Boston Acoustics SubSat Six Speaker System Review

The Boston Acoustics SubSat Six is a compact speaker system built in the increasingly popular three-piece format. It consists of a pair of small, two-way satellite speakers and a separate PowerVent bass module. Each satellite weighs 4 pounds and measures 8 inches high, 4-7/8 inches wide, and 4-3/4 inches deep, and each contains a 4-inch cone woofer operating in a sealed enclosure and a 3/4-inch dome tweeter. The black vinyl-finished particleboard enclosures have spring-loaded connectors on the back panels; normally meant to accept wire leads, they are also compatible with dual banana plugs. The black metal grilles are not readily removable.

The PowerVent module, also finished in black, weighs 17-1/4 pounds and measures 13-1/2 inches high, 7-1/4 inches wide, and 16-1/2 inches long. It contains separate 6-inch woofers for each channel, rear-loaded by a common sealed chamber and facing into a common vented chamber. The vents open through 2-inch-diameter tubular ducts that are flared at both ends to eliminate noise from turbulence at high levels. The PowerVent design provides a low-pass cutoff of 18 dB per octave without using any crossover components, and since each satellite contains its own high-pass crossover filter, the satellite and bass-module driver for each channel are simply connected in parallel and then to the amplifier output.

The system’s specifications include a frequency response of 46 to 20,000 Hz ± 3 dB, a nominal impedance of 4 ohms, and sensitivity of 87 dB sound-pressure level (SPL) at 1 meter with a 2.83-volt input. It is recommended for use with amplifier: rated to deliver between 15 and 100 watts per channel.

Like other three-piece systems, the SubSat Six offers great installation flexibility. The satellites can be placed on stands, tables, or shelves. Moreover, each satellite has a rear-panel keyhole opening for wall mounting as well as threaded inserts for use with an optional swivel bracket.

Because its output drops rapidly above about 150 Hz. the PowerVent module can be located almost anywhere without being heard as a separate sound source. In general, it is preferable to put it at the same end of the room as the satellites, and Boston Acoustics also suggests corner placement (with the vents facing the corner) for the deepest and most uniformly distributed bass output. Price: $499.95 for complete system.

Lab Tests

With the satellites on 26-inch stands and the PowerVent bass module about midway between them, the averaged room response of the SubSat Six was unusually uniform across the full audio range. There was very little difference between the response curves of the left and right channels (measured one at a time from a microphone position on the axis of the left channel), and from 500 to 20,000 Hz the averaged output varied only ±2 dB.

The close-miked response of the PowerVent module was flat within ± 1 dB from 50 to 130 Hz, falling off at 18 dB per octave above that frequency and at a precipitous 60 dB per octave between 50 and 35 Hz. Output rose slightly from 35 to 26 Hz and then continued its descent to our 20-Hz measurement limit where it was some 25 dB below the woofer’s reference operating level.

To form a composite response curve, we used a close-miked measurement of the satellite cone (midrange) driver to bridge the region between the bass and tweeter ranges. The resulting curve was flatter than could probably be justified in view of the numerous external variables that can affect the balance between lows and highs in any room. Suffice it to say that the response of each driver (bass, midrange, and treble) in its operating range was flat enough to have passed for an amplifier response not too many years ago. The only significant deviations were a slight emphasis (about 3 dB) in the octave from 10,000 to 20,000 Hz and a 2.5-dB peak at the lower limit of the PowerVent bass module’s operating range (50 Hz).

The satellite’s frequency response varied only moderately through a 45-degree angle about its forward axis, and the deviation was not much greater above 10,000 Hz than in the lower treble range. We noticed in the close-miked PowerVent response curve that a measurable amount of signal was radiated at frequencies between 500 and 1,500 Hz. These leakage signals were at least 20 dB below the bass output, however, and in actual use were never audible. The satellite’s phase linearity was very good, with an overall group-delay variation of less than 0.2 millisecond from 1,000 to 20 000 Hz.

The system’s measured sensitivity was 90.5 dB SPL at 1 meter with a pink-noise signal of 2.83 volts rms. The impedance presented to a driving amplifier depended greatly on the measurement conditions (such as whether the satellites and the PowerVent module were paralleled and whether both channels were being driven). Paralleling the satellite and bass modules and driving only one channel gave the worst results, with the impedance reaching a minimum of 3 ohms at 90 and 450 Hz and remaining less than 6 ohms from 54 to 1,300 Hz. The system’s maximum impedance was 19.5 ohms at 34 Hz.

The total harmonic distortion (THD) plus noise of the PowerVent bass module with a drive level of 2.67 volts (equivalent to a 90-dB level in a sensitivity measurement) was 1 percent at 70 Hz and fell to 0.4 percent or less from 75 to 200 Hz. At lower frequencies the distortion rose rapidly, reaching 4 percent at 50 Hz and 20 percent at 45 Hz.

In high-power pulse tests, the PowerVent cones bottomed loudly at 562 watts into their 3.2-ohm impedance at 100 Hz. At 1,000 and 10,000 Hz, the amplifier clipped before the satellite speaker limits were reached, at respective power levels of 1,250 and 825 watts into 5 and 7 ohms.

Comments

Our measurements suggested that the Boston Acoustics SubSat Six was a good speaker system, especially in its price range, and our listening tests fully confirmed that judgment. When the PowerVent module was midway between the satellites and a couple of feet from the wall, the low bass, while adequate most of the time, fell short of our expectations. Moving it into a corner (a few feet to the right of the right speaker), with the vents closest to the corner, as recommended by the manufacturer, made an impressive difference in the system’s bass performance when playing musical selections with appreciable energy below about 80 Hz.

The sound, overall, was typical of what we would expect from the very finest three-piece systems. Output in the lowest part of the system’s range (around 50 Hz) could be felt as well as heard. The higher frequencies were seamlessly joined to the bass range, giving no hint of their separate origin. Best of all, there were no obvious gaps in the spectrum, especially between the ranges covered by the PowerVent and the satellites. The position of the PowerVent unit was never detectable by listening. In fact, the smoothness of the overall sound was superior to that of most conventional two-piece systems we have used. Compared with some other speakers, the SubSat Six also sounded a trifle crisp, an effect we approve of and tend to attribute to its wide dispersion and slightly emphasized output in the top octave.

After extended listening to the SubSat Six and direct comparisons with some very good conventional speakers, we felt that it more than held its own. No one walking into the room would have the slightest inkling that its two tiny satellites were delivering the bulk of the sound he was hearing. That is the principal quality of a good three-piece system, and the SubSat Six has it in full measure, at a highly competitive price.

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