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Equipment Review

July 1999

Wilson Audio X-1 Grand SLAMM Series II Loudspeakers

by Jeff Fritz

I was 30 years old when I hit my stride. At the height of my physical abilities, I had the sense to exercise more often and eat a little wiser. I was finally old enough to appreciate my education and experienced enough to know that real-world lessons are invaluable. Sure, one day we all start going downhill, probably sooner than we’d like. There is that moment in time though when we’re mature but still possessed with enough energy to achieve. It won’t last, but damn it’s good for a while.

Some of high-end audio’s most beloved products have taken a similar road: solid designs refined to a level of maturity that few products will ever achieve. Companies such as CAT, Audible Illusions, Mark Levinson, Vandersteen, Merlin, and Martin-Logan immediately come to mind. Over a period of years, incremental improvements in a design combine to paint an ever-clearer sonic landscape. Wilson Audio Specialties hangs its hat on this long-term quest for perfection. The WATT, Wilson’s ageless monitor, was introduced in 1986 and has been in the product line ever since. 1999 saw its version "6" incarnation (up to the 5.1 designation, an original WATT could be upgraded -- a 13-year upgrade path). The WATT’s evolution will likely span another decade or longer. After all, it’s only a teenager (Wilson’s eldest child, the WAMM, is almost 20).

With Wilson’s history, the X-1 Grand SLAMM must be considered a baby. Introduced in 1994, the original version remained unchanged for almost four years. Right out of the chute, it simply dominated the class of super speakers that it created. Witness sales eight times that of its closest competitor. Reviewers and manufacturers alike have used the X-1 as a benchmark of loudspeaker design. Many of today's best products were, in fact, voiced using the SLAMMs as the aural microscope. Over 250 customers seeking sonic nirvana have found solace in front of the X-1 -- 250! Even with this success, though, time does march on, and the X-1 matures.

The Series II Grand SLAMM was introduced amid claims of increased coherence through the midrange, and a smoother but faster treble with even lower distortion. In other words, the speakers were a little closer to perfection. According to Wilson Audio, when trying to create the absolute reference, neutrality must be the goal. To build a speaker that editorializes on the input signal is the easy way out. To sonically replicate the input, without added artifacts, is the true challenge. That is, of course, if the faithful reproduction of the recorded event is what you seek. Think of the difference between a very clear photograph of a painting, versus a lesser-artist’s rendition of that same piece. The second, although possibly beautiful, is a new work. The character, the intent, and the emotion of the original are lost. The photograph, however, contains details that only the real painting would possess. If the photograph could be enlarged to the scale and grandeur of the original, you’d be close to its effect (only the real thing, is the real thing). You now understand the concept that I believe David Wilson had for the X-1: a speaker that can reproduce a faithful facsimile of the original work. In a recent interview, Mr. Wilson spoke of "concept and execution" as being keys to his design’s success. Thus, this sneak peek will examine Mr. Wilson’s execution with the Grand SLAMM.


The SLAMM, which stands for super linear adjustable modular monitor, is a four-way design with a rated sensitivity of 95dB. This provides the owner with options when choosing amplification. Users have reported excellent results with low-powered tubes and solid-state powerhouses. The system’s nominal impedance of 8 ohms is relatively benign, dropping to a minimum of 5 ohms only at extremely high frequencies. Though the X-1 is quite satisfied with 20Wpc, it can also handle the full measure of a 500-watt super amp. In-room sound-pressure levels have been measured in excess of 123dB. Rated frequency response is quoted as 19.5Hz to 23kHz +/- 3dB. Set up properly and fed the right program material, the X-1 digs deeper than its specification. It’s still strong at 17Hz, maybe lower. Dimensions are 72"H x 16.5"W x 25.25"D, with a body weight in excess of 600 pounds. Sumo material.


For all the X-1’s mass, much of its magic is owed to its adjustability. The Series II version improves on this feature with new phase-delay-correction fixtures. These are easier to read and adjust, when compared to those of the previous design. The improvement greatly aids in accurate setup. Your dealer will accomplish this for you by recording exact measurements of listening height and distance on a supplied Wilson Timing Chart. This yields the precise placement of each upper-frequency module within the timing blades. When this is done properly, the speakers are aligned in the time domain at the listening position. In fact, without this feature, the X-1 could only be aligned in the time domain for one point in space. You would have to adjust to it, not vice versa. Next time a dealer or manufacturer tells you a speaker is aligned in the time domain, ask, "at what distance?" If he can’t tell you, be skeptical. The Timing Chart procedure was developed with pulse-alignment measurements taken in the Wilson lab. If you’ve never heard the SLAMMs optimally set up while sitting in the sweet spot, you have really never heard this feature’s true benefit. Quarter-inch adjustments in the modules are easily audible.


The upper-frequency crossover is afforded its own enclosure at the rear of the speaker. The entire assembly is potted in epoxy resin. This prevents any movement of components during music playback. The acoustic hell of a cabinet’s internal airspace will modulate a "naked" crossover’s accuracy over time. Potting ensures that the crossover’s original performance characteristics remain unchanged over the life of the speaker. The low-frequency crossover is located in its own sub-enclosure at the base of the main enclosure. It is potted as well, and connects to the upper unit via a large-diameter Transparent Audio cable. The Series II SLAMM’s new crossover is fitted with a detachable aluminum plate covering a large bay. Here you will find replaceable Caddock resistors that act as fuses, in case of abuse. Wilson’s attention to detail is evident even inside this compartment, as it is completely and nicely finished. Large metal binding posts secure the resistors, which can be tailored by a Wilson dealer for optimum room matching.

Other improvements include more exact phase alignment, which allows for a more coherent midrange/treble transition. Wilson also claims lower distortion and better imaging as a result of the revamped design. Crossover points are 120Hz (woofers/mid), 3kHz (midrange/tweeter), and 12kHz (tweeter/ambient tweeters) and are electrically first order. Each individual assembly is tested, and its frequency response logged, at Wilson’s factory. If service is ever needed, an exact replacement can be built (due to the potting, crossovers cannot be repaired).


Wilson Audio achieved vanishingly low cabinet coloration with the original WATT. The material used, a methacrylate polymer, is extremely hard and rigid. According to Wilson, it has a very low natural resonant frequency. Each of the X-1's three upper-frequency enclosures, along with the crossover assembly, is constructed from this material. These WATT-like modules have metal cones imbedded in their bases to decouple each from its neighbor. They are then locked into the timing blades on either side, with large machine screws. The timing blades are actually aluminum fins, marked with the adjustment settings that correspond with the Timing Charts. Once setup is complete, ceramic fascias are applied over each blade, creating a rigid, well-damped frame for each driver/enclosure. This, theoretically, expands upon the widely accepted belief of a minimonitor’s imaging advantage. Each forward-facing mid/treble driver has a cabinet optimized for its individual use, with very little baffle available for diffraction. Although the upper enclosures are small, each is cross-braced, with the tweeter cabinet possessing a damping material on the internal walls. Methacrylate polymer is reported to be 15 times the cost of MDF.

The design of the bass enclosure presented Wilson with quite a challenge: Huge drivers require a huge airspace, which would necessitate large panel walls. This opens the door for resonance. According to Wilson, many materials were tried and rejected. Finally, a high-density phenolic resin was chosen for this duty. This extremely dense, rigid material makes up all the lower enclosure walls and cross-braces. During the upgrade (the units I reviewed were Series I upgraded to II), I had a chance to examine the internal construction. It looked very much like a maze, such was its complexity. A large (6" x 17") aluminum port exits the rear of the enclosure.

The bass cabinet as a whole, comprises most of the weight of the X-1, and a lot of the cost. Its material is approximately 20 times as expensive as MDF when you calculate manufacturing costs (it’s very hard on CNC cutting blades). The knuckle rap test simply shows no sign of ringing. Cabinet construction of this quality not only controls resonance, but provides each individual driver with perfect wave launch.

The design of the X-1 accomplishes more than just low cabinet coloration. Elements that together could interact negatively are separated. Individual drivers and crossovers are isolated so that the performance of each is optimized without interference. This is loudspeaker engineering in the extreme, but then this design is aimed at cost-no-object performance. Parts quality is top drawer throughout the speaker system. All drivers are fastened with machine screws that thread into embedded metal inserts. Large WBT binding posts (seven sets per channel!) and Transparent Audio cable electrically connect the five modules. As is the case with all Wilson speakers, only single wiring from amp to speaker is provided for.

Wilson uses a felt material around the minimal baffle area to further reduce diffraction. This material was replaced on my pair to accommodate a new grille design, developed entirely for cosmetic considerations. The latest grilles do provide for a much-improved look over the old foam cell type.

Drive units

The Grand SLAMM is a four-way design comprised of seven drive elements. Drivers are purpose built for the X-1 then modified at the Wilson factory. The 15" and 12" low-bass units are from Focal’s Audiom series. Their magnetic structure is made up of a circular array of small magnets (as opposed to one large), which combine to increase efficiency. Voice coils are 3" in diameter and are wound on Kapton formers. Each basket is cast aluminum with a chrome back plate. The cones themselves are glass-fiber-reinforced paper with an external resin treatment applied to increase rigidity. The two midrange drivers are 6.5" mineral-loaded, polypropylene units sourced from Dynaudio. They feature a dual magnet system that also enhances efficiency. The 1.5" voice coils use Dynaudio’s Hexacoil windings.

The Series II X-1 uses an updated version of a Wilson favorite: the Focal inverted-titanium-dome tweeter. The all-new unit has been completely re-engineered and according to Wilson is "sweeter, faster, and more delicate-sounding." Like the midrange drivers, a dual magnet has been specified for increased efficiency. The new version has shown faster settling times and lower distortion in lab comparisons with the old model. Two Audax titanium domes are rear-mounted for ambience. One faces straight back while the other is at about 45 degrees.


As is the case with most audiophiles, I’ve owned my share of equipment, especially speakers. Having the chance to physically inspect the build quality of many designs, I’ve come to the conclusion that a vast gulf exists between the best and worst. In fact, a small number of products have been dismal: separating joints, stripped screws, cracked finishes, mis-cut openings, bad solder jobs, etc. This is why it’s important to visit your dealer to not only hear a product, but to kick the tires as well. The Wilsons have impressed me with a build quality that is surgically precise. The finish is flawless and the entire presentation exudes a pride of workmanship that has come to be expected from Wilson Audio.

Next time we will examine, in detail, the sonic presentation of the X-1 Grand SLAMM Series II. After all, what I’ve already presented is simply a means to an end. If the physical manifestation of David Wilson’s goal does not aurally keep pace, then what is the point? Stay tuned.

...Jeff Fritz

Wilson Audio X-1 Grand SLAMM Series II Loudspeakers
Price: $75,900 USD per pair; upgrade from Series I to Series II, $8400.
Warranty: Five years parts and labor.

Wilson Audio Specialties, Inc.
2333 Mountain Vista Lane
Provo, Utah 84606
Phone: (801) 377-2233
Fax: (801) 377-2282

Website: www.wilsonaudio.com
E-mail: was@wilsonaudio.com

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