About a year and a half ago I moved to a new, downsized home that had a listening space whose acoustic characteristics I did not fully understand. The room is a second storey space and is roughly rectangular, with enclosed walls on one end and at the other end, balcony walls opening on to the vaulted ceiling of a living room (or lounge) space below. My thinking had been that the rectangular shape of the room would make for good hi-fi sound, with the loudspeakers placed at the enclosed-wall end of the room and facing toward the semi-open-wall end of the room. I reasoned that there wouldn’t be (and probably couldn’t be) reflection problems from back walls that weren’t there, and that sound waves passing over the rear balcony would bounce off the angled vaulted ceiling and be directed downward to be absorbed or diffused in the lounge space below. That was my operating theory, but to my chagrin, the actual acoustics of the room proved much different than expected.
While the room was blessedly free of unwanted bass resonances or obvious low-frequency standing wave problems, it exhibited midrange and upper midrange anomalies that were—how shall I put this? —challenging, to say the least. Specifically, the room seemed to have an issue with characteristic midrange and upper midrange brightness, plus the problem of tending to smear or obscure imaging and spatial cues in the music. In particular, imaging was not as precise and sound stages were not as fully formed as I felt they should have been (especially with loudspeakers whose performance I had observed in the past in different listening spaces). In short, it was as if my room was “singing along with the loudspeakers” in a discordant and acoustically unhelpful way—obviously not a good state of affairs.
Looking for solutions, I tried experiments with absorptive panels and with combination absorption/diffusion panels that I had on hand, but with only moderate success. The absorbers and so-call ‘diff-sorbers’ were beneficial, but only to a limited degree; they were acoustic bandages where a deeper and more profound kind of solution was needed. It was then that an old audio friend, Wendell Diller, head of Sales and Marketing for the loudspeaker manufacturer Magnepan, offered an observation that proved prophetic. “You know, Chris,” said Wendell, “my experience has been that in rooms where absorbers or ‘diff-sorbers’ aren’t getting the job done, there can be real benefits to using true, purpose-built diffusors. What’s nice is that most high-end audio systems seem almost infinitely tolerant of diffusors, so diffusors are an ideal, do-no-harm solution.”
It was at that moment that I recalled an encounter I had had with another old audio friend: John Bevier, National Sales Manager for the North American high-end and pro audio distribution company, Audio Plus Services. At a trade show John had demonstrated for me a then-new set of Focal Sopra-series stand-mount monitors, but what caught my eyes and ears were the distinctive diffusor panels John had placed within the room to tune up the otherwise ‘spotty’ acoustics of the hotel/demonstration room. Since the Focals were sounding better than they had any right to in an hotel space, I asked John about the diffusors, which he explained were Multifuser DC2 panels made by the Portuguese company Vicoustic (whose products are distributed in North America by Audio Plus Services).
“Listen to this,” John said as he removed the DC2 panels from the room. Immediately, the sound exhibited much more midrange and upper midrange ‘hash’, while losing imaging specificity and soundstage width and depth. “Now listen to what happens when I put the panels back,” John said with something akin to a magician’s flourish. As the panels went back in place, the sound transformed. The ‘hash’ went away, the imaging became sharply focused (almost the sonic equivalent of an auto-focus camera optimising focus for a photographic image), and sound stages became spacious once again.
Recalling that demonstration, and heeding both Wendell Diller and John Bevier’s advice, I approached Audio Plus Services about trying a set of Vicoustic Multifuser DC2 panels in my listening room. But what exactly are the Multifuser DC2 panels like? Let me provide a brief thumbnail sketch.
The Multifuser DC2 panels each measure 570 ×570 ×177mm (that is, 23.6 ×23.6 ×5.5 inches) and are made of EPS (expanded polystyrene). The panels are offered in three colours—white, grey, and black—but can also be painted to match room décor using water-based paints. The panels ship in boxes of six. Readers seeking a more upscale (albeit more expensive) and aesthetically more in line with domestic decor, solid wood solution might want to check out Vicoustic’s similar Multifuser Wood 64 diffusors.
The panels’ rear and side surfaces are flat, while the fronts of the panels feature a geometric grid array of posts and wells (196 of them per panel) of varying heights and depths. The exact height and depth dimensions of the posts and wells are dictated by a so-called “primitive root” numeric sequence that in essence helps maximise the range of audio frequencies over which the panel provides meaningful diffusion. What is more, the faces of the posts and wells are deliberately angled, which also helps improve diffusion characteristics.
The primary purpose of the panels is, of course, to provide two-dimensional (that is, “hemispheric”) broadband diffusion and a performance chart for the DC2 panels shows that indeed their diffusion coefficient remains remarkably consistent from 125Hz (coefficient = .67) on up to 5kHz (coefficient = .75) and beyond. However, the panels do also provide a modest degree of absorption, with their absorption coefficient becoming most effective from about 800Hz to 2kHz and then gradually tapering off from 2kHz to 5kHZ. Importantly, and unlike many of the so-called quadratic-residue diffusors on the market, the performance characteristics of the DC2 panels are the same in the vertical and horizontal axes.
How do the Multifuser DC2 panels work in practice? In my room they worked like a charm, transforming a space that initially seemed an acoustic ‘problem child’ into what frankly has become the nicest sounding listening room I have ever had. For my application, I used a total of twelve DC2 panels arranged as four columns of three panels each—two on the rear walls of the room and two on the sidewalls (positioned at the first reflection points). The results were impressive to a downright jaw-dropping extent.
First, the characteristic midrange and upper midrange brightness of the room was corrected, yet with no apparent loss of musical energy or information in either frequency band. Second, imaging became more continuous, meaning there was little if any tendency for there to be a sonic ‘hole in the middle’ between the speakers, while perceived imaging focus and specificity were dramatically improved. In layman’s terms, the diffusors seemed to take the room out of the equation, so that I could more clearly hear what the loudspeakers were doing. Third, spatial cues in the music, including very subtle recorded echoes and reverberations, became much easier to hear, as did sounds of instruments and voices interacting with the acoustics of various recording venues. The upshot was an increase in overall soundstage size and three-dimensionality. Finally, the panels worked equally well with dipole and with forward-firing loudspeakers. When you put all of these virtues and benefits together, the Vicoustics panels seemed like nothing less than acoustical miracle workers.
How are the Vicoustics panels mounted in one’s room? The answer is that in many applications the panels would be affixed to wall or ceiling surfaces using special flex glue that Vicoustics makes for this purpose. At the same time, though, I should point out that the panels don’t have to be attached to walls at all to be effective. In my case, for example, I found it perfectly acceptable to place panels on the floor, butted up against the wall, and then to stack additional panels on top. The beauty of this approach is that you can experiment with different panel placements as you wish without having any glue residue to clean up.
Saving the best for last, let me mention that the Vicoustics Multifuser DC2 panels aren’t expensive: many UK retailers offer them for £339 per six-pack box, while US retailers typically sell them for $649 per box. Either way, the value for money on offer is clear off the charts. Vicoustic says the DC2 is “the best cost/performance diffuser money can buy,” and until I discover something better for less, I would enthusiastically concur.
Type: Two -dimensional (“hemispheric”), Primitive Root sequence-based acoustic diffusor panel.
Construction: EPS (expanded polystyrene)
Dimensions (H×W×D): 570 ×570 ×177mm
(23.6 ×23.6 ×5.5 inches)
Price: £339 or $649 US/box of six
MANUFACTURER INFORMATION: Vicoustic SA
Distributor Information (UK): Source Distribution
Tel: +44 (0)20 896 250 80
Distributor Information (North America):
Audio Plus Services
Tel: +1 (800) 663-9352
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