Acoustical frictional resistance construction and apparatus for manufacturing an acoustical resistance and an associated magnetic system

摘要

An acoustical frictional resistance for electroacoustical transducers, comprises a blank sheet having a first plurality of impressions on its one surface which partially extends into the sheet and having an opposite surface with a second plurality of impressions which extend partially into the opposite surface and meet the first plurality of impressions. The first and second impressions are made so that they partially overlap and define acoustical passages through the sheet at the overlapping areas. The resistances are advantageously made of a thermoplastic material and they may be incorporated in a magnetic system, preferably by molding them integrally with an encapsulation of a magnet and its associated pot and by simultaneously forming passages in which the frictional resistances are placed. An apparatus for forming the individual resistances advantageously includes two separable mold parts defining a cavity therebetween into which the blank material may be placed or may be fed in the form of a plasticized material and which includes a punch and a counterpunch arranged in opposition and mounted for relative rotation about a concentric circle so that they may engage into the blank from respective opposite sides which are offset by amounts to form overlapped areas which are impressed deep enough so that they communicate from one side to the other and form acoustical resistance passages.