Thiel CS6 Loudspeakers
by Richard Hardesty
The CS6 is my favorite Thiel speaker. CS6s provide the satisfying deep bass that is lacking in the smaller Thiel models. The CS6s sacrifice little in terms of bandwidth and output capability to the larger CS7s, which cost about one-and-a-half-times as much, and the CS6s sound slightly more coherent and open to me.
Descriptions of the engineering and construction features of Thiel speakers in general, and the CS6 model in particular, can be found in Audio Perfectionist Journal #6/7. This article will concentrate on how these features affect sound quality and my subjective impressions of the sound of the CS6s.
Time- and Phase-Accuracy + Contoured Baffles
Thiel speakers are distinguished from conventional designs by complete time- and phase-accuracy. They can be distinguished from other time- and phase-accurate speakers by their sloped and contoured front baffles, aluminum diaphragm drivers and coaxial midrange/tweeter elements.
Thiels have elegant cabinets with great attention devoted to construction quality and appearance. Gently sloping baffles bring the drive elements into temporal alignment. The contoured shape of the baffles minimizes edge diffraction effects while diffusing coherent reflections for an open, spacious sound and precisely focused imaging.
The CS6 baffles are formed from a mineral/polymer material similar to cast granite and are several inches thick. The other enclosure panels are made from 1-inch thick, heavily braced MDF, which is veneered on both sides. Thiel enclosures are dead quiet.
Aluminum driver diaphragms reproduce all voice coil movements, converting the smallest signal details into sound. If information has been captured on the recording you will hear it through the Thiels. If other system components add colorations, you will hear them clearly through the Thiels.
Coaxial midrange/tweeter drivers provide increased vertical dispersion and make listener ear height less critical than it otherwise would be with a first-order speaker system. CS6s actually are a point source radiator from the midrange up.
Thiel CS6s are high-resolution speakers. The ability to resolve micro detail is achieved in part by incorporating engineering features that may involve some sonic trade-offs. These features include drivers with short, underhung voice coils and long magnetic gaps, the use of aluminum diaphragms on all drivers, and the coaxial arrangement of midrange/tweeter drivers.
Underhung voice coils can reduce distortion caused by magnetic nonlinearities but short coils concentrate heat in a smaller area and have minimal exposure to air for cooling. Overheated voice coils are subject to failure and, as voice coil temperatures increase, sensitivity decreases, which may cause dynamic compression.
If diaphragm excursion exceeds the linear range, distortion increases rapidly. Enormous and costly magnet structures are required to concentrate magnetic flux in the extended gaps.
Stiff metal diaphragms ensure that all voice coil movement will be translated into sound output. Metal diaphragms can perform like perfect pistons over a wider bandwidth and produce less distortion in this piston range than softer materials with more internal damping.
All diaphragms in the CS6s are made from aluminum. Aluminum provides little internal damping so small signal details will not be damped out along with minor resonances but when an aluminum diaphragm does break up it is likely to produce a sharp, high-Q resonance with undamped oscillation (ringing). I believe that aluminum diaphragms have a distinct sonic signature when used to reproduce midrange frequencies (which is not to say that other materials don’t).
Coaxial drivers produce a point source radiation pattern but generally exhibit response irregularities because of interaction between the drive elements. A moving midrange cone is not an ideal surrounding environment for a tweeter and a low-mass tweeter dome is not an ideal center piece for a midrange driver.
Jim Thiel has done a remarkable job of overcoming the potential negative aspects of these design features. This could be accomplished because Thiel is a vertically integrated company and Jim is one of the most thorough and imaginative engineers in the industry. Virtually everything in the CS6 speakers has been designed and built in the Thiel factory. No compromises were required in order to work around the limitations of off-the-shelf drivers and other components.
Thiel has created specially designed drivers with extremely wide bandwidth to place resonant frequencies well above the range of frequencies over which woofers and midrange drivers are utilized. Thiel tweeters have long excursion capability to extend low frequency response and a primary diaphragm resonance above 25kHz, which is well above the audible range.
Coaxial drivers have been designed holistically to optimize the performance of the individual elements. I think that Thiel has been largely, if not completely, successful in his efforts.
The metal diaphragms produce some overshoot and minor ringing on impulse response tests but you’ll hear surprisingly little evidence of this when listening to Thiel speakers. Response irregularities through the midrange have been reduced to inaudible levels by carefully engineering the midrange and tweeter drive elements to work in concert.
The Thiel CS6s have only a single set of input connectors and can’t be bi-wired or bi-amped. They have vented bass loading utilizing passive radiators rather than ports. Alignment is unusual and bass is tightly controlled with little evidence that the enclosures are not sealed.
The Sound of the CS6
The Thiel CS6s are significantly smaller than the Dunlavy SC-IV.As but they are still moderately large. The CS6s disappear almost completely when music is playing.
It is difficult to localize the position of the speakers in the sound stage and I never hear any structural or boxy sounds coming from the Thiel enclosures. Vandersteen 3A Signatures (without subwoofers) have a more boxy sound in the bass but still sound slightly more open and spacious to me. I believe that the contoured baffles of the CS6s reflect some energy identifying the source of sound as a speaker. The physical position of the Thiels in the sound stage is far less evident than the position of the Dunlavys but more evident than the position of the Vandersteens. I think reflected energy is the source of these audible differences.
Thiels image with precision and depth. Instruments appear behind and beyond the speaker boundaries. Images are focused in a three-dimensional space with a precision that beats the Dunlavys and shames speakers which are not time- and phase-coherent. Image depth extends quite far back if the electronic components and the room permit. The Thiels rival the Vandersteens in terms of lateral image focus.
The Thiels have a cool tonal balance with lots of midrange and high frequency energy and lean, tight bass. They sound much brighter than Dunlavys or Vandersteens on first listen. But detail is not achieved by exaggerating high frequencies and the CS6s sound smooth and musically natural delivering transients that are sharp-edged rather than rounded.
Bass can be a little dry and lightweight with amplifiers that are unable to deliver high power into the low impedance load. Amplifiers that can’t deliver high current or those that tend to be bright or harsh will be mercilessly revealed as inadequate.
The Thiels are lean in the lower midrange and bass where the Vandersteens and Dunlavys are full and warm. Tightly controlled bass and lots of high frequency information add up to a tonal character that is cool and detailed. This character may produce sound that seems too bright and/or edgy when combined with associated components with similar tonal characteristics, but in a carefully chosen system the Thiels sound neutral and revealing rather than cold and analytical.
The high resolution of the Thiels will expose inferior components in the signal chain preceding the speakers. They should be used only with the finest quality associated components and cables. The CS6s present a demanding load that requires a high-current, high-quality amplifier that can provide powerful bass response to balance the high resolution in the midrange and highs.
The Thiel CS6s are great speakers. They offer true high-end performance and elegant good looks. These high-resolution speakers demand the finest associated components for best performance. Even with the best associated equipment you may still hear a touch of the distinctive sound of aluminum in the midrange.
Thiel CS6s easily outperform Wilson Watt/Puppies and Revel Salons, neither of which is time- and phase-accurate, yet the Thiels cost less than half as much as the others.
Don’t consider speakers that cost more than $8,000 a pair without first listening to the Thiel CS6s in a system assembled from the best source and amplification components. You can’t get higher resolution by paying more. If someone tells you that a more expensive brand is built to higher quality standards, don’t believe them.