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JP2008136066

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DESCRIPTION JP2008136066
In a magnetic circuit in which a pair of flat plates are arranged in the longitudinal direction and a
magnetic gap is formed between the plates, a uniform magnetic field is formed along the
longitudinal direction of the magnetic gap. SOLUTION: A pair of flat plates 11 and 12 which are
long in one direction are provided, and the plates 11 and 12 are arranged along the longitudinal
direction so that the side faces are opposite, and a magnetic gap 10G is formed between the side
faces. The plates 11 and 12 have two end portions b and a central portion a in the longitudinal
direction, and the thickness t of the central portion a is formed smaller than the thickness t of the
end portions b. [Selected figure] Figure 2
Speaker magnetic circuit and speaker
[0001]
The present invention relates to a speaker magnetic circuit and a speaker.
[0002]
There is known a speaker provided with a magnetic circuit in which a pair of flat plates are
arranged in the longitudinal direction and a magnetic gap is formed between the plates.
One example is a ribbon type speaker as described in Patent Document 1 below.
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[0003]
FIG. 1A is an explanatory view showing a configuration example of a ribbon type speaker. A yoke
J3 is provided between one of the magnetic poles of the permanent magnets J1 and J2, and a
pair of plates J4 and J5 are provided on the other magnetic pole to form a magnetic circuit J6.
The pair of plates J4 and J5 are arranged such that their side surfaces face each other, and a
magnetic gap J7 is formed between the side surfaces.
[0004]
Then, a ribbon diaphragm J8 is provided in the magnetic field of the magnetic gap J7. The ribbon
diaphragm J8 is entirely formed in a strip or ribbon shape of a thin plate having conductivity,
and the width direction thereof coincides with the width direction of the magnetic gap J7, and
electrodes J8a and J8b are formed at two end portions in the longitudinal direction. And the
signal source J9 is connected to the electrodes J8a and J8b to supply the audio current I to the
ribbon diaphragm J8.
[0005]
According to this, the voice current I flows in the longitudinal direction to the ribbon diaphragm
J8, and the magnetic force along the thickness direction of the plates J4, J5 acts by the magnetic
field in the width direction of the magnetic gap J7. As a result, the ribbon diaphragm J8 vibrates
in the thickness direction.
[0006]
The characteristic of this ribbon type speaker is that the vibrator is simplified (in the case of a
general speaker, the vibrator is provided with a voice coil, a voice coil bobbin and a diaphragm,
but with a ribbon type speaker, an audio current is supplied to the ribbon diaphragm itself) Since
the driving force directly acts on the entire diaphragm J8, a lightweight vibrator can be
efficiently driven.
In addition, since the vibrating body itself plays a role of a voice coil, the length of the vibrating
body (voice coil) in the vibrating direction is small, so that the increase in the inductance of the
vibrating body (voice coil) in the high range can be suppressed. . Therefore, it is possible to
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increase the sensitivity, to accelerate the response to the audio signal, and to reproduce to a very
high frequency.
[0007]
JP 10-178699 A
[0008]
In the magnetic circuit in which a pair of flat plates are arranged in the longitudinal direction and
the magnetic gap is formed between the plates, a magnetic gap of the same width is formed
along the longitudinal direction as well as the ribbon type speaker described above. Since the
vibrator is disposed in the magnetic gap, it is necessary to form a uniform magnetic field along
the longitudinal direction of the magnetic gap in order to apply a uniform driving force to the
entire vibrator. become.
[0009]
However, near the end of the longitudinally extending plate, a magnetic field is formed that
wraps around, so the magnetic flux density is necessarily different from the central portion of the
plate, creating a uniform magnetic field across the magnetic gap You can not do it.
[0010]
FIG. 1B is an explanatory view schematically showing the magnetic flux density in the magnetic
gap of the conventional ribbon type speaker.
In the case of using plates J4 and J5 whose thickness is constant in the longitudinal direction, a
magnetic flux g1 which turns to the outside is generated at both ends of the plates J4 and J5, so
that the central portion J7a of the magnetic gap J7 has two The magnetic flux density is smaller
than that of the end J7b.
[0011]
Here, since the driving force F (electromagnetic force) acting on the ribbon diaphragm is
expressed by the following equation (1), assuming that the length of the diaphragm and the
magnitude of the audio current are constant, the magnitude of the magnetic flux density The
driving force of the diaphragm changes depending on the size.
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[0012]
[0013]
Further, the driving force F of the diaphragm can be correlated with the sound pressure SPL (dB)
of the speaker, and the relationship can be expressed by the following formulas (2a) to (2d).
[0014]
[0015]
As is clear from the equation (2d), the sound pressure P of the speaker increases as the driving
force F of the speaker increases.
As a result, when using a magnetic circuit formed of a plate having a constant thickness as
described above, the magnetic flux escapes to the outside and the magnetic flux density is
different between the end portion and the central portion of the plate. In the case of the section,
the magnetic flux density is reduced, and a uniform sound pressure SPL can not be obtained,
which causes a problem that the speaker sound quality is degraded.
[0016]
The present invention takes an example of the problem to address such a problem.
That is, in a magnetic circuit in which a pair of plate-like plates are arranged in the longitudinal
direction and a magnetic gap is formed between the plates, a uniform magnetic field is formed
along the longitudinal direction of the magnetic gap; It is an object of the present invention that
uniform sound pressure can be obtained in a speaker using a magnetic circuit.
[0017]
In order to achieve such an object, the present invention at least comprises the configurations
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according to the following independent claims.
[0018]
[Claim 1] A pair of flat plates long in one direction is provided, the plates are disposed along the
longitudinal direction so that the side faces are opposed, and a magnetic gap is formed between
the side faces, the plate A speaker magnetic circuit comprising two end portions and a center
portion in the longitudinal direction, wherein the thickness of the center portion is smaller than
the thickness of the end portions.
[0019]
[Claim 4] A pair of flat plates long in one direction is provided, the plates are arranged along the
longitudinal direction so that the side faces are opposite, and a magnetic gap is formed between
the side faces, and the magnetic A vibrator is disposed along the longitudinal direction of the
plate between the gaps, and vibrates in the thickness direction of the plate by supplying an audio
current along the longitudinal direction of the plate, and the plate has the longitudinal direction
A speaker comprising two end portions and a center portion in a direction, wherein a thickness
of the center portion is formed smaller than a thickness of the end portions.
[0020]
Hereinafter, embodiments of the present invention will be described based on the drawings.
FIG. 2 is an explanatory view for explaining a speaker magnetic circuit according to an
embodiment of the present invention (FIG. 2 (a) is a plan view, FIG. 2 (b) is an XX sectional view,
FIG. 2 (c) YY cross section).
[0021]
The magnetic circuit 10 according to the embodiment of the present invention includes a pair of
flat plates 11 and 12 which are long in one direction, and arranged along the longitudinal
direction so that the side surfaces of the plates 11 and 12 face each other. The magnetic gap 10G
is formed.
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The plates 11 and 12 have their ends b and a center a in the longitudinal direction, and the
thickness t1 of the center a is smaller than the thickness t2 of the ends b.
In the illustrated embodiment, the magnetic gap 10G comprises a pair of magnets 13 and 14
disposed along the longitudinal direction of the plates 11 and 12, and one yoke 15, and each
plate 11 and 12 and the yoke 15 By holding the magnets 13 and 14 together, a magnetic field is
formed from one side surface of the plates 11 and 12 to the other side surface.
The magnets 13 and 14 have magnetic poles magnetized in the thickness direction of the plates
11 and 12, and the magnetic poles are arranged in the directions opposite to each other.
[0022]
According to the magnetic circuit 10 according to such an embodiment, it is possible that the
magnetic flux density of the magnetic gap 10G decreases at the central portion a of the plates 11
and 12 due to the magnetic flux escaping from the end b of the plates 11 and 12 to the outside.
In order to prevent this, the thickness t1 of the side surfaces 11a and 12a of the plates 11 and
12 facing the magnetic gap 10G at the central portion a is smaller than the thickness t2 of the
side surfaces 11b and 12b at the both ends. The magnetic flux density in the longitudinal
direction of the magnetic gap 10G is made uniform.
[0023]
By using such a magnetic circuit 10, it becomes possible to apply a uniform driving force to the
conductor through which the audio current flows along the longitudinal direction of the magnetic
gap 10G, and it is driven by this conductor The sound pressure of the vibrating body can be
made uniform along the longitudinal direction, and a speaker with high sound quality can be
obtained.
[0024]
FIG. 3 is an explanatory view for explaining a speaker according to an embodiment of the present
invention (FIG. 3 (a) is a perspective view showing the entire configuration, and FIG. 3 (b) is a
sectional view taken along the line XX) .
Here, although the ribbon type speaker is shown as an example, it is not limited to this.
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For example, a voice coil may be disposed along the longitudinal direction of the magnetic gap,
and a part of the vibrator may be connected to a voice coil bobbin around which the voice coil is
wound.
[0025]
The speaker 20 includes flat plates 21 and 22 elongated in one direction, and is disposed along
the longitudinal direction so that the side surfaces of the plates 21 and 22 face each other, and a
magnetic gap 20G is formed between the side surfaces. .
In addition, a vibrating body 26 is provided which vibrates in the thickness direction of the plates
21 and 22 by supplying an audio current along the longitudinal direction of the plates 21 and 22
in the magnetic gap 20G.
In the illustrated example, the vibrating body 26 is a conductive ribbon-like member, and
terminal portions 26A and 26B for supplying audio current are formed at two ends of the
vibrating body 26.
The vibrating body 26 is supported by the vibrating body support portions 27A and 27B at both
ends in the longitudinal direction and disposed in the magnetic gap 20G.
[0026]
Further, in the speaker 20, the thickness of the central portion a of the plates 21 and 22 forming
the magnetic gap 20G is formed smaller than the thickness of the end portion b as in the
magnetic circuit 10 described above. . Also here, the magnetic gap 20G includes a pair of
magnets 23 and 24 arranged along the longitudinal direction of the plates 21 and 22, and one
yoke 25, and each plate 23 and 22 and the yoke 25 each magnet 23 , 24 form a magnetic field
directed from one side surface of the plates 21 and 22 to the other side surface.
[0027]
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In the illustrated example, tapered surfaces 21a and 22a directed to the magnetic gap 20G from
the outside are formed on the upper surfaces of the central portions a of the plates 21 and 22,
and the central portions a of the plates 21 and 22 in the width direction are The thickness on the
magnetic gap side is small, and the thickness on the outer side is large. That is, the thickness of
the plates 21 and 22 at the central portion a gradually decreases from the outside toward the
magnetic gap 20G.
[0028]
According to the speaker 20 according to such an embodiment, the side surfaces of the plates 21
and 22 facing the magnetic gap 20G are formed thin at the central portion a, so that the plate is
the same as the magnetic circuit according to the embodiment described above. It is possible to
prevent the magnetic flux density of the magnetic gap 20G from being reduced at the central
portion a by the magnetic fluxes fleeing outward from the end portions b of 21 and 22, and to
obtain a uniform magnetic flux density in the longitudinal direction of the magnetic gap 20G.
[0029]
FIG. 4 is an explanatory view for explaining the characteristics of the speaker according to the
embodiment of the present invention, and the measurement of the magnetic flux density of the
magnetic gap 20G in the embodiment of FIG. It is an example.
As is apparent from this measurement example, the magnetic circuit of the embodiment shown
by the solid line has a uniform magnetic flux density along the longitudinal direction, as
compared with the one in which the plate thickness shown by the broken line is constant. I
understand that
[0030]
According to this, a uniform driving force can be applied to the vibrating body 26 through which
the audio current flows along the longitudinal direction of the magnetic gap 20G, and the sound
pressure level of the speaker 20 is along the longitudinal direction of the magnetic gap 20G.
Thus, the sound pressure at the central portion a can be suppressed from decreasing.
[0031]
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As described above, according to the magnetic circuit and the speaker according to the
embodiment of the present invention, in the magnetic circuit in which the pair of flat plates are
arranged in the longitudinal direction and the magnetic gap is formed between the plates, A
uniform magnetic field can be formed along the longitudinal direction, and a reduction in sound
pressure can be suppressed in a speaker using such a magnetic circuit.
[0032]
It is explanatory drawing of a prior art.
It is an explanatory view explaining a magnetic circuit concerning an embodiment of the present
invention.
It is an explanatory view explaining a speaker concerning an embodiment of the present
invention. It is an explanatory view explaining the characteristic of the speaker concerning the
embodiment of the present invention.
Explanation of sign
[0033]
DESCRIPTION OF SYMBOLS 10 Magnetic circuit 20 Speaker 10G, 20G Magnetic gap 11, 12, 21,
22 Plate 13, 14, 23, 24 Magnet 15, 25 Yoke 26 Vibrator 26A, 26B Terminal 27A, 27B Vibrator
support a (of plate) Central part b (of the plate) end
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