PURPOSE: To flatten frequency characteristics by increasing a high-frequency-range crossover oscillation frequency by improving mechanical strength and surface hardness, by forming an electroacoustic transducer diaphragm by using nitrided "Siras sand".

CONSTITUTION: A diaphragm is made of nitrided "Siras sand" (SiN.Al2O3). To form the diaphragm, "Siras sand" and 30∼40% Al powder are mixed together and heated in an N atmosphere at about 1,400°C and the product is put in a diaphragm metallic mold of graphite for hot press at about 1,700°C. In this process, Si incorporated in the "Siras sand" reacts upon N to produce SiN and the Al powder, on the other hand, is oxidized into Al2O3 to produce a solid solution of silicon nitride at a high temperature. The diaphragm made of nitrided "Siras sand" is less in bulk specific gravity than titanium and superior in mechanical strength, surface hardness, etc., and in speaker operation, piston motion is enabled up to a high frequency range to increase the high-frequency-range crossover frequency, thereby flattening frequency characteristics in the audio frequency range.