Celestion System 6000 loudspeaker system:
Page 2 With the electronic crossover—which connects either in the preamplifier tape loop or between pre- and power amplifiers—set to 100Hz, the bass section can be adjusted for absolute level and the best extension in the nominal 20-70Hz range, with a constant Q of approximately 0.4. The 24dB/octave, 4th-order Butterworth crossover slopes are complementary, being obtained by substitution; ie, the low-pass output is obtained by subtracting the high-pass output from the input, and the crossover is DC-coupled throughout, this (unusually) including the high-pass section, which has no series capacitors. The crossover/controller is well constructed, self-powered, and employs selected integrated circuits of well-defined audio performance.

The woofer section provides a massive inert platform on which to place the SL600 speaker. For those unfamiliar with the '600, this established high-tech design uses a one-piece, pure piston, copper-dome tweeter, and a well-terminated, 6.5", synthetic flared-cone woofer. Built on cast metal frames, these drivers are mounted in a compact, low-mass enclosure of exceptional stiffness. This costly construction is fabricated of Aerolam, a low-mass aircraft structural material. No grille is supplied, as it impairs the stereo performance.

Sound Quality
I must put on record at the outset that I am an SL600 fan. I have found it to be, virtually since its inception, a consistently useful reviewing and musical tool. I know it is rather expensive in the US for its small size and limited low-frequency extension, but its fundamental performance is sufficiently high to make it a creditable, if modest, audiophile speaker.

To some degree, it was the demand for a subwoofer for the SL600 which resulted in the System 6000. When set up and properly adjusted, my first observation was that the 6000 sounded extraordinarily like a naked '600. Leaving aside for the moment matters of dynamic range and bass extension, the low-frequency sections of this speaker were remarkably unobtrusive. Since I reckon the SL600 to be most accurate, within its limits, below 1kHz, it was significant to find that the '600 sound was not particularly modified by the addition of the subwoofers. So many subwoofers immediately draw attention to themselves, almost in a manner designed to prove to the listener that they are, in fact, working!

As a complete three-way system, the 6000 sounded completely coherent, with all three driver outputs skillfully integrated, forming a uniform, wide-range, and well-balanced whole. The inherently "rich," but in the main desirable, balance of the '600 was unaffected.

Well, what does the System 6000 do that the SL600 cannot? Put on some wide-range material at decent levels and the answers will be immediately apparent. The 6000 then sounds like a louder, clearer, more articulate and more extended SL600. On powerful material, the reduction in midrange intermodulation and the resulting gain in the resolution of complex instrumental scoring is very worthwhile. The dry, extended bass provided a solid foundation for a sense of scale and place, underpinning the entire performance. SL600 bass is one of the least colored in the business, and the 6000 bass proved to be still less so. As with other extended-bass systems, the extension removes some subjective "heaviness" from the midbass, while the midrange sounds more natural.

As a system, the 6000 played to respectably high music sound levels, but not to disco intensity in large rooms. Amplifiers capable of delivering 100-200W/channel into 8 ohms are required to exploit it to the full.

Fine results were obtained with a baseline system consisting of the English Audiolab separates—two 8000 stereo power amplifiers partnered by the 8000C preamplifier.

System 6000 continued to show improvements in tonality, resolution and speed when partnered with more costly electronics. Although I don't offer this as a specific recommendation, System 6000 benefited from a trial with a Krell KSA100 driving the bass, partnered by an Audio Research M100 for the upper range, both amps driven by an Audio Research SP-11 preamplifier with a Cambridge Audio CD1 player and a Linn/SME V/van den Hul One vinyl disc source.

Comparisons were possible with a number of mid-price audiophile speakers. I was fortunate to have temporary loan pairs of Apogee Duetta II, MartinLogan CLS, and Magnepan MGIIIa speakers to hand (see Vol.10 No.1); when properly driven, the System 6000 landed squarely in their performance category. All the aforementioned speakers have good fundamental performances coupled with specific areas of greatness. The System 6000 is not outstanding in any one respect, save the consistent balance of its performance. One could argue over the merits of the speed and transparency of the CLS in the mid, or the airy, extended treble of the MGIIIA, or the low coloration and free-space "slam" of the Duetta II. The Celestion, however, fights back, without fuss or drama, to deliver a classically balanced performance: dry, controlled, and coherent.

On absolutes, the 6000 consistently satisfied over longer time periods, drawing less attention to itself and more to the program. Stereo images were a little restricted in height, but threw a considerable depth downstage. This was allied to exceptional positional focus, coupled with remarkable perspective layering. On appropriate material, the stereo width comfortably extended beyond the breadth of the speaker enclosures.