using the microfibrilated pulp in a pasty state with the canadian standard freeness of not more than 300 ml manufactured and sole by daisel kagaku kogyo kk under the trade name of mfc a liquid pulp dispersion having a concentration of 0 2 was prepared and the operation of suction and deposition on the surface of the paper diaphragm sample was performed in this liquid pulp dispersion to produce an acoustic diaphragm 0 5 g of the above pulp was deposited on the above mentioned paper diaphragm substrate sample weighing 2 0 g a paper diaphragm substrate sample having the same composition as that shown in the preceding examples but weighing 3 0 g was prepared and directly used as comparative example 30 wt of the highly beaten kraft pulp employed in example 1 were added to the composition of the paper diaphragm substrate sample of the preceding examples and a paper diaphragm sample weighing 3 0 g was prepared by using the paper making technique 30 wt of the microfibrilated cellulose manufactured and sold by daisel kagaku kogyo kk under the trade name of mfc employed in example 2 was added to the composition of the paper diaphragm substrate sample employed in the preceding examples to try to prepare a paper diaphragm by the paper making technique however it was impossible to produce the diaphragm because of extremely poor freeness a.