If I say, "terrific subwoofer," you will imagine a lacquered black mass, big as a dormitory refrigerator, and heavy as a truck motor. The gleaming rectangle is made of layered aluminum or heavily cross-braced birch plywood. Inside is a sinister-looking driver made of Kevlar and paper or milled aluminum with a magnet that weighs six kilograms. There's a digital two-kilowatt amplifier in the back, controlled by DSP. This awe-inspiring, earthquake-provoking device costs well over $5,000.
I met Duke LeJeune, the designer of AudioKinesis products, at Rocky Mountain Audio Fest in 1999. At the time, the show, now the biggest one in America, was a hobbyist's gathering. Most of the big name companies were there, but so were the little
fellows, people whose enthusiasm had not been dented by commercial considerations.
Duke was moving one of his speakers around the display room. This was an unusual design, with a single woofer and a horn-loaded tweeter in a five-sided enclosure. He was personable, intelligent, and passionate about his designs. He didn’t talk trash about other designs or designers.
What was most unusual about Duke’s design was unspoken: he had come up with a speaker that worked with the room. You might think this was self-evident, since speakers almost always wind up in home listening environments, but most speakers are designed as though they were destined for anechoic chambers.
Another interesting feature was the tweeter. Ribbons were becoming less expensive, and lots of companies were introducing these fast, linear drivers into their systems. They can sound good, but horns can usually go lower, are very sensitive, and have controlled directivity. Again, Duke was thinking about the listening room.
II. What you pay and what you get.
Flash forward to the present. The Swarm, Duke’s concept of what a subwoofer should look like and how it should perform, was reviewed in a glossy hifi magazine: link. The report was positive, and exhibited more of the same pragmatic thinking about speaker-room interactions.
I got in touch with Duke. He was as enthusiastic as I remembered him, and readily agreed to send me a set of his woofer design, The Swarm.
One afternoon, I came home from work and found five boxes in front of my garage door.
Four subwoofers? In four separate cabinets, and a freestanding amplifier?
Each of the woofer modules takes up about a square foot of real estate, and is two feet tall. They’re small enough to fit almost anywhere in any room larger than a closet, and finished nicely enough not to attract attention to themselves. To the designers who choke rooms with big designs, I say: speakers should be heard and not seen.
Each module contains a 10-inch aluminum driver. The amplifier is a simple, rack-sized device that will fit near your preamplifier. There’s a one-band parametric equalizer with controls on the front panel, as well as bass boost and subsonic filter switches on the back. It can develop a kilowatt of power, but it’s a Class A/B design. No digital artifacts to worry about.
If I were defining Duke’s design criteria, an essential element would be: only what can ride in the back of a Honda Fit. (http://automobiles.honda.com/fit/). This means no gigantic panels, no coffinesque enclosures. The art, or Duke’s genius, is to provide room-filling sound without filling the room with equipment.
Another element in the LeJeune school of thought: provide excellent sound at a price that a Honda Fit driver could afford. If you’re arbitrarily wealthy I suppose it won’t matter, but for the rest of us, the monthly appearance of the big glossy magazines with their hyperbolic praise of enormous loudspeakers is discouraging. Implicit in these reports is the notion that these monoliths are the best current technology has to offer, and if you can’t buy one, you’re listening to inferior technology. The Swarm costs $2,800.
III. A SWARM of adjustments.
This design allows you to tailor the sound more closely to your room than any other system I'm familiar with, and does so without passing the signal through a digital processor.
Even a rudimentary knowledge of acoustics (like mine) shows that room nodes are excited by low frequency signals. The single, notional woofer that I described at the beginning of this piece, no matter how well engineered, is bound to set off reinforcement and cancellation patterns. The result is uneven bass, with peaks and dips that resemble the Alps. You might not hear frequency variation, but you'd become highly aware of the way some notes seemed to linger while others appeared to disappear. Instead of a tightly defined base for your music, you'd have poorly defined mud.
Most designers have adopted one of the following solutions to this problem. The simple approach is to recommend two subwoofers. This levels the room loading to a reasonable degree, but it doubles the cost and takes up more floor space. In a modest-sized room, this may be both impractical and highly unattractive. The other solution is digital sound processing (DSP). With enough software and a calibrated microphone, you can usually adjust your way to reasonably flat response – at one location. The rest of the room will still have peaks and dips and standing waves. And remember that you've passed your precious musical signal, which comes from the best equipment you can afford, through another circuit.
Consider the possibilities:
Room placement. Duke sent me suggestions on placing the subwoofer modules. I list them here to give you a sense of how much trial and error can be involved.
Todd Welti symmetrical. One subwoofer goes a fourth of the wall length from each corner.
Todd Welti practical. One subwoofer midway along each wall.
Earl Geddes asymmetrical. One subwoofer goes in a corner, one along side walls, and the fourth somewhere away from the other three. Ideally, one of the modules should be lifted off the ground, so the sound can spread along the vertical plane.
Golden Ratios. Start with one subwoofer in a front corner, then another .62 of the length of that wall from the first woofer. The third subwoofer goes .62 of the way down from a third corner, and the fourth .62 down from the fourth corner.
A person could spend a month moving the woofers around and still not exhaust the possibilities, but I came up with another just to complicate matters further: put two modules side-by-side behind the main speakers.
Enclosure alignment. The Swam modules are ported designs, but the port can be sealed with a plug. The sound difference is what you’d expect: the ported sound goes a bit lower, and is a bit less tightly controlled than the sealed sound. Since there are four modules, you have a lot of potential to indulge your curiosity – or audiophile neurosis – by sealing some or all of the modules. Each time you adjust an enclosure the sound changes, and so you must consider the overall effect. It’s subtle, but plainly audible. Since I am using stacked Quad 57s as my reference speakers, the faster response of the sealed boxes proved to be better. If I had been using a speaker like Harbeths or Spendors, my preference might have been different.
Enclosure orientation. Duke says the woofers should face away from the listener. I tried that, but then aimed the drivers toward me.
Amplifier settings. The parametric equalizer allows the listener to boost or cut one band, while the bass boost and subsonic filters act in the mid- to high-20 Hertz range.
IV. Dialing In The Swarm
I’ll be honest. After moving woofers around my listening room for several weeks, I had the system in pretty good shape. Integration with the electrostatic panels was pretty good, and most of the lumpy frequency humps were flattened. Then I made adjustments, both large and small, with the amplifier. For closer tuning, I borrowed a real-time analyzer. This process occupied most of Spring, 2015.
V. The Swarm Sound
I did the conventional subwoofer tricks. These include soundtracks from Patriot Games, Jurassic Park and Volcano, along with the Saint-Saens C minor “Organ” symphony and Richard Strauss’s Zarathustra. I was satisfied that the Swam produced well-defined, articulate bass into the 25 Hertz range. The bass stayed pitch-correct even at barely tolerable levels. This would contrast with woofers that go low, but start to flail, or woofers that reproduce deep bass, but restrict their dynamics.
For my purposes, full orchestra music depends on a solid foundation and ample dynamics. So I put on Szell’s reading of Bruckner’s Symphony D minor symphony. A crescendo finishes the first figure’s theme. It must be as tightly controlled – and as powerful – as Maestro Szell demanded. The Swarm accomplished this. I could hear the hall ambience absorb and release the energy.
Finally I turned to Boehm’s versions of the Schubert B minor symphony, “The Unfinished,” and Wagner’s “Siegfried’s death and funeral march” from “Götterdämmerung.” The Schubert begins with strings in their lowest register. The bowing must be both subtle and well-controlled. It’s not earthquake, dinosaur or rocket launch simulation, but it does require finesse. So also the Wagner. This is tense, highly dramatic music. I was able to enter the composers’ worlds, to feel the emotion they sought to convey. I ignored the little boxes placed around my listening room and imagined myself in a concert hall on the Danube. The performances were convincing, fully wrought, and left nothing to be desired.
And that, gentle readers, is the goal. Many companies offer subwoofers that measure impressively and which draw attention to themselves; but I commend to your attention this cleverly designed system that doesn’t cost a fortune, and serves the music.
Text: Richard Weiner
The Swarm Specifications
Type: Four-piece powered multisub system
Woofer: 10" long-throw rated at 600 watts thermal
Typical in-room bandwidth, vented box mode: 18 Hz to 100 Hz
Typical in-room bandwidth, Qtc = .50 sealed box mode with 25 Hz boost engaged: 22 Hz to 100 Hz
Dimensions: 23" tall by 12" wide by 12" deep
Weight: 45 pounds
Amplifier: Kilowatt class shelf-mount class AB amp with 4th order variable lowpass filter, continuously variable phase control, and one band of parametric EQ, and switchable + 3dB @ 25 Hz bass boost flter
Price: $2800/system + shipping in Oak, Maple, or Walnut. Cherry, Black and other finishes available at additional cost. Direct sales only.