| 摘要 |
PURPOSE:To quicken the rise of sound for speaker and to obtain sound with good separation, by forming crystalline alumina layer on a base made of aluminum or aluminum alloy as a vibration diaphragm. CONSTITUTION:A crystalline alumina layer 2 having 0.5-20mum thickness is coated to a projection side of an aluminum base plate 1 having dome shape projection of 20-100mum thick to form a vibration diaphragm. Two stages of anodic oxidation is preferable to form the alumina layer 2. That is, an aluminum material >=98% high purity is used, and this is formed into dome shape and amorphous alumina layer is at first formed with a conventional alumite film forming method. Thereafter, this is immersed in an electrolyte including 1.5-2.5M/l Na2CO3 at 30-50 deg.C, and anodic oxidation is made with a high current density of 10-50A/dm<2> which causes plasma discharge on the surface. Thus, conventional amorphous alumina layer is changed into crystal alumina layer to achieve excellent alpha and gamma alumina layer. |
