Thiel CS2 Speaker System Review

In a decade or so of existence, Thiel (pronounced teal) Audio Products Company has earned a reputation for high-quality loudspeaker systems based on what is described as a “Coherent Source” design. The name refers to the goal of maintaining time and phase coherence between the outputs of the several drivers in a speaker system so that the acoustic waveform reaching a listener’s ears conforms as closely as possible to the shape of the electrical waveform at the speaker terminals. Time and phase response errors in speakers have received considerable attention from many manufacturers in recent years, although neither their audibility nor the effectiveness of many of the proposed solutions have ever been conclusively demonstrated.

The Thiel CS2 speaker system exemplifies the company’s design philosophy. A columnar three-way system, the CS2 has an 8-inch long-throw polypropylene-cone woofer that operates in a Butterworth-tuned vented enclosure and crosses over to a 4-inch treated-cone midrange driver at 800 Hz. The second crossover, to a 1.1-inch soft-dome tweeter, is at 3,000 Hz. Time coherence of the drivers’ output is achieved by the backward-sloping speaker board, which places the effective sound sources of all the drivers equidistant from a listener seated at least 7 or 8 feet from the enclosure.

Phase coherence is achieved by using first-order (6-dB-per-octave) crossover slopes. But Thiel’s synthesized first-order crossover is different from many ordinary first-order electrical crossover networks. Since Thiel’s aim was to achieve a true acoustic crossover having the desired phase and amplitude characteristics, the inherent frequency and phase response of each driver had to be considered when designing the network. The electrical response of the network combined with the natural responses of the drivers produces overall slopes of 6 dB per octave. According to Thiel, this is the only type of first-order crossover that provides uniform amplitude, phase, and power response. For the closest possible approach to ideal characteristics, the Thiel network uses low-loss polypropylene and polystyrene capacitors and air-core inductors.

It is well known that diffraction of the sound from a speaker driver, which occurs when there are sharp boundary discontinuities at the cabinet edges or between the driver and the speaker board when the driver is not flush-mounted, can smear the acoustic waveform and introduce secondary radiated signals that can alter the sonic image at the listening position. Diffraction effects are minimized in the Thiel CS2 by a unique molded-plastic “board” that covers the entire front of the speaker board and also serves as a frame for the black grille cloth. The plastic board is shaped to provide smoothly flaring transition surfaces around each driver and rounded edges at the outer portions of the grille.

The CS2’s woofer is located approximately at the middle of the speaker board, with the port below it. Above it are the closely spaced midrange and high-frequency drivers, which share a single large, flared cutout on the grille board.

The overall construction of the CS2 is exceptionally solid. The cabinet’s wood sides are 30 millimeters (about 1.2 inches) thick and are laminated with matched veneers. System specifications include a frequency response of 43 to 20,000 Hz ±2 dB, sensitivity of 87 dB sound-pressure level (SPL) at 1 meter with a 1-watt input, impedance of 6 ohms, and a recommended amplifier power of 40 to 250 watts per channel.

The cabinet of the Thiel CS2— normally finished in teak, but with other finishes available on special order—is 12-1/4 inches wide, 12-1/4 inches deep at the base, 6 inches deep at the top, and 39-3/8 inches high. The system weighs 62 pounds.

Thiel recommends placing the speakers at least 1 foot from a wall and 3 feet from a corner, with each speaker supported on three small metal pins to provide a firm contact with the floor. Two sets of pins are supplied with each speaker; one set has rounded ends for use on hard floors, the other pointed ends for use on carpeted floors. Price: $1,350 per pair.

Lab Tests

The averaged room response of the two Thiel CS2 speakers was notably flat over much of the audio range, varying less than ±1.5 dB from 200 to 12,000 Hz. The combined response of the woofer cone and port was flat within ±2 dB from 42 to 500 Hz, and splicing the low-frequency curve to the room curve gave a composite response of ± 3 dB from 35 to 20,000 Hz.

The individual room-response curves from the left and right speakers matched very closely up to 13,000 Hz, where they began to diverge. This result indicates that the Thiel tweeter has excellent dispersion up to this very high frequency, in contrast to the many other speakers whose polar patterns begin to narrow in the 8,000- to 10,000-Hz range.

These measurements agreed closely with the quasi-anechoic response curves made with our IQS FFT analyzer, which confirmed that the high-frequency directivity of the CS2 became significant only at frequencies well above 10,000 Hz and that its axial response varied only ±2.5 dB from 200 to 17,000 Hz. The response of the midrange driver, measured with close microphone spacing, was an impressive ± 1 dB from 1,000 to 4,000 Hz. In view of the system’s outstanding overall smoothness, it was not too surprising to find that its group delay (a measure of phase-shift uniformity) varied less than 0.2 millisecond overall from 1,000 to 23,000 Hz and was only 1 millisecond at 180 Hz.

The impedance curve of the CS2 was exceptionally uniform, with a minimum of 4.5 ohms at 150 Hz and maxima of 9 to 9.5 ohms at 20 and 57 Hz. Over most of the audio range the impedance was between 6 and 7 ohms, which suggests that the CS2 presents a nearly resistive load to the amplifier over most of its frequency range, minimizing the possibility of compatibility problems.

The speaker’s sensitivity was almost exactly as rated, 87.5 dB SPL at 1 meter with an input of 2.83 volts of midband random noise. Woofer distortion was measured with an input of 3.8 volts (equivalent to a midband output of 90 dB). The output of the cone was dominant above 43 Hz, and the port radiation was stronger below that frequency, so the distortion curve was plotted with a crossover at 43 Hz. The distortion was unusually low from 100 to 60 Hz, measuring about 0.5 percent over most of that range, and it increased smoothly to 2 percent at 40 Hz, 5 percent at 30 Hz, and 9 percent at 20 Hz.

Finally, we measured the shortterm power-handling ability of the system, driving it with single-cycle tone bursts at 100, 1,000, and 10,000 Hz and monitoring the acoustic-output waveform for distortion. Moderate waveform distortion appeared on the 100-Hz woofer output at 170 watts, but there was little audible distortion, such as rattling, even near the clipping power of the amplifier (1,888 watts into the 5-ohm impedance at that frequency). At the two higher frequencies, the amplifier clipped before the speaker distorted significantly, at power levels of 1,350 and 1,560 watts for the midrange and high-frequency drivers, respectively.

Comments

Following our usual practice, we listened to the Thiel CS2 speakers for some time before making any measurements. After the first couple of minutes, we had no doubt that they were exceptional speakers. In the following weeks that feeling was strongly reinforced. Obviously, our microphone and test instruments came to the same conclusion on a much shorter acquaintance.

The CS2’s were almost totally lacking in the aberrations we have come to expect from loudspeakers—even very good ones. For example, they were never shrill or strident, yet their high-end response was as smooth, extended, and transparent as we have heard. They did not impress us with floor-shaking bass, but when it was called for, it was all there. And with it came one of the rarest of speaker qualities—a total lack of mid-bass boom. Male voices were reproduced without the tubbiness or chestiness that mars the sound of many of the speakers we have heard over the years. Between the bass and the treble, the main body of the music was reproduced so naturally and unobtrusively that we tended to take it for granted.

In fact, its qualities of ease, balance, smoothness, and lack of strain separate the Thiel CS2 from most other speakers we have heard. A few sophisticated designs achieve impressive and often realistic results by ingenious exploitation of psychoacoustic effects, and we have found them to be highly worthwhile products. With most “conventional” speakers, however, we expect audible imperfections, and we tend to excuse them because they are expected. Their absence in the Thiel CS2 made it a delight to hear.

We have no way of knowing the extent to which the qualities of the CS2 derive from its Coherent Sound approach and to what extent they are the result of just plain good engineering on the part of designer Jim Thiel. Probably a good portion of both factors is involved. In any case, the Thiel CS2 is one of the better speakers you can buy, and it is worth every cent of its price.

Read all

Thiel reviews

Read all