A Matter Of Diffusion Page 3

A wide variety of high-grade components was used during more than a full year of listening evaluations, beginning in late 1986. Front-ends included a Goldmund Studietto/T5 'table/arm set-up with Linn Karma or Koetsu Black Gold Line cartridges; a Linn Sondek/Ittok with Grace F9E Super, Linn Troika, or Linn Karma; several Michell Gyrodecs with Zeta, SME, or Eminent Technology tonearms fitted with Madrigal Carnegie, sundry Koetsu, or Grado Signature series cartridges; and The Source turntable from Scotland, fitted with SME V and a Carnegie One. Original master tapes and dubs, played on a Don Alley-modified Revox B77 and a stock Tandberg TD20A-SE, were also used on occasion. On the digital side, CD players seeing the most action were the Meridian 207 Pro, Nakamichi OMS7A MkII, Tandberg 3015A, and California Audio Labs Tempest Revised; an Accuphase DC80/DP81, Kinergetics, and Stax Quattro were also used for shorter times. Electronics included the Mark Levinson ML7A and prototype No.26 preamps; Levinson No.23 and No.20 Class A monoblock amps; the full assortment of Conrad-Johnson Premiers; a Spectral DMA-100; the Jadis JA-30 class-A monoblocks; Bryston 3B and 4B; and various loaner or trade-in electronics from Audio Research, Krell, Cello, Rowland, and Accuphase.

I used a range of speakers familiar to most Stereophile readers: the Apogee Diva, Scintilla, and Duetta ribbons; Quad ESL-63 electrostatics; Magnepan MGIIIa planar magnetics; and KEF 107, Vandersteen 2C, Spendor SP1, and Spica TC50 electrodynamics. I also included two new electrodynamics that may be unfamiliar to most: the Waveform Loudspeakers and Booth Curvefront IIs. Although many others were tried as well, I shall restrict my comments to the aforementioned, as they cover a broad and representative range of operating principles, polar patterns, tonal personalities, and, as it happened, results.

For the formal listening sessions I settled on a Gyrodec turntable fitted with SME V tonearm and Carnegie One cartridge feeding the Levinson ML7A preamp (L3A phono modules) and Levinson No.23 power amp. The amplifier was selected after much care because it was found to be particularly well suited to the test, displaying both the iron grip to deal firmly with the unruly Scintillas, and the finesse to coax the Quads and Spicas to their delicate best. Cabling was by Monster, MIT/Brisson, and Belden. I brought in my recording engineer, John Oster, to record the sound of the system playing both with and without the RPGs deployed. A pair of the new B&K omni mikes, placed at the listening position, fed a modified Revox B77 reel-to-reel and a Nakamichi Dragon cassette deck. Later I went back and "A/B'ed" the room with and without the diffusors by replaying the tapes over Stax Lambda Pro electrostatic headphones and comparing my original notes.

Although the more controlled part of the test involved evaluating the diffusors with speakers of various types, it is worth noting that substituting any of the other source components, electronics, or cables for those in the reference playback system had little or no effect on results found for the RPGs. In other words, there was no case in which a different combination of source components, electronics, and/or cables produced results that were at odds with those produced with the reference system and described in this overview. However, the RPGs did alter the sonic environment in ways that often made it easier to get a handle on the sound of a particular component; they illuminated certain equipment characteristics that previously lurked only as vague impressions. I suspect this was due to the fact that the diffusors remove sonic grundge (comb filter and echo effects) that otherwise masks some of the subtleties of certain components. At any rate, the fact that the diffusors did not turn component preferences topsy-turvy is interesting.