Stators are defined as the non-moving part, which in PM headphones is the magnets. They are permanent magnets and not energized by the amp. The amp drives the circuit (conductive traces on the diaphragm), not the stators. The improved efficiency probably arrises for a number of reasons (circuit, magnet spacing, diaphragm weight), and likely not just a single parameter.
5/19/14 at 5:26am