The sound
The first task was to assemble the matching SLSi speaker stands that Celestion supplied for the review. These are available in 18" and 24" heights—I used the 18" model for the auditioning, placing the listening axis just above the tweeter—and cost $300/pair for either. A rectangular, extruded aluminum pillar, internally ribbed for torsional strength, is bolted to flat top and bottom…
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Like its predecessor, the '600Si can be extended with Celestion's stereo dipole subwoofers, the System 6000, to give a full-range speaker system that preserves the satellites' midband purity.
The lows of the '600 have always been a favorite of mine. While Richard Vandersteen can show that fourth-order LF alignments needn't boom, a good second-order, sealed-box loading seems inherently to have a cleaner mid-upper bass presentation. My ultimate torture track to test speakers in this region is the 12" Huey Lewis and the News single, "The Power of Love." With the Krell driven to the point of clipping, it is astonishing to hear the clarity with which the Celestions can present kick drum, coupled with a suitable degree of weight. Bass extension is not as generous as with, say, the…
Sidebar 1: 1989 System Context
Each pair of loudspeakers was carefully positioned for optimal performance sitting on their own stands, coupled to the floor beneath the rug with spikes. Amplification was provided by either a pair of VTL 100W Compact monoblocks or a Krell KSA-50 power amplifier, each bi-wired with Monster M1 speaker cable. The preamplifier was either the combination of the Mod Squad Line Drive Deluxe AGT and Vendetta Research SCP2 phono preamp, or the Conrad-Johnson PV9 (also reviewed in this issue). Source components consisted of a 1975-vintage Revox A77 to play my own…
Sidebar 2: 1989 Measurements
Each speaker was submitted to the following measurement schedule: The voltage sensitivity was assessed with 1/3-octave pink noise centered on 1kHz, while the change of impedance with frequency was measured using spot tones (footnote 1). The nearfield low-frequency response of each speaker was assessed with a sinewave sweep to get an idea of the true bass extension relative to the level at 100Hz.
The frequency response of each speaker in the listening area was measured using pink noise and an AudioControl Industrial SA-3050A 1/3-octave spectrum…
John Atkinson wrote again about the SL600si in August 1992 (Vol.15 No.8) and about the DLP600 DSP equalizer:
You always meet interesting people in the stairwells of hotels. Whether this is because the more interesting a person is, the more easily they become frustrated at having to wait for an elevator, or because they feel better at having expended a little physical energy, who knows? But so it proved at the 1992 Summer CES when, working my way down the Chicago Hilton's floors one by one in my usual pedestrian manner, I bumped first into David Clark, then John Eargle (footnote 1), and…
Internally, the DLP600's circuitry is laid out on a single printed circuit board. The input data are received by the ubiquitous 16-bit Yamaha YM3623B digital audio decoder IC and fed to a DSP (Digital Signal Processor) IC. This is an Analog Devices ADSP-2105, a chip said to be well-suited to being used as an FIR (Finite Impulse Response) digital filter due to an efficient instruction set.
Two families of digital filters are realizable with such a DSP chip: FIR and Infinite Impulse Response (IIR) types. An FIR filter, which in the real world of limited hardware resources is best suited to…
Then I hooked up the DLP600. Apart from slightly more HF energy, there didn't seem to be much obvious difference in the sound. I continued listening, putting on one CD after another. The system did seem to sing that evening. Then I switched out the EQ. "Good grief, Charlie Brown—who put Vaseline on the lens?" If subtle when switched in, the DLP600's effect on the system's overall quality represented a major loss of quality when switched out. To paraphrase Gertrude Stein, there was simply more there there with the DLP600.
I asked Digital Lad Robert Harley to come over for a second opinion…
Note that the DLP600 works its magic only in the upper midrange and above. The SL600 retained its rather lumpy upper-bass/lower-midrange transition, and there remained the lack of overall clarity in the tenor region. Without this, in fact, I would be tempted to say that the combination of the SL600Si and DLP600 left Celestion's flagship SL700SE in the dust. As it is, I think that the 600 tandem at least equals the more expensive speaker overall, and surpasses it in treble clarity and musical ease.
To finish my auditioning sessions with the DLP600, I dug my 1982 pair of original Celestion…
Sidebar 3: Digital Audio Filters
There has been considerable published work in recent years on the use of filters operating in the digital domain to optimize loudspeaker performance. Those interested should read the following papers: "Efficient Filter Design for Loudspeaker Equalization," Richard Greenfield and Malcolm O. Hawksford, JAES Vol.39 No.10, October 1991; "Digital Equalization Methods for Audio Systems," J. Mourjopolis, and "Application of Digital Filters to Loudspeaker Crossover Networks," Rhonda J. Wilson, J.B. Scott, and the late Glyn J. Adams, both presented at the 84th AES…
Sidebar 4: 1992 System Context
The reference system used to audition the SL600Sis and the effect of the DLP600 is the same as that used for my past few reviews. The all-digital nature of the DLP600 meant that analog playback had to be (temporarily) abandoned, however. Source components consisted of a Meridian 602 CD transport driving either a VTL Reference D/A processor or the Audio Alchemy DDE. Digital interconnect between the Meridian and the DLP600 was a 1m length of AudioQuest's new Digital Reference; between the DLP and the DACs I used a 0.5m length of the Mod Squad's Wonderlink.…