (2) are magnetized in opposite directions. It is an external
magnet type magnetic circuit. 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 Advantageously, it can be made thin (it can remain at the thickness of the
conventional top plate (3)). 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, the present invention can control
the leakage flux (.phi.L) of the magnetic gap (5) by the cancel magnet (2) disposed in the
magnetic path, The effective utilization rate of the magnets (1) and (2) can be improved, and the
magnetic flux can be easily concentrated toward the inside of the magnetic gap (5) to realize the
improvement of the magnetic flux density and thin the shape. It has come to be able to expect a
remarkable effect in practical use that makes it possible to expect also the effect that can be
achieved.
5 to 8 show distributions of leakage magnetic 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. FIG. The first embodiment is a case
where the canceling annular ring magnet (2) is a ferrite magnet, and the second embodiment is a
case where the canceling annular ring magnet is a rare earth magnet, and compared to the
conventional example in the equivalent distance from the magnetic circuit. In the magnetic flux
density of FIG. 5, the increase of about 3%, the leakage flux of FIG. 6 of Example 1 is reduced by
about 10%, the reduction of Example 2 is about 62.5%, and the leakage flux of FIG. Example 3 is
reduced by about 36.6%, Example 1 is reduced by about 11%, and Example 2 is reduced by about
30% in the leakage flux in FIG. 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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