| 摘要 |
PURPOSE:To prevent an edge from cracking by providing the number of necessary slits with fine length on parts except for a member to stick a core material to a skin material toward the center in the diameter direction from the outer peripheral part of the skin material of the surface to which an edge is stuck. CONSTITUTION:A lower skin material 3 is stuck to one surface of the core member 2 with a honycomb structure, and an upper skin material 11 is stuck to the other surface, thereby constituting a plane diaphragm. Slits with fine length are appropriately provided on the outer peripheral part of the skin material on the surface side on which the edge is stuck toward the center in the diameter direction. The slits 4 are provided on parts except for the member to stick the upper skin material 1 to the core material 2. It is prevented that the outer peripheral part of the skin material becomes a knife edge, or that the edge made of paper or urethane develops cracks.
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