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SBESL Self-Biased
ElectroStatic Loudspeaker

The first electrostatic super tweeter
up to 40KHZ flat response
Full passive design without need of external bias

Introduction: The magic of electrostatics.

There’s something undeniably fascinating about electrostatics. Their ability to resolve inner detail, to reproduce music with immediacy, transparency, and focus is unparalleled. There is what has been described from the days of the Quad 57, and through the KLH Model Nine, to present day designs an unmistakable quality about them that transports the listener into the intimate environment in which a live musical event is taking place, emotionally connecting that listener through pristine clarity to music, creating an experience that seems to transcend hi-fi. They do this by using an almost massless thin film membrane to create sound. They move air differently— static charges, not magnets and voice coils excite the air. They are free of the stored energy and coloration of a cabinet. And they have long been regarded as the Holy Grail, and what they do sonically as magic.

But they’re not for everyone.

Many have found the cumbersome requirement for an external source of polarizing voltage—the need to plug them into an AC mains receptacle, or to use an external energizer to accomplish this—to be more than they can handle. There have been issues of durability and reliability or of being affected by humidity, or of attracting dust, which are generally regarded as unfortunate byproducts of how electrostatic loudspeakers work.

Moving air and creating sound.

Audio transducers—loudspeakers—face the greatest challenge in the sound reproduction sequence. Confronted by signals of extreme complexity their task is to convert these wave-forms from electrical to mechanical energy, then to an acoustical analogue of the original signal, which is a very difficult task. Dynamic loudspeakers use electromagnetic attraction and repulsion to generate the mechanical energy to move a cone pistonically—to compress and rarefy air, and in the process to create sound waves. This mechanical energy is the result of current (the audio signal) flowing through a voice coil of either aluminum or copper to create an electromagnet which interacts with the magnetic field of the speaker’s permanent magnet. A cone attached to the voice coil is then forced to move back and forth like a piston in relation to the varying audio signal. The entire motor assembly, consisting of voice coil, voice coil former, cone, and spider, has a considerable amount of mass, thus affecting the speed at which it can respond to audio signals, particularly impulses.

How electrostatics do it.

Rather than moving air by using electromagnetic attraction and repulsion, and a relatively heavy assembly, electrostatic loudspeakers use an incredibly light film membrane suspended in an electrostatic field to generate sound. This membrane, thinner than a human hair, has a constant charge applied to its conductive coating; and when an audio signal is applied to metal stators placed on either side of the membrane, it is excited by electrostatic attraction and repulsion to move air and create sound. The lightweight membrane results in instantaneous transient response, excellent frequency extension; and since these elements are usually in a free air, box-less configuration, stored energy from a cabinet enclosure is eliminated, distortion is reduced by an order of magnitude, and the resulting sound has a remarkable transparency and focus to it.

Electrostatic vs. dynamic drivers.

Electrostatic dynamic
Driving force Charge coupled electric (Coulomb) Magnetic (Gauss)
Moving element Extremely light, virtually weightless film membrane. Weighs less than the air around it. Much heavier cone or dome
Motor assembly Biased diaphragm plus stators Voice coil, voice coil former, cone, and spider
Linearity of drive Perfectly linear push-pull action across the entire diaphragm. Nonlinear. Varies with position of coil, and variations in magnetic field across the gap.
Stored energy and resonances None. The film is microscopically thin and has essentially nothing to resonate. Or it is of such small magnitude that the surrounding air would damp it, since air is much heavier than the film. Several kinds. Kinetic energy in the piston motion of the coil, spider and cone motion, and vibrations inside the cone and dome materials. Cabinet resonances.

SBESL™ technology.

It’s been over three quarters century since Bell Labs engineers Rice and Kellogg experimented with electrostatic loudspeakers in 1923. However, aside from the somewhat predictable improvements in performance and reliability resulting from newly developed materials and modern electronics, there have been few advancements in overall architecture since those early days. This generally is the result of the rigid carry-forward of technology from decades past. That, in short, has been the case up to the present.

In electrostatic designs the bias voltage required to charge the element is high; therefore this voltage must typically be derived from an external source, such as the AC mains or an energizer. There are then additional wires and connections for the consumer to deal with in his set-up–beyond those of the speaker cables. It is here that ENIGMAcoustics has made a major contribution—one that is significant and arguably ground-breaking. Over the course of an intense development period, the company designed and perfected a proprietary self-biasing technology called SBESL™ in which the polarizing voltages for the electrostatic elements are derived from the audio signal itself. This of course eliminates the need for an external source of bias voltage, and the cumbersome requirement for additional wiring in the set-up. So electrostatic performance can be realized in all its sonic glory without the hassle of one of the roadblocks for many consumers.

In this rather radical departure from the approaches of the past, SBESL™ technology is a clear example of applying new thinking to older concepts. The goal was to find a way to permanently implant charges on a non-conductive film without the need for a conductive coating and a huge bias voltage. ENIGMAcoustics’ engineers took on the task of replacing the electrostatic diaphragm with a permanently charged film—in this case based on a unique molecular structure—and turned it into reality. The result is the complete elimination of the costly and power hungry active bias circuitry and the need for extra system wiring; and as a result SBESL™ technology was born.

SBESL™ vs. standard electrostatic design.

In summary, here is a comparison between conventional electrostatic design properties, and those of the newly developed SBESL™ driver:

SBESL™ Standard Electrostatic
Diaphragm conductivity Extremely light, virtually weightless film membrane. Weighs less than the air around it. Much heavier cone or dome
Linearity of drive None Several hundred kΩ
Bias consumption None Tens of Watts>/td>
IM distortion None Variable
Diaphragm external bias None (self-biased) Several kilovolts
Dimensions Small Large

As you can see, ENIGMAcoustics’ SBESL™ technology has advanced the science of electrostatic design.

Irvine, California, USA

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