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Description 1, title of the invention
Speaker diaphragm
3. Detailed Description of the Invention The present invention relates to a speaker diaphragm,
and in particular, to provide a speaker diaphragm that greatly contributes to weight reduction of
a vibration system. In the speaker diaphragm, the diaphragm follows with sufficient linearity the
driving force generated by the electromagnetic conversion system within the working band
frequency, and the entire surface vibrates in the same phase (piston vibration). It is considered an
ideal. Therefore, physical properties such as high elastic modulus, high rigidity, and low density
are required for the material constituting the diaphragm, and conventionally, paper, aluminum,
titanium, beryllium, poron and the like are used. However, even with boron or beryllium, which is
an ultrahigh modulus material, the rigidity as a diaphragm is insufficient in a flat plate shape, so,
for example, as proposed in JP-A-54-39625, the diaphragm has a dome shape or Apparent
rigidity has been improved by shape effects such as forming into a cone shape or strengthening
the thickness effect by using a structure, and the piston vibration area has been expanded. On
the other hand, from the viewpoint of high fidelity reproduction of the speaker, when the
EndPage: 1 moving plate is reviewed, flat radiation which is an ideal sound source is closedamplified, and a flat diaphragm is developed. The factors to improve the rigidity of the material
are only the physical properties of the material and the thickness effect, and the thickness is 0.5
to 1 own, which is 20 to 100 times the thickness of the conventional cone-shaped diaphragm.
Accordingly, the weight of the diaphragm is also greatly increased, which causes a new problem
that the efficiency and transient characteristics of the speaker are lowered. On the other hand, in
order to reduce the weight of the diaphragm, a structure such as a honeycomb core and a low
density structure such as a foamed filler are used, but none of them is sufficiently satisfactory. In
particular, in the case of a hollow body having several cell shapes such as a honeycomb core and
the like, when using paper or foil having a low elastic modulus, cell resonance occurs to cause
disturbance in frequency characteristics. At the same time, the appearance of a material with
excellent processability, in particular, with a low density, has been desired. The acoustic materials
conventionally used include those shown in the following table. Although low density paper and
plastic are excellent in processing surfaces such as thinning, since the elastic modulus is low,
improvement in resonance frequency is small even if they are formed into a structure. Among
metals, aluminum is generally used, but its density is high as a material for structural
diaphragms, while magnesium is known as a low density metal, but its crystal form is a closepacked hexagonal crystal and is poor in workability, Besides being difficult to make thin, it has
not been put to practical use as a diaphragm material because of problems with strength and
corrosion resistance.
In addition, ultra-high modulus materials such as beryllium and boron have low density and have
ideal physical properties as diaphragm materials, but their processability is extremely poor and it
has been difficult to use as materials for structures. Lithium used as the second element of the
magnesium-lithium (Mg-Li) alloy used in the present invention is an alkali metal having a specific
gravity of 0.534 and a melting point of 186 ░ C. and is used as a trace additive in aluminum and
lead alloys There is. In general, lithium is easy to form alloys with many metals, but tends to form
relatively hard, brittle and high melting point intermetallic compounds. Moreover, it is known to
deteriorate by adding 6% or more. However, not exceptionally in alloys with magnesium, the
addition of lithium improves the corrosion resistance 9 mechanical properties. In the phase
diagram of the magnesium-lithium binary alloy shown in FIG. 1, the addition amount of lithium is
0 to 5.7. In the range of wt%, it is an equivalent of magnesium, the crystal structure is a closepacked hexagonal crystal, and its inertia deformation processability is almost the same as that of
magnesium. However, when the amount of lithium added is 5.7 wt% or more, body-centered
cubic crystals that are the same as lithium begin to coexist, and the proportion of body-centered
cubic crystals increases with the amount of lithium added, facilitating plastic deformation
processability It will be. In addition, the density of the alloy decreases with the addition of
lithium, and is about 1.5 (J'z) at 9 wt% and about 1.35 (f- / C1 / l) at 13 to 15 wt%. Become
lighter. However, in the solid Li solid, the corrosion resistance decreases with an increase in the
concentration of Li, and contact with different metals forms a local battery to cause corrosion.
Therefore, the addition amount of Li and EndPage: 27, 1 or less is an appropriate amount of 20
wt% or less, and if it is greatly exceeded, the practicability in air also becomes poor. The
preferred composition of the magnesium-lithium alloy in the present invention is 5.7 to 20% by
weight of Li, more preferably 0.1 to 0.4% by weight of Si for elongation and stress corrosion. It is
an improvement. Hereinafter, the configuration and effects of the speaker diaphragm in the
present invention will be described using examples. Example 15 Raw metal is put in a carbon
crucible at a ratio of 15% by weight Li, 0.4% by weight Si and 84.6% by weight Mg and melted,
stirred and cast in a vacuum melting furnace to obtain a density of 1.35. A Mg-L4 alloy with a
modulus of 3.9s-4.2 x 10 "+ 17n6 / cJ is prepared. After removing the skin of this rod, it is made
into a foil by hot rolling at a temperature condition of 360 ░ C. to 400 ░ C. to prepare a foil of
20 ?m, 60 ?m.
266 pieces of 20 ?m thick foil are laminated and glued. Through a process of cutting 9
rotations, a honeycomb core having a thickness of 1 mm and a diameter of 320 mm is
manufactured. The Mg-Li alloy foil of 501 tm thickness 320 ?m in diameter is bonded to one
side of this core using a 20 ?m thick film-like thermoplastic adhesive, heated and processed, as
shown in FIG. Honeycomb flat diaphragms. In FIG. 2, 1 is a skin material, 2 is a core material, and
3 is an adhesive. Comparative Example Honeycomb flat plate of 60 ?m thick skin bonded to
both sides of a honeycomb core 10 ?m thick and 320 m 1 diameter by the same process and
treatment as in Example using aluminum foil (3003) of 20 ?m thickness and 50 ?m thickness
Make a diaphragm. The weight of the diaphragm thus obtained was 36.6 f in the example and
54.6 y- in the comparative example, and a weight reduction of about 33% was achieved as the
diaphragm. Furthermore, a drive part and a support part were attached to this diaphragm, and it
was set as a speaker, and this was attached to JIS standard number, and the sound pressure
frequency characteristic (1 W / 1 m) was measured. The results are shown in FIG. The solid line a
in the figure is the characteristic of the example, and the broken line is the characteristic of the
comparative example. As apparent from FIG. 3, in the present embodiment, the sound pressure
level is improved by about 2 dB as the weight is reduced, and the efficiency is improved. As
apparent from the above examples, according to the present invention, the magnesium-lithium
alloy which is insufficient in characteristics such as the elastic modulus 9 strength as the
conventional cone-shaped or dome-shaped diaphragm material has a thickness effect of the
structure. It is found that the material is sufficient as a material for a diaphragm having an
apparent rigidity enhanced and that the material is optimum as a material for a diaphragm
composed of the above-mentioned structure due to the low density of the aluminum fishing
machine. It is possible to improve the efficiency of the speaker without improving the system and
the like.
4. Brief description of the drawings. FIG. 1 is a state diagram of a magnesium-lithium binary
alloy, FIG. 2 is a partially cutaway top view showing one embodiment of a speaker diaphragm of
the present invention, and FIG. It is a sound pressure frequency-characteristics figure of the
speaker using the diaphragm for speakers of the Example and comparative example of invention.
1 иииии Skin material, 2 иииии Core material, 3 ииииии Adhesive. Name of agent Attorney Nakao and others
1 person Figure 1 Figure 2 EndPage: ?
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