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The present invention relates to an improvement of a diaphragm for an electroacoustic
transducer. Conventionally, an electro-acoustic transducer, for example, a speaker diaphragm is
often used as a pulp paper diaphragm made of paper valve fiber and formed by heating and
pressing, but this type of diaphragm has a small density in view of its characteristics, Also, it has
an advantage that the internal loss (tan δ) is appropriate, but because the sheet yaw rate is
extremely small, the rigidity of the diaphragm is not sufficient and the high frequency
reproduction limit frequency can be increased by entanglement between fibers, in press
conditions, etc. Variations inevitably occur, and it is difficult to provide a diaphragm having
uniform acoustic characteristics. On the other hand, metal diaphragms utilizing high Young's
modulus of metal are also put to practical use, but the conversion efficiency is reduced due to the
large density and the internal loss is extremely small. It is difficult to provide a speaker with such
frequency characteristics and low distortion, and is currently used only for reproduction of a
relatively small frequency band, such as a relatively small tweeter. Furthermore, diaphragms
using a Kinki, thermoplastic resin or thermosetting resin have been devised and put to practical
use. For example, a diaphragm made of polypropylene has the advantages of being relatively
lightweight and having a large internal loss, and being able to be easily molded by vacuum
forming etc after being formed into a film, and providing a large amount and uniform diaphragm.
It has the disadvantage that the high frequency band can not be increased sufficiently because
the stiffness (i.e. the Young's modulus of polypropylene) does not have a satisfactory value. There
is also a diaphragm made of a synthetic resin mixed with graphite powder and Myo flour as a
filler in order to increase the Young's modulus, but the increase in density is larger than the
increase in Young's modulus, and the aforementioned synthetic resin The internal loss of the
Therefore, in the present invention, a diaphragm in which the rigidity is increased without losing
the above advantages of such a thermoplastic resin or thermosetting resin as much as possible,
in which an organic filler is mixed with the thermoplastic resin or thermosetting resin.
Hereinafter, the case of using crystalline cellulose fine powder as an organic filler in
polypropylene will be described as an example. [Example 1] 15 wt% of crystalline cellulose fine
powder (average particle diameter 40, am) 15 wt% was mixed with 85 wt% of polypropylene to
form a bullet, and the pellet was injection-extruded to form a film of 0.5 謹 thickness. Example 2
25 wt% of crystalline cellulose fine powder (average particle diameter 40 μ) was kneaded with
25 wt% of polypropylene to produce a beret, and a film of 0.5 mm thickness was formed in the
same manner as in Example 1.
The film of Examples 1 and 2 was used as a sample of 15 m × 5.5 crn, and the density, Young's
modulus and tan δ were measured and compared with the characteristics of the conventional
diaphragm material to obtain the following table. The diaphragm material according to the
present invention can provide a diaphragm with a large rigidity and a significantly increased
Young's modulus although its density and tan δ are significantly reduced compared to
polypropylene, as is clear from the clothes. The FIG. 1 shows a speaker provided with a
diaphragm (effective vibration radius 23 an) in which a polypropylene film, a film of Example M,
and a film of Example 2 are respectively formed into a cone by vacuum forming. Example 1 is the
film of Example 1, ■ is the film of Example 2 and ■ is the frequency characteristics of a speaker
equipped with a diaphragm made of polypropylene film, which is affected by a slight reduction in
internal loss compared to conventional characteristic ■. There is almost no disturbance of the
frequency characteristic, and the treble reproduction limit frequency can be raised, and the
reproduction frequency band can be expanded. By expanding the reproduction frequency
without deteriorating the frequency characteristics, it becomes easy to apply as a full range type
speaker, and even when used in a multi-way type speaker, the reproduction bandwidth of each
speaker can be taken large, so the speaker The number can be reduced, and furthermore, there is
an advantage that the degree of freedom in designing the crossover frequency of the speaker
serving each band is increased. As described above, the present invention is a diaphragm made of
a thermoplastic or thermosetting resin containing an organic filler mixed therein, which is a
defect of the above-mentioned resin without losing the advantage of the conventional resin as
much as possible. It is possible to increase the Young's modulus, to provide a speaker having a
good frequency characteristic and an expanded reproduction zone, and to increase the internal
loss as compared with the conventional pulp paper, and to obtain a uniform acoustic
characteristic. It is possible to provide a diaphragm having the above, and to have a very
excellent effect in mass productivity. In addition to polypropylene, the above-mentioned resin
applicable to the present invention includes, for example, thermoplastic resins such as
polyethylene, phenolic resins, melamine resins, thermosetting resins such as area resins, etc. Fine
powder of body and sawdust can be applied.
Brief description of the drawings
FIG. 1 shows respective frequency characteristics of a speaker provided with a diaphragm
according to an embodiment of the present invention and a polypropylene diaphragm.
1! Number of castles (Hθ) 牟 11 sides
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