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Product Review - Electrostatic Research Vista by Sunrise Audio - June, 1996

By John E. Johnson, Jr.

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Sunrise ESL

Electrostatic Research Vista by Sunrise Audio; Hybrid electrostatic speaker; electrostatic panel area 864 square inches; one 10" cone woofer in bass reflex enclosure at bottom of panel; Crossover frequency 200 Hz, second order; Frequency response 42 Hz - 24 kHz; Sensitivity 85 dB/w/m; Size 60"H x 19"W x 15"D; Weight 90 pounds each; $3,695/pair in black or white enamel finish; Sunrise Audio, P.O. Box 1486, Newport Beach, California 92663; Phone 714-825-1196; Fax 714-825-1198.

Electrostatic speakers are not a new concept. Actually the original design of electrostatic panels dates back into the late 1800s. I remember when I first listened to electrostatics in the mid-1960s, and they just blew me away with their transparency. They consist of a thin plastic film called the diaphragm (in the case of the Vistas, 1 mil Mylar) that is suspended between two perforated metal sheets called stators. The output of the amplifier is not connected directly to the electrostatic panel itself, but rather, the audio signal first passes through a speaker transformer. The output of the transformer is a representation of the audio signal, but at a much higher voltage (up to 10,000 volts) than the original voltage from the amplifier (40 volts). It is thus a step-up transformer, necessary to generate enough voltage for the speakers to work. Each output wire from the secondary winding of this transformer is connected to one of the stators. A negative DC bias voltage (2,000 volts) is attached to the diaphragm, with the positive end connected to the center tap on the speaker transformer (see diagram). The diaphragm membrane has graphite powder embedded into both surfaces to make it conduct the static charge over the entire membrane. When the audio signal is applied, the stators vary in voltage as an AC signal, making the front and back stators alternating as positive and negative, and varying in voltage strength with the intensity of the signal (the "volume"). The diaphragm, being negatively charged, is attracted to the positive stator and repelled by the negative one, back and forth, in time with the audio signal (the music). Therefore, the sound is produced by the membrane moving back and forth as a sheet (rather than a cone in a typical speaker). The sound emerges from the perforations in the stators, and the electrostatic panel is, thus, visually transparent. The electrostatic speaker is considered a dipole, because sound comes out the back as well as the front, and the air is moving out of phase, with respect to front and back (when air is moving out of the front, it is moving into the back, and vise versa). Dipolar speakers, whether they be cone speakers [click HERE to see motion of dipolar speaker drivers], or electrostatic panels, have cancellation of much of the signal at the sides. If you stand at the side of one of the Vistas, the sound seems to be coming from everywhere except the speaker. Also, they must be carefully placed in the listening room, since half the signal comes out the back, and its perception depends on what is behind the speaker. Electrostatic speakers do not produce much air movement at low frequencies, so most of them have a cone woofer to handle the low end.

The Sunrise Audio Vistas are a relatively new model. They are 60" high, 19" wide, with the electrostatic panel being about 45" of this, and the woofer (10" cone) in a ported enclosure at the bottom 15". The front stator is continuous from top to bottom, so the woofer plays through the perforated metal sheet, as does the diaphragm. This gives the speaker a uniform appearance which is quite attractive (see photo). The woofer enclosure is attached to the panel, stabilizing the entire speaker so that it won't tip over. Two sets of binding posts (for bi-wiring if you wish), as well as the 3" port and on/off power switch (for the bias power supply) are on the rear of the woofer enclosure. Three wires must be attached to the panel during assembly: two go to the stators and one to the diaphragm.

Electrostatic speakers are famous for their transparent sound characteristics, and notorious for their idiosyncrasies. Because the Vistas crossover at 200 Hz, a frequency to which the human ear is relatively sensitive, I expected that there would be a discernible "seam" in this region, and a chestiness to the human voice because of the large woofer driver in an enclosure that appears to be only modestly damped. But this was not the case. Voices were extremely natural and seamless. We used Tony Bennett and Enya CDs for this, and although Enya's voice may not have much in the < 200 Hz region, if the woofer is the slightest bit boomy, female voices will take on that awful chesty sound. It didn't happen. She was right there in the lab, with not even the slightest deep resonance. Vivaldi's Four Seasons left us breathless, and Copland's Fanfare for the Common Man just knocked us out.

Of course it is the mid-range and high end that really show off the electrostatics. They are incredibly transparent, as the entire wall comes to life. Not all electrostatic speakers are equal, however. It really depends on the design. Think about if for a second (or two). Here is this large sheet of thin plastic, attached at the edges, being moved back and forth. Unlike a speaker cone all of which moves the same distance, the center of the electrostatic diaphragm will move more than the edges, where it is attached to the frame. As a result, lots of harmonic distortion can occur, and does in some electrostatic speakers. This manifests itself as a harsh edgy sound at high SPL. Sunrise Audio has circumnavigated this problem by using vertical strips of adhesive about 3 1/2 inches apart, to hold the diaphragm. Thus, five small panels, rather than one big panel, result (see photo). This reduces the harmonic distortion. We used our Carver Silver 9t power amps to drive these speakers, because electrostatics require lots of power. Somewhere around 50 watts rms per channel produced a moderate volume . . . not really loud, but nice for serious listening. So, if you buy these, make sure you have an amplifier that is not easy to lift. The impedance usually varies quite a bit with electrostatics, and unfortunately, down to the low numbers. Besides power then, the amp should be able to handle high current demands. I notice that many audio writers are associated with some sort of quotation. For me, let it be, "There is no substitute for raw power." You will need it for these, or any other big electrostatics for that matter. Of course, the electrostatic speaker transformer has its limits. After a certain point, the transformer "saturates" and additional current from the amplifier will not produce further increases in loudness. The Vista transformer is large enough that the diaphragm will stick to one of the stators before transformer saturation, at which point it will stop working. If this happens, one just backs off the volume a bit, and the speaker will resume functioning (one of the idiosyncrasies we mentioned).

Frequency Response Test Results (These data represent tests in a real room with furniture, not anechoic tests or simulations, and thus, may be somewhat different than you might experience in your own listening room of other dimensions and contents):

Near Field - Left speaker, 1 meter, on axis:

Frequency: 20 Hz 25 Hz 31.5 Hz 40 Hz 50 Hz 63 Hz 80 Hz 100 Hz 125 Hz 160 Hz 200 Hz
dB: 65.2 69.5 75.1 73.7 73.1 90.4 85.7 86.3 81.9 72.3 76.9
Frequency: 500 Hz 800 Hz 1 kHz 2.5 kHz 5 kHz 8 kHz 10 kHz 12.5 kHz 15 kHz 18 kHz
dB: 77.8 82.9 79.3 78.1 65.5 73.8 75.0 78.9 75.1 68.6


Far Field - Left speaker, 12 feet, on axis:

Frequency: 20 Hz 25 Hz 31.5 Hz 40 Hz 50 Hz 63 Hz 80 Hz 100 Hz 125 Hz 160 Hz 200 Hz
dB: 82.3 86.5 93.4 83.2 86.9 96.5 93.4 82.8 84.0 86.4 77.3
Frequency: 500 Hz 800 Hz 1 kHz 2.5 kHz 5 kHz 8 kHz 10 kHz 12.5 kHz 15 kHz 18 kHz
dB: 78.9 88.7 77.1 86.9 81.2 84.1 85.0 80.6 83.8 77.6

For the far field test, we had to run the amp at 50 watts rms to get a reference setting of about 80 dB at 1 kHz. This resulted in the very low frequencies having substantial readings. Such readings were due to audible harmonics rather than true output at, for example, 20 Hz. The upper mid-range became a bit harsh (evidence for some harmonic distortion) when this kind of power was fed to the speaker with single sine waves. The harshness was not audible when playing music, even at 50 watts rms practically continuous input, because the power was spread out over the entire spectrum.

For detail, electrostatics excel beyond what most cone speakers can even dream about. We tested the Vistas with steel string guitar music, and wow, what a sound! The attack of a guitar requires good transient response (meaning "fast"). Twang is a word that applies here. If there is significant harmonic distortion, your ears will suddenly ask for fingers. Not the case with the Vistas. The Twang sang, and our eyes closed, with nary a tear or a gritted tooth, even when the power meters on the 9ts crept upward. With many speakers, some reviewers say that the model under examination is best with rock or best with classical. The Vistas are great with everything! We liked them about 4 feet out from the wall, toed in at 15 degrees, 8 feet apart. Not much falloff when we moved away from the on axis position. This is another one of the electrostatic idiosyncrasies we mentioned . . . and the Vista design seems to have reduced that problem. It is probably due to the sectioning of the main panel into five smaller panels, each of which is directed at a slightly different angle. With a single panel electrostatic, the middle area of the membrane will move the most, and it is directed straight out to the front. The edges, which are directed slightly to the right and left, move less because they are near the point of attachment to the frame. With the Vista, each small panel has its own attachments on the sides, and thus, even the outermost panels will move the same amount as the center one. Now keep in mind that you have to like a BIG soundstage, because electrostatics produce just that. You have a 12 foot guitar, because the panels are radiating from a large surface, rather than a small one (such as a 1" dome tweeter). So, they are not for everybody, but they are certainly winners for me. No question, the Vistas are dynamite. And, we noticed a strange phenomenon: the women went nuts over them. They liked the sound of course, but spouses said, "now THOSE, you can put in the living room." It must be the visual transparency that makes them so sexy, I guess. Anyway, if you are having trouble convincing your significant other to let you bring some big speakers home, here is your opportunity. I've already got mine, and she won't let me ever take them away. Life is like that sometimes.

John E. Johnson, Jr.
Editor-in-Chief

Additional Reading:
http://www.york.ac.uk/~mjgw100/esl/eslhowto.htm (How to construct an electrostatic)


Copyright 1995, 1996, 1997 Secrets of Home Theater & High Fidelity
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