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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
diaphragm material for a speaker having excellent acoustic characteristics.
2. Description of the Related Art The acoustic characteristics of an electroacoustic transducer
represented by an electrodynamic speaker mainly depend on the physical characteristics of a
vibration system. Above all, the diaphragm is an important member that greatly affects the
performance of the speaker.
For example, as shown in FIG. 1, the diaphragm 10 is formed in a cone shape, and the periphery
of the edge 11 is fixed to the speaker frame 20 by a gasket 21. A center cap 30 is disposed at the
center of the inside of the diaphragm 10, and a voice coil 32 is wound around the coil bobbin 31.
A magnetic circuit is formed by the center pole 41, the yoke 42, the magnet 43 and the plate 44,
which are internally mounted on the coil bobbin 31, and the voice coil 32 is movable in the
middle of the magnetic circuit, that is, between the center pole 41 and the plate 44. Place on In
addition, the code | symbol 12 shows a damper.
The following characteristics are required for the materials used as the diaphragm 10 and the
center cap 30 incorporated in the speaker. Low density ρ to improve efficiency. In order to
widen the regeneration zone, the specific elastic modulus E / ρ is large. Having a moderate
internal loss to damp resonance and flatten sound pressure frequency characteristics.
In order to meet these requirements, polymer foam sheets of olefin type or polyurethane type are
used as diaphragm materials for mid-range tweeters, in particular. The polymer foam sheet such
as an olefin type or polyurethane type has the advantages of being lightweight and having a high
internal loss. However, these polymer foam sheets have very poor light resistance, and have a
drawback of being deteriorated by ultraviolet light in a short time. Therefore, in order to use as a
diaphragm material for car speakers, the reliability is insufficient.
The present invention was devised to solve such problems, and by using a fluorocarbon resin
foam as a diaphragm material, a speaker having excellent lightness, heat resistance, light
resistance and high internal loss It aims at providing a diaphragm for this.
A fluorine resin is a typical material having excellent heat resistance and chemical resistance.
Recently, a fluorine-based foam obtained by foaming the fluorine resin is used as a polishing
cloth, a sealing material, a heat insulating material or the like for ultra-precision polishing.
As shown in FIG. 2, the foamed fluororesin has a foamed structure in which extremely fine cells
are uniformly dispersed. In addition, the foam has physical properties as shown in Table 1 and
hardly deteriorates even after a 1000 hour Sunshine Weather Meter test. On the other hand, an
olefin-based sheet such as polypropylene completely degrades in 100 to 200 hours in the same
sunshine weather meter test.
Focusing on such physical properties, the inventors examined the possibility of using the
fluorocarbon resin foam as a diaphragm for a speaker. And when the characteristic requested |
required as a diaphragm for speakers was investigated, it was as showing in Table 2.
In the present invention, by using the fluorocarbon resin foam having such excellent properties
as a main material, coloring, distortion and the like are small, so that natural voices and musical
tones can be reproduced naturally and the durability is excellent A speaker diaphragm is
EXAMPLE As a diaphragm 10 and a center cap 30 of a speaker having the structure shown in
FIG. 1, a fluorine resin foam ETFE having a thickness of 0.5 mm and a closed cell rate of 94% is
stretched, and a distance of 1 m from the speaker The microphone was placed apart, and the
frequency characteristic was examined under the condition of a voltage of 2 V in which the
impedance of the speaker was set to 4 Ω.
As a result, as shown in FIG. 3, it was found that the frequency range of 1000 to 2000 Hz had
frequency characteristics in which the sound pressure changed smoothly.
On the other hand, when the frequency characteristics of the speaker using paper as a
diaphragm were examined under the same conditions, the frequency-sound pressure curve
shown in FIG. 4 was obtained. In this case, a large number of asperities can be seen in the
frequency-sound pressure curve.
As apparent from the comparison of FIGS. 3 and 4, in the speaker using the fluorocarbon resin
foam as the diaphragm material, the internal loss is large due to the foam structure, and
therefore, the frequency-sound pressure curve has few irregularities. It can be seen that the
reproduced sound can be obtained at a stable volume.
In addition, the durability and heat resistance possessed by the fluorocarbon resin are also
utilized, even in the use atmosphere that is exposed to direct sunlight and cyclic temperature
change particularly found in automobile mounting etc., and excellent frequency-sound pressure
characteristics are maintained for a long time It was done.
As described above, in the present invention, by using the fluorocarbon resin foam as a
diaphragm material, the frequency, which is excellent in durability, durability, chemical
resistance, etc., is stable over a long period of time -A lightweight speaker with sound pressure
characteristics is obtained.
In addition, the frequency-sound pressure characteristics of the fluorocarbon resin foam are less
uneven, and it is possible to reproduce a clean sound quality.
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