MartinLogan CLS loudspeaker Jack English, CLS IIZ, June 1994
The $3500/pair CLS is the orphan in the MartinLogan range. Everyone's attention has been drawn to this company's remarkable hybrids: the modestly priced Aerius (reviewed Vol.16 Nos.6 & 10); the very impressive Quest Z (Vol.16 No.10); the popular Sequel (Vol.11 No.12, Vol.12 Nos.8, 9, & 12, Vol.14 No.2); the large, single-box Monolith (Vol.8 No.3, Vol.9 No.3); and the newest, the multi-piece Comment (WCES report, Vol.17 No.4). Each of these speakers marries an electrostatic panel, for the mids and highs, with one or more dynamic drivers for the bass. The CLS, in all its incarnations, has remained the only full-range M-L electrostatic speaker.
The evolution of the design has resembled the swings of a pendulum. The original CLS worked well with lower-powered tube amps that could handle very high impedance loads. That was good (moderate power demands). In response to criticism, M-L redesigned the speaker and gave us the CLS II, whose impedance load didn't stretch so far into double-digit ohms (good), but dipped so low that it was below a single digit (bad).
In fixing one problem, another popped up: The II required greater amplifier power (bad). One of the original's captivating strengths was its sense of immediacy (good). But in tackling the load, the II somehow lost a great deal of immediacy (bad). The speaker was taken back to the drawing board, and eventually the IIA was born. It recaptured some of the I's immediacy (good), but its impedance load dropped so low that it drove many amplifiers nuts (bad). Relative to the original—see JA's review in Vol.9 No.7 and my review in Vol.14 No.12—the IIA had significantly improved deep-bass extension, better midbass articulation, a more extended treble, and a minimized upper-midrange glare.
MartinLogan then released the fourth version of the CLS: the IIZ, which featured a new crossover board and power supply, and a reconfiguration of the transformers. While the IIZ purportedly maintains the immediacy of the I and IIA, it more than doubles the lowest impedance load, effectively ameliorating the major complaints people had with the II and IIA.
While that may seem like quite an improvement, remember that the IIA dropped down to 0.6 ohms. The improvement means that the IIZ drops only to 1.5 ohms. Relative to earlier versions of the CLS, this is indeed big news (good); relative to most other speakers, this is still a difficult load for many amplifiers (bad). The upgrade, which actually consisted of entirely new electronics, costs $695 (bad), but the price of the IIZ remains the same as the IIA (good).
The net improvements of the Z-mod (in terms of both sonic improvements and relaxed amplification requirements) have been obvious in the many consistently positive reviews MartinLogan has received for the updated/new Aerius and Quest hybrids. While the IIZ continues to suffer from deep-bass limitations, it has taken yet another step forward in terms of both sonics and practicality. I found the Z version, as advertised, easier to drive with a broader array of amplifiers. These ranged from the low-powered, inexpensive AMC CVT-3030 to the monstrous, wondrous Conrad-Johnson Premier Eight. While the speakers perform better with better amps, the IIZ can now be used in more systems.
Of course, all would have been for naught had the sonic performance taken a step backward. Fear not. As usual, the overall performance was remarkably coherent, with every nuance cut from the same cloth. The visually transparent panels continued to be remarkably coherent sonically, allowing the IIZs to retain the magic immediacy that has captivated so many CLS owners.
The inherent shortcoming in its electrostatic technology remains the limited reproduction of deep bass. MartinLogan's CLS IIZ is still agonizingly limited in this respect, but most people who see/hear the speaker are blown away by its combination of visual splendor and sonic capabilities. Non-audiophiles are consistently astounded that such a product can even exist. If you're out to impress your friends, it's hard to think of a better product to do so with.—Jack English