The Electrostatic speaker is based on that two equally polarized charges repel each other while two oposite charges attract each other.

Electrostatic speaker element:


    .....           electrode 1
    :  )---------===-=-=-=-=-=-=-=
    :  ):  ____  #               #
  o--) ): |    | # foil membrane #
Si  :) )--|-Up+|-----------------# frame
  o--) ): |____| #               #
    :  ):        #               #
    :  )---------===-=-=-=-=-=-=-=
    :...:           electrode 2
     T1


The power supply Up is supplying the polarizing voltage(about 5000V). 'Si' is the signal from the driving amplifier, it is transformed up by T1 to a voltage high enough to move the membrane, also the elecrodes will always have an opposite charge. The electrodes are made from a perforated metal plate or a metal mesh. When electrode 1 gets a positive electric field it will push the membrane and the negative field from electrode 2 will pull on the membrane(The charge change according to Si). The moving membrane will make the air vibrate, and thus make sound.

A variation on the electrostatic speaker uses the an electret membrane. This speaker doesn't need a polerizing voltage and is most used in headphones.

Since the electrostatic speaker needs a polerizing voltage, it uses more power than a dynamic speaker. The membrane is relatively large but very light giving these speakers good frequency response at booth low and high frequency. The electret version is cheaper but has a somewhat lower sound quality.

    Advantages
  • Clarity
  • Simple
  • Imaging
  • Low mass speaker element
  • Look really cool

    Disadvantages
  • Power hungry
  • Not good for low range (less than about 250 Hz)
  • Expensive

Cone speakers and electrostatic loudspeakers (ESL) have been around for about the same time, though few people have ever heard of them. Most don't even recognize them as a speaker when they first see them. They are generally considered stylish, as they can be tall and elegant; you can see through the membrane, which causes some disbelief when people put their head up next to them. Others, like Wilson Audio's Wamms, can be downright ugly, but what do they make that isn't? If you ever watch the t.v. show 'Friends', you can see a small set in the living room of one of their apartments.

In 1923 Bell Laboratories had an electrostat that was made of a pigs intestine and coated with gold leaf. Today ESLs are made of mylar membrane that has been aluminized, which is good, because mylar doesn't rot and start to smell after a while. However, the pigs intestine supposedly sounded pretty good. Some other early obstacles to the acceptance of ESLs were that they were prone to arcing (and fire), had poor dispersion properties (since they were flat, unlike today's curved speakers), and there was little interest in consumer audio until the late 1940's. Finally, in 1956, a man by the name of Peter Walker began selling the famous Quad ESL. Many audiophiles prefer the accurate sound of ESLs.

So how expensive are they? Martin-Logan sells speakers ranging from $900 (each) for the Scripts, on up to $75,000 (pair) for the Statement E2's. My SL3's were about $1700 each.

Because of the limited ability for ESLs to reproduce low frequency sound (they could, I think, but they would have to be enormous. The panels on my speakers are already 4 feet tall), most modern ESLs are hybrid, that is, they use an electrostatic panel for the upper ranges (say 250 Hz to 22 kHz), and a tradional cone woofer for frequencies as low as 20 or 30 Hz. So this requires a crossover (which is not really ideal).

Someone could add a list of manufacturers here, or /msg me and I will, as I have only ever see Martin Logans, and though I have seen a list of like fifty makers, I wouldn't know which ones to list as being major.

    so far...
  • Magnepan
  • Thiel
  • Martin Logan
  • Quad

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