PURPOSE: To expand reproduced frequency band, to increase transient performance and to reduce strain, by using a titanium alloy having greater specific elastic modulus and high oscillation attenuating function.

CONSTITUTION: Molybdenum is an element most effective to increase the oscillation attenuating function, and a diaphragm 1 is made of an alloy where it is 11∼16wt% of molybdenum or a part of the molybdenum is replaced with one or more kind of ≤1/2wt% chromium, vanadium, and zirconium, residual titanium and associatd impurity. Machining distortion is given by forging or rolling to form a machining derivative martensite structure with excellent oscillation attenuating function for the titanium alloy. The oscillation attenuating function is twice or more than that of titanium-6% aluminum-4% vandaium on market, and the function can be increased remarkably by 3∼5 times through the presence of cold rolling.