the acoustic diaphragm the diaphragm substrate 5 may also be dome shaped as shown in fig3 instead of being a cone paper as in the above described embodiment in this case a deposited layer 12 of microfibrilated pulp may be deposited on the surface of a flat paper diaphragm substrate under suction effects by using the same technique as described above and the resulting substrate is processed into a desired dome shape with drawing by means of a metal mold having a semispherical recess and a die having a mating projection for preparing an acoustic diaphragm in the above described manner a paper diaphragm substrate was first prepared in accordance with a composition shown in table 1 table 1______________________________________ composition beating degree ml ______________________________________kraft pulp 75 500sulfite pulp 15 540manila hemp 10 600______________________________________ two paper diaphragm samples weighing 2 0 g and 2 5 g and both having a diameter of 12 cm were prepared the kraft pulp employed in the preparation of the paper diaphragm substrate samples was beaten to a canadian standard freeness of 300 ml using a beater to produce a liquid pulp dispersion having a concentration of 0 2 the operation of suction and deposition on the paper diaphragm substrate sample was performed in this liquid pulp dispersion to produce an acoustic diaphragm sample the duration of suction and deposition was one minute the substrate sample employed in the present example was that 2 5 g in weight on this sample 0.