Snell XA-90PS

A seven-driver tower with its own 300-watt bass engine and a parametric EQ on the back. One reviewer reached for the word "coffins" before he'd even unpacked it.

Overview

The first thing that arrives is the crate. Each XA-90PS shipped in a wood-and-plywood container that weighed close to 70 pounds empty. Audio (June 1999, p.48) said it was one of the few shipping containers the reviewer had no reservations about reusing. Inside is a floor-standing tower with eight drivers total: two 10-inch woofers, two lower midranges, two upper midranges, and two tweeters, one on the front baffle and one on the rear. The two 10-inch woofers are driven by an internal 300-watt amplifier. This is not a passive tower you drop into a room and forget.

The design is built around what Snell called "Expanding Array" - XA - a technique for controlling vertical directivity down to much lower frequencies than comparably sized speakers manage. According to Audio (June 1999, p.44), the approach was the brainchild of Snell's president and chief designer, David Smith. The speaker sat at the head of a five-model XA series that also included the XA-75PS tower, two center-channel speakers, and the SR-30mp surround. The XA-90PS was the flagship tower of that line.

The drivers are a mix of custom and sourced parts. All of them except the lower midranges, which came from Peerless, were custom designs made for Snell by Seas, and every one is magnetically shielded. The woofers use a dual-spider construction. The motor's stationary center pole extends out through the cone, and a second spider connects the two. That extra spider doubles as a dust cap and adds fore-and-aft stability to the moving assembly. The center pole also works as a heat pipe, ending in a heat sink you can see once the woofer grille comes off. The 1-inch aluminum-dome tweeter crosses over at 3 kHz. It is paired with the 2½-inch upper midranges in a D'Appolito-style midrange-tweeter-midrange module that Snell ran down to 400 Hz and used across the whole XA line.

The cabinet is serious work: ¾-inch medium-density fiberboard, braced internally by three shelf braces. The front baffle carries a curved subpanel that holds the top five drivers and smooths diffraction. The two 10-inch woofers sit in what look like separate cylindrical black enclosures, but the inside is acoustically common to both. Together with four flared vent tubes, 2½ inches in diameter and 9 inches long, opening at the rear, it forms one large bass-reflex system. The lower midranges and the MTM assembly each have sealed enclosures. The passive crossover is mounted to the inside of the input panel and uses air-core inductors and heavy-gauge stranded wire. Snell described most of its sections as second-order electrically but fourth-order acoustically, in an in-phase Linkwitz-Riley topology.

The back panel is where this speaker separates itself from nearly everything else in its class. It carries the rear-firing 1-inch dome tweeter, the four ports, bi-wirable double-banana jacks, the woofer amplifier's heat sink and power-cord socket, and a bank of environment-compensating controls. The main one is a single-band parametric equalizer with separate boost and cut level, center frequency, and bandwidth adjustments. Audio (June 1999, p.44) said no other speaker or subwoofer the reviewer was aware of matched that degree of bass adjustability. There are switches for the rear tweeter and a boundary control affecting mainly the lower midrange, plus an infrared remote that adjusts tweeter level, bass level, and "Bass Shape."

The measured performance backed up the hardware. Audio (June 1999, p.45) measured sensitivity at a high 89.6 dB averaged from 250 Hz to 4 kHz, essentially matching Snell's own 90-dB rating. The impedance is a genuinely low load, dipping to 2.9 ohms at 210 Hz and 3.3 ohms at 2 kHz. The reviewer advised against running two of these in parallel and recommended 14-gauge or heavier low-inductance cable for a ten-foot run. The high impedance in the low bass offloads the main amplifier, since the internal 300-watt amp is doing the bass work. Peak acoustic output was extraordinary: 103 dB SPL at 20 Hz with room gain, climbing to a maximum of 129.8 dB at 63 Hz and holding in the 124-127 dB range above that. The reviewer's verdict, printed in Audio (June 1999, p.45), was that the speaker's bass output exceeded that of several subwoofers he had measured.

Distortion figures were similarly strong. At an equivalent maximum power of 200 watts into the rated 4-ohm load, second and third harmonics at 41.2 Hz rose to 9.1% and 3.6%, with the fifth at just 0.5%. The speaker still sounded clean and powerful at that level. Intermodulation distortion between 440-Hz and 41.2-Hz tones reached only 1.2% at 200 watts. The vertical off-axis response curves were, in the reviewer's words, the best he'd seen from a non-coaxial multidriver system. The on-axis response fit a tight 5.5-dB window from 34 Hz to 20 kHz, or about 3.5 dB if the gentle 1.2-dB/octave tilt above 2 kHz were compensated. The one real caveat is group delay of about 0.15 milliseconds, which meant the speaker wouldn't preserve signal wave shapes. At 45° off axis the response also rolled off and undulated above 3 kHz.

Setup is not casual. The many controls must be dialed in with the speaker in its final position. They can be roughly set by ear, but the best result wants a third-octave real-time analyzer or a computer-based system. Individual bass controls per speaker let you match response to an asymmetrical room, which is a real advantage. The 18-page owner's manual, which also covered the XA-75PS and XA-55CR, devoted several pages to the bass controls and their adjustment. Snell supplied 1¾-inch threaded spikes with adjustment nuts for carpeted floors. Review samples came in cherry veneer, with black oak available on special order.

In listening, the XA-90PS was described as lively, dynamic, and smooth, with very even horizontal and vertical coverage and bass that stayed powerful and clean at all levels, extending smoothly into the lower 20-Hz range. Male speaking voices reproduced without chestiness or barrel effects, and even with the bass boosted heavily the sound grew louder without one-note resonances. Contemporary pricing was $7,000 per pair. For a collector today, the appeal is the combination of genuine full-range capability, the unusual active bass section with parametric EQ, and a build quality that the period review called the highest. The catch is the same one that applied in 1999: this is a large, heavy, setup-sensitive speaker that rewards an owner with measurement tools and patience — and demands an amplifier comfortable with a low-impedance load.

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