Infinity Servo-Statik 1 loudspeaker J. Gordon Holt October 1975 part 2

Another problem we have observed with some Infinity dealers' demos is their tendency to set both the bass and treble controls (on the crossover) up too high, presumably to make a point of the system's phenomenal performance at both ends of the spectrum. The result, all too often, is bass boominess and that sizzly, biting high end that many audiophiles think of as "electrostatic sound." Some SS-1A buyers, too, will tend to fall into this trap, for statistically few audiophiles ever get to hear live, unamplified music, and have no idea just how sparse but tight live bass is, or how sweet but detailed live highs are.

Our advice, if you really want to get out of the SS-1A what it is capable of, is to start with the crossover controls set for what is obviously too little bass and treble, and live with them that way for a while. Then, after you have found that all recordings sound thin and dull, advance botha little at a time until some recordings sound a bit bass-heavy and some sound a bit thin. That is the correct bass setting. For the treble, the object is to retain softness in the sound of woodwinds strings, yet crispness on hard percussion like triangle and castanet. Achieve that on a statistical majority of recordings, and you've hit the delicate balance.

At this point, you should use a china-marking pencil (or a sliver of gummed paper) to mark the control settings, and should keep the controls there unless, over a period of time, you find yourself consistently using a different setting, at which time, change the mark. What is most important is to bear in mind, and keep repeating to yourself, that unless you hear live, unamplified music frequently, your tendency will be to whoop up lows and highs too much, and if you're going to do that, you're an idiot to do it to a $4000 system that has the capability of being an accurate reproducer! If you just want something that sounds "good" to you, the SS-1A is not a very sensible choice.

We should also lay to rest what, judging by conversations with several subscribers, is a popular misconception about so-called common-bass loudspeaker systems. Infinity claims, as have previous manufacturers of other systems using a single woofer for mixed bass, that the woofer unit can be placed anywhere in the listening room. This, to many people, conjures up images (no pun intended) of the upper ranges of sound coming from the electrostatic panels while the bass drum and bass fiddles come from the far corner or wherever the woofer happens to be placed. When they are told that bass is nondirectional, and that the ear cannot distinguish direction below about 300Hz, the reaction is "Nonsense! I've been to live concerts, and I can hear exactly where the bass instruments are located."

That's true, of course. We can tell the direction from which the sounds of a bass instrument are reaching us but not from its bass frequencies. The directional cues we hear are from the musical overtones of the instrument—the impact transient of the drum head and the pluckings, bowings and harmonics of the bass strings. We have demonstrated this time and again with previous common-bass systems, and did it several times to unbelievers with the SS-1A. The best location for the SS-1A's bass "commode" in our room turned out to be directly behind the left-hand electrostatic screen where it is not visible from the listening area.

Our "demonstration" involves playing recordings that have bass instruments located at or toward the right side and asking the skeptics to tell us where the bass speaker is located. Without exception, they have been absolutely certain it was behind the right screen. Then we show them where it is.

Bear in mind, though, that since our ears can perceive directional cues from frequencies as low as 300Hz, it is necessary to cross over into a spatially separated woofer well below 100Hz, so that frequencies of 300Hz and up are sufficiently attenuated to avoid giving our ears enough directional information to lead them to the woofer. Even with Infinity's 70Hz crossover, there is enough leakthrough of 300Hz information to the woofer to reveal its location when it is placed close to and to one side of the listening area (footnote 3).

Remember also that, at 100Hz the wavelength of a sound is around 10½', which means that placing the woofer about 5' behind (or in front of) the electrostatic screens will cause phase reversal with resulting cancellation of mid bass. If this spacing must be used, the connections to all four sets of electrostatic screens should be reversed (but not interchanged, of course!). The result will be smoother response, but at the expense of some audible delay between fundamentals and their overtones. (With the woofer 10' behind the screens, mid-bass cancellation will not occur but the 100-millisecond delay in low-bass fundamentals is audible as pronounced hangover. Moral: Don't put the woofer more than a couple of feet closer or farther from you than are the upper-range screens.)

It is also argued by some theoreticians that, since bass frequencies have long wavelengths, widely-spaced recording microphones will receive bass signals with a certain amount of phase delay, and this delay will result in sane cancellation of bass if the stereo channels are blended prior to reproduction. This is a harder question to answer, as no research has (to our knowledge) been done on the subject, and our observations were inconclusive. We did notice that, by and large, deep bass from the SS-1A was not quite as prominent as from the FMI J-Modulars (although it was also tighter), but whether that was because of the bass mixing or some other difference between the woofer systems (the Infinity's is, after all, servo-damped) was moot.

Footnote 3: The SS-1A's crossover rate is about 6 dB/octave, and 300Hz is a hair less than two octaves above 70, so 300Hz will be less than 12dB down in level. (A crossover slope only approaches its nominal rate of attenuation; this one would never quite reach 6dB/octave.—J. Gordon Holt
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