According to Dr. Peter D’Antonio, head honcho at RPG® Diffusor Systems, multi-channel isn’t a thing of the future. We’re each listening to a half-dozen or so sound sources right now as a result of the way our speakers interact with our rooms. “It works like this,” said he, doodling on a piece of scrap paper in the Fi suite at a recent CES show (See Figure 1).

“You put a pair of speakers in a room, and suddenly the walls, the floor, the windows, the ceiling, even the furniture become subsidiary sources of sound. Early reflections basically act like second and third sets of narrow-band loudspeakers. When you think about it this way, it’s easy to understand how imaging, soundstaging, tonal balance, dynamics get screwed up by what is, fundamentally, an uncalibrated, unintended multi-channel set-up.”

Art Noxon of Acoustic Sciences Company (ASC) would agree with Peter’s analysis. The prime enemy is first reflections that DEW line of room boundary resonances that arrive at the ear close enough in time to the direct sound of the loudspeakers to be heard as part of the musical event. Where Art and Peter would differ is in how to fix the problem.

For ASC, whose tube traps have long been a staple in audiophile listening rooms, the answer is basically to absorb and reflect unwanted resonances. For RPG®, which is entering the audiophile market with a new, affordable line of room treatment products, the answer is primarily to absorb and diffuse them.

“Simply stated, a diffusor scatters sound arriving from any direction into many directions,” says Peter. “Because the sound is distributed into many directions, the energy in any one direction is significantly reduced. This results in a reduction of the acoustic glare that is associated with strong specular reflections, without removing energy or deadening the space. Think of the way a pane of frosted glass reduces glare without absorbing any of the light, and you have the idea.”

It is an idea that many performance art facilities and recording companies have bought into: Carnegie Hall and Lincoln Center, Juilliard and Berklee College of Music, all of the broadcast radio and TV networks, major record labels including Telarc, DMP, CBS, Mercury, and BMG, recording studios including The Hit Factory and Sony Music, audio manufacturers including Cello Music &38; Films, DTS, and JBL.

Garden-variety audiophiles, however, haven’t bought into it — at least they haven’t bought into it in the way they have other room treatments. The reasons are three-fold: price, looks, and (unfamiliarity with) performance.

On the first count, RPG®’s new line of lightweight molded-plastic Skyline® panels, upholstered Abflectors™ and stackable Corner Bass Traps are far more affordable than the heavy, expensive, furniture-grade wood diffusors with which RPG® made its reputation. While a full-bore, room-dedicated, computer-optimized RPG® system will still put you out ten grand or so—about the same amount as a full-bore, room-dedicated, computer-optimized system from ASC—individual items are quite reasonably priced, and effective enough to be used on a spot basis.

On the second count, well . . . no one would call a room-dedicated RPG® system attractive, save in a form-follows-function way. The Skyline® panels, made up of 156 “optimally located phase blocks” (i.e., hard-foam cubes of different sizes and shapes) molded on two-foot squares of foam backing, look a bit like a city block designed by a bad architect. RPG®’s seven-foot-high, L-shaped, sound-absorbing Abflectors™ are straight out of the Room-Divider School of Interior Design, while their wedge-shaped Corner Bass Traps (upholstered in Abflector™ gray) are about as winning as stuffed rhino feet.

Let’s face it: thoroughgoing room treatments, whether from RPG® or ASC, aren’t made for the family hour. All such products were originally designed for professional recording studios and playback facilities, where acoustics matter first and “decor” is a bunch of Styrofoam coffee cups, a bottle of Old Granddad, and a bag of chips. In short, if you want to experience the full benefit of an RPG® system, the first thing you’re gonna need is a separate space that can be fully dedicated to music or film—and, of course, the free and plenteous indulgence of your wife and kids. You’re also gonna need to make a scale drawing of that space—as I did for mine—send it off to RPG®, and let them calculate room treatment via their Room Optimizer™ software program (Actually, RPG® is now selling their Room Optimizer™ software for do-it-yourself calculations on the family PC).

What you will get back, in a week or so, is another scale drawing with listening position, speaker position, and the optimal combination of AcousticTools™ (RPG®’s name for diffusive room treatment products) and ImageTools™ (their name for absorptive ones) plotted therein. Diffusive devices, like Skyline® Panels, reduce specular reflections, adding what might be called “spaciousness” to the sound—bloom, air, liquidity. Absorptive devices, like Abflectors® and Bass Traps, reduce comb-filtering effects, adding what might be called “focus” to the presentation—more tightly defined pitches, dynamics, images. Both kinds of devices can be mounted directly on or against walls (via Velcro strips), or on floor-standing stands. For my listening space, the Room Optimizer™ plot ended up looking something like the illustration in figure 2.

Why you would do this to any room in your house—not to mention your wife, your kids, and visiting dignitaries—brings us to count three: performance. Here the news is very good, indeed. Properly set up, an RPG® system performs precisely as billed, minimizing the comb-filtering effects, specular reflections, and pressure drops that turn corners, walls, windows, and ceilings into subsidiary sound sources. And it does these things, quite remarkably, without blunting dynamics, or bleaching out timbres, or miniaturizing sonic images, or so reducing reverberation times that your room becomes an anechoic “dead zone” in which every source takes on the same cottony inertness.

Listening in an RPG’d room, you get the distinct sensation that you are listening in a much larger, more acoustically transparent space, where walls, windows, and celings have been removed to a distance. All those specular artifacts that you’ve grown accustomed to hearing along with your music—the rough, spitty, too-sharp edges of hard transients; the losses of pitch definition, air, and tempo in the bass and treble; chestiness on vocals; nasality on massed strings or winds; the masking or skewing of inner details on fortissimos or tuttis; the reduction in size, definition, and clarity of images at the sides and rear of the ’stage; the dark graininess or color cast that overlays the whole—largely disappear. What is left, to my ear, is the most transparent soundfield I’ve heard in my home.

Think of the way a television typically looks using factory settings—contrast, black level, sharpness, color, and tint way too high—then think of the way the picture looks like after the set has been properly adjusted (using Joe Kane’s Video Essentials, for example) and you’ll have a fair idea of the difference between the sound of your room and an RPG’d room. Sure, you may lose a bit of edgy zip—after all, resonances do add energy, distorted energy, to the presentation—but your ear will quickly adjust to the change (just as your eyes do to the well-adjusted TV set). And what you’ll realize is that undistorted, or substantially less distorted, instruments and voices are far more naturally sized, spaced, colored, textured, and dynamic than any “hyped-up” version of same.

Now those of you who have followed my writing know that I’m no pushover when it comes to resonance control devices. Deadening a component does not necessarily produce an unqualified sonic improvement, largely because the sonic signature of the “deadening” material gets added as a fresh coloration. So you’re just gonna have to trust me when I tell you that—unlike a full-bore ASC system, which often does add a too-tightly-focused, dynamics-killing, cottony deadening/damping signature to your sound—RPG’s system is very close to real-life neutral. Oh, I suppose the RPG® stuff adds a wee bit of fine light-gray grain to the soundfield (rather like what you hear listening through an ARC Reference One preamp), but instrumental timbres and dynamics, soundstage dimensions, image size and focus are so much truer than they are without the RPG® products that the cost is negligible.

Note well: RPG’s AcousticTools™ are true room treatments, intended to work at or near walls and corners. They cannot be used, as ASC Tube Traps can, directly beside or between loudspeakers to minimize panel or enclosure resonances at the source. If you feel (particularly with large planar speakers) that you’re getting a bit too diffuse a soundfield with RPG’s room treatment alone, I’d suggest adding ASC Tube Traps in a “horn-loaded” configuration. The extra absorption at either side of the speaker cabinets will tighten image focus at only a small cost in neutrality and dynamic life.

Note as well: there are some problems, particularly in the bass octaves, that no broadband acoustic room treatment can adequately solve. For these, and other severe narrow-band resonances, you can avail yourself of digital room-correction devices, such as the RDP-1. Don’t make the mistake, however, of assuming that digital EQ’ing alone will give you the same spacious, neutral, supremely transparent soundfield you get from an RPG® system. Digital EQ cannot optimize (as RPG’s AcousticTools™ can) reverberation times or adequately diffuse nasty specular reflections off windows, ceilings, or back walls. Moreover, digital equalizers add a sonic signature of their own that impacts timbres, intensities, stage depth, spacing, and image size. In addition, digital EQ cannot be used with analog sources unless those sources are themselves digitized (and you know the name of that tune).

Here, at the sunset of two-channel stereo, you may wonder why anyone should consider spending ten grand outfitting his listening space with any acoustic room treatment. For a reviewer, who must assess the colorations of components, such a move may make sense. But for the listener who doesn’t test components daily . . .?

I really can’t answer this question, save to note that rooms are the biggest and most intractable parts of your system (and with multi-channel on the horizon controlling room resonances is going to be more important rather than less). If you truly care to hear what your music, your movies, and your gear sound like at their finest—and their finest can be surprising, once the overlay of specular reflections has been removed—then you owe yourself a listen to an RPG® system. It’s like changing the water in the sonic aquarium.

Fi Spec Sheet
Product Type: Acoustic Treatment Devices
Manufacturer RPG® Diffusor Systems, Inc.
651-C Commerce Drive
Upper Marlboro, MD 20774
Ph: 301-249-0044; Fax: 301-249-3912

Prices
Skyline® Panels: $135 each
Corner Bass Traps: $269 each
7' Abflectors™: $249 each
Abflectors™ stands: $49 each
Corner Bass Trap stands: $29 each
Room Optimizer™ program: $495

Associated Equipment
Digital front end: Goldmund Mimesis 26 transport (!), Audio Note DAC-4 Signature, Z-System RDP-1 digital preamp/equalizer

Analog front end: Clearaudio Reference record playing system, Clearaudio Gold-Coil Accurate phono cartridge, Conrad-Johnson Premier 15 phono stage preamp, ARC PH-3SE phono stage preamp

Line Stage: Conrad-Johnson ART (!), Audio Research Reference One

Amplifiers: Atma-sphere MA-2 Mk. II OTLs (!), Audio Research VT-200, Goldmund SRM (!)

Speakers: Magneplanar 1.6QR, Magneplanar 20R (!), Bella Voce Signature, AvantGarde Trio (Compact), Genesis 300, Martin-Logan ReQest

Speaker Cable: Nordost SPM

Interconnect: Nordost Quatre Fil, Transparent Reference-XL interconnect and BNC digital interconnect, Transparent Reference phono interconnect

Accessories
Power cords by Synergistics Research, Aural Symphonics, Siltech, WireWorld, Transparent; SRA turntable stand; Bybee line conditioner; Brightstar sandboxes; Shun Mook pucks; Townshend Seismic Sinks.

Fi Component In A Nutshell
Pitches: Outstanding
Timbres: Outstanding
Dynamics: Outstanding
Tempo: Outstanding
Clarity: Outstanding
Soundstaging: Outstanding
Imaging: Excellent to Outstanding (depending on speaker)
Value For Dollar: Excellent
Overall Rating: Outstanding
Other Products I Should Consider: ASC Tube Traps


Fi Magazine
August, 1998

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