was prepared by the method similar to that described in example 1 but instead a block copolymer was used consisting of poly tetramethyleneoxide glycol having a molecular weight of 1000 as the soft segment and polytetramethyleneterephthalate as the hard segment said copolymer having the mole ratio of terephthalic acid part poly tetramethyleneoxide glycol 10 1 elasticity modulus of this block copolymer film was 1200 kg cm 2 and inner loss was 0 17 the adhesion strengths between diaphragm and voice coil and between diaphragm and frame of the diaphragms obtained in examples 1 and 2 were excellent and no troubles were observed in actual use additionally according to weathering evaluation test conducted by using a weatherometer if an ultraviolet absorber is added to the present diaphragm a durability 1 5 times longer than that of a diaphragm without the untraviolet absorber is attained furthermore no changes in the acoustic characteristics were observed in the diaphragm containing the ultraviolet absorber after the weathering evaluation test in the accompanying figure curves a and b indicate the acoustic pressure frequency characteristics of the speakers respectively made of the diaphragms prepared and shaped from the block copolymer film obtained in examples 1 and 2 curve c indicates the acoustic pressure frequency.