Electrostatic Theory

Electrostatic theory is basically very simple. It is the same basic theory as magnetism. The law states that like charges will repel, unlike charges will attract. This simple law is the basis for all Electrostatic loudspeakers. Remember when you were young and you rubbed an inflated balloon up and down your jumper ? It could then be placed on a wall and it would stay there. This was due to electrostatic buildup on the balloon being dissimilar to the static charge on the wall. They were attracted to each other and the friction between the balloon and the wall stopped it falling down.

In the case of electrostatic loudspeakers the balloon is a diaphragm inside the speaker. In front of and behind the diaphragm are fixed stators. The diaphragm is charged to a high voltage and the audio signal is applied to the stators. The reason that two stators are used is to reduce distortion - the speaker is designed such that the front stator 'pulls' the diaphragm and the rear stator 'pushes' the stator - hence push-pull.

At this point it is important to explain that the charge should be static i.e. it should just sit on whatever is being charged up and shouldn't move. The definition of static is, after all, stationary. This is an important concept and will be needed to be understood. The charge should just sit on the diaphragm and not go anywhere or move on the diaphragm.

For a more in depth explanation of ESL theory see the Quad ESL 57 review from the November 1957 edition of HiFi News.

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