How electrostatic loudspeakers work

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How electrostatic loudspeakers work
Of all the speaker types we're going to discuss in these three posts the electrostat is the oddest because it does not employ magnetic fields to move the diaphragm. Instead, it uses static electricity. And electrostat consists of a thin flat diaphragm usually consisting of a plastic sheet coated with a conductive material like graphite sandwiched between two electrically conductive grids—also called stators—with a small air gap between the diaphragm and grids. The grids and diaphragm are charged with high voltage, typically several thousand volts, and when the output of your power amplifier is applied, the center diaphragm is attracted or repulsed from the stators and we hear music. Electrostatic attraction is nothing new to us. Rub your feet on a dry carpet and watch your hair stand on end or a sweater cling to you. And before you think this electrostatic field is a weak novelty for attracting hair and balloons, consider that it is responsible for the attractive force between the atomic nucleus and electrons that holds atoms together, and the forces between atoms that cause chemicals to bond together. This electric field is basically what holds the physical universe together. One thing common to electrostatic loudspeaker designs is the use of extremely high voltage. These kilovolts of energy are connected via a transformer, allowing your amplifier to controls thousands of volts of weak energy. Here is a schematic. Note the step-up transformer on the left of the drawing. Remembering that transformers haven't any physical connection between their input and output, transferring energy by magnetic forces only, the input coil safely connects any size power amplifier to the speaker's high voltage. On the output side of the transformer, a very high voltage is applied, and this is what generates the electric field that eventually moves the speaker's diaphragm and makes music. Electrostats can offer a clarity and transparency to the sound unlike just about any other technology. This is because the moving membrane is so incredibly light that transients pass through with little more than a yawn. First-time listeners to an electrostatic loudspeaker generally describe the experience as listing through an opened window. Though they are quick they are not perfect. Because their diaphragms move so little they require lots of surface area to be efficient and loud. The large surface area causes beaming, which translates in practical terms to a classic phenomenon associated with electrostats known as "head in a vice" syndrome. They are definitely one person speakers. Tomorrow I'll wrap up this mini-series on speakers offering my opinion on the best of all worlds.
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Paul McGowan

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