Isodynamic transducers or magnetostats are often incorrectly termed ribbon drivers. The diaphragm consists of a thin, highly temperature-resistant plastic film onto which wavy aluminium tracks have been applied by metallisation. Strip magnets glued to a perforated pole plate are arranged close to the diaphragm in such a way that the diaphragm and the magnetic field run parallel. Due to the relatively restricted diaphragm excursion, this kind of transducer is only used as a tweeter. The efficiency of a magnetostat is equivalent to that of a dome tweeter. Impedance is at normal levels and no transformer is required. The strength of isodynamic transducers is the significantly lower level of break-up modes and the fact that it is very "fast" and can reproduce transient pulses.