Electrostatic Loudspeakers: Principles

An electrostatic loudspeaker (ESL) stands apart from conventional dynamic and ribbon loudspeakers due to its distinctive operating principle. While dynamic and ribbon drivers rely on electromagnetic interactions, ESLs operate based on electrostatic interaction.


An ESL features a thin, flat diaphragm suspended between two electrically conductive grids. In Final electrostatic loudspeakers, the grids are not made from sheet metal, but a synthetic material with a conductive layer. The diaphragm is a thin Teonex PEN film where most diaphragms are typically made of a standard polyester film. Teonex has exceptional mechanical properties and is also durable. The two grids, known as stators, are perforated and they carry the audio signal and are electrically insulated to prevent current flow to the diaphragm and, of course, the user.


The diaphragm is charged to a high DC potential (several kilovolts) relative to the stators using an external high-voltage supply. Final is using custom designed transformers, generating the high voltage. The stators are driven by the audio signal, with the front and rear stators moving in antiphase. As the audio signal varies, the electrical charge on the stators changes, causing the diaphragm to move back and forth and as the diaphragm moves, it drives the air on either side, producing sound waves, thus producing sound in your listening environment. So, the varying charge on the stators creates a uniform electrostatic field between them. This field exerts a force on the charged diaphragm, resulting in its movement.


Imagine an electrostatic loudspeaker with only one grid. A single grid would cause unacceptable harmonic distortion, but using grids on both sides minimizes this effect. The voltage-dependent non-linearity is cancelled out resulting in a near-complete absence of harmonic distortion.


Final ESLs exhibit minimal harmonic distortion, making them ideal for audiophiles. Their lightweight diaphragm responds swiftly, delivering clear and very detailed sound and also very neutral. The sound is very fast, meaning when a percussive sound stops, the driver also stops moving. ESLs also offer broad sound dispersion due to their planar design. Especially in Final designs, the famous and annoying sweet spot is gone. ESLs typically have a large surface respective to their size and can project a huge, energetic and impressive soundstage in your room.


ESLs also have some disadvantages. The principles behind an ESL are simple, but building ESLs requires precision and careful assembly. Smaller panels have a limited bass response. Smaller electrostatic loudspeakers are mostly hybrids, using a dynamic woofer for the lower frequencies.