Green Mountain Audio Diamante loudspeaker
By Steven Stone   •   June, 1994 I live in a house that has a pyramid-shaped roof, so I guess you could say that I have a thing for pyramids (footnote 1). That's probably why I was immediately drawn to the Green Mountain Audio Diamante. I'm also attracted to floorstanding speakers with small footprints, since my listening/video room is only 13' by 16'. My Holy Grail of loudspeakers is a small speaker that's flat between 20Hz and 20kHz, can do 110dB sound-pressure–levels without straining, and costs less than $1000/pair.

Dream on, Steve.

While the Diamante is quite a bit more expensive than my $1000/pair ideal speaker and it doesn't get down to 20Hz, it does get the 110dB-spl-without-strain part right, which is something that few other small-footprint speakers I've heard can do. The Diamante offers a level of dynamic accuracy that many high-volume rock and large-scale orchestra listeners will find very much to their liking. Yes, these speakers can kick some serious audiophile butt.

Technical stuff
The first thing most people notice about the Diamante is its shape: The top is a 2'-high, eight-sided pyramid which expands from a svelte 2" by 4" to 11" by 11", where it then sits on a transmission-line base that gently flares to 13.5" by 13.5". The second thing people notice about the Diamante is its slick cast-marble enclosure, which is available in white onyx, malachite, or white onyx with brown accent. For a couple hundred bucks more, you can get the Diamante in any color you want. The Diamante also has a perforated-aluminum grille in front of each driver that is 78% open space. The grille vibrated slightly at medium to high volumes, but I couldn't detect any deleterious audible effects from this slight vibration.

One thing you can't see from the outside is the Diamante's varying cabinet thickness—at its midpoint, the cabinet is almost 1.5" thick. Since the cabinet is made of a cast material, rather than an assembled box, it's extremely rigid by nature—a good thing. The same material is used for the Diamante's special chamber stand, which couples to the woofer cavity, capturing the rear-wave energy and splitting it into two halves that follow transmission-line paths of different lengths. When the two chambers recombine, they cancel out the unwanted resonances that a single transmission line would create. Green Mountain terms this an "Anechoic Transmission Line"; it suppresses the high odd-order harmonics of the transmission line's fundamental resonance.

The Diamante crossover features first-order filters with six elements in series with the drive-units and just four parallel reactive elements, including paralleled WonderCaps, Kimber Teflon-insulated hookup wire, and air-cored inductors. In combination with the sloped-back baffle, the crossover configuration gives a phase shift of no more than +20° at 200Hz, falling to –20° at 8kHz. The speaker is supplied with two modular crossover L-pads that plug into an octal-base socket just inside the speaker's base. The standard H-200 module gives a full measure of high frequencies; the alternate H-100 module drops the highs to better optimize the speaker's balance for use with inexpensive electronics.

The speaker leads are connected to a terminal strip underneath the top cabinet and must be threaded through a tunnel in the base to emerge at floor level next to the port at the end of the transmission line. Stiff wires with extra-large spade lugs may be somewhat difficult to get into position. If at first you don't succeed in connecting your favorite large-diameter cable, slowly count to ten, and try again.

Setup
Roy Johnson, the speaker's designer, and David Sckolnik, Green Mountain's sales and marketing director, delivered the Diamantes to my home in Boulder, CO—a mere three hours' drive. The Green Mountain brain trust set the speakers up in my large listening room, where they felt they would perform optimally. Unfortunately for my back (these things weigh 105 lbs each!), this proved not to be the case. The Diamantes' wide-dispersion characteristics, which are probably assets in most situations, proved less than ideal in my large room, which has quite a reflective ceiling. The Diamantes' sound promptly bounced off the ceiling and made a beeline for my ears, competing with the direct sound for supremacy in my brain's aural-reception centers. Oops, that's not supposed to happen. Until I get the chance to do a serious sound-absorption treatment to my large listening room's ceiling, only speakers with limited vertical dispersion (eg, the Apogee Full-Ranges and other planar speakers) will be allowed in there. No sense fighting physics.

After the Diamantes had broken-in for about two weeks in the large room, I moved them into my much-more-dead small listening room, which sports four 24" by 24" RoomTunes Ceiling Clouds (one in each wall/ceiling junction), CornerTunes and EchoTunes placed in ceiling corners and midpoints, two ASC Tube Traps (one in each corner behind the speakers), two ASC side-wall traps (one on each side of the room), four RoomTunes on the rear wall behind the listening position (one on each section of the bi-fold closet door), and four other RoomTunes strategically placed about the room. If this room was much deader, I'd have to install a few grave markers! Wide-dispersion speakers, such as the Diamantes, work well in this room. With pink noise, the Diamante's sonic signature changed only very slightly when I stood up or shifted from one side of my listening couch to the other. The Diamantes are definitely not one-person speakers.

Final location for the Diamantes in my small room was 38" from the rear wall, 62" from the right side wall, and 58" from the left side wall (footnote 2). At my primary listening position, my ears are 38" from the floor, which places them just about level with the Diamantes' tweeters. The Diamantes were toed-in such that, from the listening position, I could see just a bit of the speakers' inside edges.

Listening
I usually keep the Atma-Sphere MA-1 amplifiers in the small-room system (I like the way they keep the room warm and cozy in the winter). The Diamantes and the Atma-Sphere amps proved to be a less than optimal match. For some reason, a horrendous 4dB hump centered around 55Hz (footnote 3) could be heard—we're talking serious midbass bloat here. This was too bad, because other than this midbass elephantiasis, the Diamantes sounded very nice with the MA-1s: great imaging, good top-end extension, and super 3-D soundstage.

I sent the MA-1s away for some R&R in my equipment storage closet and tried some other amps. My Van Alstine 120C sounded very nice 'til it ran out of steam during 98dB peaks—poor little thing, it only has 60 solid-state watts. It joined the MA-1s in the closet. Next I tried a pair of Boulder 250 AEs, and the music really started to cook. In mono mode, each Boulder puts out about 450W peak power. Coupled with the Diamantes, that's enough power to fry eardrums as far away as Utah.

Sensitive audiophile types might ask "Why are you into playing your system so loud, Steven?" My immediate reaction would be to get sort of huffy and explain to these wimps that I'm not into playing my system loudly, I'm just into playing music that occasionally gets loud. J. Gordon Holt and I have been recording live concerts for the Boulder Philharmonic, and these recordings have become an essential part of my reference software. On our recent PCM-F1 recording of Mussorgsky's Pictures at an Exhibition, the range between the quietest passage and the loudest is about 75dB. The Diamantes, driven by the Boulder 250 AEs, handled this dynamic contrast with almost no compression (footnote 4)—something my original Quad ESLs can't do to save their lives, even with a subwoofer.

The bass of the Diamantes started at about 40Hz, below which they had very little, if anything, meaningful to say. But from 40Hz up, the bass was surprisingly tight and tuneful. Rob Wasserman's bass on Duets (MCA MCAD 42131) was noticeably deficient in the 20–40Hz range, but above 40Hz it sounded quite excellent indeed. The bass line on "The Moon is Made of Gold" was evenly presented—not prominently in-your-face or languishing somewhere just beyond audibility.

The Diamantes also handled bass transients very well. On Wasserman's "Angel Eyes" duet with Cheryl Bentyne, the bass dynamics didn't become foggy or stressed, even when the vocalist leaned on notes. Overall, the Diamantes nicely handled everything but the bottom bass fundamentals.

The box resonances that I've come to expect from most conventional-driver speakers were largely absent with the Diamantes. These speakers produced no hooty or awww sounds, and the midrange driver refreshingly lacked the colorations of typical polypropylene-cone speakers. The midrange was smooth without being too laid-back. I could play Neil Young's Ragged Glory CD (Reprise 26315-2) with 100dB peaks without suffering from listener fatigue. The Diamantes sounded the way well-designed dynamic speakers should sound: with the emphasis on dynamics.

Image focus, while quite good, was not great—other speakers, such as the Vision Acoustics Soloists or the Acoustic Energy AE-2s, have more precise focusing and vanish more completely. If a recording (eg, one of my Boulder Philharmonic recordings) had depth, it was apparent, but not exaggerated. Neither did the Diamantes provide holographic imaging when it wasn't there—artificial, digitally created depth, such as that on Dire Straits' Love over Gold (Warner Bros. 3266-2), sounded artificial, as it should.

Soundstage width was adequate, but not wowie-zowie. LA's voice on the "Mapping the Soundstage" track on Stereophile's Test CD 2 (footnote 5) sounded slightly outside, and definitely behind, each speaker. The Diamantes didn't stretch space into fantasmagorical shapes, but they did throw up a respectable, matter-of-fact soundstage on well-recorded material. On "Eden," Corey Greenberg's fractured Fender was propelled well over a foot beyond the speakers as it careened across the soundstage.

The Diamantes handled treble information very matter-of-factly. While some speakers, such as the Apogee Full-Ranges, have more top-end "air," the Diamantes didn't sound cupped or hooded. The tinkling bells on Rickie Lee Jones's "Walk Away Renee," from Girl at Her Volcano, sounded very natural, with clean attack and realistic decay. The Diamantes sounded quite natural on top—not overly sweet, like early Spendors. The dome tweeter exhibited very little coloration—it didn't have the kind of top end that experienced listeners would immediately identify as classic soft-dome–tweeter sound.

Overall resolution of information was medium-to-high. The Westlake BBSM-10VNF conveys higher levels of information, for example, but this increased definition comes at a price—I found many cherished recordings that were marginally listenable on the Diamantes to become unbearable through the Westlakes. The Diamantes' definition level was a good compromise between the overly forgiving and the hypercritical. Fortunately, for those who like rhythmically complex music, the Diamantes didn't sound sluggish or slow—the transients and dynamics of JA's demanding Fender bass lick on track 2 of Stereophile's Test CD 2 were handled very nicely.

Overall, I was quite impressed with the Green Mountain Audio Diamante. Its fit'n'finish is excellent, and it has a high degree of WAF (footnote 6). I would've liked a bit more bass extension and a hair more air on top, but, in the overall scheme of things, these sins of omission were minor. I also would have liked it had the speaker interfaced better with my Atma-Sphere OTL amps, but it worked quite nicely with the solid-state amps I had on hand. Dyed-in-the-wool tubeaholics may not care for the Diamante, however, unless they like a bit of extra midbass bloom.

Conclusion
Green Mountain Audio's Diamante is not an "impressive" speaker—a good thing, because speakers that immediately impress with sonic splendor are rarely accurate or satisfying in the long run. Given its size and price, the Diamante deserves to be heard by anyone who values music and domestic tranquility over hi-fi histrionics.

If you want hi-fi thrills, serious bass extension, and tons of top-end air, the Diamante won't be your cup of tea. But if you want a transducer that brings you close to the music with a minimum amount of fuss, you'll very much enjoy it. And if you make your own recordings, you'll quickly find that the Diamante will deliver most of the information on your tapes in a no-nonsense way. Pyramid power rules.

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Footnote 1: Just for the record, I harbor no illusions about shaving with the same razor blade for the rest of my life, or of living to be a thousand years old; I just like the sense of light and space provided by a 25'-high pyramid-shaped ceiling with pyramid-shaped skylights.

Footnote 2: I always try to avoid setting speakers up symmetrically in rooms, since standing waves tend to be exacerbated by symmetrical placement.

Footnote 3: The Diamante's impedance shoots up to 18.9 ohms at this point. According to Ralph Karsten at Atma-Sphere, the MA-1s deliver the same power output into this load as they do the 6 ohm load posed by the Diamantes over the rest of their frequency range. Roy Johnson suggested that this extra energy was a result of back-EMF as a result of the woofer's excursion, which is at its maximum point at this particular frequency. Ralph Karsten suggested that NBS cables may help ameliorate this back-EMF effect.

Footnote 4: Nothing, and I mean nothing, sounds quite as open, uncompressed, or dynamic as the live feed through my Stax Lambda Pro headphones. The minute the signal is recorded onto any medium, it sounds different. Live performances always sound better than recorded ones, period. Sad but true.

Footnote 5: As LA walks toward the microphone, there's a certain point where, instead of traveling forward, his voice darts to the left, to the right, and then back to the center as he passes by the mike. Which side of the mike did he actually walk by? [He walked past the left-hand side of the Blumlein mike array, hence his initial lurch to the left. But as he passed in front of the array, his image actually went back behind the speakers because a Blumlein array can't distinguish sound sources in front of it from those behind it. One becomes folded on top of the other. The effect of this behavior on this track's soundstaging is to give the listener the aural illusion that Larry apparently circles the microphone, just as described by SS.—Ed.]

Footnote 6: Putting to one side the sexist implications of the term, Wife Acceptance Factor is the ability of a speaker to be allowed into the presence of a non-audiophile significant other. My wife liked the look of the Diamantes—she has an affinity for forest green.