The current invention aims at improving the playability, durability, and spin generation of different playing rackets, as tennis, squash, and badminton rackets. The method to do so is by applying mechanical forces which generate relative motion of the latitudinal strings over the longitudinal strings. This is done in order to create friction that generate depressions in the contact points of the latitudinal strings with the longitudinal strings. These depressions, made by the described method and machine, induce more friction, and generate spin, while increasing the playability and durability during the play.

A device capable of generating superposed shock waves, which is applied in a racket having a racket frame and having a racket string with warp strings and weft strings mutually woven to compose a string bed, and includes: at least one first main body formed as a hard medium, a lateral wall member is convexly formed at one side or two sides thereof, a first string slot having an opening at a top end is formed at an inner side of the lateral wall member or the center of the two lateral wall members, a recess is formed at the bottom end of the first string slot; and at least one soft medium, disposed in the first string slot and allowing the racket string to be fastened. As such, the shock wave can be returned for being backwardly transferred to increase the striking force for a ball member.