Infinity Servo-Statik 1 loudspeaker Page 2
Nonetheless, there is another advantage in using the SS-1 bass speaker: It makes it easier to obtain smooth, extended low end from the system, because bass propagation need never be compromised in order to obtain the optimum imaging and center fill from the panels. These can be placed optimally, and the bass commode can then be located wherever it does the best job. In general, the smaller the room, the more critical is likely to be the location of the bass commode, but considerable experimentation may be required in any room in order to zero in on the best spot. We noticed, for instance, that in our moderately large listening room, the bass commode's response below about 50Hz remained relatively constant regardless of where it was placed, but that the upper range of the woofer was significantly affected by placement.
The problem was not one of an excess of this mid-bass range but a deficiency of it, which impaired the "fullness" of the sound.
This mid-bass weakness (when it occurred) could be easily corrected by means of the bass balance control on the crossover unit, but since this also increased the stuff below 50Hz, the result was a rather sodden, somewhat bottom-heavy balance on any program material that had deep bass in it. Further experimentation with room placements enabled us to find a spot where the entire bass range was subjectively flat, enabling the bass balance control to be run at a lower setting for adequate mid-bass, while still retaining the deep-bass range.
In this particular location in our listening room, oscillator sweeps showed the system's low end to be audibly flat down to a bit below 30Hz, with what we judged to be usable (?!) response down to an astounding 18Hz—by far the deepest bass we have ever heard reproduced. Actually, "heard" is not quite the word for it; one feels 18Hz through the floor and the viscera, and one hears only the rattling of objects in the room that have never been rattled before.
Low-end response like this may seem academic when most commercial recordings these days have their low end rolled off below 40 or 50Hz, but our ears told us that there was a murked improvement in the bass tightness and detail, even from material that didn't plumb the extreme depths. Maybe it's the old story about the 200mph automobile that just "coasts along" at 50mph, or maybe there is actually deeper stuff on most discs than we've been led to believe. After all, discs are rolled off, not cut off, so a loudspeaker that doesn't add its own rolloff will naturally reproduce more of the energy below the rolloff point than one that does (footnote 1).
We mention this business about the bass commode's placement because, until this is placed for smooth low end, it is almost impossible to adjust the SS-1 system for what sounds like good bass balance on most program material. If one part of the bass range is depressed below another, some recordings will seem to have too much bass and others not enough, and one will be forever readjusting the bass-balance control as though it is a tone control, and no recording will yield really smooth low end.
The same thing applies, although to a lesser extent, to the placement of the electrostatic panels. As Infinity points out in their (rather skimpy) instruction booklet, the SS-1's panels can be placed closer to the rear walls than is normally possible with full-range electrostatics, because there is no need to worry about cancellation of low frequencies—these are handled by the separate bass commode. But with any speakers that radiate from both front and back, the wall behind them can affect their sound according to its reflective properties. A hard, bare wall will make the sound brighter, while heavy drapes on the rear wall will soften the sound appreciably.
When using the Infinity panels, the Treble control on the crossover can help to straighten things out, but not completely, because it cannot offset an overall rising or falling tendency with increasing frequency. The best it can do is give an average correction. while putting a gentle step in the response at 1.5kHz crossover point.
On the other hand, some reflection from the rear wall may be needed, to provide the best stereo imaging of which the system is capable. In the Infinity panels, the narrow tweeter strips have very broad, smooth dispersion, but the wider midrange elements, with the gap between them (occupied by the tweeter), exhibit a small amount of phase-interference cancellation, producing slight "in-and-out" effects at upper-midrange frequencies as one moves across the area in front of the panels, and also causing a mild impairment of stereo imaging. Both can be offset to a great extent by augmenting the frontal radiation by reflections from the rear wall.
Footnote 1: It is of interest to American record buyers that the English magazine Hi-Fi News recently published a list of discs that contained low-end material down to as low as 26Hz. Most of the discs are available only in England, but they can be purchased by mail from some of the firms that advertise in English hi-fi publications.