June 2001

Green Mountain Audio Continuum 2 Loudspeakers

by Doug Blackburn

Review Summary Sound Offer "large amounts of air, immersive sonic envelopment and 3-D, holographic imaging"; also "wickedly detailed," but not "annoying, off-putting, harsh"; "not masters at deep bass extension," but the Continuum 2s "will play really loud without obvious distress or distortion." Features First-order time-and-phase-correct design; ported bass cabinet acts as a support for the adjustable midrange/tweeter modules; bass cabinet and midrange module are made of proprietary cast stone-like material. Use Two people are required for proper setup -- as is a tape measure; Doug found that the midrange sounded too prominent until he lessened the toe-in of the speakers. Value Unique design that offers another voice in the small crowd of the first-order time-and-phase-correct loudspeakers.

Green Mountain Audio is not a high-end audio manufacturer that people know a lot about -- unless they happen to own the company's speakers. Founded in 1988 by Roy Johnson, Green Mountain introduced its first loudspeaker, the Imago, at the 1991 CES. From the beginning, Johnson’s passion has been re-creating the listening experience in a way so transparent that the listener could forget the loudspeakers and concentrate solely on the performers, the instruments, the sound of the venue and the performance itself -- so transparent you can "hear the performer smile."

Johnson has a B.S. in physics from the University of Colorado. His senior project was the first mathematical derivation of "a monopole speaker with a dispersion pattern that decreases uniformly with increasing frequency." This happens to be the behavior of typical loudspeakers. He’s now just one course away from a Masters degree in solid-state physics. Being the "you ain’t gonna baffle me with your bullshit" kind of guy, Johnson spent years learning the ins and outs of all ends of the audio business: working part-time in high-end stores, woodworking and cabinet-making, running a high-end store, doing broadcast engineering, teaching physics while being a graduate student, acting as recording engineer for the Colorado Symphony Orchestra.

During all those years, building loudspeakers was a constant process. When looking at all the possibilities for the kinds of loudspeakers his new Green Mountain Audio company would build, Johnson selected time-and-phase-correct designs exclusively, knowing that the speakers would be harder to design initially, but they would better fulfill his goal of listeners being able to forget the loudspeakers and hearing only the performance. He explains his choice this way: "With time-and-phase-correct loudspeakers, you hear one sound, not three [as in a typical three-way loudspeaker design]."

Today Green Mountain Audio produces a two-way bookshelf speaker, three floorstanding three-way speakers, two center-channel speakers and two subwoofers. The first of the new Contura four-way models is coming soon. Prices range from $1600 USD to $8000 per pair.

Bottom to top, inside and outside

The three-way Continuum 2 is a departure from previous Green Mountain designs that tended to be more box oriented, even if they used interesting combinations of materials and shapes to take the cabinet out of the sonic equation. Continuum 2 prices range from $5995 per pair for theater-black finish with no grilles for the tweeter and midrange drivers to $7900 per pair for curly-maple veneer -- with stops in between. The Continuum 2 measures 55 5/8"H x 14 1/2"W x 20 3/4"D and weighs 110 pounds.

The only box in the Continuum design is the one for 12" woofer. Made from industrial-grade particle board to minimize cabinet resonances, this top-ported enclosure serves as the support base for the rest of the speaker. An aircraft-grade aluminum tube rises from the inside of the back of the woofer box. A forward-facing aircraft-aluminum cross-member (which is now black in color, as is all hardware) supports the midrange enclosure and the tweeter mounting block. The midrange and tweeter are movable front to back to permit perfect acoustic alignment with the woofer, so the drivers will be ideally integrated regardless of the listener’s seating height or listening distance.

The 12" woofer is not the seemingly omnipresent long-throw type. Johnson went for the transient response, efficiency and low distortion of a ported medium-throw woofer in a good-sized enclosure. According to Green Mountain, the Continuum 2's sensitivity is a true 90dB/W/m, and the impedance curve is said to be quite gentle and not demanding of the amplifier. The result is bass that’s solid and very well controlled down to 40Hz or so (depending on the room) and rolling off fairly rapidly after that, meaning usable bass to the mid-30Hz range. (Green Mountain claims a -3dB point of 30Hz, depending on room volume.) This arrangement makes it just about impossible to get boomy, flabby bass from the Continuum 2 unless the amp can’t control the woofer. Ported loudspeakers rely on the amplifier for control of the woofer much more than sealed boxes. I found the 300Wpc solid-state Belles 350A amp, with a damping factor of well over 1000, produced incredibly well-controlled and detailed bass. Tube amplifiers tend to have damping factors under 20, and sometimes way under 20. These would be unlikely to provide appropriate control for the large ported woofer of the Continuum 2.

The Continuum 2's 5" aero-gel midrange unit resides in a separate enclosure that is vented out the back. This permits almost all of the back-wave energy to either be damped inside the enclosure or to escape out the back, so that there is no time-delayed energy bouncing back against the inside of the cone and causing smearing of detail. Additionally, the midrange enclosure is as small as possible to minimize the baffle area around the midrange driver. Green Mountain's proprietary cast marble is used for the midrange enclosure also. The 1" sealed tweeter needs no enclosure; the "box" behind it is merely a mounting block. The tweeter baffle is minimized and treated with felt that covers the angled surfaces near the tweeter.

All crossovers are first order, and all drivers are connected with the same electrical polarity. The standard factory offering is a single pair of binding posts, and that is the configuration that was reviewed. Dual binding posts for bi-wiring are available as a $300 option, but Johnson is not all that enthusiastic about them, feeling that getting the next best speaker cable in the line is just as sonically effective as bi-wiring, perhaps even more so. I have to say that I found needing only a single pair of speaker cables a real joy.

Setup

Driver alignment in relationship to the listener is a critical factor for time-and-phase-correct loudspeakers because the ideal listening window is typically only 6-8 inches high vertically at a listening distance of 8 to 10 feet. It is important for your ears to be within this window of time-and-phase-correct sound or you might as well not bother with such loudspeakers. This vertical window does not have abrupt acoustical consequences like the vertical comb filtering you get from tall panel speakers that yield a tiny left-right sweet spot. If you are one inch above the time-and-phase-correct window, nothing terribly drastic happens. The sound does not fall apart noticeably, but there is a gradual movement away from ideal performance the farther you get outside of this vertical window.

Never make value judgments about time-and-phase-correct loudspeakers unless you are certain you are within that vertical window -- things are better there. Time-and-phase-correct loudspeakers set up for listeners seated at "normal" listening heights (ears 32-36" from the floor) tend to sound dark and slow when standing with your ears two to three feet higher than the ideal ear location. Each manufacturer of time-and-phase-correct loudspeakers has his own way of dealing with the geometry of the time-and-phase-correct listening window. Green Mountain chose the ultimate in flexibility -- moving the drivers. Nothing is free though. The movable drivers require additional setup work on the part of the owner or dealer compared to "normal" loudspeakers.

I know audiophiles who will not be able to complete the setup of the Continuum 2s by themselves. It isn’t terribly demanding, but you need a bit of technical savvy and familiarity with accurate measurement techniques using a tape measure in order to do the Continuum 2 setup optimally. However, you really need two people to do the setup -- one at the listening position and one at the loudspeaker. Space doesn’t permit a run-through of the entire setup procedure, but you essentially measure the distance from the listener to the woofer, then set the listener-to-midrange and listener-to-tweeter to distances provided in the setup instructions. A good dealer who will help with the setup really should be considered a necessity for those who don’t have well-developed technical chops. If you need to move the Continuum 2 within your room, to another room or even to another house, unless your listening height and listening distance will be identical to the previous location, you will need help again with the new setup. And be careful when getting the tip of the tape measure near the tweeter dome. One twitch in the wrong direction at the wrong time you'll need a brand-new pair of tweeters -- so you maintain the +/- .25dB factory match between drivers.

Fly away with me; I’m off to the stars

The Green Mountain Continuum 2 loudspeakers seriously cut the mustard here, but only after a rocky start. For the first half of the Continuum 2s’ stay, they sounded like the midrange was 2 or 3dB louder than the tweeter or woofer. Even though the midrange sounded too prominent, there was no measurable peak when checking with SPL meter and test tones. I measured and re-measured the midrange and tweeter distances. I re-read the setup instructions in the owner’s manual several times, and I re-did every other aspect of setup. I then complained to Roy Johnson. I persisted with trying to rid the speakers of their midrange problem because I’d heard Continuum 2s at a show playing my own music and the midrange was not too prominent there. I was convinced that there was something in my setup or in the very specific instructions that would account for what I was hearing.

One night while experimenting, I ignored the over-your-shoulder toe-in guideline, and the too-prominent-midrange problem disappeared. When the Continuum 2s were aimed almost straight ahead, I had the top-to-bottom balance I was looking for; Green Mountain has modified its setup advice to account for this problem in other rooms. The remaining portion of the review period was spent listening to music in earnest to learn the depth and breadth of the Continuum 2s’ performance.

The Continuum 2s are major-league air machines, casting impressive space around performers and throughout the soundstage. The large amount of air combined with the Continuum 2s’ ability to create very large sonic spaces meant the soundstage could appear to be dimensionless with certain studio recordings. This happened with the more open-sounding discs like Mike Oldfield’s The Songs of Distant Earth [Reprise 945933-2]. The expansive sonic-scapes could be incredibly large, creating a sensation that you were in a very large space -- without, of course, the very long reverberation times. Recordings like British and American Band Classics [Mercury 432009-2] throw a huge sonic image that seems to be every bit as large as the actual performance. This seems to be aided by the Continuum 2s’ excellent retention of the decay of instrumental and room sounds. Only after an extended orientation period with the Continuum 2s do you begin to hear the boundaries of the recording venue. This impressive spatial performance can make you giddy if you are experiencing it for the first time. The Continuum 2s spatial performance was right up there with the best I’ve heard from other spatially gifted first-order time-and-phase-correct loudspeakers. You won’t get this expansive presentation if it isn’t on the recording, though; the Continuum 2s don’t add what isn’t there in the first place.

You have to put together the characteristics of large amounts of air, immersive sonic envelopment and 3-D, holographic imaging to understand what the Continuum 2s are capable of spatially. Dire Straits’ Love Over Gold [Warner Brothers, QUIEX II Limited Edition Pressing 923728-1] has such incredibly quiet vinyl that the performance is freed from the usual vinyl reminders and seems to take place in a huge silent space. With the Continuum 2s, you feel as if you are in that space when tripping out, er, enjoying, one of the best-sounding rock recordings ever made. The Continuum 2s launched Love Over Gold into a space subjectively much larger than my listening room. The nearly frightening dynamics of this recording were well preserved as well, without a hint of compression that is all too common with less capable designs.

In addition to the air and space they generate, the Continuum 2s are also wickedly detailed. Squirrel Nut Zippers’ HOT [Mammoth MR0137-2] is a raucous conflagration of traditional and modern instruments and styles. The Continuum 2s reveal all the multi-dimensional detail present in the baritone sax -- the sound of the brass horn; the air moving through body, the reed, the keys and valves; and the human touch making it all happen. Banjo and baritone ukulele reveal sparkle, sharp pluckiness, and irrepressibly happy harmonic content -- you can’t help smiling. Male and female vocals have both nuance and microscopic detail, but not annoying, off-putting, harsh amounts of detail. It’s exciting, exhilarating detail that produces an intimate sense of the performer being right there performing for you. Katharine Whalen’s falsetto is mesmerizing and hip-mo-tizin’ -- too bad it strained her vocal cords so much she had to back off a bit in subsequent Squirrel Nut Zipper recordings. The Continuum 2s float Whalen's coquettish voice in front of the other Zippers’ instrumental hijinks, creating audio imagery ideal for the intended effect. There’s not a hint of nasality, sibilant emphasis or upper-midrange harshness to distract from the performance.

The Continuum 2s are not masters at deep bass extension. They get all the fundamentals, but bass starts to roll off fairly quickly just a bit below 40Hz. When listening to music at normal levels, you won’t notice anything missing unless the fundamentals are below 38Hz or so. Above that, the bass has great snap and detail. I could not hear any frequency zone in which the woofer and midrange integration was off, giving that unnerving sense of bass being both powerful and fast at the same time. The lower octaves of piano and the deep bass notes on Paula Cole’s This Fire [Warner Bros./Imago 946424-2] were rendered without overhang or bloat. These natural and synthesized deep-bass notes had incredible detail and perfect integration with the midrange, which preserved the sense of the bass being fast. The Continuum 2s lacked impact and weight on the lowest notes compared to a loudspeaker system that is flat to 20Hz, but you still knew the notes were there.

The midrange of the Continuum 2 -- well, there isn’t much more to say about it. I almost want to use hyper-detailed, but most audiophiles, including me, think this is a bad thing. Yet that phrase, a good version of it, keeps running through my consciousness. There is a lot of detail in the Continuum 2s’ midrange. It puts you in an almost elbow-to-elbow relationship with the performers. The Steve Davis Project's Quality of Silence [DMP CD-522] was right there in my listening room, I swear! The drums, the cymbals -- yikes! As well as this CD is reproduced on the Vandersteen 3A Signatures, it never achieves quite the same level of they-are-here disbelief as with the Continuum 2s. The differences are in the transparency of the silence and the utter clarity in the transients the Continuum 2s produce. Cymbals, sax and guitar almost seem to make the air in the room shimmer with their presence. I find this sounds less like live music from the audience perspective than the Vandersteen 3A Signatures’ presentation. But the Continuum 2s’ presentation is irresistibly seductive in spite of seeming to favor the hyper-realistic recording-engineer’s perspective on the performance. The Continuum 2s produce nuances of the musicians movement that many other loudspeakers don’t. You can almost see and feel them moving their arms and legs. And you definitely hear the small motions in relationship to the microphone when performers are using mics on stands. I suspect this result is due to Roy Johnson’s experience as a recording engineer and finding most loudspeakers wanting in regard to not being able to hear everything captured on the master tapes.

The Continuum 2s will play really loud without obvious distress or distortion, something not possible with some loudspeakers having first-order time-and-phase-correct crossovers. Generally the large amount of overlap from driver to driver will stress the drivers as the volume level is increased. The Continuum 2s seemed to have a good 3-6dB more in them compared to more typical first-order loudspeakers before the strain becomes noticeable. It was pretty hard to take 100dB+ SPLs for any length of time -- and I urge you not to partake of such levels, either live, from loudspeakers or from headphones, for more than a few minutes (literally) lest you incur permanent hearing damage that won’t be apparent until later in life. Johnson actually encourages some high-dB abuse of the Continuum 2s during the break-in period in order to maximize the performance of the drivers at normal listening levels. It’s nice to know the Continuum 2s don’t seem to mind the abuse.

Comparing

I’ve listened almost exclusively to loudspeakers with first-order crossovers and time-and-phase-correct performance for many years. When I listen to loudspeakers that aren’t time and phase correct, I almost always hear things I don’t like. Many times the things I hear are incredibly obvious and I wonder "Who could listen to these and not hear that?" The answer turns out to be "Those who are not accustomed to hearing well-designed loudspeakers with first-order crossovers and time-and-phase-correct performance."

That said, let me compare the Continuum 2s to my reference loudspeakers, the first-order, time-and-phase-correct Vandersteen 3A Signatures ($3500 per pair) with a pair of Vandersteen 2Wq subwoofers ($2500 per pair), a $6000 combination that has quite different sonic attributes. The most obvious difference is that the Vandersteen setup is flat to 20Hz in most rooms. You can position the main speakers for optimum imaging and place the subwoofers for best bass extension and linear response. The Continuum 2s have a small edge in midbass impact and detail, but the Vandersteen setup does everything else in the bass department with more authority, impact and detail.

The Continuum 2s take the air contest outright, and aside from the bottom two octaves, the Continuum 2s are more detailed than the Vandersteen setup. Interestingly, the Continuum 2's tweeter may actually be a bit down in level compared to that of the Vandersteens. All the air and detail seems to come from the Continuum 2’s midrange and upper midrange.

Spatially, things are quite different between the two systems. The Continuum 2s and Vandersteens both produce a huge image in terms of lateral and vertical space, but they do it differently. The Continuum 2s’ space comes from the midrange air and detail. The Vandersteens get some of the sense of space from their midrange and treble, but the superior low-frequency extension provided by the 300W subwoofers creates utterly convincing space in a variety of sizes, depending on the recording.

The Vandersteens are warmer and more laid-back in the midrange and with less ultimate detail, but with a more gently seductive and relaxed listening experience compared to the Continuum 2s’ more exciting and urgent presentation. While the Continuum 2s seem to be more detailed than the Vandersteens, careful listening reveals that the Vandersteens reproduce everything the Continuum 2s reproduce, but do it a bit differently. The Vandersteens’ version of detail is more integrated with the music, as opposed to the more prominent perspective of the Continuum 2s. The difference in sonic presentation between the two products should make the right choice quite obvious for each buyer. But there is no obvious winner or loser in the comparison.

The sum of the parts

The Green Mountain Continuum 2 loudspeakers are a different voice in the small first-order, time-and-phase-correct-loudspeaker club. Dunlavy, Vandersteen and Thiel loudspeakers all sound different from one another, but with only three product lines to choose from, you might find that none of them quite meet your expectations. The Continuum 2s have a lot to recommend, and they offer another alternative to choose from when searching out time-and-phase-correct performance.

The most likely Continuum 2 owner is someone who values air, excitement, detail and close contact with -- even immersion in -- the performance. Those characteristics come with the ability to re-create a very convincing and sometimes huge performance space within your listening room. The Continuum 2s are also for the musical omnivore. You won’t be limited to flute sonatas or balalaika solos with the Continuum 2s. Those are handled exceptionally well, of course, but the Continuum 2s perform well with all types of music -- from simple to the most complex. And they just may be right as the masters of your musical domain.

...Doug Blackburn
db@soundstage.com

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