A Matter Of Diffusion Page 7

I would also like to point out that in order to reduce the variables in the test, I avoided mixing in other acoustical treatments, such as Sonex or ASC Tube Traps, with the diffusors. Yet it is almost a surety that the diffusors will work best as part of an overall listening-room overhaul that would include products like the Tube Traps in corners (for dipolar speakers), and broadband absorbers against the front wall and forward portions of side walls for most forward-firing designs. The diffusors seem to have little or no effect in the sub-150Hz region where Tube Traps can be effective in "equalizing" pressure buildups in room corners. I would like to experiment with diffusion and/or absorption on the floor and ceiling (to scatter or kill those strong and largely monophonic early reflections) and Tube Traps in the corners. In the meantime, RPG has introduced their own line of additional products, including the ABFFUSOR(R), a broadband absorber offering some diffusion, and the TRIFFUSOR(R), an equilateral triangular prism that can be rotated to expose absorptive, diffusive, and reflective sides. (The TRIFFUSOR(R) is also available as the Korner-Killer[tm], which is one diffusive and two absorptive sides, for "Tube Trap"-type effects.)

There is the issue of whether similar results could be had without resort to brute-force acoustics, say with active electronic manipulation a la surround-sound or time-delay systems. My experience to date is that existing aftermarket components do not offer the same degree of blow-down-the-walls enhancement because they leave intact the normal acoustic cues that aurally define the small room; they only superimpose another set of aural cues that suggests a bigger room. I wonder if the mental "dissonance" of receiving several sets of acoustic cues might not lead to confusion and perhaps listener fatigue for some. With existing electronic enhancers, the time interval between the arrival of direct sound and its first reflections remains that of a small room; the denser and longer reverberant tail of the sound suggests a bigger room, but for me it suggests more than it persuades. Undoubtedly units like the Yamaha DSP-1 six-channel system will evolve, opening up at least the (admittedly remote) possibility of some day getting RPG-type improvements electronically.

There is no question of the diffusors' offering good value: few component upgrades or acessories can approach their price/performance ratio. There remains, though, the question of whether mass production could significantly lower the cost of the RPG units to the consumer. As it is, you could "diffuse" a couple thousand dollars in RPG's direction to get the results I've described in a typical 12'x18' listening room. I asked D'Antonio whether he'd considered moving to an injection-molding process instead of time-consuming assembly of furniture-grade wood slats and metal strips. "Yes," he said, "but at the end of the day, you have one configuration, one color, a fire-rating problem, and an acoustically diaphragmatic entity. Consequently, we made a conscious decision to use wood, a material which has endured the test of time." Despite the diffusors' high value and good finish, I suspect some Audio Cheapskate partisans will try to buy the raw materials locally and copy the RPG design as best they can. N.B. Cheapskates: D'Antonio hints that a lower-cost version may be in the offing.

Another suggestion: The manufacturer should provide an easy way to affix grille fabric to conceal the wells. The standard lacquered birch versions I received played to mixed reviews in the looks department during their year-plus of nearly continuous display. Of course, care would need to be taken in the choice of fabrics, as at high frequencies and very shallow angles of incidence some "acoustically transparent" material is actually quite reflective. Perhaps RPG could make available swatches of acoustically acceptable fabric, along with replaceable speaker-grille-type frames. On a related note, D'Antonio indicates that custom finishes---from plexiglass for see-through applications to mirror, laminate, paint, and select hardwoods---are available at extra cost.

Finally, the RPG's greatest contribution could be that it catalyzes widespread interest not only in acoustically rehabilitating existing listening rooms, but also in the next logical step: the construction of purpose-built music environments in the home. That is the high-end's next frontier, and it is now at our doorstep.