Cambridge Soundworks Model Six Bookshelf speakers
In a career spanning four decades, Henry Kloss has been responsible for the design or production of some of the most successful and trend-setting loudspeakers of their times, including the AR-1, AR-2, and AR-3, the KLH Model Six, and the original Large Advent.
Most recently he has been associated with Cambridge Sound Works, where he has developed a line of loudspeakers that carry on the tradition of offering exceptional performance for a modest price. The new Model Six, named for Kloss's KLH Model Six of the 1960's, brings that speaker's design approach into the 1990's.
Like most Kloss speakers, the Model Six is a two-way system. It is based on a newly designed 8-inch acoustic-suspension woofer that crosses over at 2 kHz to a 1.75-inch cone tweeter with a 0.5-inch center dome (the same tweeter used in Cambridge SoundWorks' costlier Ensemble systems). Not a speaker that needs to be hidden from view, the Model Six has an attractive simulated-woodgrain finish in a choice of oak, teak, or black ash, and a nonremovable cloth grille in medium charcoal gray further enhances its appearance. Heavy-duty binding-post input terminals, compatible with single or dual banana plugs, lugs, or wire ends, are recessed into the back of the cabinet.
Although the Model Six comes with none of the usual speaker performance specifications, a couple of pages of its installation instructions contain more meaningful and useful information about speakers than a comparable amount of acoustic-measurement data or even many far longer treatises. In addition to the usual suggestions on placement and connection-18-gauge or thicker wire is recommended, with a refreshing note that "there is no audible benefit with these or other speakers from very heavy (and expensive) 'audiophile' speaker cable"- other universally applicable statements inform the user that "the apparent fullness of the sound is a function of mid-bass rather than low bass" and that the "subjective 'openness' is not so much a function of the high treble as it is of the lower midrange." Finally, there is the relatively obvious (but often overlooked) suggestion that "program material varies greatly, so be sure to listen to a variety of recordings. This will prevent your being misled by the particular characteristics of a particular recording." That is valid advice for judging any speaker, and I could not have said it better myself.
Our averaged room-response curve from the two speakers spliced to the close-miked woofer response with about an octave of overlap, producing a composite curve that was unusually uniform from 1 to 20 kHz. It had a few +/-0.75-dB variations and an overall downward shift of about 1 dB above 1 kHz, but those were the only anomalies in that range.
The woofer response, flat within 2.5 dB from 75 to 600 Hz, sloped down by about 3 or 4 dB above that point as it overlapped the room curve. Overall, the woofer response seemed to be 3 to 5 dB higher than the averaged tweeter output. The bass output dropped at 12 dB per octave below 80 Hz; in the composite curve, the overall response was a very good +/-4 dB from 56 Hz to 20 kHz.
We also made a number of quasi-anechoic frequency-response measurements using the MLS program of our Audio Precision System One test set, with microphone distances of 1 and 2 meters, and some ground-plane measurements to minimize the effect of floor reflections. Although there were some differences between the resulting measurements (because of unavoidable reflections), certain key features appeared in all the MLS response curves. (Our MLS measurements are not valid below 300 Hz, but above that frequency they give information that is pretty much independent of the speaker's environment.) Typically, there was a 3-dB peak (relative to the lower frequencies) at 3 kHz, followed by a drop of 5 to 6 dB to a minimum between 6 and 7 kHz, a return to the 3-kHz level from 7 to 8 kHz, and a 3-dB drop to a plateau ending at 13 kHz, above which the response fell about 5 dB as the frequency approached 20 kHz. Describing these curves in words may make them seem rather ragged, but in fact they're quite good for a loudspeaker, and they confirmed the impression from our listening tests that the Model Six is truly a high-quality speaker.
The tweeter's dispersion was satisfactory, with the response 45 degrees off its axis down 3 dB at 6 kHz, 5 dB at 9 kHz, and 18 dB at 20 kHz. The system impedance reached a maximum of 18 ohms at the bass resonance frequency of 75 Hz. There was a broad peak of 12 ohms at 1 kHz and two minimum impedance readings of 6.6 ohms at 180 Hz and 8 kHz (plus one of 6.2 ohms at 20 Hz). All in all, we would call the nominal impedance 8 ohms.
Sensitivity, with a 2.83-volt input of random noise, was 91 dB sound-pressure level (SPL) at 1 meter. Woofer distortion was measured at 2.53 volts, corresponding to our reference level of 90 dB SPL. The distortion was between 1.5 and 3 percent from 2 kHz down to 75 Hz, rising at lower frequencies to 4.5 percent at 50 Hz, 8.5 percent at 40 Hz, and 12 percent at 30 Hz.
Despite its small size, the Model Six handled very large transient power levels without damage or even serious audible effects. The woofer cone hit its limits with a thump (but without damage) at a single-cycle 100-Hz input of 470 watts. At 1 kHz, where the cone movement for the same SPL is much smaller, the driving amplifier clipped at 550 watts, and the tweeter absorbed the full amplifier output of 950 watts at 10 kHz without difficulty.
From these measurements, one would expect the Cambridge Sound-Works Model Six to be a very fine-sounding speaker, and one would be right. Its clarity and precise imaging reflect Kloss's extensive "voicing" of the speaker to give it the optimum octave-to-octave balance. As for the lows, although the Model Six won't rattle the windows or make your ears pop with the pressure of low organ notes, you will know when they are present. It has an "all there" sound quality that belies its amazingly low price and does credit to its heritage. It even has a vinyl finish that looks and feels like real wood (our test samples were finished like teak and simply did not look as if they belonged in a bargain-basement price class). At only $119 each, the Model Six is an exceptional value.
