PSB Stratus Gold Floor standing speakers
The Stratus Gold is the top of Canadian manufacturer PSB's loudspeaker line, which also includes models from $225 to $1,400 per pair. The Stratus Gold is a large, floor-standing tower system with a vented-box low end designed around a high-excursion 10-inch woofer.
PSB was the first Canadian loudspeaker company to take advantage of the advanced testing facilities and scientific staff of Canada's National Research Council. The NRC, as pointed out in my review of the Paradigm 7se loudspeaker, is a government-funded Canadian operation whose mandate is to help Canadian manufacturers be competitive in world markets. PSB has made extensive use of NRC facilities, including controlled listening tests in NRC's International Electrotechnical Commission (IEC) Standard listening room (after which both Audio's New York listening room and my own were patterned), to optimize the Stratus Gold's performance.
PSB has emphasized minimizing resonances, which "cast a muddy veil over every sound," according to their design white paper. The large cabinet of the Stratus Gold employs an innovative scheme of internal bracing and damping to minimize resonances, and weighs in at 95 pounds!
The Gold's tweeter (source: Vifa of Denmark) uses a high-stiffness, low-mass, aluminum-alloy dome with a polyamide suspension. To make the tweeter's off-axis response in the top octave more uniform, PSB adds a phase plug in the form of a 1/2-inch diameter rigid disk held about 0.050-inch above the center of the dome by six thin plastic spokes. The disk and spokes are an integral part of the tweeter's molded mounting ring. In addition to modifying the directional response, the disk has the very practical benefit of protecting the dome from roving fingers and other objects.
The 6-inch midrange uses a very large, 28-ounce ceramic magnet, mounted in a cast-magnesium frame, which provides high efficiency and control of its low-end response. The cone is made from a mineral-filled polypropylene material, which provides the proper stiffness and a high degree of internal damping. A soft-rubber dust cap and long-excursion rubber surround complete the design. The midrange is mounted in its own closed-box sub-enclosure, which is damped with loosely packed soft fibers, and is located in the top of the cabinet. The bottom wall of the sub-enclosure, which is attached to all four walls of the larger enclosure, also serves as a brace to strengthen the main cabinet. The smaller size of the midrange allows a higher crossover frequency, thus keeping high-energy fundamental tones out of the tweeter and allowing cleaner operation at higher levels.
The crossover between the woofer and midrange, at 250 Hz, is a third-order Butterworth design, which provides both flat on-axis response and flat sound power through the crossover frequency range.
The 10-inch woofer has a massive, 54-ounce magnet and a 2-inch diameter, long-throw voice-coil. Its cone is made of felted paper fiber, treated for increased stiffness, and is held on its periphery by a rubber surround. In a phone conversation, PSB's founder, Paul Barton, stated that the spider of the woofer has been designed with deliberate nonlinearities to essentially eliminate the dynamic offset problems that many high-excursion woofers exhibit.
The Stratus Gold's cabinet has three shelf braces, strategically placed to provide maximum strength and minimize side-panel resonances. The cabinet is of furniture quality, with oak-veneered side panels and solid hardwood on the top and bottom. For maximum rigidity, the major joints at the top and bottom of the cabinet are locked into place by tongue-in-groove aluminum extrusions.
The crossovers use all air-core inductors, wound with 14-gauge wire, and high-voltage capacitors bypassed with small polypropylene capacitors. The crossover between midrange and tweeter is a sharp-cutoff, fourth-order, Linkwitz-Riley design. Its steep, 24-dB/octave slope ensures that only treble energy reaches the tweeter and minimizes lobbing problems by keeping the acoustic outputs of the midrange and tweeter in phase.
Use and Listening Tests
The Stratus Gold systems have been designed for flat response without the aid of any nearby reflective boundaries that may provide bass reinforcement. This made them very suitable for use in my usual speaker positions, a significant distance from any reflecting surfaces. All listening was done in my listening room, which measures 15-1/2 x 27 x 8 feet, with the Stratus Golds 8 feet apart and canted in toward my listening position on the sofa, about 10 feet away. This location placed them about 6 feet away from the short rear wall and 4 feet from the side walls.
Driving equipment included the Onkyo Grand Integra DX-G10 and Enlightened Audio Designs (EAD) "Ultra" modified Rotel RCD-855 CD players, along with the Jeff Rowland Consummate preamp and Model 7 power amplifiers, all connected with Staight Wire Maestro interconnects and speaker cables.
I did most of the listening before the measurements, although some listening was done after I had replaced the tweeters with known good units. It turned out that only one of the original tweeters was not typical. None of the after-the-fact listening tests changed my original impressions of the systems.
Connection to the Stratus Gold is through a pair of heavy-duty double-banana jacks on the bottom of the system. Two pairs of jacks are provided, to facilitate bi-wiring the system. For the non-bi-wired state, the pairs are connected with large gold-plated straps. Because the jacks are on the bottom of the system, attachment of the cables is difficult unless the system is lying on its side. Since I had to make and break connections several times during these tests, I took a shortcut, doing a balancing act by tipping the system slightly forward, reaching under the rear of the system with plug in hand, and making connection by feel. But this really is not the way to do it, because the system could fall forward! I did not bi-wire the Stratus Golds for my listening evaluations.
The appearance and the fit and finish of the Golds are excellent. My wife and family really liked the oak finish. Particularly handsome are the beveled top and base of the system; it's quite obvious that they are made from solid pieces of oak, because the wood grain maintains continuity all around the edge and along the bevels.
The Stratus Golds produced a very clean, balanced, wide-range sound that competed with my reference systems (B & W 801 Matrix Series 2) on nearly an equal basis. The PSB systems were slightly more bright than the references, with a very open, revealing character. With the grilles off, they were noticeably brighter than the reference systems, but with the grilles on, the high-frequency differences were much smaller. Overall, however, I preferred the system's sound with the grille off, and all the following listening was done in that condition.
Andrew Rangell's piano playing on J. S. Bach's The Goldberg Variations (Dorian DOR-90138, a great piano CD) demonstrated the Golds' good balance, presence, and smooth upper bass. Orchestral climixes on Igor Stravinsky's Petrouchka and Rite of Spring (Chesky CD 42, one of Chesky's excellent CD remasterings of early '60s analog recordings) were reproduced very cleanly and demonstrated the Golds' excellent dynamic range. The organ pedal notes played by E. Power Biggs, on the Saint-Saens "Organ" Symphony (CBS Odyssey MBK 38920, another good remastering from an old analog source) were handled very well, but the upper harmonics of the strings on the same selection were emphasized a bit too much for my taste.
With the Consummate preamplifier in mono mode, the center image of the Gold loudspeakers was very stable with frequency and was of minimal width. Imaging and sound-staging were both top-rate.
The Stratus Gold passed the pink-noise, stand-up/sit-down test with excellent results. Hardly any noticeable tonal changes in upper-mid response were noted at any position, sitting or standing. The systems' low-frequency output on third-octave band-limited pink noise equalled that of the reference systems at all frequencies from 31.5 Hz on up. However, in the two lower third octaves, at 20 and 25 Hz, the Gold's output was diminished and was accompanied by significant chuffing sounds in the vented-boxed ports. The third-octave low-frequency test signal is very demanding because the signal causes high woofer displacement (and resulting high port velocities), but it does not have any higher frequency spectral components that can mask the air-rush noises. Typical program material having high low-frequency energy levels always has some higher frequency content that usually masks these types of noises.
The bass notes between 3:41 and 3:44 on track 15 of Dorian's very demanding organ version of Pictures at an Exhibition (DOR-90117), when the organ is played all-stops-out during the finale, made my reference systems stumble. But the Stratus Golds handled the difficult passage without a whimper (and even at higher playback levels!). Track 2, however, at times 0:50 to 1:02, contained some program information that triggered the front-panel vibration in the lower area of the woofer, noted in the "Measurements" section. (I searched for such a passage after I had done the measurements.)
The dynamic range of the Stratus Gold was nicely demonstrated by playing the heavy-metal track "Rock and Roll Animal" from the CD The Final Frontier by Keel (MCA Records MCAD-5727) at near concert levels. (I'll bet you didn't know that the lead singer of this group, Ron Keel, is my twin brother-just kidding!) For those Audio readers who like to play music (?) at these levels, the Golds will do it very nicely.
The solo electric bass passage starting at time 3:04 from "The Chain" on Fleetwood Mac's Rumours CD (Warner Bros. 03010-2) could be played loud and clean, with a low end that could be felt! The hand-claps and cymbal crashes on track 9, "I Don't Want To Know," were particularly effective through these PSB systems.
At $2,000 a pair, the Stratus Golds provide considerable performance and first-class looks for the money. They should appeal both to the audiophile crowd, for whom accuracy, balance, and imaging are important, and to a wider audience that likes loud rock 'n' roll, for whom the ability to play loudly and cleanly is important. The low impedance of the Golds through the upper bass range, however, means that higher quality, more expensive amplification is required along with low-impedance cabling.
