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JP2010056755

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DESCRIPTION JP2010056755
An inexpensive electromagnetic transducer with high efficiency is provided by increasing the flux
density of magnetic flux crossing a voice coil. The electromagnetic converter 1 comprises a
diaphragm 8 having voice coils 9 formed on the surface, permanent magnet layers 6, 7
positioned on both sides of the diaphragm 8, and permanent magnets of the permanent magnet
layers 6, 7 While being attached, it comprises the frames 2 and 3 which hold the diaphragm 8 so
as to be displaceable in the thickness direction. The cross section of the permanent magnet of the
permanent magnet layers 6 and 7 is formed in a trapezoidal shape in which the length U of the
upper side facing the diaphragm 8 is longer than the length B of the bottom which is the side
attached to the frames 2 and 3. [Selected figure] Figure 2
Electromagnetic converter
[0001]
The present invention relates to an electromagnetic converter that performs sound reproduction
from an audio signal by combining a permanent magnet and a diaphragm.
[0002]
Heretofore, various techniques have been proposed for an electromagnetic transducer in which a
permanent magnet and a diaphragm are combined.
This type of electromagnetic converter includes, for example, as in Patent Documents 1 and 2, a
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permanent magnet plate and a diaphragm disposed to face the permanent magnet plate. The
permanent magnet plate and the diaphragm are supported by fixing members, and while the
permanent magnet plate is fixed mechanically mechanically, the diaphragm is attached so as to
be freely displaced in the thickness direction.
[0003]
Here, the permanent magnet plate is one in which strip-like different magnetic poles are
alternately formed at regular intervals. In the diaphragm, a voice coil formed of a meandershaped conductor pattern is formed at a position facing the gap between the different magnetic
poles of the permanent magnet plate.
[0004]
In a flat loudspeaker called a gumuzon type, copper, aluminum foil or the like is attached to a
thin film made of polyester, polyimide or the like, and a conductor pattern of a voice coil is
etched to form a diaphragm (for example, see Non-Patent Document 1).
[0005]
In this type of electromagnetic converter, magnetic flux from the N pole to the S pole crosses the
conductor pattern straight portion of the voice coil between adjacent permanent magnets.
When a current, which is an audio signal, flows to the voice coil, the voice coil and the permanent
magnet are electromagnetically coupled, audio vibration is generated on the diaphragm in
accordance with Fleming's law, and a sound wave is generated.
[0006]
Speaker system, radio technology company, published in July 1977, edited by Takeo Yamamoto,
published in International Publication WO 2003/073787.
[0007]
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Since the conventional electromagnetic transducer is configured as described above, there is a
problem that the magnetic flux density of the magnetic flux crossing the voice coil is low and the
sound pressure level proportional to the magnetic flux density is also small.
On the other hand, when an expensive rare earth magnet such as a neodymium magnet is used to
obtain a high magnetic flux density or when the permanent magnet is enlarged, the sound
pressure level increases while the electromagnetic converter becomes expensive. there were.
[0008]
The present invention has been made to solve the problems as described above, and it is an
object of the present invention to increase the magnetic flux density of the magnetic flux crossing
the voice coil and to obtain an inexpensive electromagnetic transducer with high efficiency.
[0009]
The electromagnetic converter according to the present invention is a voice of a serpentine
pattern having strip-shaped permanent magnets having trapezoidal cross sections and linear
portions parallel to the longitudinal direction of the permanent magnets, which are alternately
arranged at predetermined intervals and with different polarities. The diaphragm has a coil
formed on the surface, and a frame to which the permanent magnet is attached and which holds
the diaphragm at a position facing the permanent magnet.
[0010]
According to the present invention, by forming the permanent magnet in a trapezoidal cross
section, it is possible to increase the magnetic flux density crossing the voice coil and obtain an
inexpensive electromagnetic transducer with high efficiency.
[0011]
Embodiment 1
FIG. 1 shows an electromagnetic converter according to Embodiment 1 of the present invention,
FIG. 1 (a) is an overall perspective view showing an appearance, and FIG. 1 (b) is an exploded
perspective view showing a configuration.
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FIG. 2 is a cross-sectional view of the electromagnetic converter taken along line AA shown in
FIG. 1 (a).
The electromagnetic converter 1 includes a diaphragm 8, permanent magnet layers 6 and 7
disposed on both sides of the diaphragm 8, and frames 2 and 3 sandwiching them.
[0012]
The frames 2 and 3 are made of a magnetic member such as iron, and a plurality of sound
emission holes 4 and 5 are provided in order to emit the sound wave generated inside to the
outside. The permanent magnet layers 6 and 7 are formed by arranging a plurality of strip-like
permanent magnets in parallel at predetermined intervals. The cross section of these permanent
magnets is trapezoidal. As shown in FIG. 2, the plurality of permanent magnets of the permanent
magnet layer 6 has a direction in which different magnetic poles (N and S poles) alternately face
the diaphragm 8 and a constant pole pitch Pp of the frame 2. It is installed inside. The plurality of
permanent magnets of the permanent magnet layer 7 are installed inside the frame 3 so as to be
the same as the magnetic poles of the permanent magnets of the permanent magnet layer 6
facing each other across the diaphragm 8. In a cross section obtained by cutting a strip-like
permanent magnet along the lateral direction, the length of the side opposite to the diaphragm 8
is the length U of the upper side, and the length of the side opposite to the upper side on the
frame attachment side is The bottom length is B. Also, let L be the distance from the bottom to
the top.
[0013]
A diaphragm 8 made of a thin polymer resin sheet is disposed at an intermediate position
between the magnet surfaces facing each other, that is, at a distance D from the upper surface of
the permanent magnet. The diaphragm 8 is held movably in the thickness direction by the frames
2 and 3. A serpentine pattern voice coil 9 having straight portions 9a parallel to the longitudinal
direction of the permanent magnet is formed on both the front and back sides of the diaphragm
8. The linear portions 9a are disposed at intervals of the coil pitch Pc in the gap between the
different magnetic poles of the permanent magnet layers 6, 7. The magnetic flux 10 emitted from
one permanent magnet in the left-right direction draws an arc-shaped magnetic flux line, and
crosses the linear portion 9 a of the voice coil 9 to reach the other pole.
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[0014]
With such a configuration, when a current as an audio signal flows through the voice coil 9 in the
electromagnetic converter 1, the diaphragm 8 vibrates up and down in the thickness direction by
the magnetic flux 10 crossing the voice coil 9. Sound waves generated by the vibration of the
diaphragm 8 are emitted to the outside through the sound emission holes 4 and 5 of the frames
2 and 3. At this time, if the magnetic flux density of the magnetic flux 10 is high, the sound
pressure level of the reproduced sound becomes large. Therefore, in the present embodiment, in
order to obtain a high magnetic flux density, the relationship between the ratio of the length of
the upper side to the base of the trapezoidal cross section of the permanent magnet (upper side
base ratio) and the magnetic flux density was analyzed.
[0015]
FIG. 3 is a cross-sectional view showing an example of a permanent magnet shape constituting
the electromagnetic converter 1. FIG. 3 (a) shows a case where the upper side base ratio is large,
and FIG. 3 (b) shows a case where the upper side base ratio is small. Indicates In FIG. 3, the
configuration of a part of the electromagnetic converter 1 is extracted and shown. The length U
of the upper side and the length B of the base are adjusted in order to change the upper side
base ratio of the trapezoidal cross section of the permanent magnet, but the cross sectional area
of the trapezoidal cross section, the pole pitch Pp, and the coil pitch Pc are fixed. The distance L
from the base to the upper side is variable in order to change the top side base ratio with a
constant cross sectional area. Further, in order to eliminate the unfairness of the magnetic flux
density due to the difference in the distance between the permanent magnet and the voice coil 9,
the distance D from the upper surface of the permanent magnet 7 to the diaphragm 8 is made
constant.
[0016]
The result of measuring the magnetic flux density (horizontal direction component) of the
magnetic flux 10 crossing the voice coil 9 by adjusting the ratio of the upper side to the lower
side of the permanent magnet cross section as shown in FIG. 3 is shown in FIG. In FIG. 4, the
horizontal axis is the ratio of the upper side to the lower side of the cross section of the
permanent magnet, and the vertical axis is the magnetic flux density of the magnetic flux 10
crossing the straight portion 9 a of the voice coil 9. Here, with the coil pitch Pc and the pole pitch
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Pp of the voice coil 9 fixed at 4 mm, the magnetic flux density curve when the upper side base
ratio is changed at each of trapezoidal cross sections 3 mm <2>, 4 mm <2> and 5 mm <2> is
shown. Show. In FIG. 4, symbol A given to each magnetic flux density curve represents a
trapezoidal cross-sectional area, and D represents a distance D from the upper surface of the
permanent magnet 7 to the diaphragm 8. For example, the magnetic flux density curve A5D1
indicates the magnetic flux density when the trapezoidal cross-sectional area A is fixed at 5 mm
<2> and the distance D is fixed at 1.0 mm, and the top side ratio is changed to 1.0 to 2.7.
[0017]
From FIG. 4, the magnetic flux density changes according to the top side base ratio, regardless of
the cross-sectional area of 3 mm <2>, 4 mm <2>, or 5 mm <2>. The upper side-to-bottom ratio at
which the magnetic flux density reaches the maximum value is 2.3, and the magnetic flux density
tends to decrease when the upper side-to-base ratio becomes higher. However, if the upper side
base ratio is 1.0 or more, a magnetic flux density larger than when it is smaller than 1.0 can be
obtained even with the same trapezoidal shape, and a sound pressure level within the allowable
range in design of the electromagnetic converter 1 is realized. be able to.
[0018]
In FIG. 5, the pole pitch Pp is constant at 5 mm, and the distance D from the upper surface of the
permanent magnet 7 to the diaphragm 8 is constant at 1.5 mm, and trapezoidal cross sections 3
mm <2>, 4 mm <2>, 5 mm <2> The magnetic flux density curve at the time of changing top side
base ratio is shown. Also in FIG. 5, as in FIG. 4, the symbol A attached to each magnetic flux
density curve represents a trapezoidal cross-sectional area, and D represents the distance D from
the upper surface of the permanent magnet 7 to the diaphragm 8. From the comparison between
FIG. 5 and FIG. 4, even if the pole pitch Pp changes, the tendency of the magnetic flux density to
change according to the top side base ratio does not change. Further, if the upper side base ratio
is 1.0 or more, a magnetic flux density larger than when it is smaller than 1.0 can be obtained
even with the same trapezoidal shape.
[0019]
Thus, the magnetic flux density of the magnetic flux 10 crossing the linear portion 9a of the
voice coil 9 is increased by forming the permanent magnet into a trapezoidal cross-sectional
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shape having an upper side / breadth ratio of 1.0 or more, that is Is possible. Further, since the
magnetic flux density is increased and the efficiency is increased, the magnetic flux density
necessary for the design can be secured even if the cross-sectional area of the permanent magnet
is reduced, and the inexpensive electromagnetic converter 1 can be obtained.
[0020]
In addition, since the length B of the base of the trapezoidal cross section of the permanent
magnet is made shorter than the length U of the upper side, the distance on the bottom side of
the permanent magnet becomes wider, and the sound output holes 4 and 5 of the frames 2 and 3
are made larger can do. As a result, the electromagnetic converter 1 can be configured to easily
emit the sound wave generated by the vibration of the diaphragm 8 to the outside.
[0021]
In order to efficiently generate an electromagnetic force between the diaphragm 8 and the
permanent magnet layers 6 and 7, the voice coil 9 needs to be located in the gap between the
different magnetic poles. Therefore, it is preferable to configure the electromagnetic converter 1
so that adjacent permanent magnets do not contact each other, and the length U of the upper
side of the permanent magnet is equal to or less than the coil pitch Pc of the voice coil 9. By
defining the upper limit value of the length U of the upper side of the permanent magnet
trapezoidal cross section by the coil pitch Pc, the upper limit value of the upper side base side
ratio is also automatically defined.
[0022]
As described above, according to the first embodiment, the electromagnetic converter 1 is
configured to use a permanent magnet having a trapezoidal cross section. Therefore, it is
possible to increase the magnetic flux density of the magnetic flux 10 crossing the linear portion
9 a of the voice coil 9. When the ratio of the length U of the upper side to the length B of the
base is set to 1.0 or more, particularly high magnetic flux density can be obtained. In addition,
since the magnetic flux density is increased and the efficiency is increased by optimally adjusting
the ratio of the upper side to the lower side of the trapezoidal cross section of the permanent
magnet, it is possible to reduce the cross sectional area of the permanent magnet. Therefore, an
inexpensive and highly efficient electromagnetic converter 1 can be obtained.
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[0023]
Further, according to the first embodiment, the length U of the upper side of the permanent
magnet trapezoidal cross section is configured to be equal to or less than the coil pitch Pc of the
voice coil 9. Therefore, by setting the permanent magnet trapezoidal cross section to the upper
side base ratio such that the length U of the upper side is equal to or less than the coil pitch Pc, it
is possible to increase the magnetic flux density of the magnetic flux 10 crossing the linear
portion 9a of the voice coil 9.
[0024]
In the first embodiment, although the permanent magnet layers 6 and 7 are constituted only by
permanent magnets having a trapezoidal cross section, the present invention is not limited to
this, and permanent magnets having a trapezoidal cross section and permanent magnets having a
rectangular cross section A configuration in which a magnet is mixed may be used. For example,
the permanent magnets provided around the sound release holes 4 and 5 are permanent
magnets having a trapezoidal cross section, and the permanent magnets provided at other
portions are permanent magnets having a rectangular cross section.
[0025]
The electromagnetic converter which concerns on Embodiment 1 of this invention is shown, Fig.1
(a) is a whole perspective view which shows an external appearance, FIG.1 (b) is a disassembled
perspective view which shows a structure. It is sectional drawing which cut | disconnected the
electromagnetic converter which concerns on Embodiment 1 of this invention along the AA line
of Fig.1 (a). It is sectional drawing which shows the example of the permanent magnet shape of
the electromagnetic converter concerning Embodiment 1 of this invention, FIG. 3 (a) shows the
case where top side base side ratio is large, FIG.3 (b) shows top side base side ratio Indicates a
small case. It is a graph which shows the relationship between magnetic-flux density and top side
base ratio of the permanent magnet trapezoid cross section of the electromagnetic transducer
(pole pitch 4 mm) which concerns on Embodiment 1 of this invention. It is a graph which shows
the relationship of magnetic-flux density with the upper side base-side ratio of the permanentmagnet trapezoid cross section of the electromagnetic transducer (pole pitch 5 mm) concerning
Embodiment 1 of this invention.
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Explanation of sign
[0026]
Reference Signs List 1 electromagnetic converter, 2, 3 frame, 4, 5 sound emission hole, 6, 7
permanent magnet layer, 8 diaphragm, 9 voice coil, 9a straight portion, 10 magnetic flux, L
distance from bottom to top, B bottom Length, U length of upper side, D Distance from upper
surface of permanent magnet to diaphragm, Pp pole pitch, Pc coil pitch (length between straight
parts of voice coil).
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