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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
diaphragm constituting a speaker, a microphone and other electroacoustic transducers. [Prior Art
and Invention to be Solved] Generally, in a diaphragm which constitutes an electroacoustic
transducer. Expansion of piston area and high frequency band limit frequency (fH). There is a
demand for increased resistance to input, etc. Therefore, this material is lightweight and has a
large elastic modulus (Young's modulus). For example, light metal materials such as titanium and
aluminum are used. However, it is extremely difficult to completely satisfy the above-mentioned
characteristics by only a single material. Therefore, a diaphragm in which boron is thermally
diffused in a titanium base material (see Japanese Patent Publication No. 55-15913) and the like.
A diaphragm (see JP-B-55-7757) or the like is proposed which has a BN layer formed by heat
treatment at about 900 ° C. after applying a BN solution on a titanium substrate. However, in
the means for forming the compound layer by the above-mentioned heat treatment, it is
necessary to heat to a temperature of 550 to 700 ° C. which is a temperature at which titanium
constituting the substrate of the diaphragm is easily deformed It is necessary to heat to a
temperature of 885 ° C. or more, which is a transformation point which is easily transformed
into a face-centered cubic structure to cause deformation. Therefore, it is caused by the release of
the residual stress generated when forming into a diaphragm shape, or the precipitation of
crystals. Thermal deformation may be generated in the substrate constituting the diaphragm, and
the dimensional relationship at the joint between the voice coil bobbin and the free edge may
become abnormal, which may degrade the electroacoustic conversion characteristics. In order to
avoid these disadvantages, there are design restrictions, such as the need to select one having a
shape or material that does not cause thermal deformation. Furthermore, when the heat diffusion
layer is formed, the metal structure of the diaphragm substrate becomes nonuniform, and the
nonuniformity of the physical characteristics of the entire diaphragm is also caused, which
causes a problem that 1 quality is unstable. On the other hand, there has also been proposed a
speaker diaphragm in which a boron carbide (B, C) layer is formed on one side or both sides of a
titanium foil using a chemical vapor deposition method or an electron beam method (Japanese
Patent Publication No. 53-45136) No. 2). However, in the above diaphragm. Low adhesion
between titanium foil and boron carbide layer. The applicant himself points out that there is a
problem that the boron carbide layer is easily peeled off and the durability is inferior (see
Japanese Patent Publication No. 56-33919). An object of the present invention is to solve the
problems existing in the prior art and to provide a diaphragm for an electroacoustic transducer
which is stable in quality, light in weight, high in elastic modulus and high in rigidity.
[Means for Solving the Problems] In order to solve the problems existing in the above-mentioned
prior art. In the present invention, the diaphragm is formed of nitride-based ceramics. We
adopted the technical means of In the present invention, the thickness of the diaphragm can be
appropriately selected according to the characteristics of the electroacoustic transducer to be
used, but if the thickness is less than 30 μm, the improvement effect of the high-pitched band
expansion can not be expected. A thickness of 以上 μm or more is required. On the other hand,
when the thickness of the diaphragm exceeds 500 μm, the weight of the diaphragm increases.
This is disadvantageous because the followability of the vibration is significantly reduced and the
acoustic characteristics are significantly impaired. Next, the hardness of the nitride-based
ceramic forming the diaphragm in the present invention is disadvantageous because if it is too
low, the appropriate elastic modulus can not be obtained, while if it is too high, the residual
stress during firing becomes large. This is not preferable because the strength is insufficient, so it
is preferable to set the picker hardness (Hv) to a value of 1000 to 3500. As a means for forming
the diaphragm of the present invention by a ceramic material, a substrate made of, for example,
an organic material, which has been formed in advance corresponding to the shape of the
diaphragm, is hardened with a coagulating material etc. It is possible to use a means for firing
after forming a material of a predetermined thickness by coating or spray spraying. In this case,
since the base made of an organic material is burned off at the time of firing of the ceramic
material, a diaphragm made of the fired ceramic material can be obtained. [Embodiments] FIGS. 1
to 3 are explanatory views showing manufacturing steps of a diaphragm in the embodiments of
the present invention. First, in FIG. 1, 1 is an original model, and 1 is provided with a smooth
outer surface 1a corresponding to the shape and size of the inner surface of the diaphragm to be
manufactured by, for example, gypsum. The outer surface 1a is formed into a dome shape having
a diameter d8 and a dome height h. Next, 2 is a substrate 9 and a thin film sheet made of, for
example, a polyamide resin is formed in close contact with the outer surface 1a of the original
model l. In this case, in order to closely contact the outer surface 1a of the original model 1
without any gap. The vacuum suction from the side of the original model 1 and / or the thin film
sheet constituting the substrate 2 may be heated. After the substrate 2 is formed, for example, a
vinyl acetate resin emulsion as a coagulant is applied to the outer surface 1a by means such as
spraying or brushing, and then it is naturally dried in the air; The substrate 2 is peeled off from
the prototype model l after forming a uniform film (not shown) of a cam. In this case, the shape
of the outer surface 1a of the prototype model l is faithfully copied to the substrate 2
Alternatively, a slight air pressure may be applied between the original model 1 and the substrate
2 for transfer. After peeling the substrate 2, as shown in FIG. 2, for example, AlNi powder and
solvent are mixed with the inner surface 2a. The resulting slurry is sprayed or applied to form a
material 3 having a thickness of about 200 μm.
After evaporation of the solvent, the substrate 2 and the material 3 are both charged into the
heating furnace in a fixed state, and fired at 1700 ° C. in Nz′J atmosphere for 1 hour, the
substrate 2 is burned off and A diaphragm 4 having a predetermined hardness and elastic
modulus can be obtained (see FIG. 3). Next, the flange 4a of the diaphragm 4 is cut out. The
elastic modulus was measured by the vibration lead method. It was 3.50 x 10 'kg /-. Moreover,
the density by a water displacement method is 3.1 g / cff1. The Pickers hardness (Hv) by a
Pickers hardness tester was 1,500. Attach the same edge of polyester fiber cloth coated with an
acrylic resin to the diaphragm 4. A voice coil was connected and incorporated in the magnetic
circuit of a moving coil type drum speaker of ill, to form a dome type sound speaker unit, and a
sound pressure frequency characteristic was measured. As a result, the lower limit frequency (f
o) is about 960 Hz, the upper limit frequency ((H) is about 30.100 Hz, and the distortion rate is
also about. In the vicinity of the high frequency limit frequency, it is recognized that it has an
excellent characteristic of -45 dB with respect to the basic sound pressure. For comparison, when
the same dome-shaped acoustic speaker unit as described above was formed using a diaphragm
made of 20 μm titanium foil and the sound pressure frequency characteristics were measured,
the low frequency limit frequency and the high frequency limit were determined. The frequencies
remained at about 1,260 Hz and about 28.500 Hz, respectively. In the present embodiment, an
example in which AgN is used as a ceramic forming the diaphragm is shown, but other nitride
ceramics such as BN, sialon or 5isNs can be used. In addition, materials other than the one
embodiment can be appropriately selected and used as the original model, the base and the
solidifying material in the process of manufacturing the diaphragm. It goes without saying that
injection molding means can be used as the means for forming the substrate without using an
original model. Furthermore, as the shape of the diaphragm, other than the dome shape, a cone
shape, a flat plate shape, and other shapes can be appropriately selected. Since the present
invention is configured and operated as described above, it is light in weight, high in elastic
modulus and high in rigidity. Since the quality is stable and the high frequency band limit
frequency is high, there is an effect that an electro-acoustic transducer having a wide sound
pressure reproduction range and an excellent characteristic can be realized.
Brief description of the drawings
1 to 3 are explanatory views showing the manufacturing process of the diaphragm in each of the
embodiments of the present invention.
2: base body, 3: material, 4; diaphragm. 芥 1 concave second eye third figure 21 stem snail, 5:
material, 乙, ° 碌 fishing defense
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