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Finding the proper perspective from which to evaluate the Celestion SL-600 loudspeaker makes this an exceptionally difficult review to write. On one hand, this is an excellent loudspeaker in many ways. On the other hand, I cannot totally decouple my review from the issue of value for money. The Celestion SL-600 is a small (15 x 8 x 10 inches) two-way system selling for $1,380 a pair and requiring, almost absolutely, a heavy, rigid stand of the proper height. Celestion sells stands that match the SL-600 for an additional $350 per pair, which adds up to $1,730 for the system, while for $120 per pair, one can obtain from Celestion wood stands that are decidedly less rigid and heavy. I have reservations about how well the $350 stands match the speakers, as I'd prefer a stand whose speaker mounting plate precisely conformed to the speaker's size (this stand's edges protrude beyond the speaker) and whose height could be adjusted. However, Celestion intends to provide new stands, with properly sized mounting plates and, possibly, a lower price. And they feel that the stands' 18-inch height is precisely optimized for the speaker's vertical polar response.
In addition, I cannot in good conscience omit mentioning some of the other fine small monitors which achieve excellence at only a third the price of the Celestion. These include two that are directly competitive in terms of what the SL-600 does best, the SPICA TC-50 ($450 per pair) and the Dayton Wright LCM-1 ($499 per pair). Further, I should not ignore the fact that some of the best three-way systems I know of sell for less than, or close to, the final cost of the SL-600 including stands. Among these are the Thiel 03A and CS3, the Vandersteen 2C, the Phase Diametrics Fuselier 3.3, and the Magnepan MG-III.
I also can't ignore several real-world limitations inherent in any small monitor speaker. The potential advantage of a design like the SL-600's doesn't lie in its small size. If you select a small monitor, you're paying for coherence, imaging, a focused sound stage and uncolored sound from about 80 to 120 Hz. It will perform at its best only if put on a stand, placed at least 18 inches from a rear wall and 24 inches from a side wall, and so that no major pieces of furniture are between it and the listening position. I do not, therefore, believe a small monitor of this type saves space. A much larger three-way system will fit into any room where you can properly place this speaker.
A small monitor also cannot generate the bass power of a large speaker, and this is audible in the lower midrange as well as the bass. The 1-meter, on-axis, measured bass response doesn't adequately indicate the true bass power delivered to the ear. Design after design has shown that it takes a big woofer in a much larger cabinet to do this, regardless of woofer excursion, etc. This means that a small monitor always sounds slightly unbalanced. The much-praised LS-3/5A, for example, has a boost at about 120 Hz to make up for its lack of deep bass. It relies on illusion rather than accuracy.
In contrast, small monitors with flat frequency responses tend to sound bright and constricted. The Proac Tablette is a good example of a very small monitor speaker without enough bass power to be musical unless you add a subwoofer. The Tablette is "high fi," but I find it unacceptable as a standalone unit in terms of musical balance compared to any speaker with even adequate mid-bass. The old Spendor mini-monitor had better bass than the Tablette, but it made a fascinating contrast with the Rogers LS-3/5A. The flat bass in the Spendor simply didn't have the impact to compete with the bass hump in the LS-3/5A. This may help explain why Spendor now licenses and produces the less "accurate" (or flat) LS-3/5A. The SL-600 seems to use a variation of the LS-3/5A technique. It appears to have a rising bass characteristic, rather than a peak, down to the point where its bass response falls off. This provides a relatively flat apparent mid bass and much better upper bass than most small monitors, and does so up to moderately loud listening levels, provided the SL-600 is driven by a "stiff," high-quality power amplifier. The SL 600s really should not be used with ordinary receivers or integrated amplifiers. Ideally, they need an amplifier on the order of the Krell or Threshold or, at least, the Belles Research, Hafler DH 220 or PS Audio IIC+. Even then, the SL-600 won't display the bass power, naturalness or the smooth bass-low midrange transitions of the best three-way systems in this same price bracket. You give up some important musical information to buy this speaker.
And yet, I have to say the SL-600s are worth considering, even with their high price and sonic compromises.
Small monitors do offer some compensating advantages for what they give up. They provide a fairly close approximation of an apparent point source, and this can mean exceptional imaging and sound-stage stability. The SL 600s largely meet this test. They don't furnish the depth of some competing, high-priced, full-range speakers, but the sound stage is wide and generally well proportioned. The imaging is stable and has a good spread of instruments, rather than "dual mono." You can listen from a relatively wide range of listening positions, and the net effect is that the SL-600s provide a bigger and more natural sound stage than many much larger speakers which lack superior driver and phase alignment.
I also have to say that there is something special about the timbre of this speaker that may suit your taste in a way no other comparably priced speaker can. The SL-600s are as musical a speaker in reproducing male voice above the bass range, and female voice below upper soprano, as I have ever had the opportunity to review. Guitar and flute, small wind and string groups, small jazz combos (those which do not rely heavily on a bass line for impact), and other music whose size and sound seems natural to a home-sized room can also take on a musicality that competes directly with the best loudspeakers in the price range.
I'm not entirely happy with this musicality. I've read through the technical literature on this speaker in some depth, and it is well written and generally convincing. Nevertheless, I seem to hear irregularities and a lack of data in the transition area from lower midrange to midrange that I don't hear in my Quad ESL 63s or in similarly priced competition like the Thiels or Vandersteens. I cannot object to the sound on most music, but I have the feeling that the SL-600s' magic is at least partly the result of euphonic coloration, rather than flat response.
The SL-600s do handle fast musical changes with exceptional naturalness, and without the apparent treble rise which characterizes many small speakers that seem fast and image well. Their upper midrange and lower highs seem closer to those of electrostatics than to those of dome or cone units. They are definitely the strongest aspect of the SL-600 and may ultimately justify its cost. They're easily the equal of the upper midrange and lower highs of loudspeakers costing twice as much.
Equally important, the SL-600s do not "etch" or emphasize the upper octaves, except perhaps the top octave. I prefer the more recessed top-octave response of my Quad ESL 63s, but this is a matter of taste. There's no question that the SL-600s add a touch of top octave air and extension to a great deal of music-but the excitement, air, and transient detail come about without adding hardness or bringing you too close to the performance.
As for power response, bigger speakers produce bigger sound. Nevertheless, you can use high-power amplifiers and the SL-600s won't give up in distress. I threw the power of the conrad-johnson Premier Fives, the Futterman OTL-3s, and the Audio Research D160B at the SL-600s, and drove them to the maximum listening levels I consider natural. The bass was a bit iffy, but the midrange and treble stayed fast and clean.
I did find the SL-600s to be speaker cable and placement sensitive. You need a good, fast speaker cable, very tight connections (try the Monster Cable Xterminators instead of banana plugs), and careful attention to the rest of your system. I would recommend cables of the Powerline II, Livewire, Straightwire, Randall, and Discrete Technology caliber. Ordinary Monster Cables, or moderate quality speaker cables, don't seem to have the speed and upper-octave purity to get the best out of them.
As for placement, I ended up using a stand a friend had built, which had a sand-filled column, adjustable height, and heavy, adjustable baseplate. I found that height and speaker angle make a difference. The SL-600s seem to have a proper height for a proper listening position at which they lock in and really perform their best. They also merit "tweaking" in terms of altering angle of the speaker's face towards the listener, but this is not compulsory.
You may well find that keeping soft furniture as far away from the sides of the SL-600s as possible, and minimizing coffee tables and other clutter between the speaker and the listener, will give you outstanding results. The SL 600s will provide a good, stable sound stage without this kind of purism, but if you want the best from a $1,400+ pair of loudspeakers, you're going to have to pay close attention to your listening room.
In short, the SL-600s are a fairly esoteric choice. At $500 a pair, I could quickly recommend them, but at $1,380 plus the cost of the stands, everything depends on whether you feel they have that special magic that suits your taste. If you favor voice or small musical groups, you may well feel the SL-600s are just what you want; oddly enough, you may also feel this way if you like rock. The SL-600s' bass may be slightly restricted, but this actually benefits that large amount of rock material where poor monitoring and recording drown everything with one-note bass. When I say this speaker merits careful listening, I am not reciting a cliché. At the price, its value depends on your ears, and not mine.
-Anthony H. Cordesman
(Source: Audio magazine, Feb. 1985)
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