PSB New Stratus Speaker System Review

The Canadian-made PSB New Stratus loudspeaker is an improved version of the Stratus system first introduced about three years ago. According to the manufacturer, PSB International, it differs from the original Stratus in having about 2 dB higher sensitivity, increased power-handling capacity, less compression at very high levels, wider high-frequency dispersion, and a slightly smoother overall response. The system’s other specifications, however, including the sizes of the cabinet and drivers, the crossover, and the low-frequency response, are unchanged.

The New Stratus is a two-way system whose 8-inch woofer has a 1 Vi-inch voice coil, a PVC surround, and a 48-ounce magnet for higher output in the low bass and smoother midrange response. The woofer operates in a vented enclosure whose 3-inch-diameter duct is said to operate like an organ pipe at frequencies below 50 Hz, delivering strong bass down to 26 Hz without upper-bass boom. The woofer is located at the top of the speaker’s front panel, with the tweeter below it and the port near the midpoint of the panel.

The system’s newly designed tweeter, operating above 1,800 Hz, has a 1-inch aluminum-alloy dome with a polyamide suspension said to be able to operate as a piston up to 20,000 Hz. The aluminum voice coil, attached directly to the dome for improved heat sinking, receives additional cooling from low-viscosity ferrofluid in the magnetic gap. The crossover network, a 24-dB-per-octave Linkwitz-Riley design, uses heavy air-core inductors and high-quality film capacitors.

The wood-veneered cabinet is made of a high-density composite and is available in light-oak, dark-oak, or black-lacquer finishes. The cabinet is internally damped with felted material, and it is heavily braced, with aluminum extrusions at the top and bottom to lock the wood panels in place. It measures 11 inches wide and 13-1/2 inches deep. The 2-inch-high integral pedestal, matching the cabinet finish, is 13-1/4 inches wide and 15-3/4 inches deep, making the system height 37-5/8 inches.

Like the pedestal base, the cabinet’s top plate is made of solid hardwood. The front panel and grille frame are beveled to minimize diffraction around the edges. Separate gold-plated multiway binding posts for the woofer and tweeter inputs are located on the bottom of the cabinet. They are normally connected by jumpers but can be separated for bi-wired or bi-amplified operation. Each speaker weighs 60 pounds.

The New Stratus system’s specifications include a frequency range of 26 to 24,000 Hz with a ±1.5-dB variation between 40 and 20,000 Hz. The rated impedance is 6 ohms, with a minimum of 5 ohms. Sensitivity is specified as 88 dB sound-pressure level (SPL) in an anechoic chamber, 90 dB in a typical listening room. Rated power handling is 200 watts. Price: $1,800 a pair.

Lab Tests

The room response of the PSB New Stratus speakers was unusually uniform over the full audio range, the major variation being a slight bump at 220 Hz caused by a boundary effect. Even including that peak, the room response varied only ±4.5 dB from 20 to 20,000 Hz. In the range above 300 Hz, the variation was ±3.5 dB up to 20,000 Hz.

The close-miked woofer response, combined with the port response, was ±3.5 dB from 20 to 700 Hz, with the maximum at 40 Hz. The woofer’s output dropped at higher frequencies, leveling off at -9 dB, relative to the average midbass level, between 1,000 and 1,800 Hz (the close-miked measurements are not fully valid in that range).

When we combined the woofer response with the room response, the composite curve was very flat (within ±2 dB) from 100 to 900 Hz and fairly flat between 1,000 and 2,000 Hz but down 4 dB relative to the midrange output. The curve rose to reference level at 3,300 Hz, then sloped off smoothly to -4 dB at 10,000 Hz. The output rose again in the next octave, to + 1 dB at 18,000 Hz. The maximum bass output was +3 dB at 40 Hz, returning to reference level at 25 Hz and dropping 3.5 dB from 25 to 20 Hz.

The composite frequency response was consistent with our quasi-anechoic FFT measurements, which had the same general contours and a ±3-dB variation from below 200 Hz to beyond 23,000 Hz. An extended FFT measurement to 30,000 Hz showed a large (9-dB) tweeter resonance peak centered at about 25,000 Hz, but it had a negligible effect below 20,000 Hz.

The horizontal dispersion was good; the response curves on-axis and 45 degrees off-axis remained within 6 dB of each other up to 10,000 Hz and diverged only moderately from there to about 16,000 Hz. The group delay was virtually constant above 8,000 Hz, with variations of about ±0.2 millisecond from there to 3,000 Hz. From 3,000 down to about 600 Hz, the delay was a relatively constant 0.4 to 0.5 millisecond, suggesting a difference in effective path length of about 3 inches between woofer and tweeter.

The system’s impedance reached its minimum of about 5.1 ohms at 166 Hz and its maximum of about 13 ohms at 900 Hz. The 6-ohm rating seems conservative, since the impedance remained between 6 and 12 ohms over most of the audio range. The phase-angle variation of the impedance had a peculiar shape, reading between ±30 degrees over most of the range above 100 Hz but exhibiting numerous abrupt fluctuations at lower frequencies as it dropped to as low as -120 degrees at 30 Hz. Perhaps these fluctuations corresponded to natural resonances in the woofer vent tube (which PSB likens to an organ pipe), although they had no measurable or audible effect on the acoustic bass response.

Sensitivity (in a normal room) measured 89 dB SPL. At a 3.1-volt level, corresponding to a 90-dB SPL, the woofer distortion was between 0.35 and 1 percent from 60 to 150 Hz, leveling off at 1.2 percent from 150 to 330 Hz and rising to about 2 percent from 400 to 1,000 Hz. The effective crossover to the vent was at about 65 Hz, and the distortion measured at the port was about 1 percent down to 40 Hz and rose to 5 percent at 25 to 30 Hz. In our single-cycle-burst power tests at 100 Hz, the woofer cone emitted a rattle with an input of 360 watts into its 5.5-ohm impedance.

Comments

The measured performance of the PSB New Stratus was excellent. Its response smoothness, deep bass extension, and very low bass distortion were outstanding, especially for a two-way system with an 8-inch woofer.

When the speakers were placed as recommended, about 18 inches in front of a wall and angled slightly inward, their imaging qualities were impressive. The sound stage covered the space between the speakers and slightly beyond. The positioning of discrete sound sources in selections from the Chesky jazz sampler and test disc (JD37) was exceptionally believable, vertically as well as laterally.

The New Stratus had a distinctive sound character, especially when compared with a few other comparably priced speakers. Perhaps its most noteworthy characteristic was a silky smoothness, with never a trace of edginess or hardness. Even recordings that appeared to have a noticeable crispness or emphasis in the upper midrange or treble with other fine speakers sounded easy and free from such qualities when heard through the New Stratus.

This smoothness was not the result of a restricted frequency response— the New Stratus’s output was flat and smooth to well above the limits of human hearing. Whatever the reason for the effect, the New Stratus is an exceptionally easy speaker to listen to. There was always a believable sense of depth and height, with hardly a hint that the speakers themselves were the sound source.

The bass response of the New Stratus is real, meaning that you won’t hear any bass if there is none in the program but you will both hear and feel it when it is present. The speaker’s low bass distortion may have something to do with this characteristic. Altogether, the PSB New Stratus is an exceptionally fine speaker with livable dimensions and handsome styling.

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