The present invention provides a planar acoustic transducer including a vibrating diaphragm (114) including a spiral voice coil (118) provided on both surfaces or one surface of an insulating base film (116); and a permanent magnet corresponding to the voice coil (118), wherein at least a portion of the vibrating diaphragm (114), which portion corresponds to the loop of a first or second vibration mode, is reinforced with a rigidity imparting member (138, 140). The rigidity imparting member may take the form of island-like patterns (138) which act to reduce material strain and hence reduce the likelihood of wire breakage in the voice coil (118).