Snell XA90ps loudspeaker
Hearing and seeing this performance left me with an unforgettable mental image. From that point on, the realistic high-fidelity reproduction of Boléro had to match the many steps of crescendo and full dynamics I heard that evening. No wonder J. Gordon Holt once warned readers that "many trained ears have never heard a live orchestra, so they are hardly qualified to tell you what is and what is not realistic" (Test CD 1, track 5, Stereophile STPH002-2). With the memory of that long orchestral crescendo heard live and a recording of Boléro by the New York Philharmonic, I set out to review the Snell XA90ps loudspeaker.
Snell's new XA90ps is a four-way, floorstanding loudspeaker with eight drive-units: two 1" tweeters, two 2.5" midranges, two 6.5" lower-midranges, and two 10" active subwoofers. David L. Smith, Snell's engineer and president, designed the speaker. After stints with McIntosh, JBL, KEF, and Meridian, among others, he joined Snell after the company's previous loudspeaker designer, Kevin Voecks, moved to Revel, and owner Peter Lingdorf sold the company to Boston Acoustics.
While it still has the company's signature rear-facing second tweeter, to help equalize the speaker's HF power response, the XA90ps features new technology not seen in previous Snell models, including a dual-driver active subwoofer with its own built-in parametric equalizer, wireless remote-control adjustment of tweeter and subwoofer levels, and Smith's proprietary "Expanding Array" driver configuration. He demonstrated all these features during a visit to my listening room, when he delivered the XA90ps speakers for review.
Expanding Array (XA) refers to the five symmetrically arranged drivers that sit just above the twin subwoofers. When he was at McIntosh, Smith developed methods for improving the polar performance and frequency invariance of vertical speaker arrays (footnote 2). "Instead of concentrating on the complete polar curve," wrote Smith, "improvements to the forward beam of the array would best benefit the user." For the design of the XA90ps, he used computer modeling to reach the goal of only 1dB variation through ±15 degrees in the vertical direction. Beyond that narrow zone, the array's vertical polar pattern drops off "by 4-5dB at 40 degrees up and down," Smith added. "This reduces the energy that bounces off the floor or ceiling and reduces the contribution of the room." The resulting pattern produces a broad vertical lobe that is smoother over a wider window, "giving a much-improved response smoothness for any listening height."
Smith constructed this array with a central 1" aluminum-dome tweeter flanked by two 2.5" upper-midrange units, these in turn bracketed by two 6.5" midbass drivers. The addition of these midbass drivers—set at double the distance between the midrange-tweeter-midrange (MTM) units—extends the XA90ps' smooth response down to 100Hz. A computer program specified the exact spacing between drivers and electromechanical driver-crossover interactions to create the optimized vertical polar pattern. Most critical was the relative spacing among the MTM units, the crossover frequencies, the rolloff slopes and overlap. Smith notes that although the units are not time-aligned, "the relative phase response of the tweeter vs the upper midranges is critical."
The XA90ps is a slim tower 4.5' tall, 11" wide, and 19.5" deep. The bottom section houses two forward-firing, long-throw custom 10" subwoofer drivers with cylindrical housings and circular perforated metal grilles. The subwoofer drivers consist of mica- and carbon-filled copolymer domes, dual spiders to stabilize the lengthy excursion, and a front-mounted heatsink to draw heat away from the voice-coils (footnote 3). The woofers are reflex-aligned, with four flared port openings—two for each woofer—on the enclosure's upper section just below the rear tweeter. The internal 300W power amplifier has been optimized for use below 200Hz.
Besides the four reflex ports and the second tweeter, the rear panel features four speaker terminals for biwiring, a midbass compensation control, and a parametric equalizer for the subwoofers that includes continuously variable Q (bandwidth) and fully adjustable cutoff frequency. In addition to the usual controls for bass level and crossover frequency, the back panel has a jack for the remote-control umbilical interconnect that runs between the XA90ps speakers. This allows the remote to control both XA90pses, even when its signal is picked up by only one speaker's infrared receiver. Smith claims that the parametric subwoofer and the lower-midrange level controls can be set once during installation, then left alone. The owner then uses the wireless remote to set bass and tweeter levels, depending on the program material.
Footnote 1: Michael Steinberg, NYP program annotator, Stagebill, January 1999, p.36.
Footnote 2: See Smith's "Discrete-Element Line Arrays—Their Modeling and Optimization," JAES, Vol.45 No.11, pp.949-964 (1997).
Footnote 3: This 10" drive-unit was given a full-page picture on the Table of Contents spread of the March/April 1998 Stereophile Guide to Home Theater, Vol.4 No.3, referring to Wes Phillips' review in that issue of the Snell PS.10 compact subwoofer.