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JP2009253411

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DESCRIPTION JP2009253411
PROBLEM TO BE SOLVED: To drive the entire surface of a doughnut-shaped, circular plate-like
diaphragm having a central opening, to suppress generation of nodal circles and node diameters
in resonant modes of divided vibration over a desired frequency band, and to obtain sound
pressure frequency characteristics. The provision of a thin, lightweight circular flat-plate speaker
with a toroidal diaphragm that can be smoothed in a full range. SOLUTION: A plurality of small
circular voice coils arranged in an annular vibration area at equal intervals on concentric circles
having a diameter smaller than the outer diameter of a doughnut-shaped diaphragm are attached
to one side of the diaphragm and magnetic gaps can be inserted into each voice coil. A plurality
of thin magnetic circuits forming a ring are attached to the inner surface of the frame holding the
diaphragm via the edge, and the radius of the concentric circle is the arrangement density of all
voice coils of the outer annular portion and the inner annular portion of the concentric circle A
circular flat-plate speaker with a toroidal diaphragm set to an even value. [Selected figure] Figure
1
Round flat loudspeaker with donut diaphragm
[0001]
The present invention relates to a circular flat-plate speaker with a doughnut-shaped diaphragm,
and more particularly to a full-range circular flat-plate speaker having a thin overall shape using
a circular toroidal diaphragm having a circular opening at the center.
[0002]
In the past, the main diaphragm of diaphragms used for thin speakers is a square or elliptical
diaphragm, and a high efficiency driving method using a voice coil and a magnetic circuit for
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driving the entire surface of these non-circular diaphragms Various attempts and proposals have
been made to achieve this while adapting to the configuration of the above, but no definite
proposal has been made so far for the full drive method of the circular toroidal diaphragm.
[0003]
In the case of a circular flat diaphragm, it is ideal to drive so that the entire surface of the
diaphragm including the central part vibrates with a piston. However, as a driving method which
can be adopted conventionally, an annular voice coil is used as a circular flat diaphragm. When
concentrically mounted and driven to raise the frequency, piston vibration of the diaphragm
disappears at the frequency point of the resonance mode in which a circular vibration node due
to the divided vibration of the diaphragm, that is, a node circle is generated.
Because this resonant mode occurs at a relatively low frequency, this drive scheme is unsuitable
for speakers intended for full range.
[0004]
In order to cope with such generation of a nodal circle in a circular flat diaphragm, in a
loudspeaker mentioned as a conventional drive system, the outer peripheral end of a drive cone
coupled at the inner peripheral end with a bobbin carrying a voice coil is a circular flat plate. The
diaphragm is coupled to the position of a nodal circle generated by the primary resonance of the
diaphragm and combined with the magnetic circuit to drive the diaphragm.
In this case, the first resonance is removed and the node circle is not generated, but when the
frequency is further raised, the second resonance is generated, and the node circle associated
therewith can not be dealt with. That is, in the driving at the joint position of the first resonance,
reproduction can be performed from the low frequency band to the frequency at which the
second resonance occurs, but reproduction in a band beyond that is impossible.
[0005]
According to one proposal for a solution to this problem, two large and small apertures, one end
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of which is fixed at two nodal points generated by the first and second resonances of the circular
flat diaphragm respectively. The voice coil is provided at the other end of each coil bobbin, and
these voice coils are arranged in two magnetic gaps of large diameter and small diameter of a
magnetic circuit formed by combining magnets having anisotropy in the radial direction. The
circular flat diaphragm is driven at two nodal points of the first resonance and the second
resonance. Japanese Patent Application Laid-Open No. 4-115698
[0006]
However, not only the node circle but also the node diameter generated in the diametrical
direction of the diaphragm depending on the frequency also exists in the resonant mode of the
circular flat diaphragm, and Patent Document 1 takes measures against this node diameter Not
shown. In addition, in order to form an annular magnetic gap of two different diameters, which is
necessary to suppress only a nodal circle, a diaphragm is required to have a magnetic circuit of
huge size and weight. The structure is also increased in size, which is not only disadvantageous in
terms of downsizing of the speaker, particularly in terms of thinning and lightening, but also in
terms of manufacturing cost.
[0007]
Furthermore, if a circular central diaphragm is provided in the circular flat diaphragm and the
entire surface can be driven in a general range as a so-called donut diaphragm, a small circular
flat loudspeaker is provided by incorporating a tweeter in the central opening. Although it is
possible to extend the reproduction range to the high frequency range, Patent Document 1
suggests the use of a large-diameter circular voice coil and a large-diameter magnetic circuit
compatible therewith for driving the entire surface of a doughnut-shaped diaphragm. Yes, and
suffer from the same disadvantages as above.
[0008]
Therefore, according to the present invention, the diaphragm is driven by the small-sized and
small-sized voice coil and the magnetic circuit from the general low-pitch range to the high-pitch
range of the speaker using the doughnut-shaped circular flat diaphragm having a concentric
central opening. To provide a circular flat-plate speaker which vibrates with high efficiency a
node circle of a divided vibration changing in the whole sound range and a portion to be a node
diameter with high efficiency, thereby suppressing a resonance mode and enabling full drive of a
diaphragm in a full range. With the goal.
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[0009]
The first problem solution means according to the present invention is a doughnut-shaped
circular flat diaphragm in which a circular flat speaker with a doughnut-shaped diaphragm has a
vibration area between an outer peripheral edge and an inner peripheral edge defining a central
opening as a vibration area. And a plurality of small circular voice coils supported on one side of
the vibration area of the diaphragm, and a plurality of small circular magnetic circuits facing the
one side of the diaphragm including magnetic gaps facing each of the voice coils. And a frame for
holding the magnetic circuit on the inner surface while holding the inner and outer peripheral
edges of the diaphragm via the edges and supporting the magnetic circuit on the inner surface,
and the center of the voice coil is concentric on the vibration area of the diaphragm It is
characterized in that it is an odd number located at intervals, and the concentric circles are set to
a radius such that the areas of the inner and outer vibration regions are substantially equal.
A second problem solving means according to the present invention is characterized in that there
are five concentrically arranged odd numbered voice coils arranged at equal intervals of a central
angle of 72 degrees.
A third solution according to the invention is characterized in that the radius of the concentric
circle is 95 to 100% of the value at which the areas of the outer and inner vibration areas are
approximately equal.
[0010]
According to the first aspect of the present invention, the odd number of small circular voice
coils disposed at equal intervals concentrically in the annular vibration area of the doughnutshaped diaphragm are used in the general frequency band of the doughnut-shaped diaphragm.
Drives effectively to prevent the generation of a single nodal circle and multiple nodal diameters
due to the resonant mode of split vibration that may occur in natural vibrations, and the radius of
the concentric circles is equal to the area of the inner and outer annular portions of the
concentric circles By setting to the following values, the arrangement density of the voice coil in
both annular portions is equalized. The action of the second problem solution means according
to the present invention is to drive the five nodal diameter portions in the resonance mode
generated in the high frequency band of the doughnut-shaped diaphragm by setting the voice
coils on concentric circles at five intervals. Make it possible. The action of the third solution
according to the present invention occurs first in the low frequency band by setting the radius of
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the concentric circles of the doughnut-shaped diaphragm to 95 to 100% of the value that makes
the inside and the outside equal. Effectively suppress the occurrence of joint circles.
[0011]
In order to totally vibrate the doughnut-shaped circular plate-like diaphragm used in the circular
flat plate speaker in the general frequency band of about 1 to 15 kHz, the node circle and node
diameter in the resonant mode of the divided vibration changing with the vibration frequency are
substantially The smallest nodal circle and the largest number of nodal diameters of resonant
modes in a general-purpose frequency band, from the viewpoint that it is advantageous to
distribute a plurality of small circular voice coils at uniform density at positions where all of them
can be removed. By arranging a plurality of, preferably an odd number, of small circular voice
coils concentrically in an annular vibration area that can correspond to the number of and, the
occurrence of nodal circle and nodal diameter in a general frequency band is suppressed Do.
[0012]
First, referring to FIGS. 3 to 10, a material having a Young's modulus of 2 GPa and a specific
gravity of 0.27 gr / cm <3> generally used as a vibrating plate is 140 mm in diameter, 40 mm in
diameter at the central opening, and 4 mm in thickness. Based on the natural vibration mode in
the case where a flat diaphragm is vibrated at a frequency changing from about 1600 Hz to 15
kHz, the pattern of the vibration node changing with the resonance mode of the divided vibration
changing with the frequency rise is considered.
In particular, in FIG. 4 (2807 Hz), one annular node or nodal circle a (a circular dark portion
substantially at the center of the annular vibration region in the monochrome diagram) is seen,
and in FIG. 6 (6078 Hz) one node circle Whereas one diametrical node or node diameter b is seen
in FIG. 8 (10963 Hz), one nodal circle a and two nodal diameters b are seen, while FIG. 3 (1661
Hz), FIG. 5 (4120 Hz), FIG. In FIG. 9 (11091 Hz) and FIG. 10 (15579 Hz), 2 to 6 node diameters b
appear respectively.
[0013]
Here, attention is paid to the split resonance modes of FIGS. 9 and 10, in which the vibration is
divided into 10 and 12 sections in the radial direction by 5 and 6 node diameters b respectively,
and the clear vibrations are It can be seen only in the outer peripheral part of the 10 or 12
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sections, and no vibration can be seen in the inner peripheral part connecting the inner
peripheral side of each node diameter b. Therefore, in order to obtain full-scale vibration in the
full range of the general-purpose frequency band of the doughnut-shaped circular flat plate-like
diaphragm, see FIG. 9 (11091 Hz) at least with a system other than the conventional large
diameter voice coil and large diameter magnetic circuit. It is considered effective to consider just
before the occurrence of the five nodal diameters.
[0014]
1 and 2 show an embodiment of a circular flat plate speaker using a doughnut-shaped
diaphragm according to the present invention, and FIG. 1 is a plan view on the inner surface side
of a doughnut-shaped circular flat plate-like diaphragm 11 used for this circular flat plate
speaker 10. FIG. 2 is a cross-sectional view of the circular flat loudspeaker 10 taken along the
line A-A of FIG. For example, an annular so-called doughnut-shaped diaphragm 11 made of a
synthetic resin material or pulp material having Young's modulus and specific gravity as
described above in the figure and having a central opening 12 at the center is, for example, a
metal plate having a shallow U-shaped cross section. It is elastically supported by the outer
peripheral wall 13a and the central projection 13b of the disc-shaped dish-shaped frame 13
through an annular outer peripheral edge 14 made of an elastic material and a circular central
edge 15. As a feature of the present invention, a plurality of small diameter cylindrical voice coils
V1 to Vn are attached to the inner surface side of the diaphragm 11, and a magnetic gap of a
diameter capable of inserting each of the voice coils V1 to Vn on the inner bottom surface of the
frame 13 A plurality of small-diameter thin magnetic circuits M1 to Mn to be formed are
mounted facing the voice coils V1 to Vn.
[0015]
In this embodiment, as shown in FIG. 1, five radial radius lines 16 for dividing the doughnutshaped diaphragm 11 into five equal parts at 72 degrees in the radial direction and a radius R set
as described later The five voice coils V1 to V5 whose centers are located at five intersections
with the concentric circles 17 are attached to the inner surface of the diaphragm 11. The voice
coils V1 to V5 desirably have a cylindrical shape and are directly bonded to the surface of the
diaphragm by an adhesive at one end, which means that the speaker 10 can be made thinner and
lighter and reproduction efficiency compatible. However, it may be mounted via a coil bobbin.
Further, it is advantageous to make all of these voice coils V1 to V5 have the same diameter, and
a diameter substantially one tenth of the diameter of the diaphragm 11 is sufficiently effective.
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[0016]
Similarly, in the magnetic circuits M1 to M5, the magnetic circuits M1 to M5 (only M2 and M5
are shown in FIG. 2) corresponding to the five voice coils V1 to V5 on the concentric circles 17 of
the diaphragm 11 are the inner bottom surface of the frame 13. It is fixed to As shown in FIG. 2
as magnetic circuits M1 to M5, an annular magnetic gap is formed between the pole piece outer
peripheral surface and the yoke peripheral wall inner peripheral surface by sandwiching the disc
type magnet with the center pole piece and the plate type yoke A voice coil is inserted into the
magnetic gap, but the invention is not limited to this, as long as it achieves substantially the same
drive efficiency and space uniformity in combination with a small circular voice coil. It may be of
the type.
[0017]
The five radiation radius lines 16 for arranging the respective combinations of the voice coils V1
to V5 and the magnetic circuits M1 to M5 correspond to the radius portions of the five nodal
diameters b described above with reference to FIG. Since the distance between the node
diameters does not change even if it moves, the driving of the diaphragm 11 by the voice coils
V1 to V5 at these five fixed positions corresponds to driving the diaphragm at five node
diameters. Therefore, usually up to just before the peak dip that occurs in the high range,
especially around 11 kHz, is suppressed. Moreover, these five nodal diameter drives are also
effective in suppressing the generation of a small number of nodal diameters at other frequencies
from the low range to the high range.
[0018]
If the number of voice coils is not five but six, it can be considered that it can cope with the
resonance mode with six node diameters shown in FIG. 10, but actually, the number of voice coils
is an even number. It has been found that the vibration pattern breaks down at half the number
of resonance modes of nodal diameter, that is, the mode generation time point of FIG. In the case
of four, therefore, it is already broken at the time of FIG. 3, and even node diameter generation in
the low frequency band can not be suppressed. Therefore, it is advantageous to set the number
of voice coils to an odd number, and it is particularly effective to set it to 5 in the general
frequency band.
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[0019]
As for the arrangement positions of the five voice coils V1 to V5 arranged on the concentric
circle 17 at equal intervals, it is desirable that the arrangement density be uniform over the
entire annular vibration area of the toroidal diaphragm 11. For this purpose, the radius of the
concentric circle 17 in the diaphragm 11 may be set so that the distribution density of the voice
coils V1 to V5 at the inner side and the outer side of the concentric circle 17 matches the area
ratio of the diaphragm inside and outside the concentric circle.
[0020]
Assuming that the radius of the toroidal diaphragm 11 is RO, the radius of the central opening
12 is r, and the radius of the concentric circle 17 is R, the area ratio of the inside to the outside of
the concentric circle 17 is πRO <2>. It becomes −πR <2> = πR <2> −πr <2> (1), and the ratio
of R to RO is obtained from this equation (1) R = R {(RO <2> + r <2>) / 2 } (2) The radius R of the
concentric circle 17 is about 51.5 mm by applying the radius RO of the doughnut-shaped
diaphragm 11 shown in FIGS. 3 to 10 to 70 mm and the radius r of the central opening 12 of 20
mm. The five voice coils V1 to V5 are mounted on the concentric circle of concentric radius 72
degrees on the concentric circle of this radius R, and if they are magnetically driven, they can be
driven almost equally to the front of the annular vibration area. It will be done.
[0021]
On the other hand, considering the relationship between the calculated value of approximately
51.5 mm of the concentric circle 17 and the actually measured value of approximately 48.9 mm
of the radius of the nodal circle a that occurs first at 2807 Hz in FIG. Since the ratio of thickness
to diameter is increased and apparent rigidity is increased as compared with, the natural
frequency at this frequency causes the nodal circle a to be slightly inside the calculated
concentric circle, that is, at a radial position of about 95%. Become. Therefore, if the concentric
circle 17 is set to a value of 95 to 100% of the radius calculated by the above equations (1) and
(2), it is effective to suppress a nodal circle generated in the general-purpose frequency band.
[0022]
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The resonance mode of split vibration in the doughnut-shaped circular flat diaphragm changes
depending on the conditions such as the size of the diaphragm, elastic modulus, specific gravity,
etc., and the same frequency band as shown in FIGS. The number and position of the generated
nodal circle and nodal diameter are not the same. Accordingly, the number of voice coils
arranged concentrically is selected corresponding to the number of the largest node diameter
generated in the desired frequency band, and the radius or diameter of the concentric circle is
calculated corresponding to this number.
[0023]
In the first embodiment, the vibration node pattern in the natural vibration mode shown in FIGS.
3 to 10 was considered for the doughnut-shaped circular flat diaphragm, but in actual speaker
assembly, a voice coil is used as a diaphragm using a jig. It is necessary to insert the hole into the
provided hole and to withdraw the jig from the hole, so at the voice coil installation position, a
hole having a diameter equivalent to the inner diameter of the bobbin carrying the voice coil
must be provided in the diaphragm. Therefore, corresponding to the configuration of the first
embodiment, in the same general-purpose frequency band by the diaphragm provided with holes
at five voice coil installation positions along the concentric circles of the radius calculated by the
above equations (1) and (2) The natural vibration modes thus obtained are shown in FIGS.
However, in this case, the peripheral wall surface of the hole has a thickness of 0.1 mm instead of
the usual elastic vibration plate in consideration of increasing the rigidity by directly bonding a
cylindrical voice coil or bonding a bobbin supporting the voice coil. Aluminum foil is used.
[0024]
FIG. 11 shows a mode with two frequencies of 961 Hz and two modes of nodal diameter, and FIG.
12 shows a mode with one frequency of 2832 Hz and FIG. 13 shows three modes of diameter
with 3671 Hz. Mode: Fig. 14 shows a mode with one joint circle and one nodal diameter at
frequency 5910 Hz, Fig. 15 shows a mode with four nodal diameters at frequency 6690 Hz, Fig.
16 does not have five holes without frequency at 9501 Hz FIG. 17 shows a mode of a pentagonal
node, FIG. 17 shows a mode of five nodal diameters at a frequency of 11916 Hz, and FIG. 18
shows a mode of two nodal circles at a frequency of 13616 Hz.
[0025]
In the natural vibration mode of five holed toroidal diaphragms, it is at 11916 Hz in FIG. 17 that
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five node diameters occur, and in the holeless toroidal diaphragm 11 of FIGS. 3 to 10, five voices
The frequency is slightly higher than the frequency 11091 Hz in FIG. 9 which is the limit of
resonance pattern suppression in the case of coil installation.
It is clear that this is due to the increase in rigidity due to adhesion of the coil or bobbin to the
peripheral wall of the five holes as described above, and resonance in a general frequency band
by concentrically equidistant arrangement of five voice coils It raises the limit in the high
frequency band of pattern suppression, and also proves the effectiveness of installing 5 voice
coils.
[0026]
The top view by the side of the inner surface which attached the voice coil of the doughnutshaped circular flat plate diaphragm used for the circular flat plate speaker by this invention. FIG.
2 is a cross-sectional view of the circular flat plate speaker by the doughnut-shaped diaphragm of
the present invention using the diaphragm of FIG. 1, taken along line AA of FIG. 1. Fig. 6 shows a
split vibration resonance mode of natural vibration at a frequency of 1,661 Hz, which is the same
doughnut-shaped circular flat diaphragm material used in the present invention but which has
not yet been provided with a hole for voice coil attachment. Fig. 4 shows a resonant mode of a
single vibration at a frequency of 2,807 Hz of the same holeless diaphragm material as that of
Fig. 3; Fig. 6 shows the resonance mode of the natural oscillation at a frequency of 4,120 Hz of
the same holeless diaphragm material as in Fig. 3; Fig. 6 shows the resonant mode of the natural
oscillation at a frequency of 6,078 Hz of the same holeless diaphragm material as in Fig. 3; Fig. 6
shows the resonant mode of the natural oscillation at a frequency of 7,266 Hz of the same
holeless diaphragm material as in Fig. 3; Fig. 6 shows the resonant mode of the natural
oscillation at a frequency of 10, 963 Hz of the same holeless diaphragm material as in Fig. 3; Fig.
6 shows the resonance mode of the natural oscillation at a frequency of 11,091 Hz of the same
holeless diaphragm material as in Fig. 3; Fig. 6 shows the resonant mode of the natural
oscillation at a frequency of 15,579 Hz of the same holeless diaphragm material as in Fig. 3; The
material is a donut shaped circular flat diaphragm material as used in the present invention, and
provided with five concentric holes for voice coil attachment, but showing a natural vibration
resonance mode at a frequency of 961 Hz. FIG. 12 shows the resonance mode of the natural
oscillation at a frequency of 2,832 Hz of the same perforated diaphragm material as that of FIG.
FIG. 12 shows the resonance mode of the natural oscillation at a frequency of 3,671 Hz of the
same perforated diaphragm material as in FIG. FIG. 12 shows the resonance mode of the natural
oscillation at a frequency of 5,910 Hz of the same perforated diaphragm material as that of FIG.
FIG. 12 shows the resonance mode of the natural oscillation at a frequency of 6,690 Hz of the
same perforated diaphragm material as in FIG. FIG. 12 shows the resonance mode of the natural
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oscillation at a frequency of 9,501 Hz of the same perforated diaphragm material as in FIG. FIG.
12 shows the resonance mode of the natural oscillation at a frequency of 11,916 Hz of the same
perforated diaphragm material as in FIG. FIG. 12 shows the resonance mode of the natural
oscillation at a frequency of 13,616 Hz of the same perforated diaphragm material as in FIG.
Explanation of sign
[0027]
DESCRIPTION OF SYMBOLS 10 Speaker 11 diaphragm 12 center opening 13 frame 14 outer
periphery edge 15 center edge 16 radial radius line 17 concentric circle V1 to V5 voice coil M1
to M5 magnetic circuit a node circle b node diameter
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