Most headphones and speakers use electromagnetic force to drive speaker coils. Electrostatic speakers use electrostatic force to modulate a diaphragm. Mylar is used as the diaphragm in these headphones. Two insulating rings sandwich the mylar and a perforated stator is placed on either side. Ideally these stators would be acoustically transparent, but sheets of metal with 2mm (or smaller) holes that make up at least 25% of the area work. Construction problems can arise from glue not sticking to the mylar and the mylar having not enough or too much tension. A special amp has to be built for the headphones to generate a 450V difference between the stators.