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The present invention relates to a diaphragm for an electroacoustic transducer, and more
particularly to an improvement of the diaphragm made of an alloy containing magnesium
(hereinafter Mg) as a main component. Conventionally, aluminum (At), titanium (Ti), etc. have
been used as diaphragms for medium to high-pitched reproduction speakers such as horn type
speakers and dome type speakers, but these metal diaphragms are heavy and are also internally
Due to the disadvantage of small losses, the loudspeakers using the diaphragm have not obtained
satisfactory results in conversion efficiency and frequency characteristics. As a means to solve
this defect, an alloy of magnesium (Mg) and lithium (Li), which has a relatively small specific
gravity in a metal material, a Mg-Li-Zn alloy, a PJg Li-At alloy, a y-Zr alloy, etc. are devised. It is
done. This focuses on the small density and relatively large internal loss of pigeons and Li
compared to other conventional examples, but the alloy has a large rigidity due to its small
Young's modulus. I can not get a diaphragm. Although Mg-Lt-Zn alloy and 隨 Lt A1 alloy have
been considered to increase the blowout rate of this Mg-Li alloy, the advantage of low density
(about 1.3 to 1.5) is maintained. However, the internal loss is significantly reduced (tan δ:
around 0.008), resulting in deterioration of the frequency characteristics. Also, the rm-zr alloy
has the advantage that the internal diameter (tan δ = 0.2) is large, but the density is large (−175), which is inferior to the above alloy in terms of conversion efficiency. It was difficult to
practically satisfy the conditions of low density, high Young's modulus and large internal loss,
which are required as the diaphragm material, respectively, because each alloy has advantages
and disadvantages. Therefore, the present invention is to provide a diaphragm made of a 1-Li-Zr
alloy mainly composed of one electric charge and li and zircon (Zr), which will be described in
detail below. A mother metal of Zr is introduced into a molten molten metal in a molten steel
crucible in a sulfur hexafluoride gas (SFa gas) atmosphere and melted to form a molten metal of Zr. On the other hand, the Mg-Li molten metal produced in a similar manner is gradually added
to the n--Zr molten metal while stirring in an SFa gas atmosphere, and -e-m is cast in a sand mold
to obtain Mg-Li of diameter 10 crn 1 length 5 crn -A Zr alloy ingot (Li: 12 wt%, Zr: Q, 5 wt%,
other Mg) was obtained. This was forged in SF6 gas at 260 ° C. to 270 ° C., cooled to around
200 ° C., and the process of forging was repeated to form a disc having a thickness of 5 m.
This was subjected to surface grinding, and a disc of 3 mm in thickness was rolled by several
steps at 80 ° to 90 ° to obtain a 50 μm foil. The Mg-Li-Zr alloy foil was temporarily stored in
argon (Ar) gas. Next, it was formed into a dome shape of 25 mm square at a pressure of 4 kf / ctI
in a mold press heated to a lower mold temperature of 120 ° C. and an upper mold 80 C and
stored in Ar gas. Next, the dome-like alloy foil is immersed in an alkaline solution (NaOH, 150 f /
l) at about 40 ° C. for about 30 seconds to adjust the surface, and immersed in an alkaline
chromate bath of pH 7, 6 to 7.8 to be chromate. After processing to form a coating of chromium
compound, it is stored in a desiccator. Next, a 600 angstrom xylene resin film was formed on the
chromium compound film by a vacuum evaporation method, and then an unnecessary portion
was cut to obtain a 25ψ dome dome diaphragm. And the physical property of the said domeshaped diaphragm was measured, and the value of Young's modulus 5.7 * 10''d'fn / 7s density
1.38, tandelta0.045 was obtained. The frequency characteristic of a speaker incorporating the
diaphragm is shown in FIG. In FIG. 1, 1 indicates the characteristics of the diaphragm of the
present invention, 2 indicates the characteristics of an alloy (ASTM: LA-141A) as a comparative
example of 1-Li-p. As apparent from the figure, the diaphragm of the present invention has
significantly reduced unevenness of the frequency characteristics in the high sound reproduction
frequency region as compared with the conventional bead-alloy diaphragm, and it is possible to
reproduce with less distortion. This proves that, as described above, the diaphragm of the present
invention has a large internal loss of the material itself with almost no loss of other
characteristics, and the effect of suppressing harmful resonance is remarkable. This effect also
changes depending on the content ratio of 隨 -ti-zr, but in the experiment of the present
invention, the results are relatively good at values of 11 to 13 wt% of Li content and 0.3 to 0.75
wt% of Zr content I was able to get
Brief description of the drawings
FIG. 1 is a frequency characteristic diagram of a speaker provided with a diaphragm of the
present invention and a conventional diaphragm.
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