Snell Acoustics XA Reference Tower loudspeaker:
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Tuneable Tower
As David Smith completed the design of the crossover network, he discovered that a handful of crossover component values, if varied, could control the XA Reference's balance across the acoustic spectrum. For example, the primary tweeter input capacitor, if varied, modified the output between 1500Hz and 7kHz. By using five switches on the XA Reference's back panel, the owner can vary the response of the entire system ±1.5-2dB in four frequency bands, from 100Hz up, in order to tune the speaker to be truly neutral despite room effects and associated equipment. The lower-mid switch compensates for the effects of floor bounce and floor-to-ceiling dimensions on bass response. The upper-mid switch adjusts for room midrange reverberance. The upper- and lower-treble switches can compensate for the perceived hardness of electronics or sources, and can modify the listening perspective.

In addition, there are three physically different woofer-tuning options: port tubes of two different lengths, to give 22Hz or 32Hz tuning frequencies, and a blanking plate to give sealed-box operation when the XA Reference is used with a subwoofer. (The system is shipped with the long ports.) These tuning options were included to compensate for rooms with walls and dimensions that give too little or too much low bass.

Each XA Reference Tower is 18" taller, 6" wider, 2" deeper, and 12 lbs heavier than the ca 1995 Type A Reference's treble-midrange tower. The XA Reference's massive cabinet has heavily damped walls; its internal and external layers are bonded with a highly lossy polymer adhesive that absorbs resonant energy. The three-layered front baffle is contoured to smooth the drivers' acoustic output. Besides the reflex ports, tone control switches, and second tweeter, the rear panel features four gold-plated WBT terminals for biwiring.

Overall, the XA Reference Tower's fit'n'finish is superb. The review sample's rosewood veneer equals or surpasses finishes on all previous Snell loudspeakers. Hardware, switches, rotary controls, and connections are sturdy and easily accessible.

Setup
The XA Reference loudspeaker arrived on a bright Sunday afternoon. David Smith and his wife, Melinda—a very good sport and unexpectedly strong for a slender pastry chef—worked with me to move the XA References into the listening room. Rocking them to and fro, we managed to position the 300-lb, 7' crates so that David could unscrew the covers and carefully move the tall, smooth, slippery speakers out into the sunlight. With the three of us working very hard (child psychiatrists don't always pump iron; we should), we managed to move them up a flight of stairs and into my listening room.

Smith moved furniture so the Reference Towers could be walked to the back of the room. In the next hour he positioned them 48" from the back wall, 36" from the side walls, and 89" apart (measured from the tweeter centers), facing the full length of the narrow room (26' long, 13' wide, and 12' high, with a semi-cathedral ceiling), and toed-in to focus on the nearfield listening position. (The other end of the room adjoins a 25' by 15' kitchen through an 8' by 4' doorway.) This large listening area—more than 5000 cubic feet—works best with a full-sized loudspeaker system like the XA Reference.

Playing Test CD 3 (Stereophile STPH006-2) to identify channels and check phase, I adjusted the speaker positions until I could hear the in-phase pink-noise signal as a tightly focused image centered between the Towers. Imaging and soundstaging were optimized when the speakers and my listening chair formed the apices of an isosceles triangle measuring 91.5" wide (between the speakers) and 108" from each speaker (measured from tweeter centers) to the chair.

Even though its voltage sensitivity is lower than average, the XA Reference produced good sound-level output when connected to three different solid-state amplifiers: a 200Wpc Mark Levinson No.334, an 800Wpc Bryston 14B-ST, and a 1200Wpc Krell FPB 600c. Each amplifier added its characteristic sound: the Krell was fast and dynamic, with tight bass; the Levinson was detailed, transparent, and sweet; and the Bryston was neutral and had ample bass slam.

First, I drove the XA Reference Towers with low-frequency warble tones from Test CD 3, using a RadioShack SPL meter resting on the arm of my listening chair. The XA Reference's deep-bass output was flat to 31.5Hz, shelved down by 2dB at 25Hz, and was -4dB down at 20Hz. As the signal dove below 25Hz, I felt a tightening pressure surround me like a cloud, accompanied by floor vibrations. With the exception of the Revel Ultima Salon, this was the deepest bass frequency response I had measured from a loudspeaker in my listening room. Despite driving the amplifier hard on these warble tests, I was unable to detect any port chuffing.