Wilson Audio Specialties X-1/Grand SLAMM loudspeaker system Page 3

The cones are made of a glass-fiber-reinforced pulp impregnated with a catalyzed resin, and are both rigid and pistonic over the required frequency range. Placed uppermost on the baffle, the 12" driver has an additional surface treatment to damp cone resonant modes, since in terms of its natural response and position in the stack, it reaches further into the low midrange than the 15" unit. The edge suspensions are foam half-roll surrounds of high mechanical "Q."

These are low-loss drivers, with high electrical damping and consequently great electromagnetic control (high Qm and low Qts, a highly desirable if expensive combination). Their corrugated spiders are surprisingly stiff; these are no "soft," long-throw units. Instead, their motor design is directed toward linear control under high-power excitation, while their fundamental resonances are matched to the requirements of bass-reflex loading. By using two differently sized bass units, sharing a common enclosure and vent, the usual single, sharp port resonance peak is broadened, extending its range and smoothing the response both in the port range and in the upper enclosure-resonance range (footnote 2).

Given the high power capacity of the bass pair, the choice of midrange driver was critical. In addition to the usual requirements for response smoothness, low coloration, and transparency, the X-1's midrange also had to be efficient, dynamic, and remain linear under high power inputs. To meet these demands, two 7" drivers, custom-made for Wilson by Dynaudio, are operated in parallel. Their high sensitivity is reinforced by a double-magnet system, 2.83V driving the pair to 96dB at 1m in the upper midrange. These drivers use rigid pressed-steel baskets and high-power 1.5" alloy voice-coils with dense "Hexacoil" windings. Copper shading rings and caps minimize magnetic third-harmonic distortion. The polypropylene cones are flared BBC-style, mineral-loaded to improve both rigidity and damping, and suspended on natural rubber surrounds.

Much development has gone into the new 1" tweeter built by Focal for Wilson Audio. It has a double magnet to raise its sensitivity to an all-time high for a direct-radiator type of 96dB. While the WATT 3 used a fiberglass material for its distinctive inverted dome (not Kevlar, as is commonly stated), the new version of this tweeter uses titanium. This metal's great stiffness helps push the primary resonance up to 23kHz from the 16kHz of the earlier fiberglass type. Now the intrinsic response is essentially flat to 20kHz at the greatly increased sensitivity.

The new, highly stable synthetic suspension is fitted with a small half-roll termination to control sub-harmonic rocking. Wilson has also fine-tuned the viscosity of the ferrofluid cooling medium in the gap, as well as the size and treatment of the air volume behind the dome. A tapered hollow pole leads to a sealed rear chamber within the ferrite magnet rings. The 1" ambience tweeters are single-piece titanium-dome units sourced from Audax, chosen for their good performance in the final audible treble octave.

Systems & components
The X-1/Grand SLAMM review story began in my living room. I'd been commissioned to write two separate reviews: an early review to appear in the October 1994 issue of the UK's Hi-Fi News & Record Review, with a more in-depth analysis to follow for Stereophile. This was made possible through the good will of the X-1's owner, Ricardo Franassovici of Absolute Sounds UK, who suffered agonies for the several weeks he was without his new audiophile babies.

The speakers left my studio after specially extended listening sessions using a wide choice of ancillary equipment had been carried out for Stereophile. I packed my set of reference discs, my MLSSA-equipped Toshiba 6400 laptop, my trusty B&K condenser microphone, and accompanied the X-1s to their final home at Ricardo's. There they were installed in a still more spacious listening room whose different character provided me with a new challenge, together with the potential for free-space location and improved bass extension. I continued my evaluation at the new location.

A stunning array of ancillary equipment—mine, begged, or borrowed—was assembled to test the X-1/Grand SLAMM's claims to greatness. Room treatment included Combak Harmonix wall dampers. Power amplifiers comprised the Mark Levinson No.27.5, Jeff Rowland Design Group Model 8, Conrad-Johnson Premier Twelve, Krell KSA-200S, Naim NAP250, a hand-built single-ended triode amplifier, and pairs of Audio Research VT150s, Meridian 605 monoblocks, and Jadis JA 500s. For fun, I also tried the little Exposure Fifteen integrated amplifier.

Analog sources included a van den Hul Grasshopper IV GLA in a Naim ARO tonearm on a Lingo'd Linn LP12, plus a Koetsu and a Lyra Clavis DC on a Wilson Benesch ACT One tonearm fitted to a Wilson Benesch turntable. The turntables were sited on a four-tier Mana Reference table.

Digital sources included the Wadia 16 CD player, used both as a complete entity, and as a separate transport and digital decoder. Additional transports included a Meridian 200 and Krell MD-10. Further D/A processors comprised the latest Theta Generation 5, the Accuphase DP70-V, the Krell 64X and Studio, and the Audio Synthesis DAX. On the control front, the Wadia 16 CD player has its own digital volume control and source selection, while discrete units included the disc sections of the Conrad-Johnson PV12 and PF2, the Krell KPE phono equalizer, the Krell KRC-2, Audio Research LS7 and LS2B units, the Mark Levinson No.38 and No.26S, and the Audio Synthesis Vishay-Passion passive controller.

Cables ordered for X-1 installation included Transparent Music Wave Ultra and Music Link Ultra; use of these network-terminated cables is recommended by Wilson Audio, who used them during the development and final voicing of the X-1. Other cables may subtly shift the system's inner balance. Conversely, some amplifiers, notably tube equipment, may react adversely to the greater electrical loading imposed by the network; alternatives may well be advisable according to the balance and source properties of the matching electronics. Alternative interconnects employed in this review included van den Hul The Second and Siltech '56 for balanced working, with van den Hul The First and Siltech used for RCA link-ups.

The amplifier/loudspeaker link is critical for the X-1—any inherent defects of lower-grade cables are immediately audible. Siltech Silver Ribbon, Transparent Ultra, and van den Hul Revelation (a silver/copper/carbon hybrid) proved up to the task, the choice dependent on the rest of the chain.

Footnote 2: It's rarely appreciated that, in its low-frequency region, a loudspeaker is operating on one or more resonances, and that these have a large influence on all aspects of perceived bass quality. The remarkable articulation and transparency of the X-1's bass is largely a function of its designer's skill in judging and voicing these resonances.—Martin Colloms
Wilson Audio Specialties
2233 Mountain Vista Lane
Provo, UT 84606
(801) 377-2233