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Quad ESL 57, the famoust?
How to build your own ESL system
DIY ESL Kits, Electronics and Parts
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. |
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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.
Advantages of electrostatic loudspeakers include the extremely light weight of the diaphragm, and exemplary frequency response (both in amplitude and phase) because the principle of generating force and pressure is not as prone to resonances as in the operating principle of the more common electrodynamic driver.
Musical transparency can be better than in electrodynamic speakers because the radiating surface is much lighter mass than most other drivers and so more responsive to the applied signal.
Disadvantages include a lack of bass response (due to phase cancellation from a lack of enclosure, and the difficult physical requirement to reproduce low frequencies with a vibrating taut film with little excursion amplitude), and sensitivity to ambient humidity levels. While bass is lacking quantitatively, it can be of better quality ('tighter' and without 'booming') than that of electrodynamic (cone) systems. Phase cancellation can be somewhat compensated for by electronic equalization (a so-called shelving circuit that boosts the region inside the audio band where the generated sound pressure drops because of phase cancellation).
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| Speaker Setup |
1. Dipole speakers like breathing room behind them. Use as
much space as you can afford. If the speakers must be placed directly against
the back wall (the worst possible condition for a dipole device) life doesn't
end. Simply toe-in the speakers to reduce direct reflections from the back
wall. The toe-in angle can be large, on the order of 30 to 40 degrees. Use as
large an angle as necessary.
2. Room modes "generally" cause a low-frequency
"suck-out" in the geometric center of the room. This is
"generally" no the best place to put your couch. I say generally
because some rooms like to make me appear incompetent by not following my
rules-of-thumb. Just use this advice as a starting point.
3. Low-frequency energy seems to socialize near walls.
Therefore, if you wish to increase bass frequency energy, put your couch near a
wall. By judiciously placing the couch, you can get the best spectral balance
that pleases you the most.
4. Side-wall placing is not particularly critical with this
speakers. This is because an energy null exists at the sides of the speakers
and little energy reaches the side walls. The exception is low-frequency
energy, which goes everywhere with careless abandon. Acoustical devices to
control "lows" must be huge to really effective, since the
wavelengths are so long. From long, hard experience in trying to induce bass
energy to go where I want it I have found it less frustrating to go where it is
camping by moving either the couch or the speakers (or both in some cases).
5. As a starting point, set the speakers about 3 feet from the
back wall and toe them in such that if imaginary perpendicular lines were to
extend from the center of each speaker, they would cross at your head position
as you sit at your favorite listening spot. Initially, place your couch about
12 to 16 feet from the speakers. Separate the speakers approximately 8 feet
apart, center-to-center. The closer you sit to the speakers, room influence on
the sound is less.
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| Bron:
Soundlab-Speakers.com |
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Electrostatic Loudspeaker