Acoustat 2+2 loudspeaker

While I refuse to admit publicly how long I have been sitting on these loudspeakers before doing the report on them, I must say that it is probably a good thing I wasn't in all that of a hurry to get around to it. They did not sound very good in the room where I had initially installed them, and had I written the report on that basis, it would have been lukewarm, to say the least.

I have now had the opportunity to live with the Acoustat 2+2s in my usual listening room, which is more like a typical listening environment (19' by 24' by 9' and moderately padded), and I am more than a little impressed. This is an extremely good speaker, particularly at its price of $2100/pair.

The 2+2 resembles the Model Four in that it contains four of Acoustat's full-range electrostatic panels per side, but differs from it in that two of the panels (per side) are stacked on top of the first pair to produce a radiating surface twice as high and half as wide as that of the Four. The result, particularly in the case of the black-grilled version we tested, bears a startling resemblance to the mysterious obelisk in 2001, A Space Odyssey. The 2+2 system towers almost to the ceiling (and at just under 8' may be too high for some ceilings), and although it is more graceful in appearance than a pair of Fours, it tends to dominate a listening room at least as much.

The stacked configuration is not, however, for cosmetic purposes; it is to improve the system's vertical dispersion—a major weakness of the Model Four. A line-source radiator, such as a straight row of closely spaced cone drivers or a narrow electrostatic panel, radiates a broad pattern of sound at right angles to the line, but the dispersion angle parallel to the line tends to become increasingly narrow as the length of the line increases. Thus the Model Four, four panels wide but one high, has fairly good (although irregular) dispersion in a horizontal plane but produces a pronounced beam in the vertical plane. This causes the system's spectral balance to change markedly when one goes from being seated to standing.

But an interesting thing happens when a line source extends from the floor all the way to the ceiling: the vertical beaming virtually disappears. With the Acoustat 2+2s, there is hardly any change in sound with changes in listening height. You can be on the floor, the ceiling, or anywhere in between without shooting down the system's high end.

There are other advantages to the 2+2's stacked configuration. Two side-by-side panels, rather than four, reduce by a factor of 8 the amount of interference between them (because each of the four interferes with all three of the others while two interfere only with one another. Selective cancellation at various middle and upper-range frequencies is what gives the Model Four its pronounced Vertical Venetian-Blind effect—the tendency for sounds to ping-pong back and forth from one side to the other as the listener moves horizontally in front of the speakers. It is also what makes the Acoustat Fours so difficult to orient properly, and gives them such a narrow "sweet spot" from which proper imaging is heard.

Another problem frequently encountered with wide electrostatic systems like the Four is excessive excitation of standing-wave resonances in the listening room. Most listening rooms have many resonant modes in the 60&#150Hz range, but with some experimentation, woofers of smallish radiating area can be placed so that they generate relatively little activity from these resonances. But the wider the radiating area, the harder it is to avoid having at least part of that area in a location that sets off the room resonances. This, it turns out, is why the Model Fours tend to sound overly bass-heavy in all but the largest listening rooms, and why the 2+2s are much less prone to the problem.

Sound Quality
In other sonic areas, the Acoustat 2+2s are among the most listenable speaker systems I've heard. Even their low end is better than I am accustomed to hearing from full-range electrostatics, most of which tend to be full but loose at the bottom. The 2+2s still don't have the awesome low-end detail of a large transmission-line system (let alone a very large horn), but their bass is very much in control, it has more detail and impact than most large electrostatics, and it blends seamlessly with the upper ranges (thanks to the lack of a crossover). The high end is typical of electrostatics—open, airy, and incredibly quick in response to hard transients and subtle inner details in complex material.

The 2+2s are not, however, the most ultimately accurate speakers around. Although they will play cleanly at very high listening levels (over 100dB), they are a little lacking in "punch"—what some audiophiles call "dynamics." Loud, full-orchestral passages sound neither as loud nor as exciting as they do from some other systems. Part of the reason for this and (also) for their apparent ease in listening, is due to a somewhat laid-back quality, resulting from what sounds like a broad suckout in the brightness range (2–5kHz).

Acoustat Corp.
Company no longer in existence