Electrostatic headphones are the undisputed kings of headgear when it comes to sound quality – it is only their price and power consumption which stops everybody wanting them! Some of their mystique can be dispelled by knowing the internal workings, but they’re still going to impress!
They operate on the principal that ‘opposites attract’, although Paula Abdul is not involved here. The technique has a thin membrane of plastic held in place between two electrode plates called ‘stators’. The membrane is coated in a conductive substance which allows a static field to be built upon it, and this in turn reacts with any audio signal which is fed to the stators.
Being statically charged, the membrane is attracted by any positive force held within the stators, and opposed by any negative force within them. Since any similar forces in the stators either side of the membrane will be effectively cancelled out, one of the stators is wired out of phase so that one stator is pulling the membrane whilst the other is pushing it. The effect of this is to double any force acting upon the membrane, much like two sawyers operating each end of a large saw.
This is also happening on the opposite side of the headphones; so along with energy required to build up the static fields on the membranes, more energy is needed to move them.
The combination of ultra-light membrane and powerful moving forces makes for a very accurate sound with great separation; since the membrane is acted on as a whole, it does not bend and this also avoids distortion. Also due to the fact this technology can cover all frequencies well beyond 20kHz, there is no need for the crossovers and multiple drivers which would cause distortion in a dynamic or balanced armature equivalent.