Boston Section

The meeting was held in the large listening room at Goodwins High end audio store on Main Street, in Waltham, Massachusetts. It began with the playing of a 2-channel recording of a selection from Gustav Holst's The Planets, made with a Schoepps sphere omni microphone.

When this recording had finished, owner Alan Goodwin spoke. He became involved in audio by constructing a high-quality analog recording system back in the 1970s; he later sold this and built a digital recording system, and spent so much time figuring it out that he is now a dealer for all the parts of it. He uses Genex recorders going straight to hard disk, 192/24 and 176.4.4/24/

This room has been revised 3 times; it is equipped with Pacific Microsonics converters for A to D and D to A, and 4-channel surround with Wilson speakers.

Goodwins also has three rooms all the same size with different acoustic treatment, good for checking on the differences.

The next speaker was Grant Carpenter, of Gordon Instruments, manufacturer and designer of Gordon mike preamps. These have a 1 Megohm high-impedance input to minimize colorations. Carpenter uses variable gain open loop amplifiers, and "what goes in is what comes out" except for the gain. The gain control is in the amplifier, instead of at the input (reducing noise with higher-level inputs) or in the feedback loop (avoiding changes in bandwidth and impedance). Every element in preamp including even the output stage is accordingly variable to minimize signal processing and even out the signal handling. Output load compensation is employed to best drive the load. These are the big picture features. Carpenter states that he tried to carry through even to sweat the small stuff including ceramic circuit boards, point to point wiring etc. "Much coloration attributed to transformers is due to the inability of the preamp to drive the transformer."

The final speaker was Peter McGrath, from Florida, who has retired from high-end audio retailing and is now with Wilson Audio. Wilson Audio makes only the finest, no- compromise loudspeakers it knows how to build, and does not go down into the range of $300 bookshelf speakers.

When McGrath was going to grad school in Chicago, and managing the Stereophile high-end shop, a talk blond fellow named David Wilson came in, and over his wife's objections, bought an Audio Research preamp. Wilson modified it and voided the warranty. He modularized the RIAA equalization stage so he could substitute another to use the preamp for microphones. Wilson moved to California, where he recorded music including string quartets. He made the "WAM" loudspeaker for his own use, then a small monitor for his recordings, the Wilson Watt. This was "beastly hard to drive." It used the Focal driver and exotic materials. Later, Wilson developed other speakers including the Wilson Audio Tiny Tot, followed by the Wilson Puppy and the combination has sold 13,000 pairs. The speakers are very expensive but have gained acceptance. The Watt Puppy 7 combination (using both of these speakers) has eclipsed the other Wilson speakers.

Wilson Audio does not use wood or MDF, having abandoned them about 7 years ago, because man-made materials give better control over resonance. The speakers are available in a wide variety of colors. The finish is superior to that of a Steinway piano.

Wilson does not make its own drivers. The speakers are relatively efficient, 90 to 95 dB, and can be driven with any flavor of amplifier. Sony Music is developing a new single-end SDM amplifier, and bought several pairs of Wilson speakers to test them because these were the most transparent Sony could find. The speakers are of relatively small size.

The Wilson speakers are installed in the Goodwins listening room, along with subwoofers that cut off at 30 Hz at 18 dB/octave -- infrasonic only. The subwoofers do make the hall sound more spacious. Their F3 is typically around 14 Hz. No EQ is used in amplification for them. The boxes are ported and rather large. The woofer driver has a 4 inch throw and a 4-inch voice coil 8 inches long.

The Wilson company is small, still owned by the founder, makes only speakers, lives and dies on its product. The manufacturing facility is in Provo, Utah, 50 miles outside Salt Lake City, and employs 50 people.

For multichannel recording, McGrath has been working on a microphone array developed by Gunter Tyler and Jerry Brooke, with figure 8 mikes facing forward and back, for coincidence w/out affecting the pattern of main omnis. He records two tracks from each, then adding outputs using DSP in and out of phase to create left and right, front and rear channels – a classic M/S setup only one on each side, creating separation between front and back rather than left and right. The system is symmetrical front to rear, and so is the room.

The first 4-channel recording that was played was of the Holst, the same performance as had been played before in 2-track. The orchestra was the Florida Philharmonic. The recording was made at 44.1, 24 bits, using Millennia mike preamps and a Meitner converter at 44.1. The playback converters are Pacific Microsonic, with upconversion to 176.6. The recording and playback machine is a Nagra 4-channel digital tape deck using a helical scan, like a video cassette recorder, on 1/4 inch tape, the same tape as is used in the Sony Dash machine.

The recording had an extremely wide dynamic range, but its spatiality got mixed reactions from the audience. The speaker setup was like that of 1970s quad, with a front- firing speaker at ear level at each corner of the room. McGrath indicated that there was no delay used in the recording or playback, but the ability to localize sounds to the rear depends almost entirely on delay, rather than amplitude differences. In the demonstration, instruments often localized into the rear speakers for listeners behind the midline of the room. [It is usual these days to place rear speakers high in the room, and to use delay as needed so the first sound from any rear-channel speaker arrives at the listeners later than that from the front speakers. In large rooms, multiple speakers with differing delays are required so the first rear-channel sound arrives everywhere within the Haas fusion limit, and the delay to the sound arriving from each additional speaker is also within that limit, avoiding slap echo. JSA]

McGrath recommended standing at one side of the room facing the other side in order to hear the audio even floating from front to rear. [At that location and orientation, the M/S microphone arrays interact optimally with the sense of hearing. JSA]

Other music played included the Allegretto from a Mozart piano concerto, played by Pyotr ?shevsky, recorded for Virgin in a smaller hall. This was played both with and without the rear channels. One listener commented that the piano sounded muddy with rear channels in, but nobody came up with an explanation. [Possibly it is that the slight drop in pitch during the duration of a piano note results in beats as reverberation from the rear of the hall mixes with the direct sound from the front. JSA]

Yet another example was a choral performance in another hall, at the University of South Florida, designed by Larry Kierkegaard, and described by McGrath as "a little gem which seats only 800 but has a huge sense of air and space." The music was one of Aaron Copland's Old American Songs, "Zion".

The final example was an excerpt from Verdi Requiem. The orchestra had had a poor bass drum; McGrath commissioned a better one but on this night the player was "homicidal. Use your digital filters" (fingers).

--John S Allen, Boston Acoustical Society