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Technology: Electrostatic Principles
The underlying theory of electrostatic speakers couldn't be more simple. The laws of physics
teach that "like" electrical charges repel one-another and "unlike"
electrical charges attract one-another. Using this principle, let's construct a conceptual
electrostatic speaker. First, let's stretch a thin plastic membrane on a rigid frame. Then, let's
coat it with a low-mass electrically-conductive substance. Next, we fabricate two stiff, flat
electrodes, called the stators. They are insulated to prevent electrical discharge.
We give each stator the same area as the membrane and place one on either side of it. The membrane
is placed exactly equidistant between the two stators.
Finally, the stators must have holes in them to permit sound to pass
through. We now have a primitive electrostatic speaker.
To make our simple electrostatic speaker work, a dense population of electrons is forced onto the
membrane using a power supply. The audio signal voltage from the amplifier is connected to the two
stators, but in a special manner: the signal applied to each stator is identical with the exception
of phase, one signal is 180 degrees out of phase with the other. Thus, as the signal voltage on one
stator increases positively, it attracts the negative electron charge on the
membrane. The signal voltage on the other stator is increasing negatively and,
hence, repels the charge on the membrane. Thus, a "push-pull" force is exerted on the
membrane. When the audio signal reverses, the push-pull force also reverses. Since the membrane is
compliant, the push-pull electrostatic force applied to it causes it to move. Thus, air is moved and
sound is created in the image of the electrical driving force.
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