PURPOSE: To increase the specific Young's modulus, improve the frequency characteristics, and enhance the acoustic characteristics, by impregnating a solvent to dissolve acetyl cellulose into a diaphragm formed by sheeting acetylated fibers, and then drying.

CONSTITUTION: A diaphragm formed into a corn type by sheeting the acetylated sheeting raw materials is in state bonded due to interlocking of acetyl cellulose 3 caused by fibrillation due to beating. When a solvent to dissolve acetyl cellulose is impregnated or sprayed to the surface of this diaphragm, the acetyl celluose is dissolved by the solvent, and the interlocked parts 4 are joined together, so that the fibers are bonded with a large bonding force, resulting in a sufficient Young's modulus. By drying this diaphragm, furthermore, the solvent is fled away, so that the specific Young's modulus may be increased without substantially increasing the mass of the diaphragm.