Thiel CS1.2 Speaker System Review

Thiel’s approach to speaker design emphasizes the importance of controlling time and phase response, as well as frequency response, in order to provide accurate reproduction of the spatial image and the tonal quality of a program. Its Coherent Source speaker systems demonstrate the validity of this conception of speaker performance.

The CS1.2 is the smallest member of the Thiel family of Coherent Source speakers. It is a two-way, floor-standing system consisting of a 6-1/2-inch woofer in a vented enclosure and a 1-inch dome tweeter. Its basic design closely resembles that of larger Thiel systems, with the woofer in the middle of a gently sloping front panel, the tweeter above it, and the woofer port at the bottom. To minimize diffraction of the sound waves, the edges of the molded-plastic panel are smoothly rounded, and the tweeter is recessed slightly into the panel. The slope of the panel is intended to place the drivers equidistant from a seated listener, thereby preserving the time coherence of the program.

For minimum crossover phase shift, Thiel uses a 6-dB-per-octave slope between the two drivers. The crossover network, which uses high-quality capacitors and air-core inductors, is surprisingly complex, having been designed to complement the phase and amplitude characteristics of each driver to produce a true first-order response.

Despite the small diameter of its woofer, the CS1.2 is rated for a frequency response down to 50 Hz at the — 3-dB point. The woofer has a rigid, die-cast magnesium basket, and its long voice coil and large magnet give it the same bass capability as most 10-inch drivers. The tweeter dome is made of aluminum, with a resonance above the audible range, and its voice coil is cooled by ferrofluid.

The CS1.2 stands 36 inches high and 10-1/2 inches square, and it weighs 47 pounds. Heavy internal bracing and thick cabinet walls (1 inch at the sides and 1-1/2 inches for the front panel) minimize cabinet vibration, and the sloping front panel helps to reduce internal standing waves. The cabinet is teak-veneered on all sides (a black laminate is also available), and it has a black cloth grille. Pointed mounting feet are supplied to improve the speaker’s contact with the floor (it is supported at three points for stability). The multiway binding-post connectors are under the cabinet. System specifications (measured with 10-foot spacing in an anechoic room) include a frequency response of 52 to 18,000 Hz ±2 dB, sensitivity of 87 dB, impedance of 4 ohms, and recommended amplifier power of 40 to 150 watts.

Though placement is not critical, the Thiel CS1.2 speakers should be well away from all walls. Their wide dispersion permits (and encourages) spacing the speakers fairly far apart. Optimum phase and time alignment is said to be provided only for a seated listener more than 8 feet from the speakers. Price: $1,090 a pair.

Lab Tests

We tried to follow the manufacturer’s placement recommendations as closely as possible, although our listening tests indicated that the CS1.2’s basic sound character was not affected to any great degree by reasonable variations.

The room response at 0 and 30 degrees off the axis with the microphone was virtually identical. This characteristic is stressed in Thiel’s brochures, and our experience totally confirmed the superb dispersion of the system. Also, there was no sign of the usual middle or upper-bass irregularity caused by room resonances; the smooth response extended to 70 Hz and below.

Combining close-miked response measurements of the woofer cone and port produced a very flat response curve, ± 1 dB from 70 to 1,100 Hz. This spliced easily to the room-response curve to form a composite frequency response of ±2.5 dB from 46 to 20,000 Hz, slightly surpassing Thiel’s rating. We noted with interest that our composite response curve closely resembled anechoic curves on the same speaker units that were supplied to us by Thiel. Our quasi-anechoic FFT measurements gave generally similar results, although we found a considerable variation with different microphone heights.

The speaker’s horizontal dispersion in the FFT measurement was extraordinary. The response curves on-axis and at 45 degrees off-axis matched within 3 or 4 dB from 200 to 18,000 Hz, differing for the most part only by a small level shift. These results were obtained at the optimum microphone height and spacing; other positions introduced more conventional divergences between the curves at the higher frequencies. The group-delay variation was only about 0.2 millisecond overall from 300 to 20,000 Hz, confirming the system’s excellent phase linearity.

The system’s impedance was unusually constant with frequency, remaining between 3 and 6 ohms and averaging about 4 ohms from 20 to 20,000 Hz. Its sensitivity measured 87.5 dB sound-pressure level (SPL) at 1 meter with a pink-noise input of 2.83 volts. At an input level corresponding to a 90-dB SPL at 1 meter, bass distortion increased almost linearly from about 0.5 percent at 100 Hz to 5.3 percent at 50 Hz and 10 percent at 20 Hz.

Surprisingly, the CS1.2 was able to absorb large peak inputs in our pulse power tests, in which it was driven at frequencies of 100, 1,000, and 10,000 Hz with a one-cycle burst followed by 128 cycles off.

The impedance of the system was between 4 and 4.4 ohms at these frequencies. At 100 Hz, the woofer output began to sound slightly hard with an input of a couple of hundred watts, but it did not develop a solid rattle until we reached 410 watts. At the other frequencies, our amplifier clipped (at 1,400 to 1,600 watts output) before any significant distortion appeared in the speaker’s output waveform.

Comments

The Thiel CS1.2 not only lived up to its manufacturer’s claims but sounded every bit as good as it measured. Although it was most effective when placed as recommended, the exact listening position was not at all critical.

The most striking overall characteristic of the speaker’s sound was its smoothness and lack of coloration. As usual, we listened to it for some time before making any measurements. Our test results were quite consistent with the system’s subjective performance.

Several years ago we tested the larger Thiel CS2 and had the same reaction to its sound and measured performance. The similarity is no coincidence. Jim Thiel is one of those rare people who knows what music should sound like and— equally important—who knows how to design a speaker that translates his ideas into reality without doing violence to one’s budget or aesthetic sensibilities.

The open, effortless quality and seamless sound stage of the CS1.2 made it very easy to listen to for extended periods. Even the bass (at least down to 50 Hz or so, which covers a large part of that range) was reproduced with clarity and believability. Of course, the CS1.2 cannot match a speaker whose bottom end extends to 30 or even 40 Hz, but the difference was obvious only when listening to organ, bass drum, or other sounds requiring extended low-bass response.

You might hope for this caliber of sound from a speaker selling for upwards of $2,000, but it is not at all common in the price range of the Thiel CS1.2. Listen to it if possible—it is worth hearing even if you have no plans to buy a speaker.

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