Celestion SL600si loudspeaker & DLP600 digital equalizer Page 2

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 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 plates. The pillar can be filled with whatever you choose to increase the stand's mass and damp its own resonant modes. Dry sand is an option, as is lead shot. As Celestion kindly provided lead shot, that is what I used, 37 lbs per stand.

The final steps were to screw in the spikes and sit an SL600Si on top of each stand, putting some thought toward how the speaker's Aerolam enclosure should best be coupled to the stand. Celestion warns against the use of upturned Tiptoes or metal cones, which will penetrate the thin aluminum skin, instead recommending small pads of some non-reactive, resistive-damping material, such as the E.Z.Tak mastic material used to pin up posters and pictures (great value at $1.59 for about 50 times the quantity you actually need from your local Woolworth's). This is what I ended up using—without anything at all, the lower midrange noticeably thickens up, adding a "hooded" quality, particularly to female voice—but I should think that the thin Sorbothane sheet marketed by AudioQuest ($12.50 from The Audio Advisor) would also be worth experimenting with.

One thing that has always been true for the best British loudspeakers is that they need plenty of room to breathe, and it applies to the SL600s in spades. Whereas the SL700s will put up with a relatively close rear-wall placement, usefully reinforcing the bass, the '600s need at least three feet's grace, in my opinion, if the sound is not to become too dark. But like the '700, the side walls need to be well away from the speakers' immediate environment. The precision of the stereo imaging that these speakers can produce is very sensitive to reflections that are spaced too close in time to the intial wave, the result being a considerable degree of image collapse. If your listening room doubles as the family room, it would be wise to consult your partner before you commit yourself to purchasing a pair of these Celestions.

Listening to a pair of speakers with just the tweeters connected reveals how little energy is carried by the HF driver. The Celestion SL600Si, for example, has just a whispy thread of sound reproduced by its tweeter, which leads almost to a feeling of puzzlement, even wonder, that improvements in the reproduction of this small wedge of musical information can have such a major effect on the sound. Yet it was the treble of first the SL6, then the SL600, that had convinced me of the fundamentally musically correct nature of metal-dome tweeters.

Listen to the Hildegard of Bingen track on the HFN/RR Test CD, for example. At high levels with many—no, most—conventional fabric- or plastic-dome tweeters, the listener becomes uneasy as Emma Kirkby's voice rises in pitch as she nears the danger area in the crossover region, finally jumping up to back down the volume control as the tweeter is forced into aberrant behavior in its first octave. Listening to that track via the SL600Si's reminded me of the first time I'd heard this tweeter, back in 1981, for again, I found myself marveling at the complete absence of upper-midrange problems. Emma Kirkby's divine voice just soared, unbound by earthly resonances or any sibilance emphasis. And when it came to reproducing the sound of violin, unlike just about any other box speaker, the '600Si gets right the balance between midrange aggression and treble sweetness.

Yet this lack of upper-midrange coloration featured by the SL600Si revealed slight problems lower down in frequency, problems that might have been overlooked in a more earthly design. Particularly on piano recordings, a degree of sonic confusion, even slight congestion could be heard in the 500-700Hz region. While this coloration added to the speaker's sweet tonal balance, it nevertheless must be counted as a fault, and added a slight hardness in this region at high levels.

In the high treble, the HF was slightly depressed; but, more important, the sound lacked a little immediacy, suggesting a lack of energy in the presence region. It was for this reason that I ultimately changed back from the PV9 to the Vendetta/Mod Squad combination. Though the system sensitivity was now a little too low, limiting the ultimate loudness with the Krell, the sound was now usefully less dark.

The dark presentation was perhaps exacerbated by a lack of retrieval of ultimate detail. In the Hildegard track mentioned above, for example, the voices are smoother, more natural than on the Vandersteen 2cis. But the American speakers allow you to hear that a softly struck chime joins the regal in accompanying those voices. On the SL600Si's, the leading edge of the sound of that chime melds into the background drone.