From the glossary:
Electrostatic headphones - "Stats" for short. Use an electrically conductive membrane clamped a short distance between two metal grills. They require special balanced amplifiers that output very high voltages, but can produce a very accurate sound with a lot of detail. The membranes are basically capacitive plates which move based on the varying voltage (i.e. the audio signal) applied to them. Most commonly manufacturered by Stax in Japan, but other well known models were made by Koss and Sennheiser in the past. Most of the discussion of these can be found in the High End Audio forum, specifically the Stax Thread (New).
essentially, they are headphones that use a different method than the usual dynamic-style drivers that are in your Senn's, and that are most commonly used in most headphones today. Another alternative is orthodynamic / planar-magnetic.
I don't think you would ever use a stat amp with a non-stat headphone, but I don't actually know if it would work or not, but I doubt it.
On the topic of Balanced:
Balanced amplifier - An amplifier that has both non-inverting and inverting output circuitry in each channel. A fully balanced stereo (2 channel) device will contain 4 separate analogue amplification circuits: Left and Right Inverting and Non-Inverting amplifing chains. Some balanced-output equipment use a single ended circuit per channel which outputs into a balancing transformer, to create the balanced signal. See also "Balanced Audio". (needs disambiguation)
For a basic, visual guide to balanced amps, see HeadRoom's Balanced Drive Article Series.
For the technical discussion of what a balanced amp is, see "Why Balanced Headphone Amps?"
Balanced audio is a method of interconnecting audio equipment using impedance-balanced lines [The impedance of each conductor plus (+) and minus (-) is the same referenced to chassis ground.] This type of connection is very important in sound recording and production because it allows for the use of long cables while reducing susceptibility to external noise. Balanced connections use three-conductor connectors, usually the XLR or TRS connector. The three conductors are Plus (+) i.e. Non-Inverting, Minus (-) i.e. Inverting , and ground/common/shield. XLR connectors, for instance, are usually used with microphones because of their durable construction, while TRS jack plugs are usually used for mixer inputs and outputs because of their smaller profile. A Non-Inverting signal may be described as: when a positive acoustic pressure wave strikes a microphone diaphragm, the (+) terminal on that microphone capsule will see a positive going waveform, and if carried through the entire audio reproduction chain, that same positive going amplified signal when applied to the (+) terminal of the speaker of headphone driver will cause the diaphragm to move toward the listener, recreating that same positive acoustic pressure wave to be produced.
An Inverting signal may be described as: when a positive acoustic pressure wave becomes negative going waveform in the audio reproduction, usually caused by passing through an inverting amplifier.
Edited by thievesarmy - 6/3/14 at 11:18pm
Balanced headphones - Headphones that are terminated with a 4-pin XLR or 2x3-pin XLR plugs to use with a balanced amplifier. The term is a misnomer as headphones are balanced (electrically with both a + and - but no ground) by definition, along with their cable, but are typically terminated with a "single-ended" TRS plug where the signal return wires for the left and right channels are joined together.