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JPS55124399

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DESCRIPTION JPS55124399
1-Specification 1, title of the invention
Electro-acoustic transducer
3. Detailed Description of the Invention The present invention relates to an electroacoustic
transducer, in which the diaphragm is constituted by providing a facing on both sides of a
honeycomb core, and the thickness of each core part is changed. Thus, the influence of variations
in design is reduced by setting the driving point of the diaphragm to a point other than the nodal
circle of the first-order natural vibration while reducing distortion. EndPage: 13.1 shows a
dynamic speaker, 1 is a diaphragm, 2 is an edge, 3 is a plate, 4 is a magnet, 6 is a chair coil 6.6 is
a center pole, 7 is a damper, 8 is a frame, 9 Generally, the diaphragm 1 used for a speaker of this
type must have a large rigidity to prevent deformation during vibration, and must be lightweight
to improve efficiency. . Since the diaphragm 1 shown in FIG. 1 is made of paper, its efficiency is
poor, but its rigidity is weak. Therefore, it has been practiced to use a diaphragm 11 comprising a
core having a so-called honeycomb structure in the form of a honeycomb as shown in FIGS. 2
and 3 and a surface plate adhered on both sides thereof. If such a diaphragm 11 is used, even if it
is a cone shape as shown in FIG. 2 or a flat plate as shown in FIG. 3, it is lightweight and has high
rigidity. In the case of the diaphragm 11 shown in FIGS. 2 and 3, the thickness of the diaphragm
11 is substantially one pair over the entire area of the diaphragm, and the volume density is also
substantially It is constant. Making the volume density constant in this way is advantageous in
terms of facilitating the manufacture of the diaphragm, but has been found to be insufficient in
characteristics. The present invention provides a diaphragm that solves such conventional
problems. An embodiment of the present invention will be described below with reference to
FIGS. 4 to 6. In FIG. 4 and FIG. 5, 12 is a core having a core structure at 7, 13 and 14 Ld is a
surface material attached to both sides, 15 is an edge, 16 is a bobbin and 17 is a damper. As is
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apparent from FIGS. 4 and 6, in the diaphragm in this embodiment, the thickness of the center
(near the driving portion) of the green 12 is gradually decreased toward the periphery of 11. FIG.
The strain characteristics can be sufficiently improved only by this constitution, but it is also
effective if the volume density equivalent to the central volume density is further increased. FIG.
6 shows how this embodiment is effective in improving the characteristics of the speaker.
FIG. 6 illustrates the result of theoretical calculation by a calculation program using a general
purpose program (NASTRAN) of the finite element method in one part. In this case, with the total
mass of the diaphragm kept constant, the driving point admittance or laminated anti-resonance
point (first natural frequency with one nodal circle) of the speaker is taken as the vertical axis,
and the diameter of the voice coil is taken as the horizontal axis. It is shown. Here, the
antiresonance point is a point at which the mechanical impedance viewed from the drive point
takes a minimum value. The anti-resonance point gives the limit of piston movement, since the
first order peak on the sound pressure characteristic corresponds to the maximum point
following this anti-resonance point. In terms of calculation, the equivalent coating ratio is
determined from the bending stiffness of the core material having a honeycomb structure.
Therefore, when another core different in rigidity is used, although the absolute value changes,
the relationship shown in FIG. 6 can be used as it is regardless of the uniqueness of each
diaphragm. In FIG. 6, A indicates the characteristic 2C when the honeycomb flat portion of the
conventional example shown in FIG. 3 is thickened, and the characteristic when the density of the
central portion and the equivalent rigidity (Young's modulus) are further increased. From FIG. 6,
the anti-resonance point is maximum at a certain voice coil diameter, and the maximum diameter
is the above-mentioned A. It differs according to B and C 2 The maximum value of antiresonance
point is A. It turns out that B and C differ. And from FIG. 6, the maximum value of the
antiresonance point increases in the order of A, B, C, and when the two voice coil diameter is 45
JlaB, the antiresonance point also increases in the order of A, B, C I understand. As is well known,
when the diaphragm is vibrated, the diaphragm resonates at a plurality of unique frequencies.
Normally, the higher the lowest resonance frequency (ie, the antiresonance point), the more the
diaphragm as a whole vibrates integrally, less distortion due to unnecessary vibration, and the
more faithful to the input signal. However, as shown in FIG. It can be understood that an
excellent diaphragm with less distortion can be obtained by thickening the vicinity of the center
and further achieving the volume density near the center and EndPage: 2 <. In order to change
one volume density, the size of each cell of the honeycomb of the core material 12 may be
changed. Still, the smaller the surface density of the core material 12, the higher the resonant
frequency. This is explained below in the case of a disc. The natural frequency fr of the disk is
expressed by the following equation. However, as a disk with ?2; constant 41 disk radius
according to mode order; bending rigidity or as a disk with ... и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и
и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и Is represented.
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Dz EIIt (t + t) 2/8 ? 0 иии (2) where Ef: Young's modulus of the surface material 'и и и, tf: thickness
of the surface material tc; thickness of the core material t; t + t?; 1-(pointon ratio 2) It can be
seen from the equation (1) that the natural frequency f increases as the flexural rigidity is
increased and the surface density ? is decreased. Further, it can be understood that it is
sufficient to increase the thickness of the honeycomb according to the equation (2) to increase
the bending rigidity. From this, it is understood that the natural frequency fr is increased by
decreasing the volume density of the honeycomb and increasing the thickness per constant
surface density. For this purpose, it is effective to provide through-holes on the side walls of each
cell of the honeycomb so as not to reduce the shear rigidity. Next, such a diaphragm can be
designed to be quite freely shaped, but by making the radiation surface side substantially flat, it
is possible to receive the acoustic center from the conventionally used speaker of FIG. It is
advantageous because it can be close to the point. Further, as the surface material, a thick fiber
of Young's modulus or a composite plate of mica and resin is suitable according to the equation
(2). Table 1 shows the Young's modulus and density of each material. In Table 1 and Table 1,
carbon fiber / resin shows 60% carbon fiber and 40% resin by volume ratio, and mica / resin
shows 8o% mica by weight ratio. It can be seen from Table 1 that carbon fiber / resin and mica /
fiber have a smaller density and a larger Young's modulus than aluminum. Although the circular
diaphragm has been described in the above embodiment, the present invention can be applied to
a diaphragm having any shape other than circular, and in this case as well, the same effect can be
obtained by increasing the thickness di near the driving point. It can be easily compared to 1 ░
to be obtained. Next, the case where the diaphragm according to the present invention is actually
manufactured will be described in detail. Table 2 shows the materials used in the experiment.
The results of Table 2 are shown in FIG. Since the stretching stiffness is different from that of
FIG. 6, the high-pass resonant frequency is lower than that of FIG. The weirs 2 and 7f3 are
designed to use the same material and to have approximately the same weight. However, while fh
of 53 is around 1.3 KHz in FIG. 7, fh of f2 is about 2.1 KHz, demonstrating that it is described in
the present invention. The peak EndPage at fh is as low as about 3 to sdB, which is advantageous
for the design of a two-speaker system. Furthermore, fh of fl is about 2.4 KHz, which indicates
that it is effective to use mica with large rigidity as one surface material, and in such bending
vibration, the peripheral surface is generally used. Reducing the density raises the resonant
frequency.
Therefore, by reducing the thickness of the surface material 13.14 of the peripheral portion, the
surface density of the peripheral portion of the diaphragm can be reduced, and a wider band can
be achieved. Finally, an arrangement for driving such a diaphragm with low distortion will be
described. The ratio to the coil diameter Dv is large for a large aperture speaker (nominal 25 crn
or more), for example 30 (7 FI speaker DC: Dy 76: 1 to 4: 1 or so), and for a small aperture
speaker Dc: Dy-= 3,5: 1 to 1: 1) 1. It is an extent. This is generally determined by the conditions
such as the efficiency, etc., + 1 ░. On the other hand, the nodal diameter DN of the primary
natural vibration is DN = 0.68 DC, and the diameter of the driving boy coil is uniquely
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determined by the diaphragm outer diameter DC. However, matching the diameter Dv of the
driving voice coil to the diameter DN of the nodal circle means that the ratio of the diaphragm
outer diameter DC to the diameter Dv of the voice coil can not be freely selected, and the voice of
large diameter speakers The fact that the diameter of the coil is large (for example, the diameter
of the voice coil is as large as 150 all in the case of a 30-woofer) is extremely disadvantageous in
practical design. Furthermore, when only a node circle is driven, there is also a problem that a
slight variation in voice coil diameter causes an unnecessary undulation on the sound pressure
frequency characteristic. Fig. 8 shows an example of this. A diaphragm with a nodal diameter of
161.61 LIk should have a voice coil whose diameter is deviated 2 ░ 511 above the nodal
diameter (a voice coil 13 with a solid line of 154 all in diameter). Therefore, in the present
invention, the diameter of the voice coil is shaken in order to cause unnecessary undulations in
the vicinity of the frequency. The diameter of the primary natural vibration of the moving plate is
set to a diameter other than the nodal circle, and the degree of freedom in design is increased to
suppress the variation of the characteristics. As described above, according to the second aspect
of the present invention, it is possible to realize excellent characteristics with less distortion as
compared with the conventional cone diaphragm and flat diaphragm. 1 to 3 are sectional views
showing a conventional speaker, and FIGS. 4 and 5 are fragmentary perspective views and
sectional views of an essential part of one embodiment of the present invention, and FIG. 6 is a
conventional diaphragm and this The characteristic diagram of the diaphragm according to the
invention, FIG. 7 is a characteristic diagram showing the measurement result, and FIG. 8 is a
characteristic concealment to explain the influence on the sound pressure frequency
characteristic due to the variation of the voice coil diameter. 12 conflict e11111I + 1 core
material, 13, 14 @ * ...-surface material. Name of agent Attorney Nakao, Toshio et al. 1 person
Fig.1 EndPage: 4 Fig.2 Fig.3 Fig.4 Fig.6 6 Boyes Boyling Jl 10% m) EndPage: ?
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