Another one of those characteristics is that a Mobius strip has only one edge as well as only one surface. We can demonstrate this, too.
Go back to the simple loop, the two-sided one. It has, obviously, two edges as well as two sides. You can show this by cutting along the line that you drew on the loop. When you do that, you'll have two loops, each with a new edge created by the cut you made. No surprise there.
You may be surprised, however, by making a corresponding cut down the center of the half-twist loop, the Mobius strip. You'll find that the Mobius strip does not fall into two piece when fully cut along the line you drew. You still have a one- piece loop. That's because there was only one edge to start with, not two. Cutting created a second edge and formed a doubly-twisted loop twice as long as the original.
That's the experience. Now for the interpretation.
The simple loop represents the common, familiar "drivers in a box" approach to dynamic speaker design. To be more specific, it corresponds to the overwhelmingly typical practice of mounting those drivers on a flat, usually rectangular or trapezoidal, panel. This can lead to some very fine but generally unenlightening speakers.
The Mobius strip, with its intriguing and somewhat surprising physical characteristics, corresponds to Artistic Audio's Mobius speaker which offers intriguing listening characteristics from a surprising and striking physical design.
The core of that design is a spherical enclosure about the size of a soccer ball. The enclosure is made of an acoustically transparent mesh material and holds two eight-inch midbass drivers. These are not cones, but rather domes with six-inch voice coils in a bipolar configuration. In other words, they move outward and inward in sync with each other. The goal is to approach the motions that would be produced by a pulsating sphere. A pulsating sphere, in turn, comes close to emulating an acoustic point source for sound. That's the loudspeaker equivalent of the "straight wire with gain" theoretical ideal for amplifiers.
The distinctive characteristic of the point source for sound, as far as Artistic Audio is concerned, is its 360 degree dispersion pattern and that's what the Mobius produces. That, in turn, makes for unusual--and in my opinion highly desirable--listening room performance.
The main thing you'll notice is that location, of both the listeners and the speakers, is much less critical than with conventionally designed systems. You might expect just the opposite from the speakers, but the uniform dispersion of sound in all directions doesn't activate room anomalies. It pretty much ignores them.
That also means that the traditional toeing-in of the speakers to get better coverage of a preferred listening area isn't acoustically necessary. I have to admit that I did it anyway, but it was for the look and not the sound. In fact, just to check things out, I turned the Mobius systems to face sideways, and then to face away from the listening area. Those admittedly extreme and recommended placements produced only minor listening differences. In particular, stereo effect and overall frequency balance barely varied.
The Mobius systems are equally forgiving of odd listener placement. You can get quite close to one speaker, even position yourself so one speaker is directly between you and the other, and still hear something approaching a stereo experience.
(That's assuming, of course, that you're not playing one of the multitude of current recordings with so little difference between left and right channels as to be effectively indistinguishable from mono.)
If Bose hadn't trademarked the phrase "Stereo Everywhere," it would be my description of choice for the Mobius listening experience.
I'm not convinced, however, that the effects I've described absolutely require the full 360 degree polar pattern of the Mobius systems. I've had considerable experience with systems that have uniform 180 degree coverage that do quite the same thing as Mobius and also avoid, through a different design approach, the difficulties of drivers on flat boards.
You can hear those difficulties yourself in this second experiment that I'd like you to try. This one's really easy once you find another person to work with. Simply ask that person to face you and say a few words at a normal speaking distance using his or her normal speaking voice. Now have that person simulate a speaker on a flat baffle by placing his or her hands along side his or her mouth with palms out and facing you. Then have the person once again speak to you in a normal voice. Note the tonal differences. They won't be subtle.
Every speaker designer has to contend with this effect, particularly at higher frequencies. Typical approaches include rounding off of baffle edges, adding absorptive material around the drivers, and tapering the mounting board so that there's less width affecting the smaller drivers. Less common, but much more effective, are designs like Mobius that totally take the flat mounting board away.
There is a front surface to the Mobius enclosure, by the way. But it has no drivers mounted on it. It has a swooped Gumby shape to it with two arms that support the spherical enclosure. Artistic Audio calls the arm structure a "velocity stack." The arms are open inside and connect the midbass array to the lower enclosure, allowing back energy to be absorbed below.
That lower enclosure of each speaker holds an eight-inch driver that provides smooth response down to 45 Hz. It's not, by the way, a rectangular enclosure. That shape and the very low placement of the low bass driver are major contributions to the smoothness of bass performance in the room.
Artistic Audio's specs rate the system at 88 db sensitivity, 250-watt RMS power handling capacity at a nominal 8 ohm impedance, and a frequency response of 45 Hz to 20 kHz +/- 3db.
Now for personal reactions to living with Mobius. The first must discuss the unique look of the systems. I mentioned Gumby. Some other people who saw them brought up Marvin the Martian from classic Warner Brothers cartoons. But don't take either of those references as scorn. The Mobius systems visual design garnered universal approval. In terms of spouse acceptance, I can tell you that my wife's first comment on seeing them was, "If they're really good, can we arrange to keep them?"
The Mobius contemporary industrial form and satin metallic finish might not sit comfortably in an Early American decorating context, but I'd say that it would work with almost anything else from Arts & Crafts through Deco and Moderne to today's eclectic looks.
Now for the "really good" question posed above.
You should have picked up some of my response to that already. Chalk up pluses for the Mobius systems for smooth overall response, non-critial placement and positioning, accuracy of musical timbre, and appropriate stereo listening from almost any spot in the room. The dynamic response of the systems is very good for most musical genres but falls a bit short of my absolute ideal on demanding big jazz band, pipe organ, and massed symphonic orchestral music. Another half octave at the bottom would have helped there, too.
But the fact of the matter is that the unique (there's that word again) combination of positives that Mobius offers cannot be duplicated by any other current speaker system that I know of at any price.
Artistic Audio's ambitious plans call for selling 10,000 Mobius units this year. The way I see it, all they have to do is get them within earshot of musically aware listeners to accomplish that goal.”
Thomas Krehbiel – Sensible Sound Magazine |
